JPH0758841B2 - Microwave phase shifter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a microwave phase shifter aiming at improving performance.

(Prior Art) In recent years, in the radar system, gallium and arsenic (GaAs)
Microwave phase shifters that use field effect transistors (FETs) such as the above have been widely adopted for phased array antennas and the like, and downsizing of antenna devices has been realized. The required performances of microwave phase shifters include low phase shift error, low insertion loss, small insertion loss fluctuation range, low VSWR, and miniaturization, among which low phase shift error is emphasized.

However, in order not to deteriorate the antenna pattern of the array antenna, it is most important to keep the fluctuation range of the insertion loss of the phase shifter small. FET for switching element
In the microwave phase shifter using, the FET is switched to the ON state or the OFF state to selectively switch the phase shifter circuit to the reference state or the phase shift state to obtain the desired phase shift amount. To be done.

FIG. 3 is an equivalent circuit of a conventional microwave phase shifter called a loaded line type phase shifter (45 degree phase shifter).

That is, the 1/4 wavelength distributed constant line 3 is connected between the microwave input / output terminals 1 and 2, and the matching distributed constant lines 41 and 42 are provided at both ends of the 1/4 wavelength distributed constant line 3. FET5
1,52 are connected. In addition, FET 51, 52 gate terminal 51G,
52G has a common control input terminal 7 to which a control signal Q is supplied via gate resistors 61 and 62, respectively.

Therefore, in this conventional microwave phase shifter, the passing phase of the phase shifter is switched by switching the FETs 51 and 52 to the ON state and the OFF state by the control signal Q, and thereby the required passing phase difference is obtained. That is, the amount of phase shift is obtained. By the way, the impedances of the FETs 51 and 52 in the on and off states are equivalently drained to the source terminal (S) which is mainly determined by the channels of the FETs 51 and 52 as shown in FIGS. 4 (a) and 4 (b), respectively. ON resistance between terminals (D) Ron and F
The same off capacitance (Coff) determined by the depletion layer of ET51, 52
It is represented by. Therefore, for example, gate width Wg = 300μm, 10G
As shown in FIG. 5, the impedance between the source (S) and the drain (D) of the FETs 51 and 52 at Hz is about 1 as the reflection coefficient of the impedance (Zoff) in the off state, but is on. In this state, the magnitude of the reflection coefficient of the impedance (Zon) becomes smaller than 1 due to the influence of the on-resistance Ron. That is, the difference in the magnitude of the reflection coefficient between the ON state and the OFF state of the FETs 51 and 52 affects the fluctuation range of the insertion loss in the phase shifter.

Generally, the insertion loss of the phase shifter depends on the Q value of the circuit. Sixth
The figure shows the loaded line type phase shifter shown in Fig. 3, where the value of the circuit Q in the reference state is Qref and the value of Q in the phase shift state is Qdif.
Then, the insertion loss fluctuation width for the ratio Qc (≡Qdif / Qref) of both is calculated at 10 GHz, and Qc = 1,
That is, it shows that the insertion loss fluctuation width is minimum when Qdif = Qref (reference A). The Q value of the circuit is proportional to the magnitude of the reflection coefficient of the impedance between the source (S) and the drain (D) of the FETs 51 and 52, ignoring the loss of other circuit elements. The magnitude of the impedance reflection coefficient when the FETs 51 and 52 are on is 1 because of the resistance Ron.
Since it becomes smaller, Qdif = Qref does not hold, and Qref
<Qdif (or Qref> Qdif). That is, the Q value of the circuit is smaller when the FETs 51 and 52 are in the on state than when it is in the off state, and the insertion loss of the circuit is larger in the on state than in the off state.

As described above, in the conventional microwave phase shifter, the fluctuation range of the insertion loss accompanying the switching operation becomes large, and as shown by the actual value B in FIG. 6, the fluctuation range of the insertion loss in the unit phase shifter is about 0.7. It was dB. Therefore, when such a unit phase shifter is used to construct a 4-bit phase shifter, for example, the total insertion loss fluctuation range is approximately 2.8 dB, and when a phased array antenna is constructed, the beam wave at the antenna aperture plane is However, there is a drawback in that the synthesis efficiency of is reduced and the antenna pattern is greatly deteriorated.

(Problems to be Solved by the Invention) In the conventional microwave phase shifter, the Q value of the circuit differs between the reference state and the phase shift state of the phase shifter due to the presence of the ON resistance of the FET. The fluctuation range of the insertion loss of the vessel was large, and the effective antenna pattern of the planar antenna was deteriorated.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a microwave phase shifter which eliminates the above-mentioned conventional drawbacks and reduces the fluctuation width of insertion loss to prevent deterioration of the antenna pattern.

[Structure of Invention]

(Means for Solving the Problem) In order to achieve the above-mentioned object, the present invention provides a microwave phase shifter having a FET as a switching element so that the insertion loss is substantially equal in the reference state and the phase shift state. A resistance having a value sufficiently larger than the resistance between the source terminal and the drain terminal when the field effect transistor is on is connected.

(Operation) In the microwave phase shifter of the present invention, the resistance connected between the source terminal and the drain terminal of the FET lowers the Q value of the circuit when the FET is off and the Q value when the FET is on. Since the difference from the value of is small, the fluctuation range of insertion loss is small. Further, the value of the resistance connected between the source terminal and the drain terminal of the field effect transistor is made sufficiently larger than the resistance between the source terminal and the drain terminal when the field effect transistor is in the ON state. Therefore, it is possible to prevent an increase in insertion loss as a phase shifter.

Embodiment An embodiment of the microwave phase shifter according to the present invention will be described below with reference to the drawings. The same components as those of the conventional configuration shown in FIGS. 3 to 6 are designated by the same reference numerals for description.

FIG. 1 is a circuit diagram showing an embodiment of a microwave phase shifter according to the present invention, showing an X band, 45 degree loaded line type phase shifter. That is, the 1/4 wavelength distributed constant line 3 between the input / output terminals 1 and 2 has matching distributed constant lines 41 and 4 at both ends thereof.
FETs 51 and 52 are correspondingly connected via 2. The FETs 51 and 52 are commonly connected to the control input terminal 7 through the gate resistors 61 and 62, and resistors 81 and 82 are connected between the source (S) and drain (D) of the FETs 51 and 52. ing.

2 shows that the FETs 51 and 52 shown in FIG.
The impedance between the source (S) and the drain (D) at a frequency of 10 GHz at 0 μm is shown. In FIG. 2, Zon 'is the impedance when the FETs 51 and 52 are on, and Zoff' is the impedance when the FETs are off. In both cases, resistors 81 and 82 are connected. Zoff represents the impedance in the off state when the resistors 81 and 82 are not connected in FIG. If the resistors 81 and 82 are selected to have a value sufficiently larger than the on resistance of the FETs 51 and 52, for example, 1.5KΩ, the value when the FETs 51 and 52 are off between the source (S) terminal and the drain (D) terminal is: Since the resistance is determined mostly by the resistances 81 and 82, the magnitude of the reflection coefficient in the off state can be arbitrarily moved by selecting the resistance value.

On the other hand, the Q value of the circuit is neglected by the loss of other circuit elements.
Since it is proportional to the magnitude of the reflection coefficient of the impedance between the source (S) and drain (D) of the FETs 51 and 52, the FETs 51 and 52 are turned on when the values of the resistors 81 and 82 are properly selected. Only the Q value of the circuit can be reduced to bring Qdif and Qref close or equal.

Thus, in the microwave phase shifter according to the present invention, the FET 51,
By connecting resistors 81 and 82 between the source (S) and drain (D) of 52, it is possible to make the Q value in the ON state and the Q value in the OFF state of the phase shifter substantially equal. Because you can
The fluctuation range of insertion loss as a phase shifter becomes small. That is, in the circuit diagram shown in FIG. 1, resistors 81,8 having a resistance value of 1.5 kΩ
As a result of connecting 2 between the source (S) and drain (D) of FET51,52, as shown in FIG.
The ratio Qc between the value of (Qref) and the value of Q in the phase shift state (Qdit) becomes approximately 1 as indicated by the symbol A, indicating that the fluctuation range of the insertion loss of the phase shifter can be significantly improved. Moreover, resistance 81,82
Since the FET controls only the Q value when the FETs 51 and 52 are in the off state, and the influence on the Q value when the FET is in the on state can be ignored, the resistor 8
The addition of 1,82 does not increase the insertion loss as a phase shifter.

Therefore, in the microwave phase shifter according to the present invention,
When an array antenna is constructed, if there is a problem with the variation of insertion loss, only the variation range of insertion loss due to mismatch between unit phase shifters is considered.When a 4-bit phase shifter is constructed with the phase shifter of the present invention , If the VSWR of the unit phase shifter is 1.2, the insertion loss fluctuation range is only about 0.3 dB. With such a fluctuation range, deterioration of the antenna pattern does not occur and a good antenna can be configured.

Although the loaded line type phase shifter has been described as an example in the above embodiment, the Q value of the circuit in the reference state of the phase shifter is equalized between the source (S) terminal and the drain (D) terminal. Since it suffices to connect a resistor whose value is set in advance, the present invention can be applied not only to a loaded line type phase shifter but also to a phase shifter having another configuration.

〔The invention's effect〕

As described above, in the microwave phase shifter according to the present invention, a resistor is provided between the source terminal and the drain terminal so that the Q value of the circuit of the phase shifter becomes equal in the reference state and the phase shift state of the phase shifter. The simple structure of connection can reduce the fluctuation range of insertion loss, and can be applied to a phase array antenna to obtain a remarkable effect. Also, the insertion loss as a phase shifter does not increase. Furthermore, it is easy to connect the resistors.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a microwave phase shifter according to the present invention, FIG. 2 is a Smith chart showing the impedance characteristics of the FET of the circuit shown in FIG. 1, and FIG. Circuit diagram showing the wave phase shifter, FIG. 4 (a) and FIG.
FIG. 5B is an equivalent circuit diagram of the FET of the circuit shown in FIG.
FIG. 6 is a Smith chart showing the impedance characteristic of the FET of the circuit shown in FIG. 3, and FIG. 6 is a characteristic diagram showing the insertion fluctuation width of the circuit shown in FIG. 1 …… input terminal, 2 …… output terminal 3 …… 1/4 wavelength distributed constant line 41,42 …… matching distributed constant circuit 51,52 …… FET, 7 …… control input terminal 81,82 …… resistor

Claims (1)

[Claims] 1. A microwave phase shifter having a field effect transistor as a switching element, wherein a source terminal and a drain terminal of the field effect transistor are
In order to make the insertion loss almost equal in the reference state and the phase shift state,
A microwave phase shifter, wherein a resistance having a value sufficiently larger than a resistance between the source terminal and the drain terminal when the field effect transistor is turned on is connected.