Provided is a high-frequency switch formed by a first switch circuit connected in parallel to a first λ/4 signal transmission path for transmitting a transmission signal from a transmission terminal and a second switch circuit connected in parallel to a second λ/4 signal transmission path for transmitting a reception signal to a reception terminal. The high-frequency switch further includes a directivity coupler which has the first λ/4 signal transmission path as a constituent element and detects a reflected wave of the transmission signal. The directivity coupler includes: the first λ/4 signal transmission path; a λ/4 signal line arranged to oppose to the first λ/4 signal transmission path; a reflected wave output terminal connected to one end of the λ/4 signal line; and a terminal resistor connected to the other end of the λ/4 signal line.

TECHNICAL FIELD

The present invention relates to a high frequency switch for switching between high frequency signals, and more particularly to a high frequency switch suitable for use as an antenna switch connected to an antenna, e.g., a TDD (Time Division Duplex) switch or the like.

BACKGROUND ART

Conventional high frequency switches such as antenna switches include a microwave switch disclosed in Japanese Patent No. 2532122 and a transmission and reception switching device disclosed in Japanese Patent No. 2830319, for example.

The microwave switch disclosed in Japanese Patent No. 2532122 has PIN diodes inserted in series and parallel in a signal line. Forward currents are passed through the PIN diodes to turn them on, and the PIN diodes are reversely biased to turn them off, thereby switching between high frequency signals.

The transmission and reception switching device disclosed in Japanese Patent No. 2830319 employs a circuit scheme wherein a switch is constructed of transmission lines and PIN diodes or the like which are connected in series to the transmission lines, the transmission lines and the PIN diodes being connected parallel to a signal transmission line.

SUMMARY OF INVENTION

There are two types of transmission and reception switching schemes (a first transmission and reception switching scheme and a second transmission and reception switching scheme) using high frequency switches, as described below.

According to the first transmission and reception switching scheme, as shown inFIG. 17, a transmission amplifier108and an isolator111are connected to a transmission signal line106between a transceiver100and a transmission and reception antenna102(or via a bandpass filter104), and a reception amplifier112is connected to a reception signal line110between the transceiver100and the transmission and reception antenna102(or via the bandpass filter104). A high frequency switch114is connected to the junction between the transmission signal line106and the reception signal line110.

According to the second transmission and reception switching scheme, as shown inFIG. 18, a transmission amplifier108is connected to a transmission signal line106, and a reception amplifier112and a high frequency switch114are connected to a reception signal line110. A circulator116is connected to the junction between the transmission signal line106and the reception signal line110.

In the above high frequency switch, a feeding line such as a coaxial line is connected between the transceiver100and the antenna102. After a transmission signal output from the transceiver100is carried by a travelling wave to the antenna102, the transmission signal is radiated into air. In this case, if the antenna102and the feeding line become mismatched for some reason, the transmission signal is reflected at the antenna102and returns to the transceiver100as a reflected wave. Then, the communication cannot be made normally, which may also lead to malfunction or breakdown of the transceiver100. Therefore, it is preferable to watch a reflected wave all the time. Also, it is preferable to watch the level of a travelling wave to control it so as to have an appropriate value.

For this purpose, it is considered that a directional coupler is inserted and connected in order to detect a reflected wave and a travelling wave of a transmission signal.

In the first transmission and reception switching scheme, for example, as shown inFIG. 17, a first directional coupler120is inserted and connected between the high frequency switch114and the bandpass filter104, for detecting a reflected wave. Further, a second directional coupler122is inserted and connected between the transmission amplifier108and the isolator111, for detecting a travelling wave.

In the second transmission and reception switching scheme, as shown inFIG. 18, a first directional coupler120is inserted and connected between the high frequency switch114and a terminating resistor124, for detecting a reflected wave. Further, a second directional coupler122is inserted and connected between the transmission amplifier108and the circulator116, for detecting a travelling wave.

In both of the first and second transmission and reception switching schemes, however, it is necessary to insert and connect two new electronic components of the first directional coupler120and the second directional coupler122. Thus, the number of parts used in a system becomes large, and also the size thereof becomes large, which will lead to high production cost. Further, a transmission loss will become large.

In Japanese Patent No. 2532122 and Japanese Patent No. 2830319, there is no idea disclosed to detect a reflected wave (and a travelling wave). The switch or device disclosed in these patents can merely be used as a substitution for the high frequency switch114in the first or second transmission and reception switching scheme.

The present invention has been made in view of the above problems. It is an object of the present invention to provide a high frequency switch which can detect at least a reflected wave of a transmission signal even with a single high frequency switch, enhance the reduction in the number of parts used for a transmission system or a transceiving system with a reflected wave detection function, enhance the reduction in size, enhance the reduction in a production cost, and enhance the reduction in a transmission loss.

According to the present invention, a high frequency switch includes a first switch circuit connected parallel to a first signal transmission line for transmitting a transmission signal from a transmission terminal, and a second switch circuit connected parallel to a second signal transmission line for transmitting a reception signal to a reception terminal, the high frequency switch comprising a directional coupler having the first signal transmission line as a component thereof, for detecting at least a reflected wave of the transmission signal.

With the above arrangement, at least a reflected wave of a transmission signal can be detected even with a single high frequency switch. Also, it is possible to enhance the reduction in the number of parts used for a transmission system or a transceiving system with a reflected wave detection function, the reduction in size, the reduction in a production cost, and the reduction in a transmission loss.

According to the present invention, the directional coupler may further comprise a line disposed so as to face the first signal transmission line, a reflected wave output terminal connected to one end of the line, and a terminating resistor connected to another end of the line.

In the present invention, a third switch circuit may be connected parallel to a third signal transmission line connected between the transmission terminal and the first signal transmission line, the high frequency switch may further comprises a second directional coupler having the third signal transmission line as a component thereof, for detecting at least a travelling wave of the transmission signal. In this case, the directional coupler may further comprise a first line disposed so as to face the first signal transmission line, a reflected wave output terminal connected to one end of the first line, and a terminating resistor connected to another end of the first line, the second directional coupler may further comprises a second line disposed so as to face the third signal transmission line, a travelling wave output terminal connected to one end of the second line, and a second terminating resistor connected to another end of the second line.

In the present invention, the directional coupler may detect the reflected wave and a travelling wave of the transmission signal. In this case, the directional coupler may further comprise a line disposed so as to face the first signal transmission line, a reflected wave output terminal connected to one end of the line, and a travelling wave output terminal connected to another end of the line.

In the present invention, the first switch circuit may comprise a first transmission line and a circuit including one or more first PIN diode, the first transmission line and the circuit being connected in series to each other, and the second switch circuit may comprise a second transmission line and a circuit including one or more second PIN diode, the second transmission line and the circuit being connected in series to each other.

Further, the third switch circuit may comprise the third transmission line and a circuit including one or more third PIN diode, the third transmission line and the circuit being connected in series to each other.

Further, an electrical length of the above-mentioned signal transmission line is not limited, and a signal transmission line may have a length such as a 3λ/4 signal transmission line and a λ/4 signal transmission line. It is, however, preferable to use a λ/4 signal transmission line in view of the reduction in size or the like. Further, as to the above-mentioned line, either a 3λ/4 line or a λ/4 line may be used. It is, however, preferable to use a λ/4 line. Further, as to the above-mentioned transmission line, either a 3λ/4 transmission line or a λ/4 transmission line may be used. It is, however, preferable to use a λ/4 transmission line in view of the reduction in size or the like.

With the high frequency switch according to the present invention, as described above, at least a reflected wave of a transmission signal can be detected even with a single high frequency switch. Also, it is possible to enhance the reduction in the number of parts used for a transmission system or a transceiving system with a reflected wave detection function, the reduction in size, the reduction in a production cost, and the reduction in a transmission loss.

DESCRIPTION OF EMBODIMENTS

Embodiments wherein a high frequency switch according to the present invention is applied, for example, to an antenna switch will be described below with reference toFIGS. 1 through 16. It is assumed that λ represents a wavelength corresponding to the central frequency of an operating frequency band of the switch, and refers to a wavelength in transmission lines described below.

As shown inFIG. 1, an antenna switch according to a first embodiment (hereinafter referred to as a first antenna switch10A) comprises a first λ/4 signal transmission line18aconnected between an antenna connection terminal14and a transmission terminal16, a second λ/4 signal transmission line18bconnected between the antenna connection terminal14and a reception terminal20, a first switch circuit22aconnected parallel to the first λ/4 signal transmission line18a, and a second switch circuit22bconnected parallel to the second λ/4 signal transmission line18b. Capacitors C1through C4are connected respectively between the transmission terminal16and the first λ/4 signal transmission line18a, between the first λ/4 signal transmission line18aand the antenna connection terminal14, between the antenna connection terminal14and the second λ/4 signal transmission line18b, and between the second λ/4 signal transmission line18band the reception terminal20. The capacitors C1through C4are capacitors for blocking currents for turning on and off PIN diodes, to be described later, and operate as a short circuit at high frequencies.

The first switch circuit22ais connected between a signal line between the capacitor C1and the first λ/4 signal transmission line18aand GND (ground). The first switch circuit22acomprises a series-connected circuit of a first λ/4 transmission line24aand a first parallel resonant circuit26awhich are connected in series to each other at a first junction a1.

The first parallel resonant circuit26acomprises a first PIN diode28aconnected between the first junction a1and GND, a first inductor30aconnected between the first junction a1and a first control terminal Tc1, and a first capacitor Ca connected between the first control terminal Tc1and GND. The first capacitor Ca operates as a capacitor for blocking currents for turning on and off the first PIN diode28a.

To the first control terminal Tc1, there are applied a forward bias voltage Vc1for passing a forward current through the first PIN diode28ato turn on the first PIN diode28aand a reverse bias voltage Vc2for reversely biasing the first PIN diode28ato turn off the first PIN diode28a.

As with the first switch circuit22adescribed above, the second switch circuit22bis connected between a signal line between the second λ/4 signal transmission line18band the capacitor C4and GND (ground). The second switch circuit22bcomprises a series-connected circuit of a second λ/4 transmission line24band a second parallel resonant circuit26bwhich are connected in series to each other at a second junction a2.

The second parallel resonant circuit26bcomprises a second PIN diode28bconnected between the second junction a2and GND, a second inductor30bconnected between the second junction a2and a second control terminal Tc2, and a second capacitor Cb connected between the second control terminal Tc2and GND. The second capacitor Cb operates as a capacitor for blocking currents for turning on and off the second PIN diode28b.

To the second control terminal Tc2, there are applied the forward bias voltage Vc1for passing a forward current through the second PIN diode28bto turn on the second PIN diode28band the reverse bias voltage Vc2for reversely biasing the second PIN diode28bto turn off the second PIN diode28b.

When the forward bias voltage Vc1is applied to the first control terminal Tc1, the reverse bias voltage Vc2is applied to the second control terminal Tc2. When the reverse bias voltage Vc2is applied to the first control terminal Tc1, the forward bias voltage Vc1is applied to the second control terminal Tc2. The reverse bias voltage Vc2which is applied to the first control terminal Tc1and the reverse bias voltage Vc2which is applied to the second control terminal Tc2may have different voltage levels.

The first antenna switch10A comprises a directional coupler36having the first λ/4 signal transmission line18aas a component thereof. The directional coupler36detects a reflected wave of a transmission signal.

The directional coupler36comprises the above-mentioned first λ/4 signal transmission line18a, a λ/4 line38disposed so as to face the first λ/4 signal transmission line18a, a reflected wave output terminal40connected to one end of the λ/4 line38, and a terminating resistor42connected to the other end of the λ/4 line38. Another end of the terminating resistor42is grounded.

The principles of operation of the directional coupler36will be described below with reference toFIG. 2. First, a first end φ1to a fourth end φ4of the directional coupler36will be defined as follows. The first end φ1refers to an end of the first λ/4 signal transmission line18aon the side of the transmission terminal16, the second end φ2refers to an end of the first λ/4 signal transmission line18aon the side of the antenna connection terminal14, the third end φ3refers to an end of the λ/4 line38on the side of the transmission terminal16, and the fourth end φ4refers to an end of the λ/4 line38on the side of the antenna connection terminal14.

When a travelling wave electric power Pa by a transmission signal from the transmission terminal16is applied to the first end φ1of the directional coupler36, a travelling wave is produced at the second end φ2, and also an electric wave (signal) is produced at the third end φ3, having an electric power dPa in proportion to the travelling wave electric power Pa. The wave is reflected at an antenna, and a reflected wave electric power Pb is applied to the second end φ2of the directional coupler36. Then, a reflected wave is produced at the first end φ1, and also an electric wave (signal) is produced at the fourth end φ4, having an electric power dPb in proportion to the reflected wave electric power Pb. In other words, a signal in proportion to the reflected wave electric power Pb is output from the reflected wave output terminal40that is connected to the fourth end φ4of the directional coupler36. Accordingly, the reflected wave can be detected.

Next, circuit operation of the first antenna switch10A will be described below with reference toFIGS. 3 through 7.

The first switch circuit22awill primarily be described below. When the forward bias voltage Vc1is applied to the first control terminal Tc1, the first PIN diode28ais turned on. At this time, the first switch circuit22ais represented by an equivalent circuit shown inFIG. 3A. Specifically, a circuit comprising an inductance La and an ON resistance Ro of the first PIN diode28awhich are connected parallel to each other is connected in series between the first λ/4 transmission line24aand GND.

Conversely, when the reverse bias voltage Vc2is applied to the first control terminal Tc1, the first PIN diode28ais turned off. At this time, the first switch circuit22ais represented by an equivalent circuit shown inFIG. 3B. Specifically, a parallel resonant circuit comprising an inductance La, a parasitic capacitance Cf due to the depletion layer of the first PIN diode28a, and a parallel resistance Rf of the first PIN diode28awhich are connected parallel to each other is connected in series between the first λ/4 transmission line24aand GND.

In the first antenna switch10A, the inductance La has a value established such that the central frequency fo of the first antenna switch10A and the resonant frequency of the parallel resonant circuit that is made up of the parasitic capacitance Cf, the parallel resistance Rf, and the inductance La are in agreement with each other.

The ON resistance Ro is generally of about 1 ohm or less. Since the ON resistance Ro can be expressed as Ro<<2πfoLa, the first switch circuit22acan be represented by an equivalent circuit shown inFIG. 4Ain the vicinity of the central frequency fo when the first PIN diode28ais turned on, and can be represented by an equivalent circuit shown inFIG. 4Bin the vicinity of the central frequency fo when the first PIN diode28ais turned off.

It is assumed that, as shown inFIG. 5, a transmission line z=L is terminated by the load of an impedance Z(L).

If the transmission line has a characteristic impedance Zo, a travelling wave is represented by Ae−γz, and a reflected wave is represented by Be−γz(γ indicates a propagation constant), then a voltage V(z) and a current I(z) at a reference point z are expressed by the following equations:
V(z)=Ae−γz+Beγz
I(z)=(A/Zo)e−γz−(B/Zo)eγz

Therefore, the impedance Z(L) at z=L is expressed by the following equation:

A reflection coefficient Γ(L) has a relationship expressed by the following equation (a):

An impedance Z(0) of the load as seen at z=0 is expressed by the following equation (b):
Z(0)=Zo{(A+B)/(A−B)}  (b)

From the equation (a),
B/A=[{Z(L)−Zo}/{Z(L)+Zo}]e−2γL

By substituting this equation into the equation (b), the following equation (c) is obtained:
Z(0)/Zo={Z(L)+ZotanhγL}/{Zo+Z(L)tanhγL}(c)

where γ=α+jβ (α represents an attenuation constant and β a phase constant expressed by β=2π/λ).

Since α=0 and γ=jβ for a lossless line, the equation (c) can be modified into the following equation (d):
Z(0)/Zo={Z(L)+jZotan γL}/{Zo+jZ(L)tan βL}(d)

By substituting L=λ/4 into the equation (d), the following equation (e) is obtained:
Z(0)/Zo=Zo/Z(L)
Z(0)=Zo2/Z(L)  (e)

Inasmuch as Z(L) is a low resistance of about 1 ohm or less when the first PIN diode28ais turned on, the impedance (in this case, Z(0)) of the first λ/4 transmission line24aon the signal line side is of a large value, and the signal line is ideally in an open state, as can be understood from the equation (e). Conversely, inasmuch as Z(L) is a high resistance of about 10 k ohms or more when the first PIN diode28ais turned off, the impedance (in this case, Z(0)) of the first λ/4 transmission line24aon the signal line side is of a small value, and the signal line is ideally in a short-circuited state, as can be understood from the equation (e).

Therefore, when the forward bias voltage Vc1is applied to the first control terminal Tc1, turning on the first PIN diode28a, and the reverse bias voltage Vc2is applied to the second control terminal Tc2, turning off the second PIN diode28b, the first antenna switch10A is represented by an equivalent circuit shown inFIG. 6wherein only the transmission terminal16is connected to the antenna connection terminal14at high frequencies. A transmission signal Sa supplied to the transmission terminal16is thus transmitted via the antenna connection terminal14. In other words, a first signal line34afrom the transmission terminal16to the antenna connection terminal14serves as a signal transmission side, and a second signal line34bfrom the reception terminal20to the antenna connection terminal14serves as a signal cutoff side.

Conversely, when the reverse bias voltage Vc2is applied to the first control terminal Tc1, turning off the first PIN diode28a, and when the forward bias voltage Vc1is applied to the second control terminal Tc2, turning on the second PIN diode28b, the first antenna switch10A is represented by an equivalent circuit shown inFIG. 7wherein only the reception terminal20is connected to the antenna connection terminal14at high frequencies. A reception signal Sb received by the antenna is thus supplied to the antenna connection terminal14and output from the reception terminal20. In other words, the first signal line34afrom the transmission terminal16to the antenna connection terminal14serves as a signal cutoff side, and the second signal line34bfrom the reception terminal20to the antenna connection terminal14serves as a signal transmission side.

If the first parallel resonant circuit26ais dispensed with and only the first PIN diode28ais connected, then the first switch circuit22ais not represented by the equivalent circuit shown inFIG. 4Bin the vicinity of the central frequency fo when the first PIN diode28ais turned off, but the parasitic capacitance Cf remains, as shown inFIG. 3B, shifting the resonant frequency into a low frequency range. As a result, the phase characteristic of the first λ/4 transmission line24asuffers an error, thereby causing a loss.

With the first antenna switch10A, the constant of the first inductor30aof the first parallel resonant circuit26ais adjusted to equalize the resonant frequency of the first parallel resonant circuit26aat the time the first PIN diode28ais turned off with the central frequency fo of the first antenna switch10A. Similarly, the constant of the second inductor30bof the second parallel resonant circuit26bis adjusted to equalize the resonant frequency of the second parallel resonant circuit26bat the time the second PIN diode28bis turned off with the central frequency fo of the first antenna switch10A.

Since the ON resistance Ro of the PIN diode is expressed as Ro<<2πfoLa, only the ON resistance Ro is connected to GND of the first λ/4 transmission line24awhen the first PIN diode28ais turned on, and only the parallel resistance Rf is connected to GND of the first λ/4 transmission line24awhen the first PIN diode28ais turned off, as shown inFIGS. 4A and 4B. Consequently, the resonant frequencies of the first λ/4 transmission line24aat the time the first PIN diode28ais turned on and off do not deviate from each other.

With the first antenna switch10A, therefore, the phase characteristics of the first λ/4 transmission line24aand the second λ/4 transmission line24bdo not suffer an error, and the passband at the time the switch circuits are turned on and the isolation band at the time the switch circuits are turned off are held in conformity with each other. In other words, the first antenna switch10A is capable of appropriately minimizing the insertion loss caused when the switch circuits are turned on and maximizing the isolation provided when the switch circuits are turned off in a band that is used by the antenna switch. As a result, the loss of a transmission signal caused in the switch circuits is reduced, and an appropriate amount of attenuation at the time the switch circuits are turned off is secured.

In particular, the first antenna switch10A has the directional coupler36having the first λ/4 signal transmission line18aas a component thereof. Thus, when an output transmission signal is reflected at an antenna, a signal in proportion to a reflected wave can be read out at the reflected wave output terminal40of the directional coupler36, so that the reflected wave can be detected. In this case, it is only necessary that the λ/4 line38is disposed so as to face the first λ/4 signal transmission line18a. Therefore, a reflected wave of a transmission signal can be detected without increasing the number of parts used.

Thus, since the first antenna switch10A can detect a reflected wave of a transmission signal even with a single antenna switch, it is possible to enhance the reduction in the number of parts used for a transmission system or a transceiving system with a reflected wave detection function, and the reduction in size thereof. Also, it is further possible to enhance the reduction in a production cost and in a transmission loss.

Next, an antenna switch according to a second embodiment (hereinafter referred to as a second antenna switch10B) will be described below with reference toFIG. 8.

As shown inFIG. 8, the second antenna switch10B is of a configuration substantially similar to the first antenna switch10A described above, but is different in a configuration of a directional coupler36as follows:

The directional coupler36comprises the first λ/4 signal transmission line18a, and the λ/4 line38disposed so as to face the first λ/4 signal transmission line18a. The third end φ3(an end of the λ/4 line38on the side of the transmission terminal16) is connected to a travelling wave output terminal44, and the fourth end φ4an end of the λ/4 line38on the side of the antenna connection terminal14) is connected to the reflected wave output terminal40.

Thus, a signal in proportion to the travelling wave electric power Pa (seeFIG. 2) is output from the travelling wave output terminal44connected to the third end φ3of the directional coupler36. Also, a signal in proportion to the reflected wave electric power Pb is output from the reflected wave output terminal40connected to the fourth end φ4of the directional coupler36. Therefore, a reflected wave and a travelling wave of a transmission signal can be detected.

An antenna switch according to a third embodiment (hereinafter referred to as a third antenna switch10C) will be described below with reference toFIG. 9.

As shown inFIG. 9, the third antenna switch10C is of a configuration substantially similar to the first antenna switch10A described above, but is different therefrom as follows:

A third λ/4 signal transmission line18cis connected between the transmission terminal16and the first λ/4 signal transmission line18a, and a fourth λ/4 signal transmission line18dis connected between the reception terminal20and the second λ/4 signal transmission line18b.

A third switch circuit22cis connected in association with the third λ/4 signal transmission line18c, and a fourth switch circuit22dis connected in association with the fourth λ/4 signal transmission line18d.

Furthermore, a first parallel resonant circuit26aof a first switch circuit22ahas a plurality of parallel first PIN diodes28a, and a second parallel resonant circuit26bof a second switch circuit22bhas a plurality of parallel second PIN diodes28b. Similarly, a third parallel resonant circuit26cof a third switch circuit22chas a plurality of parallel third PIN diodes28c, and a fourth parallel resonant circuit26dof a fourth switch circuit22dhas a plurality of parallel fourth PIN diodes28d.

In this case also, each of the constants of the first inductor30aof the first parallel resonant circuit26aand a third inductor30cof the third parallel resonant circuit26cis adjusted to equalize the resonant frequency of the first parallel resonant circuit26aat the time the first PIN diode28ais turned off and the resonant frequency of the third parallel resonant circuit26cat the time the third PIN diode28cis turned off with the central frequency of the third antenna switch10C.

Similarly, each of the constants of the second inductor30bof the second parallel resonant circuit26band a fourth inductor30dof the fourth parallel resonant circuit26dis adjusted to equalize the resonant frequency of the first parallel resonant circuit26aat the time the second PIN diode28bis turned off and the resonant frequency of the fourth parallel resonant circuit26dat the time the fourth PIN diode28dis turned off with the central frequency of the third antenna switch10C.

When the first switch circuit22aand the third switch circuit22care turned on, i.e., when all the first PIN diodes28aand the third PIN diodes28care turned on, each resistance between the first junction a1and GND and between the third junction a3and GND is represented by a resistance which is lower than one ON resistance. As can be understood from the equation (e) above, each impedance at the end on the first signal line34aside of the first λ/4 transmission line24aand at the end on the first signal line34aside of the third λ/4 transmission line24cis an impedance higher than with one ON resistance. The switch circuits thus approach an ideal open state.

Conversely, when the first switch circuit22aand the third switch circuit22care turned off, i.e., when all the first PIN diodes28aand the third PIN diodes28care turned off, only parallel resistances, which are high, are connected between the first junction a1and GND and between the third junction a3and GND. As can be understood from the equation (e) above, each impedance at the end on the first signal line34aside of the first λ/4 transmission line24aand at the end on the first signal line34aside of the third λ/4 transmission line24cis a low impedance depending on the high resistance. In other words, the insertion loss of the switch circuits upon signal transmission can further be reduced.

The third antenna switch10C comprises the first directional coupler36aand a second directional coupler36b. The first directional coupler36ahas the first λ/4 signal transmission line18aas a component thereof, for detecting a reflected wave of a transmission signal. The second directional coupler36bhas the third λ/4 signal transmission line18cas a component thereof, for detecting a travelling wave of a transmission signal.

The first directional coupler36acomprises the above-mentioned first λ/4 signal transmission line18a, a first λ/4 line38adisposed so as to face the first λ/4 signal transmission line18a, a reflected wave output terminal40connected to one end (fourth end φ4) of the first λ/4 line38a, and a first terminating resistor42aconnected to the other end (third end φ3) of the first λ/4 line38a.

The second directional coupler36bcomprises the above-mentioned third λ/4 signal transmission line18c, a second λ/4 line38bdisposed so as to face the third λ/4 signal transmission line18c, a travelling wave output terminal44connected to one end (third end φ3) of the second λ/4 line38b, and a second terminating resistor42bconnected to the other end (fourth end φ4) of the second λ/4line38b. Other ends of the first terminating resistor42aand the second terminating resistor42bare grounded.

In this case, a signal in proportion to the travelling wave electric power Pa (seeFIG. 2) is output from the travelling wave output terminal44connected to the third end φ3of the second directional coupler36b. Also, a signal in proportion to the reflected wave electric power Pb is output from the reflected wave output terminal40connected to the fourth end φ4of the first directional coupler36a. Therefore, a reflected wave and a travelling wave of a transmission signal can be detected.

Further, even if the characteristics of a monitor circuit (reflected wave detection circuit) connected to the reflected wave output terminal40and the characteristics of a monitor circuit (travelling wave detection circuit) connected to the travelling wave output terminal44are different from each other, each of the output characteristics of the first directional coupler36aand the second directional coupler36bcan be set independently to be in accordance with the characteristics of each of the monitor circuits. Therefore, the directional couplers can be designed more freely.

An antenna switch according to a fourth embodiment (hereinafter referred to as a fourth antenna switch10D) will be described below with reference toFIG. 10.

As shown inFIG. 10, the fourth antenna switch10D is of a configuration substantially similar to the first antenna switch10A described above, but is different therefrom as follows:

Specifically, the fourth λ/4 signal transmission line18dis connected between the reception terminal20and the second λ/4 signal transmission line18b, and a fourth switch circuit22dis connected in association with the fourth λ/4 signal transmission line18d.

As with the second switch circuit22b, the fourth switch circuit22dis connected between a signal line between the fourth λ/4 signal transmission line18dand the capacitor C5and GND (ground). The fourth switch circuit22dcomprises a series-connected circuit of the fourth λ/4 transmission line24dand a fourth parallel resonant circuit26dwhich are connected in series to each other at a fourth junction a4.

The fourth parallel resonant circuit26dcomprises a fourth PIN diode28dconnected between the fourth junction a4and GND, the fourth inductor30dconnected between the fourth junction a4and the second control terminal Tc2, and a fourth capacitor Cd connected between the second control terminal Tc2and GND. The fourth capacitor Cd operates as a capacitor for blocking currents for turning on and off the fourth PIN diode28d.

The fourth switch circuit22dalso includes a series-connected circuit of a resistor Rr for forming a reception terminating resistance and a capacitor Cr, connected parallel to the fourth PIN diode28d. The capacitor Cr operates as a capacitor for blocking currents for turning on and off the fourth PIN diode28d.

Operation of the fourth switch circuit22dwill primarily be described below. In the fourth switch circuit22d, when the forward bias voltage Vc1is applied to the second control terminal Tc2, the fourth PIN diode28dis turned on. At this time, the fourth switch circuit22dis represented by an equivalent circuit shown inFIG. 11A. Specifically, a circuit comprising an inductance La, an ON resistance Ro of the fourth PIN diode28d, and the resistor Rr for forming a reception terminating resistance which are connected parallel to each other is connected in series between the fourth λ/4 transmission line24dand GND.

Conversely, when the reverse bias voltage Vc2is applied to the second control terminal Tc2, the fourth PIN diode28dis turned off. At this time, the fourth switch circuit22dis represented by an equivalent circuit shown inFIG. 11B. Specifically, a parallel resonant circuit comprising an inductance La, a parasitic capacitance Cf due to the depletion layer of the fourth PIN diode28d, a parallel resistance Rf of the fourth PIN diode28d, and the resistor Rr for forming a reception terminating resistance which are connected parallel to each other is connected in series between the fourth λ/4 transmission line24dand GND.

In this case, the inductance La also has a value established such that the central frequency fo of the fourth antenna switch10D and the resonant frequency of the parallel resonant circuit that is made up of the parasitic capacitance Cf, the parallel resistance Rf, and the inductance La are in agreement with each other.

As described above, the fourth switch circuit22dis of a configuration including the parallel-connected resistor Rr for forming a reception terminating resistance. Since the ON resistance Ro and the resistor Rr have a magnitude relationship of Ro<<Rr, the resistor Rr does not affect the operation of the fourth switch circuit22dwhen the fourth PIN diode28dis turned on. Since the parallel resistance Rf and the resistor Rr have a magnitude relationship of Rf>>Rr, the impedance on the signal line side is determined by the resistor Rr.

Specifically, if the characteristic impedance of the fourth λ/4 transmission line24dis of 50 ohms and the resistor Rr for forming a reception terminating resistance is of 50 ohms, then the combined resistance (Rf//Rr) of the parallel resistance Rf (e.g., 10 k ohms) and the resistor Rr is of 49.751 ohms. The impedance of the fourth λ/4 transmission line24don the signal line side is terminated with 50×50/49.751=50.250 ohms according to the equation (e) (the terminating resistance is of 50.250 ohms). Actually, the value of the resistor Rr is determined so that the terminating resistance is of 50 ohms, for example.

When the fourth PIN diode28dis turned on, if the ON resistance Ro=1 ohm, then since the combined resistance (Ro//Rr) of the ON resistance Ro and the resistor Rr is of 0.9804 ohm, the impedance of the third λ/4 transmission line24con the signal line side is of 50×50/0.9804=2550 ohms according to the equation (e).

Therefore, when the forward bias voltage Vc1is applied to the first control terminal Tc1, turning on the first PIN diode28a, and the reverse bias voltage Vc2is applied to the second control terminal Tc2, turning off the second PIN diode28band the fourth PIN diode28d, the fourth antenna switch10D is represented by an equivalent circuit shown inFIG. 12wherein only the transmission terminal16is connected to the antenna connection terminal14at high frequencies, and a terminating resistor Re of 50 ohms, for example, is connected to the reception terminal20. A transmission signal Sa supplied to the transmission terminal16is thus transmitted via the antenna connection terminal14. In other words, the first signal line34afrom the transmission terminal16to the antenna connection terminal14serves as a signal transmission side, and the second signal line34bfrom the reception terminal20to the antenna connection terminal14serves as a signal cutoff side.

If the fourth switch circuit22dwere not present, then the impedance of the second λ/4 transmission line24bon the signal line side would be of a small value, and the signal line is ideally in a short-circuited state, as described above. In other words, since the impedance on the receiver side when the switch is turned off is of 0 ohm, resulting in total reflection, the reception amplifier connected to the reception terminal20may become unstable in operation.

Inasmuch as the fourth antenna switch10D includes the fourth switch circuit22d, the impedance on the receiver side when the switch is turned off is of the value of the terminating resistor Re, e.g., 50 ohms, thereby allowing the fourth antenna switch10D to achieve impedance matching with other circuits. Therefore, the reception amplifier connected to the reception terminal20is rendered stable in operation.

Conversely, when the reverse bias voltage Vc2is applied to the first control terminal Tc1, turning off the first PIN diode28a, and the forward bias voltage Vc1is applied to the second control terminal Tc2, turning on the second PIN diode28band the fourth PIN diode28d, the fourth antenna switch10D is represented by the equivalent circuit shown inFIG. 7wherein only the reception terminal20is connected to the antenna connection terminal14at high frequencies, and a reception signal Sb received by the antenna is thus supplied to the antenna connection terminal14and output from the reception terminal20. In other words, the first signal line34afrom the transmission terminal16to the antenna connection terminal14serves as a signal cutoff side, and the second signal line34bfrom the reception terminal20to the antenna connection terminal14serves as a signal transmission side. Therefore, the resistor Rr does not affect reception of the signal.

As with the first antenna switch10A, the fourth antenna switch10D comprises the directional coupler36having the first λ/4 signal transmission line18aas a component thereof. Thus, a signal in proportion to the reflected wave electric power Pb is output from the reflected wave output terminal40that is connected to the fourth end φ4of the directional coupler36. Accordingly, the reflected wave can be detected.

An antenna switch according to a fifth embodiment (hereinafter referred to as a fifth antenna switch10E) will be described below with reference toFIG. 13.

The fifth antenna switch10E is of a configuration which is substantially similar to the fourth antenna switch10D described above, but is different therefrom as follows:

The fifth antenna switch10E has the third λ/4 signal transmission line18cconnected between the first λ/4 signal transmission line18aand the transmission terminal16and the third switch circuit22cconnected parallel to the third λ/4 signal transmission line18c.

The third switch circuit22cis connected between a signal line between the third λ/4 signal transmission line18cand a capacitor C1and GND (ground). The third switch circuit22ccomprises a series-connected circuit of the single third λ/4 transmission line24cand the third parallel resonant circuit26cwhich are connected in series to each other at the third junction a3.

The third parallel resonant circuit26ccomprises a third PIN diode28cconnected between the third junction a3and GND, the third inductor30cconnected between the third junction a3and a first control terminal Tc1, and a third capacitor Cc connected between the first control terminal Tc1and GND. The third capacitor Cc operates as a capacitor for blocking currents for turning on and off the third PIN diode28c.

The third switch circuit22calso includes a series-connected circuit of a resistor Rt for forming a transmission terminating resistance and a capacitor Ct, which is connected parallel to the third PIN diode28c.

The third switch circuit22cis thus of a configuration identical to the fourth switch circuit22don the receiver side.

Therefore, when the forward bias voltage Vc1is applied to the first control terminal Tc1, turning on the first PIN diode28aand the third PIN diode28c, and the reverse bias voltage Vc2is applied to the second control terminal Tc2, turning off the second PIN diode28band the fourth PIN diode28d, the fifth antenna switch10E is represented by the equivalent circuit shown inFIG. 12wherein only the transmission terminal16is connected to the antenna connection terminal14at high frequencies, and a terminating resistor of 50 ohms, for example, is connected to the reception terminal20. In this case, the impedance on the receiver side when the switch is turned off is of the value of the terminating resistor Re, e.g., 50 ohms, thereby allowing the fifth antenna switch10E to achieve impedance matching with other circuits. Therefore, the reception amplifier connected to the reception terminal20is rendered stable in operation.

Conversely, when the reverse bias voltage Vc2is applied to the first control terminal Tc1, turning off the first PIN diode28aand the third PIN diode28c, and the forward bias voltage Vc1is applied to the second control terminal Tc2, turning on the second PIN diode28band the fourth PIN diode28d, the fifth antenna switch10E is represented by an equivalent circuit shown inFIG. 14wherein only the reception terminal20is connected to the antenna connection terminal14at high frequencies, and a terminating resistor Re of, for example, 50 ohms is connected to the transmission terminal16. In this case, the impedance on the transmitter side when the switch is turned off is of the value of the terminating resistor Re, e.g., 50 ohms, thereby allowing the fifth antenna switch10E to achieve impedance matching with other circuits.

As with the above-mentioned third antenna switch10C, the fifth antenna switch10E shown inFIG. 13comprises the first directional coupler36aand the second directional coupler36b. The first directional coupler36ahas the first λ/4 signal transmission line18aas a component thereof, for detecting a reflected wave of a transmission signal. The second directional coupler36bhas the third λ/4 signal transmission line18cas a component thereof, for detecting a travelling wave of a transmission signal.

Thus, a signal in proportion to the travelling wave electric power Pa is output from the travelling wave output terminal44connected to the third end φ3of the second directional coupler36b. Also, a signal in proportion to the reflected wave electric power Pb is output from the reflected wave output terminal40connected to the fourth end φ4of the first directional coupler36a. Therefore, a reflected wave and a travelling wave of a transmission signal can be detected.

In the above-mentioned first through fifth antenna switches10A through10E, the central frequency fo of the operating frequency band has mainly been described. Actually, the above advantages are offered at each of the frequencies contained in the operating frequency band.

An antenna switch according to a sixth embodiment (hereinafter referred to as a sixth antenna switch10F) will be described below with reference toFIG. 15.

The sixth antenna switch10F is of a configuration which is substantially similar to the fourth antenna switch10D described above, but has a first switch circuit22a, a second switch circuit22b, and a fourth switch circuit22dwhich are different therefrom in configuration as follows:

The first switch circuit22acomprises the series-connected circuit of the first PIN diode28aand the first capacitor Ca, connected between the first λ/4 transmission line24aand GND, and the first control terminal Tc1connected to the junction between the first PIN diode28aand the first capacitor Ca.

The second switch circuit22bcomprises a series-connected circuit of the second PIN diode28band the second capacitor Cb, connected between the second λ/4 transmission line24band GND, and the second control terminal Tc2connected to the junction between the second PIN diode28band the second capacitor Cb.

The fourth switch circuit22dcomprises a series-connected circuit of the fourth PIN diode28dand the fourth capacitor Cd, connected between the fourth λ/4 transmission line24dand GND, the second control terminal Tc2connected to the junction between the fourth PIN diode28dand the fourth capacitor Cd, and the resistor Rr for forming a reception terminating resistance, connected between the cathode of the fourth PIN diode28dand GND.

Therefore, when the forward bias voltage Vc1is applied to the first control terminal Tc1, turning on the first PIN diode28a, and the reverse bias voltage Vc2is applied to the second control terminal Tc2, turning off the second PIN diode28band the fourth PIN diode28d, the sixth antenna switch10F is represented by the equivalent circuit shown inFIG. 12wherein only the transmission terminal16is connected to the antenna connection terminal14at high frequencies, and a terminating resistor Re of, for example, 50 ohms is connected to the reception terminal20. In this case, the impedance on the receiver side when the switch is turned off is of the value of the terminating resistor Re, e.g., 50 ohms, thereby allowing the sixth antenna switch10F to achieve impedance matching with other circuits. Therefore, the reception amplifier connected to the reception terminal20is rendered stable in operation.

Conversely, when the reverse bias voltage Vc2is applied to the first control terminal Tc1, turning off the first PIN diode28a, and the forward bias voltage Vc1is applied to the second control terminal Tc2, turning on the second PIN diode28band the fourth PIN diode28d, the sixth antenna switch10F is represented by the equivalent circuit shown inFIG. 7wherein only the reception terminal20is connected to the antenna connection terminal14at high frequencies.

As with the fourth antenna switch10D, the sixth antenna switch10F comprises the directional coupler36having the first λ/4 signal transmission line18aas a component thereof. Thus, a signal in proportion to the reflected wave electric power Pb is output from the reflected wave output terminal40that is connected to the fourth end φ4of the directional coupler36. Accordingly, the reflected wave can be detected.

The equivalent circuit of the sixth antenna switch10F in the vicinity of the central frequency fo when the first PIN diode28ais turned off, is not the same as shown inFIG. 4B, but includes a parasitic capacitance Cf which remains as shown inFIG. 3B, thereby shifting the resonant frequency into a low frequency range. Thus, the sixth antenna switch10F is poorer in performance than the fourth antenna switch10D. However, since the sixth antenna switch10F is structurally simple, it is effective in applications where small size and lower cost are preferable to performance.

An antenna switch according to a seventh embodiment (hereinafter referred to as a seventh antenna switch10G) will be described below with reference toFIG. 16.

The seventh antenna switch10G is of a configuration including the first directional coupler36aand the second directional coupler36bthat are connected to a conventional antenna switch.

The seventh antenna switch10G has the first λ/4 signal transmission line18aand the third λ/4 signal transmission line18cthat are connected between the transmission terminal16and the antenna connection terminal14, a first switch circuit22aof the first PIN diode28athat is connected parallel to the first λ/4 signal transmission line18a, and a third switch circuit22cof the third PIN diode28cthat is connected parallel to the third λ/4 signal transmission line18c.

Similarly, the seventh antenna switch10G has the second λ/4 signal transmission line18band the fourth λ/4 signal transmission line18dthat are connected between the reception terminal20and the antenna connection terminal14, a second switch circuit22bof the second PIN diode28bthat is connected parallel to the second λ/4 signal transmission line18b, and a fourth switch circuit22dof the fourth PIN diode28dthat is connected parallel to the fourth λ/4 signal transmission line18d.

Each of the first through fourth PIN diodes28athrough28dis grounded at the cathode side.

The first control terminal Tc1is connected to a signal line between the capacitor C1on the transmitter side and the third λ/4 signal transmission line18c, through an inductance element L11. A capacitor C11is connected between the first control terminal Tc1and GND. Similarly, the second control terminal Tc2is connected to a signal line between the capacitor C4on the receiver side and the fourth λ/4 signal transmission line18d, through an inductance element L12. A capacitor C12is connected between the second control terminal Tc2and GND.

The seventh antenna switch10G comprises the first directional coupler36aand the second directional coupler36b. The first directional coupler36ahas the first λ/4 signal transmission line18aas a component thereof, for detecting a reflected wave of a transmission signal. The second directional coupler36bhas the third λ/4 signal transmission line18cas a component thereof, for detecting a travelling wave of a transmission signal.

Thus, a signal in proportion to the travelling wave electric power Pa is output from the travelling wave output terminal44connected to the third end φ3of the second directional coupler36b. Also, a signal in proportion to the reflected wave electric power Pb is output from the reflected wave output terminal40connected to the fourth end φ4of the first directional coupler36a. Therefore, a reflected wave and a travelling wave of a transmission signal can be detected.

Accordingly, it is only necessary that the λ/4 line is disposed so as to face the λ/4 signal transmission line of the conventional antenna switch. Therefore, an antenna switch can be configured for detecting a reflected wave and a travelling wave of a transmission signal without increasing the number of parts used.

In the embodiments as described above, though the first through fourth λ/4 signal transmission lines18athrough18dare used, which are advantageous particularly to reduction in size, 3λ/4 signal transmission lines may be used instead. Further, though the embodiments described above use the λ/4 line38, the first λ/4 line38a, or the second λ/4 line38bfor various lines, 3λ/4 lines etc. may be used instead in accordance with signal transmission lines. Also, though the embodiments described above use the first through fourth λ/4 transmission lines24athrough24dare used, which are advantageous particularly to reduction in size for various transmission lines, 3λ/4 signal lines etc. may be used instead.

The high frequency switch according to the present invention is not limited to the above embodiments, but may adopt various configurations without departing from the scope of the invention.