US3443231A - Impedance matching system - Google Patents

Description

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INVENTOR.

JORGE E. ROZ

Mmmm/ N ow mmefa m2. ON oN UNK Sax wak Nom mumz 8x EBEE Eozon Sonar- 552B `IIIIIIIIIIIIAII.IIIIIIIIIIIIII...||I.lll|||| May 6, 1969 J. E. RozA IMPEDANCE MATCHING VSYSIEM- Filed April 27, 1966 I N VE N TOR. JORGE E. ROZA A T TOR/VE Y United States Patent O U.S. Cl. 325-174 8 Claims ABSTRACT F THE DISCLOSURE A fully automatic antenna coupler having three variable reactance elements, one of which is connected to the antenna output terminal. Impedance and phase sensors at the output terminal side ofthe coupler are in series between the coupler input terminal and the output terminal. These sensors control a logic circuit which operates a motor which tunes the reactive element which is con.- nected to the output terminal until a tuned condition looking into the antenna terminal is sensed. The logic circuits then enable the tuning of the other reactive elements under control of another set of sensors connected at the input terminal side of the coupler.

The present invention relates to an impedance matching system, and more particularly to an improved automatic antenna coupler.

Although the present invention is suited for more general applications, it is particularly adapted for use in an automatic impedance matching system of the type used in mobile service for matching the impedance of an antenna to a transmitter during transmission of 4RF power. More specifically, the present invention is directed to a fully automatic antenna coupler which is adaptable for use with a large variety of antenna types and operable overa lwide range of frequencies and antenna impedances.

It is Well known that the impedance of an antenna may change rapidly and unpredictably when used in radio cornmunication systems of automobile, airplane, boats, ships and the like.

Many attempts have been made to automatically match the impedance of an antenna to a transmitter by the use of an antenna coupler comprising, for example, a pior T-section network configuration having at least three branches. One of the branches generally included one reactive element having a fixed reactance depending upon the expected operating frequency and antenna type. Each of the two other branches included a variable reactive element which was tunable manually or automatically to attempt a desired impedance match over a given range of impedance variations. The reactance of the fixed element in the one branch was selected to anticipate all possible impedance variations that the antenna may present within a range of frequencies. By all the possible impedance variations that the antenna may present is meant to include those impedances which might change rapidly and unpredictably, as above mentioned.

The reactance of the one element modified the impedance of the antenna so that it substantially fell within the anticipated range of impedance variations (viz. the matchable impedance range of the other two tunable reactive elements). This eknown type of antenna coupler was -unable only in a limited frequency range, and the efficiency thereof was actually compromised by the use of the fixed reactance of the one reactive element. The limited frequency range of the antenna coupler required frequent switching of different fixed reactive elements into the one branch to accommodate the various antennas employed. In a true sense, the antenna couplers of the prior art were not fully automatic because at least one of the reactive elements in the antenna couplers was not tunable.

Accordingly, it is a principal object of this invention to provide an yimproved impedance matching system.

It is another object of the present invention to provide an improved fully automatic impedance matching system for automatically matching the impedance of a load to the internal impedance of an active device, say a transmitter or the like.

It is a still further object of the present invention to provide an improved matching system which efficiently transfers power from an active output ydevice to a load.

It is yet another object of the present invention to prov1de an improved antenna impedance matching system which automatically matches the impedance of the antenna to a transmitter independent of the operating frequency and the type of antenna employed.

It is still another object of the present invention to provide an improved automatic antenna coupler which is relatively inexpensive to manufacture and overcomes the drawbacks and disadvantages of known antenna couplers.

It is a further object of the invention'to provide an improved automatic antenna coupler which quickly and smoothly matches the input impedance of various antenna types to the output impedance of a transmitter.

Briefly described, an impedance matching system embodying the invention is operative for coupling a radio frequency output of an active output device, such as a final amplifier of a transmitter having a given internal impedance to a load, such as an antenna having a load impedance. The system comprises a two port network including first, second and third variable reactive elements in series and parallel branches connected between the device and the load. A phase discriminator is provided in the series branch rfor detecting an out-of-phase condition between a voltage referenced to a point of reference potential, such as ground in the series branch and current flowing therein to derive a phase error voltage when that condition exists. One of the first, second and third reactive elements is coupled to the load and the phase discriminator in the series branch connected to the antenna. An impedance sensing circuit is also connected in the series branch for deriving an impedance error voltage when the magnitude of the load impedance modified by the one reactive element differs from a given reference impedance.

The system also includes logic circuitry for operating a motor coupled to the one reactive element to tune the one of reactive elements which is coupled to the load and series branch phase discriminator in accordance with certain combinations of the error voltages produced by the phase discriminator and the impedance sensing circuit for further modifying the load impedance previously modified by the one reactive element so that the load impedance falls at a given boundary in an area of a matchable impedance as may appear in an impedance plot. The matchable impedance area is generated by tuning the other reactive elements in the network over their given range. Thus, an impedance falling within this matchable range may be matched to the internal impedance of the device by tuningthe other reactive elements. The final match of the load impedance to the internal impedance of the device is accomplished by another impedance sensing circuit 'and phase discriminator in the series branch. The transmitter is connected to the series branch. The latter circuit and discriminator control motors coupled to the variable reactive elements in the other series and parallel branches when the load impedance or the modified impedance differs from the internal impedance of the device.

The invention itself, both as to its organization and method of operation as well as additional objects and advantages thereof, will 'become readily apparent from a 3 reading of the following description in connection with the accompanying drawings in which:

FIG. 1 is a block diagram of one embodiment of an antenna coupler system in accordance with the invention;

FIG. 2 is a block diagram of an antenna coupler system in accordance with another embodiment of the invention;

FIG. 3 is a circuit diagram of an impedance sensor utilized in the antenna coupler systems of FIGS. 1 and 2;

FIG. 4 is a circuit diagram of a phase discriminator utilized in the antenna coupler system of FIGS. 1 and 2;

FIG. 5 is a schema-tic diagram of a logic circuit for the antenna coupler systems of FIGS. 1 and 2;

FIG. 6 illustrates a typical inverted L-section matching network;

FIG. 7 is an impedance plot of the network of FIG. 6 illustrating an area of matchable impedance in an impedance plane generated by varying the reactive elements in the network of FIG. 6;

FIG. 8 is a schematic diagram of a two port matching network having variable reactive elements therein for modifying or transforming an impedance presented thereto; and

FIG. 9 is an impedance plot for the network of FIG. 8 which illustrates the matchable impedance area in the impedance plane of the network of FIG. 8.

An antenna 2, such as a whip antenna, half-wave doublet, or the like, all of which, as previously mentioned, many present different load impedances to a high frequency transmitter 3 (viz. 2-30 mc./s. output), initially and when used in mobile service. The transmitter 3 supplies RF power to the antenna 2 through an antenna coupler which functions as an impedance matching system. The transmitter 3 has a relatively fixed internal impedance during the transmission of RF power through the impedance matching system to the antenna 2.

The impedance matching system comprises a two port network, including series and parallel branches connected in a T-section network configuration. However, it should be understood that a pi section network configuration, such as the one seen in the impedance matching system in FIG. 2, may be used in the practice of the invention. The T-section network includes first and second series connected tunable inductors 6 and 7, respectively defining the series branches and a tunable capacitor 8 connected between a junction or node 9 of the first and second inductors 6, 7 and ground defining a parallel branch. The first and second inductors 6 and 7 are connected between a node 5 and another node 10.

The first and second inductors 6 and 7 may be, for example, coils, the turns of which may be shorted out by varying mechanisms including a roller or wiper (not shown) to vary the inductive reactance thereof. The varying mechanisms for the first and second tunable inductors 6 and 7 are coupled to a reversible 'DC motor 11 and a reversible servo motor 12, respectively, both of which may be energized in either a forward or reverse direction to increase or decrease the inductance of the first and second inductors -6 and 7 respectively.

The impedance matching system 1 also includes a reference impedance sensor 14 and a phase discriminator 15, connected between the node 9 and the first tunable inductor 6 for sensing the RF voltage at node 9 with respect to ground and the RF curent owing through the first inductor 6 to derive impedance and phase information as will be described more fully together with FIGS. 3 and 4. The first inductor 6 may modify the impedance of the antenna 2 as seen looking into the node 5. The impedance sensor 14 and the phase discriminator 15 each produce an error voltage output when the impedance of the antenna 2, or the load impedance as modified by the inductor 6 has an impedance magnitude which varies from a reference impedance and the phase of the RF voltage at node 9 with respect to ground is out -of phase ,4 with the RF current flowing in the inductor 6, respectively.

A logic circuit 16 is connected to the reference impedance sensor 14 and the phase discriminator 15. The logic circuit 16 has its output terminal 17 connected to the DC motor 11. The logic circuit 16 is shown in more detail in FIG. S. The logic circuit 16 tunes the inductor 6 by energizing the DC motor 11 in a reverse or forward direction until certain combinations of error voltage outputs from the phase discriminator 15 and the impedance sensor 14 are satisfied, as will -be more fully explained with reference to FIGS. 5 to 9.

Another set of sensing means, includes an impedance magnitude sensor 18 and an input phase discriminator 15a, similar to the reference impedance sensor 14 and the phase discriminator 15, respectively. The impedance pedance sensor 14 in that the impedance magnitude sensor 18 derives an output error voltage only when the impedance as seen looking into the node 10 differs from the internal impedance of the transmitter 3. The output of the impedance sensor 18 is applied to the servo motor 13 through an amplifier 22, which includes an input terminal 23 and inhibiting means, not shown, which blocks the output of the amplifier 22 whenever the logic circuit 16 has van output voltage at terminal 17. The inhibiting means may be, for example, an AND gate. Terminal 17 is connected to the input terminal 23 by a lead 24. Thus, servo motor 13 cannot rbe energized as long as logic circuit 16 has an output voltage at terminal 17.

The phase discriminator 15a includes output terminals 63a and 64a connected to the servo motor 12 through an .amplifier 26 which also includes an input terminal 27 connected to the output terminal 17 of the logic circuit 16 by way of the lead 24. The amplifier 26 is also blocked as long as the logic circuit 16 has an output voltage at terminal 17 so that the servo motor 12 cannot be energized unless output terminal 17 is at ground or at a reference potential. Thus, as will -be seen later, the first tunable inductor 6 is tuned first, before the second inductor 7 and the capacitor 8 are tuned.

Referring to FIG. 3, the impedance sensor 14 is shown in a schematic diagram to illustrate a typical impedance sensor which may be used in the practice of the invention. The impedance sensor 14 may be any one of the type which has a zero output or null at terminals 31 or 32, as long as the magnitude of the load impedance of the antenna 2 or the impedance as modified by the first inductor 6 has a value substantially equal to the reference impedance. In other words, as long as the quotient of the RF voltage at junction node 9 divided by the RF current fiowing therethrough has a magnitude substantially equal to the reference impedance. However, if the quotient (impedance) of the RF voltage and RF current has a different magnitude than the reference impedance magnitude, one of the terminalsy 31 or 32 will have a more positive potential with respect to the other terminal.

The impedance sensor 14 comprises a transformer 33 which has a primary winding 34, connected in series between the first inductor 6 and the junction node 9. The transformer has a secondary 35, connected at one end to ground and to a rectifier 36 at the other end. The primary 34 is illustrated as a single turn of a coil to show that the impedance sensor 14 has relatively no electrical effect on the RF voltage and current in the series branch which includes the inductor 6. A loading resistor 37 is connected between the anode 38 of the rectifier 36 and the other end of the secondary 35. The cathode 39 of the rectifier 36 is connected via a resistor 41 and a capacitor 42 to ground. One of the outputs of the impedance sensor 14 is taken off at the output terminal 32 connected to the output of the rectifier 36, The impedance sensor 14 also includes a capacitor divider 44 connected from the series branch (inductor 6) to ground. The capacitor divider' 44 has an output at junction 45, connected to a rectifier 46. The output of the rectifier 46 is connected -to the output terminal 32 and to a filter circuit, including a capacitor 47 and a loading resistor 48, both of which are connected to ground.

The voltage across secondary 35 is proportional to the line current. Thus, voltage is rectified by the rectifier 36 and ltered by the filter 42 and applied to the output terminal 31. At the same time, the capacitor voltage divider 44 producesl a voltage proportional to the line voltage which is rectified by the rectifier 46 and applied to the output terminal 32. The parameters of the electrical elements mentioned above in the impedance sensor 14 are selected such that the output voltage on the terminals 31 and 32 are equal when the ratio or quotient which equal the impedance) is at a predetermined magnitude, for example when the impedance magnitude is substantially equal to the reference impedance magnitude. If the load impedance as seen through the node 9 and the inductor 6 varies from the reference impedance, one of the terminals 31 or 32 may have a more positive DC Voltage with respect to the other terminal or, in other words, the potential on terminal 31 may be negative or positive with respect to the potential on terminal 32, depending on whether the actual load impedance or the modified impedance of the antenna 2 is higher or lower than the reference impedance.

The impedance sensor 18 is similar to the impedance sensor 14 except that it is responsive to a different impedance magnitude, namely, an absolute impedance substantially equal to the internal impedance of the transmitter 3. Thus, an error voltage output will be produced by the impedance sensor 18 at output terminals 28 and 29 if the impedance as seen by the transmitter 3 looking into the node differs from the internal impedance 0f the transmitter 3.

The phase discriminator is shown in detail in FIG. 4, and is but one example of the type of phase discriminator which may be employed in the system without departing from the invention. The phase discriminator 15 includesl a transformer. 50 having a center tapped secondary 51 connected at its center to a capacitive voltage divider 52 at a junction 53. The other ends 54 and 55 of the secondary 51 terminate at rectifiers 57 and 58 respectively. The output of the rectifiers 57 and 58V are applied to filter circuits 61 and 62 and have an output at terminals 63 and `64. In the operation of the phase discriminator 15, a sample of the line voltage is taken by the capacitive voltage divider 52 and added vectorially to the induced voltage in the two halves of the center tapped secondary 51 of the transformer 50. These voltages are in quadrature with the line current in the serres branch which includes the first inductor 6. If the line voltage and current are in phase, the resultant voltage vectors applied to the rectifiers 57 and 58 are of equal magnitde, so that the outputs of the rectifiers 57 and 58 at terminals 63 and 64 respectively, are at the same potential. A phase change between the current and voltage, however, in the RF line or series branch including the inductor 6 will disturb this balance and produce a difference in potential in a direction corresponding to the phase sign and magnitude roughly corresponding to the phase angle. A difference in potential at terminals 63 and 64 indicate a capacitive or inductive reactance in the series branch which includes the tunable inductor 6.

The phase discriminator 15a is similar to the reference phase discriminator 15. Elements of the absolute phase discriminator 15a corresponding to the elements of the reference phase discriminator 15 are similarly numbered except that a lower case letter a hasv been added after each numeral of the absolute phase discriminator 15a.

The logic circuit 16 is shown in detail in FIG. 5. The logic circuit 16 includes a first relay 71 having a solenoid coil 72 connected to the reference impedance sensor 14 at terminals 31 and 32. The first relay 71 includes normally open contacts 73 and 74. Normally open contact 73 comprises a fixed contactor 73a and a moveable contactor 73b. The normally open contact 74 comprises a fixed contactor 74a and a moveable contactor 74b. Contactor 74b is' connected to a source 75 of positive DC voltage which may be, for example, 24 volts DC positive with respect to ground for energizing the DC motor 11 in a reverse direction. The relay 71 includes an armature 76 coupled to the moveable contactors 73b and 74b. The armature 76 is of the type which may be moved in an upward direction when terminal 31 has a positive potential with respect to terminal 32 so as to close contact 73 and keep contact 74 in an open position. When terminal 31 has a negative potential with respect to terminal 32, armature 76 is moved in a downward direction keeping contact 73 open and closing contact 74. When terminals 31 and 32 have a balanced output or null (0), the contacts' 73 and 74 remain normally open.

Logic circuit 16 also includes a second relay 77 having a solenoid coil 78 connected to terminals 63 and 64 of the reference phase discriminator 15. Relay 77 includes normally open contacts 8.1 and 82. Contact 8-1 comprises a :fixed contactor l81a and a moveable contactor 81h. Contact y82 comprises a fixed contactor 82a and a moveable contactor 82b. The relay 72 also includes an armature 83 coupled to the moveable contactors 81b and 82h. The armature '83 is at a quiescent or neutral position `when terminals 63 and 64 have a null and balanced output. However, if terminal `63 has a positive output with respect to terminal 64, the armature 83 will be moved in an upward direction closing contact 81 and keeping contact 82 open. When terminal "63 has a negative potential with respect to terminal 64, armature 63 is actuated in a downward direction keeping contact 8'1 opened and closing contact 82.

Moveable contactor 81b of relay 77 is connected to a source 84 of negative potential so that when contact 81 and contact 73 are closed a negative potential will exist at terminal 17a by Iway of lead 85. Moveable contactor `82b of relay 77 is connected to the source 75 of positive potential so that when contact 74 or contact 82 is closed, a circuit is completed from the source of positive potential 75 to terminal 17a by way of lead 85.

Relays 71 and 77 are interconnected to derive a null, or a positive or negative potential on terminals 17a and 17 in response to certain error voltage outputs from the reference impedance sensor 14 and the impedance phase discriminator 15. Moveable contactor 73b is connected to fixed contactor 81a by a lead 67. Fixed contactors 73a, 74a and 82a are connected in common to lead 85 at junction 68.

It may now be seen that each of the armatures 76 and l83 of relays 7-1 and 77 respectively, may be disposed in three different positions, namely, up, down and a neutral position in response to three diterent potentials, namely, positive, negative, or a null voltage on terminal '31 of the impedance sensor 14 and on terminal 63 of the phase discriminator 15. Thus, nine combinations of armature positions are possible to derive a null, a positive or negative voltage on terminals -17a and 17 for cle-energizing or energizing the DC motor 11 in a forward or reverse direction.

Logic circuit 16 also includes an upper limit switch 86 and lower limit control switch 87. 'I'he upper limit switch 86 includes a normally closed contact 88, and a bypass diode `89 to terminal 17a. Diode 89 may be forward biased by a negative potential on terminal 17a to short circuit contact l88. The lower limit switch 87 includes normally closed contact 91 and a bypass diode 92 which is forward biased when terminal 17aI has a positive potential and contact l88 is closed. Thus, upper and lower limit switches 86 and 87 are thus useful for providing control circuits when the roller or wiper (not shown) of the inductor -6 is at either end of its extreme travel. The diodes 90 and 91 provide an alternate circuit path for re-energizing the DC motor 11 in the reverse direction when either of the contacts 88 or 91 are open.

Before the operation of the impedance matching system 1 is described, it is believed that it will be helpful to describe the impedance matching characteristics of an inverted L-section network and a T-section network. Referring to FIG. 6, the second inductor 7 and the capacitor 8 define an inverted L-section network connected between the nodes 9, 10, and ground. Assuming that the inductor 7 and the capacitor 8 are tunable over an infinite range, the inverted L-section network has a matchable arca Zx defined by the shaded area in FIG. 7. The shaded matchable area extends into infinity along the reactive axis (jx) and a pure resistance axis (R) except for a small unshaded area 100 'wherein the inductor 7 and the capacitor 8 can not be tuned to modify the load impedance to an absolute impedance (Zo) In actual practice, the matchable area ZX of FIG. 7 is defined by the parameters of the inductor 7 and the capacitor 8, and is smaller (viz. does not extend to infinity or is bounded) than the matchable area shown in FIG. 7.

FIG. 7 shows the T-section network of FIG. 1 comprising the series connected first and second inductors 6 and 7 and the capacitor 8 in shunt from the node 9 to ground. The T-section network has an overall matchable area defined by the shaded area ZX in the impedance plane -which is larger than the matchable area Zx of FIG. 7. The matchable area ZX is shown as extending to infinity, however, it should be understood that the matchable area is smaller for practical or actual inductors and capacitors. The matchable area ZX includes the area 100 which was not matchable in FIG. 7. The first inductor 6 of the T-section network effectively increases or complements the matchable area, or in other words, the T-section network can modify the load impedance of the antenna 2 even if it were to fall within the unmatchable area 100 of FIG. 7. Further, the inductor 6 may modify the load impedance of the antenna 2 an irnpedance having a value shown by a line i101 in FIG. 9. A load impedance having a magnitude and phase angle which would place it below the line .101 may be modified by tuning the inductor 6 to achieve a modified impedance having a phase angle and impedance magnitude falling along the curved section 102 of line 101, or the load impedance may be modified to a pure resistance having a value falling along section 10'3 of line 101, as will be more fully described in the operation of the impedance matching system of FIG. 1.

`In the operation of the impedance matchingsystem, the transmitter 3 supplies RF power to the antenna 2 through the impedance matching system. rInitially, the impedance matching system is adjusted to effectively provide only a low resistance conducting path between the transmitter 3 and the antenna 2. This is accomplished in the first instant by adjusting the capacitor 8` to achieve an open AC circuit between node 9 and ground. The first and second inductors 6 and 7 are also adjusted to provide this low resistance path by shorting out all the active turns in each coil (not shown) of the inductors 6 and 7. rIhe coil roller or wiper which shorts out all the active turns of the inductor i6 is disposed at one end of the coil, as previously mentioned, so that contact 9'1 of the low limit switch l87 is open. Only a positive voltage on terminal y17a will forward bias diode 92, short circuit contact 91, and energize the DC motor `.111 in a direction to increase the inductance of the first inductor 6.

When RF power is being transmitted to the antenna 2, the reference impedance sensor 14 and the reference phase discriminator 15 each sense the RF voltage with respect to ground in the branch containing the first inductor 6 and the current flowing in that branch. As was previously mentioned, if the magnitude of the antenna impedance is equal to the magnitude of the reference impedance, a null or balanced output will exist on terminals 31 and 32. However', if the magnitude of the antenna impedance is higher or lower than the magnitude of the reference impedance terminal 31 will be more positive or more negative respectively, with respect to terminal 32. The phase discriminator 1S has a null or a balanced output on terminals 63 and 64 when the voltage in that branch containing the first inductor 6 with respect t0 ground is in phase with the current flowing in that branch. However, if the current is out-of-phase with the voltage terminal 63 will be more positive or more negative with respect to terminal 64 as a function of the phase angle.

In accordance with the invention, the output voltages of the reference impedance sensor 14 and the reference phase discriminator 15 derive nine possible error voltage output combinations which are used to signify that the antenna impedance is within a matchable range or area ZX (FIG. 9) of the inverted L-section network comprising inductor 7 and capacitor 8, or that the antenna impedance must be transformed or modified to fall within this matchable area by tuning the rst inductor 6. The matchable area of the inverted L-section defined by thc inductor 7 and the capacitor 8 is defined as that area bounded by the vertical axis jx, the line 101 which includes sections 102 and 103, and that area above the line 101.

The nine possible combinations of output voltages of the reference phase discriminator 15 and the reference impedance sensor 14 are shown in the table and legend below.

(-|) represents that DC motor 11 is energized in a direction to increase the inductance of indicator 6;

Do--Sub letter o indicates DC motor 11 is deenergized; and

( l represents that DC motor 11 is energized in a direction to decrease the inductance of indicator 6.

The output of the impedance sensor 14 is shown in the top box while the output of the reference phase discriminator 15 is shown in the side box and the nine possible combinations of the output voltages at terminals 17a and 17 are shown within the nine squares.

Each of the nine possible combinations of output voltages at terminal 17 shown in the table will be described briefly together with FIG. 9. Assuming first that the antenna impedance has a zero (0) phase angle and an impedance magnitude equal to the reference impedance aS shown as point E in FIG. 9, it will be seen that the impedance sensor 14 and the phase discriminator 15 will each have a (0) or balanced output on terminals 31. 32

and 63, 64 respectively. The relays 71 and 72 connected to the impedance sensor 14 and the phase discriminator 15 respectively, are de-energized in response to this balanced output and the contacts 73, 74 and 81, 82 remain normally open, in which case, terminals 17a and 17 have a zero potential. When terminal 17 has a (0) potential, the DC motor 11 is de-energized and amplifiers 22 and 26 are enabled. When amplifiers 22 and 26 are enabled, the output of the phase discriminator a and the impedance sensor 18 may be coupled directly to the servo motors 12 and 13 respectively. The phase discriminator 15a has a null (0) or balanced output on terminals 63a and 64a since the assumed antenna impedance has a zero (O) phase angle, as previously mentioned. The output of the phase discriminator 15a applied to the amplifier 26 and the servo motor 12. The servo motor 12 remains in a de-energized state in response to the null output of the phase discriminator 15a. The absolute impedance sensor 18, however, has an unbalanced output on terminals 28 and 29, which output is amplified by the amplifier 22 and applied to the servo motor 13. The servo motor 13 tunes the capacitor until the antenna impedance substantially equals the internal impedance of the transmitter 3 and the impedance sensor 18 has a balanced output on terminals 28 and 29.

Effectively, the impedance matching system transforms or modifies the antenna impedance in two sequential stages. In the first stage, the inductor 6, the reference impedance sensor 14, the reference phase discriminator 15, the logic circuit 16 and the DC motor 11 coupled to the inductor 6 are used. In the second stage, the inverted L- section network including the inductor 7 and the capacitor 8 are used. The second stage also uses the impedance sensor 18, the amplifier 22 and the servo motor 13 coupled to the capacitor 8. The absolute phase discriminator 15, the amplifier 26 and the servo motor 12 coupled to the second inductor 7 are also used in the second stage. The second stage operation modifies or transforms the antenna impedance as presented directly to the transmitter 3 or the antenna impedance as modified during the first stage.

The inverted L-section network including inductor 7 and the capacitor 8 may modify the antenna impedance provided it falls within the matchable impedance area, as shown and previously described in connection with FIG. 9. That is, the inverted L-section network may be tuned for those impedances which fall in the matchable area ZX and along the boundary defined by the curved section 102 and the resistance axis R shown generally as section 103 along line 101. In accordance with the invention, the antenna impedance is modified by the first stage if the antenna impedance falls within the shaded area below the line 101 including curved section 102 and 103.

Referring back to the table and FIG. 9, an antenna impedance having a phase angle and magnitude shown generally at point G may be modified in the following manner in accordance with the invention. The reference phase discriminator 15 produces a negative potential on terminal 63 as a function of the phase angle of the antenna impedance, while the impedance sensor 14 produces a positive output on terminal 31 in response to the magnitude of the antenna impedance. The output of the phase discriminator 15 energizes solenoid coil 78 and causes armature 83 to be displaced in a downward direction opening contact 81 and closing contact 82. At the same time, the error voltage output of the impedance sensor 14 energizes solenoid coil 72 causing armature 76 to be displaced in a downward direction opening contact 73 and closing contact 74. When either of the contacts 74 or 82 are closed, a positive potential or voltage is supplied from source 75 to terminal 17a by way of lead 85. The positive potential on terminal 17a energizes the DC motor 11 in a direction to increase the inductance of the first inductor 6. The antenna impedance is thus modified from point G (FIG. 9) to a point along section 103 of line 101. The antenna impedance may now be further modified by the inverted L-section network defined by the inductor 7 and the capacitor 8 to match the internal impedance of the transmitter 3, as previously described.

An antenna impedance which has a magnitude and phase angle, shown generally at point A of FIG. 9, may also be modified in accordance with the invention. The impedance sensor 14 in response to the impedance shown at point A produces a more positive potential on terminal 31 than on terminal 32 since the impedance at point A is greater than the reference impedance magnitude shown generally by the curved section 102 of line 101. A positive potential on terminal 31 energizes the coil 72 in a direction which displaces the armature 76 in an upward direction closing contact 73 and keeping contact 71 open. The phase discriminator 15 also produces an unbalanced output wherein terminal 63 is more positive than terminal 64 so that armature 83 is displaced in an upward direction keeping contact 82 open and closing contact 81. A circuit is completed from the source 84 of negative potential through the contacts 81 and 73 to terminal 17a. A negative potential on terminals 17 and 17a energizes the DC motor 11 in a direction to decrease the inductance of the first inductor 6. In other words, the roller or wiper, not shown, shorts out the active turns of the coil in response to the energization of the DC motor by a negative potential until the impedance shown at point A has a zero (0) phase angle and a magnitude equal to the magnitude of the reference impedance, or until contact 91 of the low limit switch 87 is opened by the wiper. The antenna impedance shown at point A is thus first modified by the first inductor 6 and then modified to match the internal impedance of the transmitter by the inverted L-section network comprising the second inductor 7 and the capacitor 8.

Referring back to the table, it may also be shown that antenna impedances C, F, I and H, shown in FIG. 9, may also be modified to fall within the matchable area of the inverted L-section network comprising the inductor 7 and the capacitor 8. If the reference impedance sensor 14 or the phase discriminator 15 have a negative output on terminals 31 or 63 respectively, the coils 72 and 78 respectively, are energized in a direction to move the armatures 76 or 83 in a downward direction. If the armatures 76 or 83 are moved in a downward direction, contacts 74 or 82 are closed completing a circuit from the source of positive potential 75 through one of the contacts 74 or 82 to the terminals 17 and 17a to the DC motor 11. A positive potential applied to the DC motor 11 energizes the DC motor 11 in a direction to increase the inductance of the first inductor 6. The motor 11 is energized until the antenna impedance is modified to fall along the line 101, in which case, the inverted L-section network may further modify the antenna impedance to match the internal impedance of the transmitter 3. It may now be seen that the first inductor 6 is tunable in response to the error output voltages of the impedance sensor 14 and the phase discriminator 15 applied to the logic circuit 16.

FIG. 2 shows another embodiment of the invention in an impedance matching system 200. The impedance matching system 200 differs from the impedance matching systern 1 in that a pi section network is employed instead of a T-section network configuration. The pi section network comprises a reactive element 207 in a branch 208 and first and second reactive elements 205 and 206 respectively, in shunt branches 209 and 210 respectively, to ground. The impedance matching system 200 is connected between the antenna 202 and the transmitter 203 at nodes 204 and 211. A reference impedance sensor 214 and a reference phase discriminator 215 are connected in the series branch 208 between the reactive element 207 and the node 204 for sensing the voltage at node 204 with respect to ground and the current flowing through the series branch 208. The reference impedance sensor 214 is similar to the reference impedance sensor 14 of the impedance matching system 1. The reference phase discriminator 215 is similar to the reference phase discriminator 15 of the impedance matching system 1. Thus, the reference phase discriminator 215 derives an error output voltage which is applied to a logic circuit 216. The error output voltage of the reference phase discriminator 215 is derived whenever the voltage at node 204 with respect to ground is out of phase with the current flowing through the branch 208. A null or zero error voltage output is derived whenever the voltage at node 204 is in phase with the current flowing through the branch 208. The reference impedance sensor 214 also derives an error voltage output whenever the impedance of the antenna 202, as presented at node 204, varies from a given refence impedance. The error output voltage from the reference impedance sensor 214 is also applied to the logic circuit 216, as previously described in the impedance matching system 1 of FIG. l.

The logic circuit 216 corresponds to the logic circuit 16 of the impedance matching system 1 and is also used for driving or energizing the DC motor 211. The output of the logic circuit 216 is also applied to amplifiers 222 and 226. The amplifiers 222 and 226 are enabled only when the logic circuit 216 has a zero (0) output (viz.) ground or some other reference potential).

The impedance matching system 200 also includes an absolute impedance sensor 218 and an absolute phase discriminator 215a connected in series with the series branch 208. The absolute phase discriminator 215a and the absolute impedance sensor 218 are similar to the absolute phase discriminator 15a and the impedance sensor 18 of the impedance matching system 1. A servo motor 213 is connected between the amplifier 222 and the reactive element 205. Another servo motor 212 is connected between the reactive element 207 and the amplifier 226. The output of the logic circuit 216 is connected to the amplifiers 222 and 226 by a conductor 224.

The operation of the impedance matching system 200 is similar to the impedance matching system 1. Initially the impedance matching system 200 is adjusted to provide a low resistance AC conducting path between the antenna 202 and the series branch 208 to the transmitter 203. This is accomplished by adjusing the reactive elements 205 and 206 to provide an open circuit between the branch 208 and ground. The reactive element 207 is also adjusted to provide a minimum reactance and resistance. The antenna impedance is thus presented directly to the transmitter 203 and RF power is supplied from the transmitter directly to the antenna 202. The reference impedance sensor 214 and the phase discriminator 215 sense the voltage and current in the branch 208 and derive error output voltages in the same manner as described for the impedance matching system 1 of FIG. l; that is, the impedance sensor 214 derives a null or zero (0) potential whenever the antenna impedance substantially equals the reference impedance. The reference impedance sensor 214 derives a positive or negative error voltage whenever the antenna impedance varies from the reference impedance. The phase discriminator also produces an error voltage whenever the phase of the voltage at node 204 with respect to ground differs from the phase of the current owing through the branch 208. The output error voltages from the impedance sensor 214 and the reference phase discriminator 215 are applied to the logic circuit 216, which derives an output potential as a direct function of the combination of the outputs from he phase discriminator 215 and the impedance sensor 214 as previously described for the impedance matching system 1 of FIG. 1. The reactive element 206 is thus tuned to modify the antenna impedance to fall within the line 101 of FIG. 8 so that the antenna impedance may be later modified by the inverted L-section network defined by the reactive elements 205 and 207. Thus, once the antenna impedance is modified to fall within the matchable area, as shown in FIG. 9, the inverted L-section network defined by the reactive elements 205 and 207 may further modify the antenna impedance to derive an absolute impedance having a zero (0) phase angle and a magnitude equal to the internal impedance of the transmitter 203.

From the foregoing descriptions, it will be apparent that there has been provided a fully automatic impedance matching system which is readily adapted to couple a load having a variable impedance to an active output device having a relatively fixed impedance. While several embodiments of the invention have been described, it should be understood that variations and modifications thereof within the spirit of the invention will undoubtedly suggest themselves to those skilled in the art. Accordingly, the descriptions should be taken merely as illustrative and not in any limiting sense.

What is claimed is:

1. An impedance matching system for coupling a radio frequency output of an active output device having a given internal impedance to a load having a load impedance, said system comprising (a) a two port network including first, second and third variable reactive elements in series and parallel branches connected between said device and said load, a node of said network being coupled to said load impedance and having at least a series branch of said network connected thereto,

(b) a phase discriminator for detecting an out-of-phase condition in said series branch between voltage and current therein to derive a phase error voltage output when said condition exists,

(c) impedance magnitude sensing means for deriving an impedance error voltage output when the magnitude of said load impedance differs from a given reference impedance,

(d) logic means for varying the impedance of said first element in response to said phase error voltage output and said impedance error voltage output,

(e) where said node has both the series and a parallel branch of said network connected thereto, said first element being in said last named parallel branch; where said node has only said series branch connected thereto, then said first element being in said last named series branch, and

(f) means coupled to said other reactive elements for tuning said other reactive elements to match said load impedance to said internal impedance of said device.

2. The invention defined in claim 1 wherein said two port network is a T-section network.

3. The invention defined in claim 1 wherein said two port network is a pi section network.

4. The invention defined in claim 1 wherein said last named means includes another phase discriminator and another impedance magnitude sensing means for deriving an impedance error voltage only when the magnitude of said load impedance varies from said internal impedance of said active output device.

5. The invention as set forth in claim 1 wherein said active device is a transmitter having a variable output frequency and said load is an antenna.

6. The invention set forth in claim 1 wherein said logic means includes a motor coupled to said first element for tuning said first element in response to certain combinations of said phase error voltage output and said irnpedance error voltage output until said load impedance has an impedance value as seen through said first element falling within a given matchable impedance area in an impedance plane.

7. The invention set forth in claim 6 wherein said logic means inhibits the operation of said means set forth in subparagraph (b) during operation of said motor.

8. The invention defined in claim 7 wherein said logic means includes first and second relays connected to said impedance sensor and said phase discriminator respectively, and to a source of positive and negative potential 13 14 for energizing said motor in response to said certain com- 3,160,832 12/ 1964 Beitman etal. ---T T 325-174 X binations of said phase error voltage output and said 3,160,833 12/1954 LudVgSOIl et al 33317 t. Impedance voltage error cmp ROBERT L. GRIFFIN, Primary Examiner.

References Cited 5 BENEDICT V. SAF OUREK, Assistant Examiner. UNITED STATES PATENTS U.S. Cl. X.R. 2,745,067 5/1956 True et al. 333-17 325-177; 333-17 19j-,p30 UMTED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent: No. 3suu323l Dated May 6, 1969 Inventor(s) Jorge E. ROZa It is certified that error appears in the above-identified patent and that; said Letters Patent are hereby corrected as shown below:

Column 1, lines 3 to 5 should read:

--Jorge E. Roza, Rochester, N. Y. assignor to General Dynamics Corporation, a Corporation of Delaware-- SIGNED ANU SEALED OCT 21 1969 am wenn EdwardMFletdmJr.

mlm E. sommm, .nu Attestmg Offlcer Comissfioner of Patents

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