WO2002031907A1

WO2002031907A1 - Switchable power combiner

Info

Publication number: WO2002031907A1
Application number: PCT/KR2001/001631
Authority: WO
Inventors: Rack-June Back; Jung-Hak Ahn; Jong-In Ryu; Chang-Hwan Kim; Young-Sang Yoon
Original assignee: Ace Technology
Priority date: 2000-09-27
Filing date: 2001-09-27
Publication date: 2002-04-18

Abstract

A switchable power combiner which ensures the impedance matching characteristics regardless of the change in the number of signal combining paths. The switchable power combiner receives a plurality of input signals through a plurality of input ports and combines the receives the signal to output the combined signal through an output port. First switching means (30) is arranged between the plurality of input ports and a combing node (40) to connect at least one of the input ports to the combining node. A plurality of impedance matching circuits (50, 52, 54) are selectively activated by second switching means (60) to electrically connect the combining node (40) to the output port (PO).

Description

SWITCHABLE POWER COMBINER

Technical Field

The present invention relates to a power combiner of a RF or a microwave frequency bandwidth and, more particularly, to a switchable power combiner of which number of signal combining paths is variable.

Background Art

A switchable power combiner, typically being used in an amplification stage which controls the output power of a base station in a communication system, combines a plurality of signals provided by respective power amplifiers. In other words, the switchable power combiner carries out, along with a counterpart power divider, the functions dividing and combining of signals while providing a redundant signal path against an abnormality of any power amplifier. In a Wilkinson type divider/combiner having fixed signal paths, the optimum

characteristic impedances of impedance matching lines are determined based on the number

of signal paths to be divided or combined. For example, the characteristic impedances of the impedance matching lines are determined to be V^"2Z₀ in case of 2-way divider/combiner and V^~3Z₀ in case of 3 -way divider/combiner, where₀Z is the common characteristic

impedance, 50Ω. On the other hand, in the case that the number of combined signal paths

is variable rather than being fixed, the average of optimum values for different operation

modes have been chosen as the characteristic impedances of the impedance matching lines. FIG. 1 illustrates an example of the average-matched 3 -way switchable power

combiner. One or more desired signals of the input signals received through input ports PI_l5 PI₂, and PI₃ are selected by switches SI through S6 to be combined, and a combined signal is output through an output port PO. The number of combined paths is determined

by the number of power amplifiers being operated in the system. Switching control signals for controlling the switching operation of the switches SI through S6 are provided by a controller not shown in the Figure. For example, when the signals received through the input ports PI_X and PI₂ are to be combined, the switches SI, S2, S4, and S5 are turned on

while the switches S3 and S6 are turned off and the combining signal is output through the output port PO. Meanwhile, isolation resistors Rl, R2, and R3 and terminators 14, 16, and 18 are provided after the input ports PI_1: PI^ and PI₃. Additionally, each of the switch pairs SI and S4, S2 and S5, and S3 and S6 operate simultaneously responding to a respectively common switching control signal.

As mentioned above, however, the characteristic impedance Z_m of each of the impedance matching lines 4, 6, or 8 shown in FIG. 1 is generally determined to be the average, Z₀/2( 2 V^"3Z₀) (=78.7Ω), of /2Z, (=70.7Ω) and V^"3Z (=86.6Ω) which are optimal impedances for 2- way and 3 -way combining operation modes, respectively. While

the average matching may provide satisfactory reflection loss requirements in 2-way or 3-

way operation mode, it may be difficult to use the combiner for 1-way operation mode since the reflection loss characteristics is deteriorated. To avoid such a problem, some

devices employ a combination of a single path transmission line and the average-matched transmission lines alternatively, which, however, cannot accomplish the perfect matching

condition for 2-way or 3 -way operation mode, either.

Disclosure of the Invention

To solve the above problem, the object of the present invention is to provide a switchable power combiner which ensures the impedance matching characteristics

regardless of the change in the number of signal combining paths.

The switchable power combiner receives a plurality of input signals through a plurality of input ports and combines the received signals to output the combined signal through an output port. First switching means is arranged between the plurality of input

ports and a combining node to electrically connect at least one of the input ports to the combining node. A common node is electrically connected to the combining node. A plurality of impedance matching paths, each of which has a characteristic impedance different from that of one another, is disposed behind the common node. Second switching

means electrically connects a first terminal of a path selected from the plurality of impedance matching paths to the common node and connects a second terminal of the selected path to the output port. The selected path is determined according to the number the input ports connected to the common node. According to the present invention, the

characteristic impedance of at least one of the plurality of impedance matching paths may

be variable.

In a preferred embodiment, at least one of the plurality of impedance matching

paths includes a variable impedance matching unit. The housing of the variable impedance matching unit is made of metallic material, and a cavity is formed inside the housing. Two connectors are installed outside the housing, and a transmission line for connecting the

connectors is disposed along the cavity. Distance varying means facilitates the change of a distance between the transmission line and a ground plane in the cavity. The variable impedance matching unit may further includes means for supporting the transmission line

in the cavity.

The first switching means preferably includes a plurality of switches each of which has a switching bar. The plurality of switches have the same length and are arranged being spaced by the same distance with respect to a point on the combining node connected to the common node.

Brief Description of the Drawings

The above objectives and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:

FIG. 1 illustrates an example of a conventional 3 -way switchable power combiner;

FIG. 2 is a block diagram of an embodiment of a 3 -way switchable power combiner of the present invention;

FIG. 3 illustrates an implementation of the switchable power combiner of FIG. 2;

FIG. 4 is a magnified view of "CC" portion shown in FIG. 3;

FIG. 5 illustrates the structure of any one of the switches shown in FIG. 3; FIG. 6A illustrates a first and a second variable impedance matching units shown

FIGS. 2 and 3;

FIG. 6B is a bottom view of the variable impedance matching unit of FIG. 5A; FIG. 6C is a cross-sectional view taken along lines A-A as shown in FIG. 5 A; and FIG. 6D is a cross-sectional view taken along lines B-B as shown in FIG. 5 A.

Embodiments

Referred to FIG. 2, a 3 -way switchable power combiner according to a preferred embodiment of the present invention includes three input ports PI_l3 PI₂, and P^, a first switching unit 30 for selectively coupling the input ports PI_l5 PI₂, and PI₃ to a combining node 40, a first through a third impedance matching lines 50 - 54 disposed between a common node 44 and an output port PO, a second switching unit 60 for selectively activating one of the impedance matching lines 50 - 54, and a controller 70 for providing a switching control signal to the first and the second switching units 30 and 60. Each of the input ports PI , PI₂, and PI₃ is connected to the first switching unit 30 through a respective transmission line 20, 22, or 24, and receives a RF signal from a power

amplifier (not shown in the figure) to provide such a signal to the first switching unit. According to the switching positions of the switches in the first switching unit 30, some

or all of the input signals provided through the input ports PI_b PI₂, and PI₃ are combined at the combining node 40, and a combined signal is provided to the common node 44

which is identical with or electrically connected to the combining node 40. A separate

transmission line 30 may be provided further between the combining node 40 and the common node 44. The combined signal is transmitted to the output port PO through one of the impedance matching line 50 - 54 selected by the second switching unit 60.

In the preferred embodiment, the first switching unit 30 includes three switches

SW_n, SW₁₂, and SW₁₃. The switch SW_U has a first terminal connected to the input port P^ and a second terminal connected to the common node 40. The switch SW₁₂ has a first terminal connected to the input port PI₂ and a second terminal connected to the common node 40. The switch SW₁₃ has a first terminal connected to the input port PI₃ and a second

terminal connected to the common node 40. Switching control signals CONT1 - CONT3 for operating the switches SW_U, - SW₁₃, respectively, are provided by the controller 70. The second switching unit 60 includes six switches SW₂₁ through SW₃₃. Switches

SW₂₁ and SW₃₁, which are controlled by a common switching control signal CONT1 to be switched simultaneously to the same switching position, makes the first impedance matching line 50 to connect the common node 44 to the output port PO when being turned

on. In the present embodiment, the switching control signal CONT1 is activated when two input signals are combined at the combining node 40. Switches SW₂₂ and SW₃₂ , which are controlled by a common switching control signal CONT2 to be switched

simultaneously to the same switching position, makes the second impedance matching line 52 to connect the common node 44 to the output port PO when being turned on. The

switching control signal CONT2 is activated when just a single input signal is provided to

the combining node 40. Switches SW₃₂ and SW₃₃, which are controlled by a common

switching control signal CONT3 to be switched simultaneously to the same switching

position, makes the third impedance matching line 54 to connect the common node 44 to the output port PO when being turned on. The switching control signal CONT3 is

activated when three input signals are combined at the combining node 40.

Each characteristic impedance of the impedance matching line 50 - 54 is different from one another. For example, the characteristic impedance Z₂ of the second impedance matching line 52 is Z₀ (50Ω) which is the same as that of a common transmission line. The

characteristic impedance Z_j of the first impedance matching line 50 may be 2Z₀, and the

characteristic impedance Z₃ of the third impedance matching line 54 may be ₀V^"3Z . Particularly, the characteristic impedances Z. and g of the impedance matching lines 50 and 54 are variable in the preferred embodiment as described below, so that an operator of the combiner may arbitrarily change the impedances to obtain optimum values. The switchable power combiner operates as follows.

When just a single port of the input ports PI_l5 PI₂, and PJ is coupled to the combining node by the first switching unit 30, the input signal is provided to the common node 44 via the combining node 40 and the connection line 42. Switches SW₂₂ and SW₃₂

in the second switching unit 60 are turned on while the other four switches are turned off in response to the switching control signals CONT1 - CONT3 from the controller. Thus, the second impedance matching line 52 connects the common node 44 to the output port PO. Accordingly, the input signal is transmitted to the output port PO through the second

impedance matching line 52. In the case that two of the three input ports PI_l3 PI₂, and PI₃ are coupled to the

combining node by the first switching unit 30, the input signals received through the two

ports are combined at the combining node 40 and provided to the common node 44 via the connection node 42. Switches SW₂₁ and SW₃₁ in the second switching unit 60 are turned on while the other four switches are turned off in response to the switching control signals

CONT1 - CONT3 from the controller. Thus, the first impedance matching line 50 which enables an optimal impedance matching in 2-way combining mode connects the common node 44 to the output port PO. Accordingly, the combined input signal is transmitted to the output port through the first impedance matching line 50.

In the case that all the input ports PI PI₂, and PI₃ are coupled to the combining node by the first switching unit 30, the input signals are combined at the combining node 40 and are provided to the common node 44 via the connection node 42. Switches SW₂₃ and SW₃₃ in the second switching unit 60 are turned on while the other four switches are turned off in response to the switching control signals CONT1 - CONT3 from the controller. Thus, the third impedance matching line 54 which enables an optimal impedance matching in 3-way combining mode connects the common node 44 to the

output port PO. Accordingly, the combined input signal is transmitted to the output port PO through the third impedance matching line 54.

FIG. 3 illustrates an example of an implementation of the switchable power combiner of FIG. 2. In the example of FIG. 3, each of the switches SW_n through SW₁₃ of the first switching unit 30 and the switches SW₂₃ and SW₃₃ of the second switching unit

60 shown in FIG. 2 is implemented by use of a switch having a switching bar, namely, a connection segment. Particularly, the connection line 42 and the switch SW₃₂ are merged

into a single switch SW₄₁, and the second impedance matching line 52 and the switch SW₃₂

are merged into a single switch SW₄₂. In FIG. 3, each of the switches SW_π through SW₁₃ of the first switching unit 30 has the same size or length to one another. Further, the switches are arranged symmetrically with respect to the combining node 40. In other words, as shown in FIG

4, all the distances (£>, E, and F) between the switches SW_n - SW₁₃ and a first contact of the switch SW₄₁, respectively, are the same as one another. Since the switches §W through SW₁₃ are arranged symmetrically in such a manner, any phase unbalance due to the geometrical shape or the structure of switches is obviated when two or more signals

are combined by the combiner.

In the preferred embodiment, all the switches SW_U through SW₄₂ shown in FIG. 3 have the same configuration as one another. FIG. 5 illustrates the structure of any one of the switches SW_n - SW₄₂ shown in FIG. 3. A first and second connector 100 and 102, which correspond to input and output terminals of each switch, respectively, are fixed at a bottom plate of a combiner housing 104 and selectively connected with each other by a driving mechanism 110 in response to control signals applied through control lines 106 and 108 The signals applied through control lines 106 and 108 are DC signals having the same magnitude but opposite polarity.

The driving mechanism 110 includes a first and second electromagnet 116 and 118, a rotating segment 120, and the connecting segment 128. The first and second

electromagnet 116 and 118 are fixed under the bottom surface of an upper plate 112 and

arranged symmetrically with respect to the horizontal position where the first connector 100 is located. On a lower panel 114 is installed a supporting member 113. The rotating

segment 120 is made of magnetic material and connected to the upper portion of the supporting member 113 by a pin 126 so as to be rotated within a certain angle range. The

rotating segment 120 has a shape extending from its horizontal center connected to the supporting member 113 to the position under the first and second electromagnet 116 and 118, and has a plate spring 123 thereunder. The connecting segment 128 includes a vertical portion 129 and a connecting portion 134 extending laterally from the bottom end

of the vertical portion 129 to the location of the first and second connectors 100 and 102. The connecting segment 128 is installed by inserting the vertical portion 129 through a not- shown hole formed in the lower plate 114, mounting a spring 130 to the upper side of the

vertical portion 129 and putting a cap 132 on the vertical portion 129. The switch of FIG. 5 operates as follows. When non-zero control signals are applied through the first and second control lines 106 and 108, currents having opposite directions flows through the first and second electromagnets 116 and 118. At this time,

the first electromagnet 116 draws a first end 121 of the rotating segment 120 and the second electromagnet 118 retracts a second end 122 of the rotating segment 120. Accordingly, the plate spring 123 of the rotating segment 120 presses the connecting segment 128 downward, and the first and second connectors 100 and 102 are electrically connected with each other by the connecting portion 134 of the connecting segment 129.

On the other hand, when control signals of zero magnitudes are applied through the first and second control lines 106 and 108, the connecting portion 134 moves upward by the restoring force of the spring 130 and the first and second connectors 100 and 102 are

electrically disconnected. Since the switch is configured electromehanically as above, the switchable power combiner is prevented from being damaged in an application handling large current.

FIGS. 6 A through 6D shows the first and the second variable impedance matching line 52 and 54, in detail. Two coaxial connectors 152, 154 are provided outside a metallic housing 150. A "J"-shaped cavity 156 is formed inside housing 150. A microstrip transmission line 158 disposed along the cavity 156 connects the coaxial connectors 152

and 154. At least one position of the strip transmission line 158 is supported by a supporting dielectric member 160.

In a preferred embodiment, most of the space inside the cavity 156 being not specified otherwise is not filled with any dielectric material other than air having unit relative permittivity (e =l). In such a transmission line structure, the characteristic impedance of the microstrip transmission line 158 varies according to the width of the line 158 and height from the ground plane. In the present embodiment, two tunning units 162 and 164 are provided on the bottom plane of the housing 150 to facilitate the tuning of the characteristic impedance of the transmission line 158. Each tunning unit includes a tunning knob 166 and a disk-shaped flange 168 attached on the top of the of knob 166. If the user rotates the tunning knob 168, the flange 168 moves up or down according to the rotating

direction. Accordingly, the distance between the transmission line 158 and ground is

varied, and thus the characteristic impedance of the transmission line 158 is changed.

Although the present invention has been described in detail above, it should be

understood that the foregoing description is illustrative and not restrictive. Those of

ordinary skill in the art will appreciate that many obvious modifications can be made to the invention without departing from its spirit or essential characteristics. Thus, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. We claim all modifications and variation coming within the spirit and scope of the following claims.

Industrial Applicability

As described above, the insertion loss of the switchable power combiner according

to the present invention can be minimized because the impedance matching state is maintained regardless of the change in the number of the signal combining paths. Additionally, since the switches having the same lengths are arranged symmetrically at their connection, there is little phase unbalance between the signals received through separate input ports.

Claims

What is claimed is:

1. A switchable power combiner for receiving a plurality of input signals

through a plurality of input ports and combining the received signals to output a combined signal through an output port, comprising: a combining node; first switching means, disposed between said plurality of input ports and said combining node, for electrically connecting at least one of said input ports to said combining node; a common node electrically connected to said combining node; a plurality of impedance matching paths each having a characteristic impedance different from the characteristic impedance of one another; and second switching means for electrically connecting a first terminal of a path selected from said plurality of impedance matching paths to said common node and connecting a second terminal of the selected path to said output port; wherein the selected path is determined according to the number said input ports

connected to said common node,

wherein the characteristic impedance of at least one of said plurality of impedance

matching paths is variable.

2. The switchable power combiner as claimed in claim 1, wherein at least one

of said plurality of impedance matching paths comprises a variable impedance matching

unit, wherein said variable impedance matching unit comprises:

a housing made of metallic material and having a cavity formed therein; two connectors installed outside said housing;

a transmission line, disposed along the cavity, for connecting said two

connectors; and means for varying a distance between said transmission line and a ground

plane in the cavity.

3. The switchable power combiner as claimed in claim 2, wherein said variable impedance matching unit further comprises: means for supporting said transmission line in the cavity.

4. The switchable power combiner as claimed in claim 1, wherein said first

switching means comprises: a plurality of switches each having a switching bar, wherein said plurality of switches have the same length and are arranged being

spaced by the same distance with respect to a point on said combining node connected to

said common node.