CN1925354A - Transmit-receive antenna switch in a TDD wireless communication system - Google Patents

Abstract

Provided is a TRAS in a TDD wireless communication system. In this TRAS, the circulator transmits the signal received from the PA to the antenna feeder, and transmits the signal received from the antenna feeder to the reflector. When reflective operation is turned on in transmit mode, the reflector sufficiently reflects the signal received from the circulator, and when reflective operation is turned off in receive mode, transmits the signal received from the circulator to a wireless switch such as , RF switch. The RF switch transmits the signal received from the reflector to the LNA or blocks the signal received from the reflector from the LNA in transmit or receive mode.

Description

Transmitting and receiving antenna switch in time division duplex wireless communication system

technical field

The present invention relates generally to transmit-receive antenna switches (TRAS) in time division duplex (TDD) wireless communication systems, and more particularly to means for protecting low noise amplifiers (LNAs) in receivers in transmit mode.

Background technique

Typically, in a TDD wireless communication system, TRAS toggles between a high-power radio frequency (RF) transmit (Tx) signal and a low-power RF receive (Rx) signal, which divides a given frequency by time in order to transmit and receive. The TRAS protects the LNA at the receiver by blocking transmit power introduced in transmit mode, and reducing noise introduced to the transmitter in receive mode.

Typically, RF switches or circulators are used for this TRAS function.

Figure 1 illustrates a conventional RF switch used as a TRAS. Referring to FIG. 1 , a single pole double throw (SPDT) switch 105 switches the Tx signal from the transmitter 101 to the antenna feeder when in the transmit mode, and switches the Rx signal from the antenna feeder to the receiver 103 when in the receive mode. The RF switch 105 toggles between the Tx path and the Rx path according to the TDD control signal. This structure is used in systems with less than 1W transmit power.

Figure 2 illustrates a conventional circulator used as a TRAS. Referring to FIG. 2 , the circulator 205 provides a Tx signal from the transmitter 201 to the antenna feeder in the transmission mode, and switches the Rx signal from the antenna feeder to the receiver 203 in the reception mode. Transmission and reception respectively rely on the principle that signals are transmitted downstream with minimal signal attenuation and large signal propagation losses occur upstream. This structure is used in systems with less than 8W transmit power.

Although the TRAS described above applies to TDD systems using low-power RF signals, it is not feasible in systems using high-power RF signals of at least 10 W due to power ratings and failures of components and the impractical cost of circuit implementation . In particular, when TRAS is implemented in the manner illustrated in Figure 1, its cost is impractical (approximately $1500). Despite its ability to handle moderate power signals, the TRAS exemplified in Figure 2 has a prominent drawback, where a defect in the antenna feed leads to the introduction of reflected transmit power into the LNA, causing permanent damage to the LNA .

Contents of the invention

An object of the present invention is to substantially solve at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described herein below. Accordingly, an object of the present invention is to provide a TRAS for processing high-power RF signals in a TDD wireless communication system.

Yet another object of the present invention is to provide an apparatus for protecting an LNA at a receiver in a transmission mode in a TDD wireless communication system.

Another object of the present invention is to provide an apparatus for completely reflecting a signal applied to a receiver in a transmission mode in a TDD wireless communication system.

Still another object of the present invention is to provide an apparatus for minimizing power loss in a Tx path from a power amplifier (PA) to an antenna in a TDD wireless communication system.

Still another object of the present invention is to provide an apparatus for minimizing insertion loss in a Rx path from an antenna to an LNA in a receive mode in a TDD wireless communication system.

Still another object of the present invention is to provide an apparatus for improving isolation between a Tx path and an Rx path in a TDD wireless communication system.

A further object of the present invention is to provide a device for protecting an LNA in a TDD wireless communication system by connecting a relay switch on the front end of the LNA.

Still another object of the present invention is to provide an apparatus for protecting an LNA regardless of whether power is supplied to a protection circuit of the LNA in a TDD wireless communication system.

According to an aspect of the present invention, in TRAS of a TDD wireless communication system, a circulator transmits a signal received from a PA to an antenna feeder, and transmits a signal received from the antenna feeder to a reflector. The reflector sufficiently reflects the signal received from the circulator when the reflection operation is turned on in the transmission mode, and transmits the signal received from the circulator to the wireless switch when the reflection operation is turned off in the reception mode, Such as, RF switch. The RF switch transmits the signal received from the reflector to the LNA or blocks the signal received from the reflector from the LNA according to a transmit or receive mode.

According to another aspect of the present invention, in TRAS of a TDD wireless communication system, a circulator transmits a signal received from a PA to an antenna feeder, and transmits a signal received from the antenna feeder to a reflector. A transmission line is connected between the circulator and the LNA. A plurality of PIN diodes are connected to the transmission line in a branch configuration at predetermined positions. The controller controls biasing of the plurality of PIN diodes according to transmission or reception mode.

Description of drawings

From the following detailed description in conjunction with the accompanying drawings, the above and other objects, features and advantages of the present invention will become more apparent, wherein:

Figure 1 illustrates a conventional RF switch used as a TRAS;

Figure 2 illustrates a conventional circulator used as a TRAS;

3 is a block diagram schematically illustrating a TRAS in a TDD wireless communication system according to the present invention;

Figure 4 is a detailed block diagram schematically illustrating the reflector illustrated in Figure 3 in accordance with the present invention;

5A, 5B and 5C are schematic illustrations for better understanding of the equivalent circuit diagram of the PIN diode of the present invention;

Figure 6 illustrates an example of the reflector illustrated in Figure 3;

Figure 7 illustrates a wireless switch, such as the RF switch illustrated in Figure 3, in accordance with the present invention; and

FIG. 8 is a block diagram schematically illustrating a TRAS in a TDD wireless communication system according to the present invention.

Specific implementation method

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

The present invention provides a TRAS for protecting an LNA while using a receive mode in a high-power TDD wireless communication system.

FIG. 3 is a block diagram schematically illustrating a TRAS in a TDD wireless communication system according to the present invention. Referring to FIG. 3 , the TRAS 350 according to the present invention includes an insulator 351 , a circulator 352 , a first controller 353 , a reflector 354 , a second controller 355 and an RF switch 356 .

In operation, PA 320 amplifies the power of the Tx signal received from transmitter 310 . The insulator 351 is connected to the output terminal of the PA320 for protecting the terminal circuit of the PA320. That is, the insulator 351 terminates the signal reflected from the antenna feed line due to some imperfection in the antenna feed line. Insulator 351 may be incorporated into PA 320 . The circulator 352 transmits the signal received from the insulator 351 to the front end block (FEB) 360 and transmits the signal received from the FEB 360 to the reflector 354 according to directions designated by arrows shown in FIG. 3 .

The first controller 353 turns on/off reflection of the reflector 354 according to the TDD control signal received from the TDD controller 300 . In the transmission mode, the first controller 353 turns on the reflection of the reflector 354 , and thus the reflector 354 completely reflects the signal received from the circulator 352 . The reflected signal is terminated at the insulator 351 via the third to first ports of the circulator 352 .

In the receiving mode, the first controller 353 turns off the reflection of the reflector 354 . Reflector 354 then transmits the signal received from circulator 352 to RF switch 356 with little signal loss. The reflector 354 includes a transmission line and a PIN diode, which will be described in greater detail later with reference to FIGS. 4 and 6 .

The second controller 355 controls switching of the RF switch 356 according to the TDD control signal received from the TDD controller 300 . In transmit mode, the second controller 355 closes the RF switch 356 , thereby preventing signal transmission from the reflector 354 to the LNA 340 . In receive mode, the second controller 355 turns on the RF switch 356 so that the RF switch 356 switches the signal from the reflector 354 to the LNA 340 . RF switch 356 may be a SPDT or a single pole single throw switch (SPST). In a practical implementation, SPDT switches and SPST switches can be implemented using PIN diodes and transistors (eg, Gallium Arsenide Field Effect Transistors (FETs)). LNA 340 amplifies the signal received from RF switch 356 with low noise and provides the amplified signal to receiver 330 . The operation of the TRAS having the above structure will now be described in more detail. In transmit mode, it is very important to prevent high power Tx signal from being introduced into LNA340. The Tx signal output from PA 320 is transmitted to antenna 370 in a path from insulator 351 to circulator 352 and FEB 360 .

Under the control of the first controller 353 , the reflector 354 completely reflects the leakage power (RF signal) received from the circulator 352 so as to prevent the Tx signal from being introduced into the path from the reflector 354 to the LNA 340 . Meanwhile, the reflected signal is transmitted via the third to first port of the circulator 352 and then terminated by the insulator 351 . Thus, the insulator 351 protects the PA 320 by absorbing the reflected Tx signal. In the transmit mode, under the control of the second controller 355 , the RF switch 356 is closed, preventing the signal from the reflector 354 from propagating to the LNA 340 . In this way, power is prevented from being introduced into LNA 340 by utilizing reflector 354 and RF switch 356 . In particular, since the reflector 354 can attenuate the signal to a great extent, the LNA 340 can be protected according to the present invention by utilizing the low power RF switch 356 despite the high power in the transmission path.

In receive mode, it is important to reduce the signal loss between the antenna 370 and the LNA 340, which has a direct impact on the system noise figure (NF). Signals received via antenna 370 are provided to LNA 340 in a path from FEB to circulator 352 , reflector 354 and RF switch 356 .

The reflector 354 (the reflective operation of which is turned off under the control of the first controller 353 ) transmits the signal received from the circulator 352 to the RF switch 356 with minimum loss. Under the control of the second controller 355 , the RF switch 356 is turned on, and transmits the signal received from the reflector 354 to the LNA 340 . In this way, in receive mode, the signal from circulator 352 is provided to LNA 340 without loss.

As mentioned above, the TRAS350 of the present invention isolates the Tx signal from the Rx path in the transmit mode, regardless of whether the Tx path is normal, and isolates the Rx signal from the Tx path in the receive mode, thereby minimizing the path loss.

Figure 4 is a detailed block diagram schematically illustrating reflector 354 in accordance with the present invention. Referring to FIG. 4, the reflector 354 is composed of transmission lines TL1, TL2 and TL3 and two parallel impedance transformers VI1 and VI2. The impedance transformers VI1 and VI2 are connected to the transmission line in a shunt like structure at predetermined positions. The first transmission line TL1 covers the connection from the beginning of the entire transmission line connected to the circulator 352 to the first impedance transformer VI1, the second transmission line TL2 covers between the first impedance transformer VI1 and the second impedance transformer VI2, and the second transmission line TL2 covers The three transmission line TL3 covers the end of the entire transmission line from the connection of the second impedance transformer VI2 to the connection to the RF switch 356 .

The reflector 354 of FIG. 3 having the above structure is connected to the RF 356 so that in the case of an impedance on the rear end, it can sufficiently reflect the signal received from the circulator 352 in the transmission mode (i.e., a reflection coefficient of 0 dB ), and in the receive mode, the path loss caused by the spurious components of the impedance transformers VI1 and VI2 is minimized by compensating the spurious components. The impedance transformer is a device whose impedance varies with bias. For example, a PIN diode can be used as the impedance converter. Separate detailed descriptions are now provided for the transmit mode and the receive mode.

In the transmission mode, the second controller 355 turns off the RF switch 356 connected to the output terminal of the reflector 354 according to the TDD control signal received from the TDD controller 300 . In particular, the impedance of the RF switch 356 should be in an open state (reflection coefficient of 0 dB). Typically, when the RF switch 356 is open, it is placed in an impedance state with reflection loss, and thus not an open state, even in the open state it can happen that some power of the input signal is dissipated, and thus the high power Tx signal damage to the RF switch.

However, in the present invention, RF switch 356 and LNA 340 prevent high power since the reflector 354 is configured so as to reflect sufficiently in transmit mode. Since the characteristic impedance Z ₀ of the first transmission line TL1 , the characteristic impedance and electrical length of the second transmission line TL2 and the characteristic impedance Z ₀ of the third transmission line TL3 affect the performance of the reflector 354 , these parameters are set to empirically optimum values.

In the receiving mode, the second controller 355 turns on the RF switch 356 connected to the output terminal of the reflector 354 according to the TDD control signal received from the TDD controller 300 . RF switch 365 (whose input impedance is 50 ohms) transmits the RF Rx signal to LNA 340. Likewise, the first controller 353 turns off the reflection operation of the reflector 354 according to the TDD control signal from the TDD controller 300 . In particular, it switches off this reflection by controlling the bias of the two impedance transformers VI1 and VI2 of the reflector 354 . Since the input impedance of the reflector 354 becomes 50 ohms, the reflector 354 provides the RF Rx signal received from the circulator 352 to the RF switch 356 without signal loss.

Under the control of the first controller 353, the impedance transformers VI1 and VI2 are turned on in the transmission mode and turned off in the reception mode. In different modes, impedance converters VI1 and VI2 each have a different resistance, inductance and capacitance. When two impedance transformers (PIN diodes) of the same characteristics are arranged in parallel as illustrated in Fig. 4, their parasitic components (inductance and capacitance) are compensated by the transmission line between the impedance transformers. Thus, they form a state of near total reflection in transmit mode and minimize insertion loss in receive mode.

5A, 5B and 5C are schematically illustrating equivalent circuit diagrams of PIN diodes for better understanding of the present invention.

Referring to FIG. 5A, the PIN diode has a resistance Rp that varies with bias, a series resistance Rs, and parasitic components Ls and Rs. When a forward bias is applied to the PIN diode, the current flowing in the PIN diode increases so that Rp approaches "0". FIG. 5B is an equivalent circuit diagram of a PIN diode to which a forward bias is applied. On the other hand, if a reverse bias voltage is applied to the PIN diode, the current becomes "0" in the PIN diode, maximizing Rp. FIG. 5C is an equivalent circuit diagram of a PIN diode to which a reverse bias is applied. In this way, by arranging two PIN diodes in parallel and inserting a predetermined length of transmission line therebetween, the parasitic components Ls and Ct that appear with the application of forward bias and reverse bias can be eliminated.

FIG. 6 illustrates an example of reflector 354 . Referring to FIG. 6, the reflector 354 includes two parallel PIN diodes D1 and D2 and a transmission line. The first transmission line TL1 covers the connection from the beginning of the entire transmission line connected to the circulator 352 to the first PIN diode D1, the second transmission line TL2 covers between the first PIN diode D1 and the second PIN diode D2, and the third transmission line TL3 covers the end of the entire transmission line from the connection of the second PIN diode D2 to the connection to the RF switch 356 .

In the transmission mode, the first controller 353 applies a forward bias to the PIN diodes D1 and D2, which operates in the manner illustrated in FIG. 5B. The parasitic components Ls of the PIN diodes D1 and D2, which degrade the reflection characteristics of the reflector 354, are compensated by the second transmission line TL2. Theoretically, the electrical length (EL) of the second transmission line TL2 is preferably λ/4.

In receive mode, the first controller 353 applies a reverse bias to the PIN diodes D1 and D2, which operate in the manner illustrated in FIG. 5C. The parasitic components Ls and Ct of PIN diodes D1 and D2 (which increase the insertion drop of the reflector 354) are compensated by the second transmission line TL2. Thus, reflector 354 with PIN diode is connected to RF switch 356 such that in transmit mode it provides ideal total reflection characteristics (reflection coefficient of 0 dB) at the third port of circulator 352, and in receive mode , the path loss (or insertion loss) caused by the parasitic components, inductance and capacitance of the two paralleled PIN diodes is minimized by compensating for this parasitic component.

The characteristics of this reflector 354 can be affected by the characteristics of the PIN diodes and the characteristic impedances Z ₀ 1, Z ₀ 2 and Z ₀ 3 and the electrical lengths EL1, EL2 and EL3 of the transmission lines TL1, TL2 and TL3, in particular, the second transmission line The influence of TL2's characteristic Z ₀ 2 and EL2. Therefore, optimization of TL2 rather than TL1 and TL3 is critical. Theoretically, it is best to set the characteristic impedances Z ₀ 1, Z ₀ 2 and Z ₀ 3 to 50 ohms, and set the electrical length EL2 to λ/4 to minimize the insertion loss.

As previously stated, the RF switch 356 may be a diode switch, a transistor (eg, FET) switch, or the like. The diode switch can be used in three ways: parallel PIN diodes, series PIN diodes, or a combination of both.

Figure 7 illustrates an RF switch 356 in accordance with the present invention. Referring to FIG. 7, the wireless switch, such as RF switch 356, includes at least two PIN diodes D3 to DN connected in parallel to the transmission line. This structure eliminates the parasitic components of the PIN diodes based on the forward and reverse bias characteristics of the PIN diodes and the electrical length between the PIN diodes. Therefore, in the transmission mode, isolation is ensured between the input and the output, and in the reception mode, the insertion loss between the input and the output will be minimized.

In the transmission mode, the second controller 355 applies a forward bias to the PIN diodes D3 to DN, which operate in the manner illustrated in FIG. 5B. The parasitic content of the PIN diodes, which degrades the isolation characteristics of the RF switch, is compensated by the transmission line between the PIN diodes.

In receive mode, the second controller 355 applies a reverse bias to the PIN diodes D3 to DN, which operate in the manner illustrated in FIG. 5C. The parasitic components Ls and Ct of the PIN diodes (which increase the insertion loss of the RF switch 356) are compensated by the transmission line between the PIN diodes.

Theoretically, it is preferable to set the characteristic impedance of the corresponding transmission line defined by the PIN diode to 50 ohms, and to set the electrical length of the transmission line to λ/4 to minimize the insertion loss. However, the length of the transmission line can vary according to the number of PIN diodes used, the impedance of the transmission line, and the input impedance of the LNA 340 . That is, the parameters are set to optimum values through simulation.

Also, when both reflector 354 and RF switch 356 are configured by means of PIN diodes, they can be controlled by a single controller.

FIG. 8 is a block diagram of TRAS in the TDD wireless communication system according to the present invention. TRAS is configured so as to protect the LNA even when power is not supplied to the receiving board, specifically, due to board mounting/non-mounting or some abnormal protection circuit of the LNA. Similar reference numerals denoting and describing the same components as those provided in the first embodiment of the present invention are not provided here.

Referring to FIG. 8 , a TRAS 350 according to another embodiment of the present invention includes an insulator 351 , a circulator 352 , a first controller 353 , a reflector 354 , a second controller 355 , an RF switch 356 and a relay switch 357 .

A relay switch 357 is provided on the front end of the LNA 340 . It is turned on when power is normally supplied to the receiving board (or receiver), and is turned off when power is not supplied to the receiving board. That is, even when power is not supplied to the receiver board, and therefore, the protection circuit of the receiver, ie, the reflector 354 and the RF switch 356 is not activated, the introduction of power to the LNA 340 is prevented by closing the relay switch 357.

When power is not supplied to the receiver, the transmit power introduced into the LNA 340 is calculated as set forth in equation (1),

2.1dBm＝+47.8dBm(PA output, 60W)-0.3dB(insulator loss)-20dB(circulator insulation)-0.4dB(SPDT loss)-25dB(relay switch insulation) …(1)

For another example, when power is not supplied to the receiver, the antenna is open-circuited, and thus the transmitted power is fully reflected, the reflected power introduced into the LNA 340 is calculated as set forth in equation (2)

19.1dBm＝+47.8dBm(PA output, 60W)-0.3dB(insulator loss)-0.3dB(circulator loss)-0.9dB(filter insertion loss)-0.6dB(directional coupler loss)-0.9dB(filter insertion loss) -0.3dB (circulator loss) -0.4dB (SPDT loss) -25dB (relay switch insulation) ...(2)

In the case of the model ATF54143LNA sold by Agilent, although the maximum input power rating is 13dBm when power is supplied, the LNA is not damaged even with respect to 19.1dBm if power is not supplied to the LNA. In this way, in the second embodiment of the present invention, the LNA is double protected by utilizing the relay switch working with the power supply.

As described above, in the transmission mode, the present invention advantageously protects the LNA by supporting high isolation between the Tx path and the Rx path in the TDD wireless communication system. Likewise, the manufacturing cost of TRAS is reduced and the system space utilization is improved by utilizing low power RF switches to isolate between the two paths. In addition, the LNA can be protected even when power is not supplied to the receiver, and thus the protection circuit of the receiver does not function. In currently developing an RF module applied to a high-speed portable internet (HPI) system, technical problems encountered with TDD operation of a high-power signal can be easily solved.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it should be understood by those skilled in the art that, without departing from the spirit and scope of the invention as defined in the appended claims, it may be employed in the form and various changes in details.

Claims (24)

1. A transmitting and receiving antenna switch (TRAS) in a time division duplex (TDD) wireless communication system, comprising: a circulator for transmitting the signal received from the power amplifier (PA) to the antenna feeder and for transmitting the signal received from the antenna feeder to the reflector; a reflector for substantially reflecting the signal received from the circulator when the reflection operation is turned on in the transmission mode, and for transmitting the signal received from the circulator when the reflection operation is turned off in the reception mode for radio frequency (RF) switches; and The RF switch is used to transmit or block the signal received from the reflector to the Low Noise Amplifier (LNA) in transmit or receive mode. 2. The TRAS according to claim 1, wherein said reflector comprises: a transmission line connected between the circulator and the RF switch; and Two PIN diodes connected to the transmission line in a branch configuration at predetermined locations. 3. TRAS according to claim 2, wherein the electrical length between two PIN diodes is λ/4. 4. The TRAS according to claim 2, wherein the characteristic impedance of the transmission line is 50 ohms. 5. The TRAS of claim 1, wherein the RF switch is one of a single pole double throw (SPDT) switch and a single pole single throw (SPST) switch. 6. The TRAS of claim 1, wherein the RF switch is configured with one of a PIN diode and a transistor. 7. The TRAS of claim 1, wherein the RF switch comprises: a transmission line connected between the reflector and the LNA; and At least two PIN diodes connected to the transmission line in a branch configuration at predetermined locations. 8. TRAS according to claim 7, wherein the electrical length between at least two PIN diodes is λ/4. 9. The TRAS of claim 1, further comprising an insulator for terminating signals reflected from the reflector. 10. TRAS according to claim 9, wherein said insulator is included in PA. 11. The TRAS according to claim 1, further comprising a controller for turning on or off the reflective operation of the reflector according to the TDD control signal. 12. The TRAS of claim 1, further comprising a controller for controlling switching of the RF switch according to the TDD control signal. 13. The TRAS according to claim 1, further comprising a controller for controlling the reflection operation of the reflector and the switching operation of the RF switch according to the TDD control signal. 14. The TRAS according to claim 1, further comprising a relay switch provided at a front end of the LNA for cutting off and preventing power from being introduced into the LNA when power is not supplied to the receiver. 15. A transmit-receive antenna switch (TRAS) in a time division duplex (TDD) wireless communication system, comprising: a circulator for transmitting the signal received from the power amplifier (PA) to the antenna feeder and for transmitting the signal received from the antenna feeder to the reflector; a transmission line connected between the circulator and the low-noise amplifier (LNA); a plurality of PIN diodes connected to the transmission line in a branch-shaped configuration at predetermined locations; and A controller for controlling the biasing of multiple PIN diodes according to transmit or receive mode. 16. The TRAS of claim 15, wherein the electrical length between the plurality of PIN diodes is λ/4. 17. The TRAS of claim 15, wherein the characteristic impedance of the transmission line is 50 ohms. 18. The TRAS of claim 15, further comprising an insulator for terminating signals reflected from the transmission line. 19. TRAS according to claim 18, wherein said insulator is included in PA. 20. The TRAS of claim 15, wherein the transmission line substantially reflects the signal received from the circulator in the transmission mode, and transmits the signal received from the circulator to the LNA in the reception mode. 21. The TRAS according to claim 15, further comprising a relay switch provided at a front end of the LNA for cutting off and preventing power from being introduced into the LNA when power is not supplied to the receiver. 22. A transmit-receive antenna switch (TRAS) in a time division duplex (TDD) wireless communication system, comprising: A circulator for transmitting the transmission signal to the antenna feeder and for transmitting the signal received via the antenna to the reflector; a reflector for reflecting the signal received from the circulator when the reflective operation is turned on in the transmit mode, and for transmitting the signal from the circulator to the switch when the reflective operation is turned off in the receive mode; and A switch to transmit or block the signal from the reflector to the Low Noise Amplifier (LNA) depending on the transmit or receive mode. 23. The TRAS of claim 22, further comprising an insulator for terminating signals reflected from the reflector. 24. A transmitting and receiving antenna switch in a time division duplex wireless communication system, comprising: a circulator for transmitting the signal from the power amplifier to the antenna and the signal received via the antenna to the reflector; a transmission line connected between the circulator and the low-noise amplifier; a plurality of diodes connected to the transmission line in a branch-shaped configuration at predetermined locations; and A controller for controlling the biasing of multiple diodes according to transmit or receive mode.

Images