CA2096150A1 - Filter - Google Patents
FilterInfo
- Publication number
- CA2096150A1 CA2096150A1 CA002096150A CA2096150A CA2096150A1 CA 2096150 A1 CA2096150 A1 CA 2096150A1 CA 002096150 A CA002096150 A CA 002096150A CA 2096150 A CA2096150 A CA 2096150A CA 2096150 A1 CA2096150 A1 CA 2096150A1
- Authority
- CA
- Canada
- Prior art keywords
- resonators
- signal
- filter
- port
- subset
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
- H04B1/40—Circuits
- H04B1/54—Circuits using the same frequency for two directions of communication
- H04B1/56—Circuits using the same frequency for two directions of communication with provision for simultaneous communication in two directions
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
- H04B1/40—Circuits
- H04B1/44—Transmit/receive switching
- H04B1/48—Transmit/receive switching in circuits for connecting transmitter and receiver to a common transmission path, e.g. by energy of transmitter
Abstract
Abstract The invention discloses a three-port filter being able to connect alternately a receiver and a transmitter to a common antenna in a radio system operating by the time division principle. The first signal path between the first and the third ports comprises all resonators (R1, R2, R3, R4) The second port is connected to one (e.g. R3) of the resonators in the first signal path, whereby a first subset (R1, R2) of resonators lies between the first and the second ports, and a second subset (R3, R4) of resonators forming the signal path between the second and the third ports lies between the second and the third ports. The resonators of either subset are switchable resonators, whose resonance frequencies can be shifted between two frequencies by an external control (Control). At the first control value of the control (Control) the resonators of this subset pass the RF-signal substantially without attenuation, and at the second control value they strongly attenuate said signal.
Description
A filter The present invention relates to a filter. In particular the present invention relates to a filter operating as a change-over switch.
For example in radio engineering a filter of this kind is known as a duplex filter, through which the transmitter and the receiver of an apparatus is connected to a common antenna. The filter is designed so that the transmit signal can not reach the receiver but propagates to the antenna, and so that the received signal from the antenna can not reach the transmitter but propagates to the receiver. This is possible as the filters of the transmit branch and the receive branch are dimensioned so that when one is passing, then the other is stopping. This in turn is possible only when the transmit frequency band and the receive frequency band are separated. All present duplex filters of analog radiotelephones operating in duplex mode work in this way.
The same principle natuxally holds true for any three-port filter, which in a common circuit means incorporates two siynal paths for different frequency bands.
However, the situation is different if the three-port circuit means must process signals at the same frequency band. Then it is not possible to use the duplex principle, because the same attenuation would be present between different ports, whereby power into one port is divided into the two other ports. If the signals to be processed appear at different moments, then the three-port circuit means can be realized as a simple change-over switch being able to connect e.g. port 1 and port 2 alternately to port 3. In fact the situation is like this in radiotelephone systems operating according to the time division principle . " .
. .
, :' on a single frequency, and as an example of these we can mention the DECT system (Digital European Cordless Telephone). In such systems transmission and reception occur at the same frequency but in different time slots, so that a change-over swi-tch can be used -to connect the antenna to the receiver during the receive time slot and correspondingly the transmitter to the antenna during the transmit time slot.
When a change-over switch is used as a three-port circuit means for the above described purpose it must naturally be dimensioned to tolerate the highest transmit power of the apparatus, which could be of the order of 20 kW. This results in a power consuming "heavy" switch, which means attenuation of the signal passing through the switch. The attenuation of the antenna switch is of the order of 7 dB, which has an adverse effect when a weak signal is being received. An active semiconductor switch is non-linear and therefore it presents an inconvenience in circuit design.
Thus a filter realized with passive components would be a good solution, but this far no three-port filter having a change-over function suitable for the processing of two signals with the same frequency was presented.
This invention presents a means using passive filter components to realize a change-over switch for signals having the same frequency but appearing at different moments. The invention is well suited to be used also when the frequencies are different, but even then time division multiplexing is required.
Here we utilize the known basic fact that the resonance frequency of a resonator can be changed, e.g. by converting .
. :
'~` ' '-. ,:
- ~ ' ,.... ,, ,; . :
.
a quarter-wave transmission-line resonator to be a half-wave resonator, whereby the resonance ~req~lency is doubled. It is well known that radio frequency filters in practice may have adjusting means, e.g. adjusting screws, which in one way or another act on the capacitive ].oad at the open end of the resonator when they are manually turned. In fact frequency shift methods are based on a similar ad~ustment method, which is modified so that the adjustin~ means is not manually bu-t electrically controlled.
Filters based on helix resonators can use a stepping motor acting on a means moving in the capacitive or inductive field of the resonator. In a ceramic resonator a capacitance diode can be mounted at the loaded end of the resonator, between the upper end of the bore and the earthed top or side face, whereby the load capacitance and thus the resonance frequency is adjusted by adjusting the capacitance. The capacitance diode could also be mounted in the bore of the resonator.
The applicant's Finnish patent application FI-913088, dated 25.6.1991, discloses a means to shift the resonator characteristic in the frequency plane. According to the method a strip line resonator is mounted in the electroma~netic field of the resonator, below called the main resonator, whereby the other end of the strip line can be shorted with a controllable switch. When the switch is open the strip line resonator is a lambda/2 resonator havin~ the resonance frequency fO, which is so far from the main resonator's resonance frequency that it hardly at all affects the main resonator. When the switch is closed it shorts the other end of the strip line, transforming the ,. . . .
.
strip line into a lambda/~ resonator with the resonance frequency fo/2~ ~his is arranged to be so close to the resonance frequency of the main resonator that its resonance frequency will have a frequency shi~t deltaf. By suitable connections at the ends of the strip line it is also possible to arrange the switch to have the opposite action compared to the above. The method is particularly well suited for application in connection with dielectric resonators, particularly with known resonator structures having on one uncoated side surface coupling patterns for the coupling to the resonator. The length of the strip line is selected to suit the resonator frequency.
The method's effect is based on the fact an electromagnetic coupling is created between the strip line and the main resonator because the strip line acts as a "secondary resonator". The stronger the coupling, the stronger effect the secondary resonator has on the frequency shifto The design of the main resonator and the dimensions of the secondary resonator and its location relative the main resonator affect the strength of the coupling. Preferably the switch can be a diode or a capacitance diode.
Some known means to shift the resonance frequency of the resonator were described above, and in this invention any known means may be used~
According to a present invention there is provided a ~ilter comprising resonators, in which a first signal can pass in a first time slot between a first port and a third port and a second signal can pass in a second time slot between a second port and the third port, characterized in that the first signal path between the first and the third ports .
comprises a plurality of resistors, the second port is connecte~ to one of said plurality of resonator in the first signal path, whereby a ~irst subset of resonators lies between the first and the second ports, and a second subset of resonators lies between the second and the third ports, forming the signal path between the second and the third ports, the resonators of one subset are switchable resonators, whose resonance frequencies can be shifted between two frequencies, the resonators of said one subset being connected to an external control means, such that on receipt of a first control signal from the control means the resonators of said subset allow the signal to pass through substantially without attenuation, and on receipt of a second control signal from the control means the resonators attenuate said signal.
The filter disclosed in claims 2 - 6 is suited for single frequency time division systems, and the filter disclosed in claims 7 - 10 is particularly suited for dual frequency systems.
The filter to be used is thus a filter in which the signal between the first and the third ports passes all resonator circuits, but on the signal path between the second and the third ports there is only a part of the resonator circuits.
The function is as follows: the resonator circuits are tuned so that the operating frequency signal propagates substantially without attenuation from port 1 to port 3 (or vice versa) and from port 2 to port 3 (or vice versa).
Other frequencies than the operating frequency are strongly attenuated. It is essential that the operation is time divided, whereby signals propagate at different moments between ports 1 - 3 and ports 2 - 3. If the operating :, ...................... . ...
, . . .
. .. ~, frequency signal now has to pass without att~nuation from port 2 to port 3, then the frequencies of the resonators between ports 1 and 2 are controlled to shift so much that the transmission characteristic of the filter part between ports 1 and 2 shifts far away from the original frequency and instead we have a stop-band function. Then the signal meets a high impedance in the direction from port 2 towards port 1, but a very low impedance towards port 3. The signal power supplied to port 2 is thus output from port 3, but hardly no power is output from port 1.
An embodiment of the invention is described, by way of example, with reference to the drawings, in which;
Figure 1 illustrates a three-port filter operating as a change-over switch and comprising two circuits;
Figures 2a and 2b show the filter's transmission characteristics for transmission and reception;
Figure 3 shows a three-port filter comprising four circuits;
Figures 4a and 4b show the transmission eharacteristics for transmission and reception of the filter in figure 3;
Figure 5 shows a filter, when there are two operating frequencies;
F.igure 6a shows the transmission characteristics of the antenna filter of a known system; and Figures 6b and 6c show the transmission characteristics of ' ' ' . . ~ .
, . . . .
.
the filter in figure 5. `!
For the sake of clarity the embodiment in the below described examples concerns an an-tenna switch of a radiotelephone/ but it should be noted that ~he invention is applicable for other purposes.
The circuit arrangement of figure 1 shows an antenna filter realized with a minimum number of components. Port 1 of the filter is connected to the receiver, port 2 to the transmitter and port 3 to a common antenna. The basic assumption is that the transmit frequency Tx and the receive frequency Rx are the same, but that transmission and reception occur interleaved in dif~erent time slots, as `
is the case in the TDMA system.
The filter comprises two resonator circuits R1 and R2. The resonators can be of any known type: coaxial, strip line, helix or ceramic resonators. The coupling between the circuits is marked by k12. Assume first that we have a receive time slot. Then the signal from the antenna Ant is received in port 3. The resonator circuits are tuned so that their frequency response has a pass-band at the receive frequency. This is illustrated by fi~ure 2a, in which the attenuation characteristic shows the response of a two-circuit filter. The center frequency fO is tuned to be the same as the system's operating frequency (c transmit and receive frequency). The received signal is only slightly attenuated when it propagates from port 3 to port 1, because according to figure 2a the filter formed by the resonators R1 and R2 has a negligible attenuation. Of course the signal can also pass through port 2 to the receiver, but this causes no inconvenience because the .
receiver is off.
When the transmit time slot begins, the control logic of the radio apparatus switches on the transmitter and at the same time also supplies a control signal Control to the resonator Rl. Then the resonance frequency of this resonator changes to f'. If the control transformed the quarter-wave transmission-line to a half-wave transmission-line, then the frequenc~ f' of resonator R1 would be the double compared to the frequency before control was implemented, or f' would be close to 2*fo. The transmit branch now contains a filter of a single resonator R2, whose response is shown in figure 2b by a continuous line. It has a negligible attenuation at the operating frequency f0, and thus the transmit signal Tx is attenuated hardly at all when it propagates from port 2 to port 3 and further to the antenna. On the other hand the transmi~
cignal is strongly attenuated towards port 1, because the pass-band of the resonator 1 is shifted far away from the operating frequency f0. The dashed line characteristic of figure 2b illustrates the frequency response between ports 2 and 1. Thus the transmit power can not propa~ate to the receive branch Rx.
The circuit arrangement of figure 1 is a minimum arrangement in order to realize the invention. In practice the filter must use a plurality of resonators in order to meet the specifications of each application. Thus the filter of figure 3 operating as a change-over switch is intended to be an antenna filter in a DECT telephone, and a four circuit filter is required to meet the specification. It contains the resonators R1/ R2, R3 and R4. Port 1 connects the first circuit R1 to the receive branch Rx, port 2 connects the transmit branch Tx to the third circuit R3, and the antenna line is connected through port 3 to the fourth circuit R4. The connections to the resonators are made by any known method, inductively, capacitively, or galvanlcally, which is not essential for the invention. During the receive time slot the signal propagates from port 3 to port 1, and thus all circuits are used. In order to meet the requirements presented by the specifications the resonance frequencies are selected and the couplings k12, k23, k34 calculated to provide the desired transmission characteristic around the center frequency fO, which is illustrated in figure 4a. Then the received signal, which depending on the channel can vary within the transmission characteristic, will pass without hindrance to the receiver. The transmitter is off, so that no power passes from the port 2 to the receive branch T~.
When the transmit interval begins, the control logic supplies the control signal Control, whereby the resonance frequencies of the resonators Rl and R2 shift substantially, e.g. downwards in the frequency plane. Then the transmission characteristic measured between ports 1 and 2 will be according to figure 4b. The narrower pass-band A at the center frequency fO is provided by the resonator circuits R3 and R4. A part of the original pass-band according to figure 4a provided by the resonators R1 and R2 is shifted far away to a lower frequency. This is seen in the chaxacteristic of figure 4b as a "shifted band", which thus represents the transmission characteristic between ports 1 and 2. Then the transmit signal at the port 2 having the same frequency as the receive frequency will see a high inpedance towards the port 1, and thus the transmit signal o~tput from port 1 is .
- ' strongly attenuated and does not damage the front end of the reGeiver. The impedance seen towards port 3 is low, and the trans~it signal passes without hindrance to port 3 and from there to the antenna. The pass-band between ports 2 and 3 is shown in figure 4b marked as "band A~'.
In the case of figure ~ the transmit branch has a filter with two circuits (resonators R3 and R4) and the receive branch has a filter with four circuits (resonators R1, R2, R3 and R4). It is important to note that no exact shift is required when the resonator R1 and R2 is offset during the transmission. A sufficient shift is enough. This is important, because it is substantially more demanding to realize an exact offset than to ha~e a "sufficient" shift.
Figure 5 illustrates a four~circuit filter with a change-over function and ha~ing shiftable resonators between ports 2 and 3, instead of havin~ them between the ports 1 and 2 as above. This design i5 suitable to be used particularly when the tr~nsmit and receive frequencies are different. The application could be eOg. a GSM telephone, in which the receive band is 935 - 960 MHz and the transmit band 890 - 915 MHz. Presentl~ an antenna filter of the GSM
telephone is realized using 7 resonators, of which four are required for the band-pass filter of the Rx branch and three for the low-pass filter of the Tx branch. This is done in order to have the required GSM antenna filter's transmission characteristic of figure 6a. The required transmission characteristic can be obtained usin~ a filter operating as a change-o~er switch and connected according to figure 5 using only four resonators. In the ~ilter of figure 5 the frequencies of the three resonators R2, R3 and R~ between ports 2 and 3, or the transmit branch filter's :,' ' . :
- . ~
response, can be shi~ted in the frequency plane by the control signal Control~ The received signal propagates from port 3 through all four resonators to port 1 and further to the receiver.
The resonance frequencies of the resonators and the couplin~s kl2, k23, k34 between the resonators are selected so that during the receive time slot the transmission characteristic of the fi~ter between port 3 and port 1 is according to figure 6b. When the transmit time slot begins the telephone's control logic supplies a control signal Control to the resonators ~2, R3 and R4. The frequency of these resonators is shifted downwards, e~actly so that the filter formed by them and through which the transmit signal passes, has a transmission characteristic with a pass-band at the transmit frequency of 890 - 91S MHz. This is illustrated by the left side of the transmission characteristic of figure 6c. On the right hand side the resonator R1 causes at the receive frequency a small rise, whose frequency is not shifted. This rise has no significance for the transmitted signal, and the transmit signal supplied to port 1 is sufficiently attenuated and does not damage the receiver.
The control signal Control is changes its state when the receive time slot begins, whereby the frequency of the resonators R2, R3 and R4 shifts upwards and the transmission characteristic is again according to figure 6b. The transmission characteristic can be changed in accordance with the control signal, and the filter for the transmit signal has three circuits and the filter for the receive signal has four circuits. Thus it is possible to realize the required GSM filter with only four resonators, - : :
..
instead of the seven resonators used in prior art. The filter is thus considerably smaller and lighter, which is a great advantage (when we aim at small-sized and light telephones).
The above described filter operating as a change~over switch meets well the requirements on the switch and the filtering. It causes a small attenuation compared to a swi-tch, which strongly attenuates the signal. The number of mounted components decreases compared to known antenna filters. When the invention is used in single frequency s~stems having the same signal frequency at the ports, then we shift some filters sufficiently far away from the operating frequency. This is a great advantage as it is much easier to shift a filter away from its operating fre~uency than to shift it to the operating frequency. In the last mentioned case the shift must be very exact and this is more difficult to obtain. An exact shift is required if the invention is applied to double frequency systems, of which figures 5 and 6 are examples.
The invention is above described as an embodiment for an antenna switch. Obviously, and remainin~ within the scope of the claims it is possible to apply it in any environment requirin~ a three-port filter with a change-over feature.
The fre~uency shift can be provided in accordance with the application, either for the filter part between ports 1 and 2, or for the filter part between ports 2 and 3, whereby the ener~y is directed to pass throu~h the desired circuits. The number of resonators is not limited in any way, and they could be of any type. The invention is particularly well suited to be used in connection with ceramic resonators, and in connection with such shiftable ,~
resonators which are described in the above mentioned Finnish patent application FI-913088. When the resonator is shifted away ~rom the resonance frequency, it is then possible to utilize a capacitance diode acting as a switch, because the RF-voltage superposed in the capacitance diode causes no inconvenience because an offset with an exact magnitude is not at all required.
, ' , .. .: . :
For example in radio engineering a filter of this kind is known as a duplex filter, through which the transmitter and the receiver of an apparatus is connected to a common antenna. The filter is designed so that the transmit signal can not reach the receiver but propagates to the antenna, and so that the received signal from the antenna can not reach the transmitter but propagates to the receiver. This is possible as the filters of the transmit branch and the receive branch are dimensioned so that when one is passing, then the other is stopping. This in turn is possible only when the transmit frequency band and the receive frequency band are separated. All present duplex filters of analog radiotelephones operating in duplex mode work in this way.
The same principle natuxally holds true for any three-port filter, which in a common circuit means incorporates two siynal paths for different frequency bands.
However, the situation is different if the three-port circuit means must process signals at the same frequency band. Then it is not possible to use the duplex principle, because the same attenuation would be present between different ports, whereby power into one port is divided into the two other ports. If the signals to be processed appear at different moments, then the three-port circuit means can be realized as a simple change-over switch being able to connect e.g. port 1 and port 2 alternately to port 3. In fact the situation is like this in radiotelephone systems operating according to the time division principle . " .
. .
, :' on a single frequency, and as an example of these we can mention the DECT system (Digital European Cordless Telephone). In such systems transmission and reception occur at the same frequency but in different time slots, so that a change-over swi-tch can be used -to connect the antenna to the receiver during the receive time slot and correspondingly the transmitter to the antenna during the transmit time slot.
When a change-over switch is used as a three-port circuit means for the above described purpose it must naturally be dimensioned to tolerate the highest transmit power of the apparatus, which could be of the order of 20 kW. This results in a power consuming "heavy" switch, which means attenuation of the signal passing through the switch. The attenuation of the antenna switch is of the order of 7 dB, which has an adverse effect when a weak signal is being received. An active semiconductor switch is non-linear and therefore it presents an inconvenience in circuit design.
Thus a filter realized with passive components would be a good solution, but this far no three-port filter having a change-over function suitable for the processing of two signals with the same frequency was presented.
This invention presents a means using passive filter components to realize a change-over switch for signals having the same frequency but appearing at different moments. The invention is well suited to be used also when the frequencies are different, but even then time division multiplexing is required.
Here we utilize the known basic fact that the resonance frequency of a resonator can be changed, e.g. by converting .
. :
'~` ' '-. ,:
- ~ ' ,.... ,, ,; . :
.
a quarter-wave transmission-line resonator to be a half-wave resonator, whereby the resonance ~req~lency is doubled. It is well known that radio frequency filters in practice may have adjusting means, e.g. adjusting screws, which in one way or another act on the capacitive ].oad at the open end of the resonator when they are manually turned. In fact frequency shift methods are based on a similar ad~ustment method, which is modified so that the adjustin~ means is not manually bu-t electrically controlled.
Filters based on helix resonators can use a stepping motor acting on a means moving in the capacitive or inductive field of the resonator. In a ceramic resonator a capacitance diode can be mounted at the loaded end of the resonator, between the upper end of the bore and the earthed top or side face, whereby the load capacitance and thus the resonance frequency is adjusted by adjusting the capacitance. The capacitance diode could also be mounted in the bore of the resonator.
The applicant's Finnish patent application FI-913088, dated 25.6.1991, discloses a means to shift the resonator characteristic in the frequency plane. According to the method a strip line resonator is mounted in the electroma~netic field of the resonator, below called the main resonator, whereby the other end of the strip line can be shorted with a controllable switch. When the switch is open the strip line resonator is a lambda/2 resonator havin~ the resonance frequency fO, which is so far from the main resonator's resonance frequency that it hardly at all affects the main resonator. When the switch is closed it shorts the other end of the strip line, transforming the ,. . . .
.
strip line into a lambda/~ resonator with the resonance frequency fo/2~ ~his is arranged to be so close to the resonance frequency of the main resonator that its resonance frequency will have a frequency shi~t deltaf. By suitable connections at the ends of the strip line it is also possible to arrange the switch to have the opposite action compared to the above. The method is particularly well suited for application in connection with dielectric resonators, particularly with known resonator structures having on one uncoated side surface coupling patterns for the coupling to the resonator. The length of the strip line is selected to suit the resonator frequency.
The method's effect is based on the fact an electromagnetic coupling is created between the strip line and the main resonator because the strip line acts as a "secondary resonator". The stronger the coupling, the stronger effect the secondary resonator has on the frequency shifto The design of the main resonator and the dimensions of the secondary resonator and its location relative the main resonator affect the strength of the coupling. Preferably the switch can be a diode or a capacitance diode.
Some known means to shift the resonance frequency of the resonator were described above, and in this invention any known means may be used~
According to a present invention there is provided a ~ilter comprising resonators, in which a first signal can pass in a first time slot between a first port and a third port and a second signal can pass in a second time slot between a second port and the third port, characterized in that the first signal path between the first and the third ports .
comprises a plurality of resistors, the second port is connecte~ to one of said plurality of resonator in the first signal path, whereby a ~irst subset of resonators lies between the first and the second ports, and a second subset of resonators lies between the second and the third ports, forming the signal path between the second and the third ports, the resonators of one subset are switchable resonators, whose resonance frequencies can be shifted between two frequencies, the resonators of said one subset being connected to an external control means, such that on receipt of a first control signal from the control means the resonators of said subset allow the signal to pass through substantially without attenuation, and on receipt of a second control signal from the control means the resonators attenuate said signal.
The filter disclosed in claims 2 - 6 is suited for single frequency time division systems, and the filter disclosed in claims 7 - 10 is particularly suited for dual frequency systems.
The filter to be used is thus a filter in which the signal between the first and the third ports passes all resonator circuits, but on the signal path between the second and the third ports there is only a part of the resonator circuits.
The function is as follows: the resonator circuits are tuned so that the operating frequency signal propagates substantially without attenuation from port 1 to port 3 (or vice versa) and from port 2 to port 3 (or vice versa).
Other frequencies than the operating frequency are strongly attenuated. It is essential that the operation is time divided, whereby signals propagate at different moments between ports 1 - 3 and ports 2 - 3. If the operating :, ...................... . ...
, . . .
. .. ~, frequency signal now has to pass without att~nuation from port 2 to port 3, then the frequencies of the resonators between ports 1 and 2 are controlled to shift so much that the transmission characteristic of the filter part between ports 1 and 2 shifts far away from the original frequency and instead we have a stop-band function. Then the signal meets a high impedance in the direction from port 2 towards port 1, but a very low impedance towards port 3. The signal power supplied to port 2 is thus output from port 3, but hardly no power is output from port 1.
An embodiment of the invention is described, by way of example, with reference to the drawings, in which;
Figure 1 illustrates a three-port filter operating as a change-over switch and comprising two circuits;
Figures 2a and 2b show the filter's transmission characteristics for transmission and reception;
Figure 3 shows a three-port filter comprising four circuits;
Figures 4a and 4b show the transmission eharacteristics for transmission and reception of the filter in figure 3;
Figure 5 shows a filter, when there are two operating frequencies;
F.igure 6a shows the transmission characteristics of the antenna filter of a known system; and Figures 6b and 6c show the transmission characteristics of ' ' ' . . ~ .
, . . . .
.
the filter in figure 5. `!
For the sake of clarity the embodiment in the below described examples concerns an an-tenna switch of a radiotelephone/ but it should be noted that ~he invention is applicable for other purposes.
The circuit arrangement of figure 1 shows an antenna filter realized with a minimum number of components. Port 1 of the filter is connected to the receiver, port 2 to the transmitter and port 3 to a common antenna. The basic assumption is that the transmit frequency Tx and the receive frequency Rx are the same, but that transmission and reception occur interleaved in dif~erent time slots, as `
is the case in the TDMA system.
The filter comprises two resonator circuits R1 and R2. The resonators can be of any known type: coaxial, strip line, helix or ceramic resonators. The coupling between the circuits is marked by k12. Assume first that we have a receive time slot. Then the signal from the antenna Ant is received in port 3. The resonator circuits are tuned so that their frequency response has a pass-band at the receive frequency. This is illustrated by fi~ure 2a, in which the attenuation characteristic shows the response of a two-circuit filter. The center frequency fO is tuned to be the same as the system's operating frequency (c transmit and receive frequency). The received signal is only slightly attenuated when it propagates from port 3 to port 1, because according to figure 2a the filter formed by the resonators R1 and R2 has a negligible attenuation. Of course the signal can also pass through port 2 to the receiver, but this causes no inconvenience because the .
receiver is off.
When the transmit time slot begins, the control logic of the radio apparatus switches on the transmitter and at the same time also supplies a control signal Control to the resonator Rl. Then the resonance frequency of this resonator changes to f'. If the control transformed the quarter-wave transmission-line to a half-wave transmission-line, then the frequenc~ f' of resonator R1 would be the double compared to the frequency before control was implemented, or f' would be close to 2*fo. The transmit branch now contains a filter of a single resonator R2, whose response is shown in figure 2b by a continuous line. It has a negligible attenuation at the operating frequency f0, and thus the transmit signal Tx is attenuated hardly at all when it propagates from port 2 to port 3 and further to the antenna. On the other hand the transmi~
cignal is strongly attenuated towards port 1, because the pass-band of the resonator 1 is shifted far away from the operating frequency f0. The dashed line characteristic of figure 2b illustrates the frequency response between ports 2 and 1. Thus the transmit power can not propa~ate to the receive branch Rx.
The circuit arrangement of figure 1 is a minimum arrangement in order to realize the invention. In practice the filter must use a plurality of resonators in order to meet the specifications of each application. Thus the filter of figure 3 operating as a change-over switch is intended to be an antenna filter in a DECT telephone, and a four circuit filter is required to meet the specification. It contains the resonators R1/ R2, R3 and R4. Port 1 connects the first circuit R1 to the receive branch Rx, port 2 connects the transmit branch Tx to the third circuit R3, and the antenna line is connected through port 3 to the fourth circuit R4. The connections to the resonators are made by any known method, inductively, capacitively, or galvanlcally, which is not essential for the invention. During the receive time slot the signal propagates from port 3 to port 1, and thus all circuits are used. In order to meet the requirements presented by the specifications the resonance frequencies are selected and the couplings k12, k23, k34 calculated to provide the desired transmission characteristic around the center frequency fO, which is illustrated in figure 4a. Then the received signal, which depending on the channel can vary within the transmission characteristic, will pass without hindrance to the receiver. The transmitter is off, so that no power passes from the port 2 to the receive branch T~.
When the transmit interval begins, the control logic supplies the control signal Control, whereby the resonance frequencies of the resonators Rl and R2 shift substantially, e.g. downwards in the frequency plane. Then the transmission characteristic measured between ports 1 and 2 will be according to figure 4b. The narrower pass-band A at the center frequency fO is provided by the resonator circuits R3 and R4. A part of the original pass-band according to figure 4a provided by the resonators R1 and R2 is shifted far away to a lower frequency. This is seen in the chaxacteristic of figure 4b as a "shifted band", which thus represents the transmission characteristic between ports 1 and 2. Then the transmit signal at the port 2 having the same frequency as the receive frequency will see a high inpedance towards the port 1, and thus the transmit signal o~tput from port 1 is .
- ' strongly attenuated and does not damage the front end of the reGeiver. The impedance seen towards port 3 is low, and the trans~it signal passes without hindrance to port 3 and from there to the antenna. The pass-band between ports 2 and 3 is shown in figure 4b marked as "band A~'.
In the case of figure ~ the transmit branch has a filter with two circuits (resonators R3 and R4) and the receive branch has a filter with four circuits (resonators R1, R2, R3 and R4). It is important to note that no exact shift is required when the resonator R1 and R2 is offset during the transmission. A sufficient shift is enough. This is important, because it is substantially more demanding to realize an exact offset than to ha~e a "sufficient" shift.
Figure 5 illustrates a four~circuit filter with a change-over function and ha~ing shiftable resonators between ports 2 and 3, instead of havin~ them between the ports 1 and 2 as above. This design i5 suitable to be used particularly when the tr~nsmit and receive frequencies are different. The application could be eOg. a GSM telephone, in which the receive band is 935 - 960 MHz and the transmit band 890 - 915 MHz. Presentl~ an antenna filter of the GSM
telephone is realized using 7 resonators, of which four are required for the band-pass filter of the Rx branch and three for the low-pass filter of the Tx branch. This is done in order to have the required GSM antenna filter's transmission characteristic of figure 6a. The required transmission characteristic can be obtained usin~ a filter operating as a change-o~er switch and connected according to figure 5 using only four resonators. In the ~ilter of figure 5 the frequencies of the three resonators R2, R3 and R~ between ports 2 and 3, or the transmit branch filter's :,' ' . :
- . ~
response, can be shi~ted in the frequency plane by the control signal Control~ The received signal propagates from port 3 through all four resonators to port 1 and further to the receiver.
The resonance frequencies of the resonators and the couplin~s kl2, k23, k34 between the resonators are selected so that during the receive time slot the transmission characteristic of the fi~ter between port 3 and port 1 is according to figure 6b. When the transmit time slot begins the telephone's control logic supplies a control signal Control to the resonators ~2, R3 and R4. The frequency of these resonators is shifted downwards, e~actly so that the filter formed by them and through which the transmit signal passes, has a transmission characteristic with a pass-band at the transmit frequency of 890 - 91S MHz. This is illustrated by the left side of the transmission characteristic of figure 6c. On the right hand side the resonator R1 causes at the receive frequency a small rise, whose frequency is not shifted. This rise has no significance for the transmitted signal, and the transmit signal supplied to port 1 is sufficiently attenuated and does not damage the receiver.
The control signal Control is changes its state when the receive time slot begins, whereby the frequency of the resonators R2, R3 and R4 shifts upwards and the transmission characteristic is again according to figure 6b. The transmission characteristic can be changed in accordance with the control signal, and the filter for the transmit signal has three circuits and the filter for the receive signal has four circuits. Thus it is possible to realize the required GSM filter with only four resonators, - : :
..
instead of the seven resonators used in prior art. The filter is thus considerably smaller and lighter, which is a great advantage (when we aim at small-sized and light telephones).
The above described filter operating as a change~over switch meets well the requirements on the switch and the filtering. It causes a small attenuation compared to a swi-tch, which strongly attenuates the signal. The number of mounted components decreases compared to known antenna filters. When the invention is used in single frequency s~stems having the same signal frequency at the ports, then we shift some filters sufficiently far away from the operating frequency. This is a great advantage as it is much easier to shift a filter away from its operating fre~uency than to shift it to the operating frequency. In the last mentioned case the shift must be very exact and this is more difficult to obtain. An exact shift is required if the invention is applied to double frequency systems, of which figures 5 and 6 are examples.
The invention is above described as an embodiment for an antenna switch. Obviously, and remainin~ within the scope of the claims it is possible to apply it in any environment requirin~ a three-port filter with a change-over feature.
The fre~uency shift can be provided in accordance with the application, either for the filter part between ports 1 and 2, or for the filter part between ports 2 and 3, whereby the ener~y is directed to pass throu~h the desired circuits. The number of resonators is not limited in any way, and they could be of any type. The invention is particularly well suited to be used in connection with ceramic resonators, and in connection with such shiftable ,~
resonators which are described in the above mentioned Finnish patent application FI-913088. When the resonator is shifted away ~rom the resonance frequency, it is then possible to utilize a capacitance diode acting as a switch, because the RF-voltage superposed in the capacitance diode causes no inconvenience because an offset with an exact magnitude is not at all required.
, ' , .. .: . :
Claims (11)
1. A filter comprising resonators, in which a first signal can pass in a first time slot between a first port and a third port and a second signal can pass in a second time slot between a second port and the third port, characterized in that - the first signal path between the first and the third ports comprises a plurality of resistors, - the second port is connected to one of said plurality of resonator in the first signal path, whereby a first subset of resonators lies between the first and the second ports, and a second subset of resonators lies between the second and the third ports forming the signal path between the second and the third ports , - the resonators of one subset are switchable resonators, whose resonance frequencies can be shifted between two frequencies, the resonators of said one subset being connected to an external control means, such that on receipt of at first control signal from the control means the resonators of said subset allow the signal to pass through substantially without attenuation, and on receipt of a second control signal from the control means the resonators of said subset attenuate said signal.
2. A filter according to claim 1, wherein that the frequency of the first and second signals is substantially equal to the operating frequency of a system with which the filter is used.
3. A filter according to claim 2, wherein the control signal of the control means during the first time slot controls the resonators of the first subset to pass a signal at the operating frequency.
4. A filter according to claim 2 or claim 3, wherein that the resonant frequencies of the resonators between the first and the third ports and the couplings between the resonators are dimensioned so that the filter thus formed has a low attenuate function at the operating frequency.
5. A filter according to any of claims 2 to 5, wherein that the control value from the control during the second time slot controls the resonators of the first subset to attenuate a signal at the operating frequency.
6. A filter according to claim 5, wherein that the control signal of the control means shifts the resonance frequencies of the first subset of resonators away from the operating frequency.
7. A filter according to claim 1, wherein that the first and second signals have a different frequency, and that the control means during the first time slot controls the resonators of the second subset to transmit the first signal.
8. A filter according to claim 7, wherein that the frequencies of the resonators between the first and the third ports and the couplings between them are dimensioned so that the filter formed by them transmits at the frequency of the first signal.
9. A filter according to claim 7 and 8, wherein that the control means during the second time slot controls the resonators of the second subset to transmit the second signal.
10. A filter according to claim 9, wherein that the control means offsets the resonance frequencies of the first subset of resonators by an exact amount.
11. Filter according to any previous claim, wherein that the filter is the antenna filter of a radio apparatus and that the first port is connected to the receiver branch, the second port is connected to the transmitter branch and the third port is connected to the antenna, whereby the filter operates as a change-over switch between the first and the second ports.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI922210A FI90926C (en) | 1992-05-14 | 1992-05-14 | High frequency filter with switching property |
| FI922210 | 1992-05-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2096150A1 true CA2096150A1 (en) | 1993-11-15 |
Family
ID=8535291
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002096150A Abandoned CA2096150A1 (en) | 1992-05-14 | 1993-05-13 | Filter |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US5387886A (en) |
| EP (1) | EP0570184B1 (en) |
| JP (1) | JPH06204710A (en) |
| AU (1) | AU660793B2 (en) |
| CA (1) | CA2096150A1 (en) |
| DE (1) | DE69326097T2 (en) |
| FI (1) | FI90926C (en) |
Families Citing this family (52)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH07147503A (en) * | 1993-11-24 | 1995-06-06 | Murata Mfg Co Ltd | Dielectric filter |
| FI97086C (en) * | 1994-02-09 | 1996-10-10 | Lk Products Oy | Arrangements for separation of transmission and reception |
| JPH0851381A (en) * | 1994-08-04 | 1996-02-20 | Uniden Corp | Integratable port selection circuit for high frequency |
| KR0164410B1 (en) * | 1995-07-21 | 1999-03-20 | 김광호 | Strip line filter with switching function |
| FI100040B (en) * | 1995-11-02 | 1997-08-29 | Nokia Telecommunications Oy | Interference-protected power supply method and power supply arrangement |
| FI99174C (en) * | 1995-11-23 | 1997-10-10 | Lk Products Oy | Switchable duplex filter |
| FI102430B (en) * | 1996-09-11 | 1998-11-30 | Filtronic Lk Oy | Filtering device with impedance stage resonators |
| EP0851526B1 (en) * | 1996-12-27 | 2003-07-30 | Murata Manufacturing Co., Ltd. | Filtering device |
| JPH11122139A (en) * | 1997-10-17 | 1999-04-30 | Murata Mfg Co Ltd | Antenna multicoupler |
| JP2000114804A (en) * | 1998-10-08 | 2000-04-21 | Murata Mfg Co Ltd | Antenna sharing device and communication equipment device |
| JP2000151228A (en) * | 1998-11-09 | 2000-05-30 | Murata Mfg Co Ltd | Resonator device, oscillator, filter, duplexer and communication device |
| DE10028189A1 (en) * | 2000-06-09 | 2001-12-20 | Daimler Chrysler Ag | Operation of a number of peripheral communication units from a common aerial using coupling network |
| ATE295632T1 (en) | 2000-11-03 | 2005-05-15 | Paratek Microwave Inc | METHOD FOR CHANNEL FREQUENCY ALLOCATION FOR RF AND MICROWAVE DULEXERS |
| CN1989652B (en) | 2004-06-28 | 2013-03-13 | 脉冲芬兰有限公司 | Antenna component |
| FI20055420A0 (en) * | 2005-07-25 | 2005-07-25 | Lk Products Oy | Adjustable multi-band antenna |
| US20070116649A1 (en) | 2005-09-29 | 2007-05-24 | Nektar Therapeutics | Antibiotic formulations, unit doses, kits, and methods |
| FI119535B (en) * | 2005-10-03 | 2008-12-15 | Pulse Finland Oy | Multiple-band antenna |
| FI119009B (en) * | 2005-10-03 | 2008-06-13 | Pulse Finland Oy | Multiple-band antenna |
| FI118782B (en) | 2005-10-14 | 2008-03-14 | Pulse Finland Oy | Adjustable antenna |
| FI119577B (en) * | 2005-11-24 | 2008-12-31 | Pulse Finland Oy | The multiband antenna component |
| US8618990B2 (en) | 2011-04-13 | 2013-12-31 | Pulse Finland Oy | Wideband antenna and methods |
| US10211538B2 (en) | 2006-12-28 | 2019-02-19 | Pulse Finland Oy | Directional antenna apparatus and methods |
| FI20075269A0 (en) * | 2007-04-19 | 2007-04-19 | Pulse Finland Oy | Method and arrangement for antenna matching |
| FI120427B (en) | 2007-08-30 | 2009-10-15 | Pulse Finland Oy | Adjustable multiband antenna |
| FI20096134A0 (en) | 2009-11-03 | 2009-11-03 | Pulse Finland Oy | Adjustable antenna |
| FI20096251A0 (en) | 2009-11-27 | 2009-11-27 | Pulse Finland Oy | MIMO antenna |
| US8847833B2 (en) * | 2009-12-29 | 2014-09-30 | Pulse Finland Oy | Loop resonator apparatus and methods for enhanced field control |
| FI20105158A (en) | 2010-02-18 | 2011-08-19 | Pulse Finland Oy | SHELL RADIATOR ANTENNA |
| US9406998B2 (en) | 2010-04-21 | 2016-08-02 | Pulse Finland Oy | Distributed multiband antenna and methods |
| FI20115072A0 (en) | 2011-01-25 | 2011-01-25 | Pulse Finland Oy | Multi-resonance antenna, antenna module and radio unit |
| US9673507B2 (en) | 2011-02-11 | 2017-06-06 | Pulse Finland Oy | Chassis-excited antenna apparatus and methods |
| US8648752B2 (en) | 2011-02-11 | 2014-02-11 | Pulse Finland Oy | Chassis-excited antenna apparatus and methods |
| US8866689B2 (en) | 2011-07-07 | 2014-10-21 | Pulse Finland Oy | Multi-band antenna and methods for long term evolution wireless system |
| US9450291B2 (en) | 2011-07-25 | 2016-09-20 | Pulse Finland Oy | Multiband slot loop antenna apparatus and methods |
| US9123990B2 (en) | 2011-10-07 | 2015-09-01 | Pulse Finland Oy | Multi-feed antenna apparatus and methods |
| US9531058B2 (en) | 2011-12-20 | 2016-12-27 | Pulse Finland Oy | Loosely-coupled radio antenna apparatus and methods |
| US9484619B2 (en) | 2011-12-21 | 2016-11-01 | Pulse Finland Oy | Switchable diversity antenna apparatus and methods |
| US8988296B2 (en) | 2012-04-04 | 2015-03-24 | Pulse Finland Oy | Compact polarized antenna and methods |
| US9979078B2 (en) | 2012-10-25 | 2018-05-22 | Pulse Finland Oy | Modular cell antenna apparatus and methods |
| US10069209B2 (en) | 2012-11-06 | 2018-09-04 | Pulse Finland Oy | Capacitively coupled antenna apparatus and methods |
| US9647338B2 (en) | 2013-03-11 | 2017-05-09 | Pulse Finland Oy | Coupled antenna structure and methods |
| US10079428B2 (en) | 2013-03-11 | 2018-09-18 | Pulse Finland Oy | Coupled antenna structure and methods |
| US9634383B2 (en) | 2013-06-26 | 2017-04-25 | Pulse Finland Oy | Galvanically separated non-interacting antenna sector apparatus and methods |
| US9680212B2 (en) | 2013-11-20 | 2017-06-13 | Pulse Finland Oy | Capacitive grounding methods and apparatus for mobile devices |
| US9590308B2 (en) | 2013-12-03 | 2017-03-07 | Pulse Electronics, Inc. | Reduced surface area antenna apparatus and mobile communications devices incorporating the same |
| US9350081B2 (en) | 2014-01-14 | 2016-05-24 | Pulse Finland Oy | Switchable multi-radiator high band antenna apparatus |
| JP6334316B2 (en) * | 2014-08-20 | 2018-05-30 | 株式会社東芝 | Filter device, receiving device, transmitting device, antenna device, and switching device |
| JP6334315B2 (en) * | 2014-08-20 | 2018-05-30 | 株式会社東芝 | Switching device, transmission / reception device, and antenna device |
| US9948002B2 (en) | 2014-08-26 | 2018-04-17 | Pulse Finland Oy | Antenna apparatus with an integrated proximity sensor and methods |
| US9973228B2 (en) | 2014-08-26 | 2018-05-15 | Pulse Finland Oy | Antenna apparatus with an integrated proximity sensor and methods |
| US9722308B2 (en) | 2014-08-28 | 2017-08-01 | Pulse Finland Oy | Low passive intermodulation distributed antenna system for multiple-input multiple-output systems and methods of use |
| US9906260B2 (en) | 2015-07-30 | 2018-02-27 | Pulse Finland Oy | Sensor-based closed loop antenna swapping apparatus and methods |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4987392A (en) * | 1988-10-17 | 1991-01-22 | Motorola, Inc. | Gallium arsenide antenna switch |
| US5023935A (en) * | 1989-11-17 | 1991-06-11 | Nynex Corporation | Combined multi-port transmit/receive switch and filter |
| JP2830319B2 (en) * | 1990-03-08 | 1998-12-02 | ソニー株式会社 | Transmission / reception switching device |
| FR2664766A1 (en) * | 1990-07-11 | 1992-01-17 | Talco Sa | Radio telephony |
-
1992
- 1992-05-14 FI FI922210A patent/FI90926C/en active
-
1993
- 1993-05-07 US US08/058,772 patent/US5387886A/en not_active Expired - Fee Related
- 1993-05-10 EP EP93303608A patent/EP0570184B1/en not_active Expired - Lifetime
- 1993-05-10 DE DE69326097T patent/DE69326097T2/en not_active Expired - Fee Related
- 1993-05-12 AU AU38531/93A patent/AU660793B2/en not_active Ceased
- 1993-05-13 CA CA002096150A patent/CA2096150A1/en not_active Abandoned
- 1993-05-13 JP JP5111721A patent/JPH06204710A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE69326097D1 (en) | 1999-09-30 |
| AU3853193A (en) | 1993-11-18 |
| US5387886A (en) | 1995-02-07 |
| EP0570184B1 (en) | 1999-08-25 |
| JPH06204710A (en) | 1994-07-22 |
| FI90926B (en) | 1993-12-31 |
| DE69326097T2 (en) | 2000-05-25 |
| EP0570184A1 (en) | 1993-11-18 |
| FI922210A0 (en) | 1992-05-14 |
| AU660793B2 (en) | 1995-07-06 |
| FI90926C (en) | 1994-04-11 |
| FI922210A (en) | 1993-11-15 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US5387886A (en) | Duplex filter operating as a change-over switch | |
| EP0776059B1 (en) | Switchable duplex filter | |
| US5903820A (en) | Radio communications transceiver with integrated filter, antenna switch, directional coupler and active components | |
| EP0643481B1 (en) | Radio frequency filter | |
| US4896124A (en) | Ceramic filter having integral phase shifting network | |
| FI97086B (en) | Arrangement for separating transmission and reception | |
| US6308051B1 (en) | Antenna duplexer | |
| FI93679B (en) | A frequency selective microstrip transformer as well as a diode mixer | |
| CA1317649C (en) | Band rejection filtering arrangement | |
| EP1976134A2 (en) | Radio circuit arrangement with improved decoupling | |
| JPH07283603A (en) | Variable filter | |
| KR19990036189A (en) | Receiver and stripline filter with stripline filter | |
| US5241291A (en) | Transmission line filter having a varactor for tuning a transmission zero | |
| US5138288A (en) | Micro strip filter having a varactor coupled between two microstrip line resonators | |
| GB2345615A (en) | Transmitting/receiving switch and portable terminal unit | |
| GB2238193A (en) | Band-pass filters controlled in dependence on signal frequency | |
| US20040251958A1 (en) | Active filter | |
| JPH06120708A (en) | Filter | |
| WO1992000634A1 (en) | Full duplex/half duplex power radio | |
| GB2257335A (en) | Antenna switching circuit | |
| KR100504813B1 (en) | Front end transceiver for dual mode terminal | |
| JPH0758520A (en) | Dielectric branching filter |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |