Microwave phase shifter having an active layer under the phase shifting line and power amplifier using such a phase shifter

A phase shifter according to this invention includes a circuit board having a semi-insulating layer. An active layer is formed in a transmission line forming portion on one surface side of the semi-insulating layer, a first ground conductive layer is formed on the other surface side, a transmission line is formed on the upper side of the active layer, and a second ground conductive layer is formed on the transmission line forming surface of the semi-insulating layer in close proximity to one side of the transmission line. If a bias voltage of negative polarity is applied to the transmission line, reverse bias is applied to the active layer to form a depletion layer and capacitance is equivalently connected to the transmission line having inductance. A phase shift amount can be freely controlled by changing the value of the capacitance according to the bias voltage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a microwave phase shifter which gives a desired phase shift amount to a high-frequency signal and a power amplifier using the microwave phase shifter.

2. Description of the Related Art

A microwave phase shifter is a circuit which gives a preset phase shift amount to a high-frequency signal of microwave, millimeter wave or the like and is normally configured by combining several transmission lines, a switch circuit and the like. For example, it has a transmission line used as a reference and transmission lines having delay amounts corresponding to preset phase differences with respect to the reference side transmission line, and a phase shift amount corresponding to the phase difference with respect to the reference is acquired by selecting one of the transmission lines by use of the switch circuit.

The microwave phase shifter with the above configuration is formed in an IC form by forming a plurality of transmission lines with different delay amounts and a switch circuit to switch the transmission lines on a substrate and thus an attempt is made to make the whole device small. However, since the switch circuit simultaneously makes selection of and switching to a single line from a plurality of lines on the input side and output side, a plurality of switch elements and driving control circuits are required. As a result, the circuit configuration of the microwave phase shifter formed on the substrate becomes complicated, the substrate becomes larger and the cost rises due to an increase in the number of manufacturing steps.

In the latest microwave communications devices for satellite communications, mobile communications, etc, a power amplifier using a semiconductor amplifier element is used, from the viewpoint of size, weight, reliability, etc. In a power amplifier using this semiconductor amplifier element, the output power which can be acquired by use of one element is not necessarily sufficient. Therefore, a power synthesizing type of power amplifier is proposed which, when a high output power is required, distributes an input signal into plural paths, amplifies them by use of semiconductor amplifier elements while controlling the signal phases, and then re-synthesizes the signals (for example, Jpn. Pat. Apln. KOKAI Publication No. 2001-196870 (p 5, FIG. 1)).

In the power amplifier, since a power loss occurs if the phases of the signals are deviated at the time of power synthesis, the phase differences between the signals are eliminated and the loss at the time of power synthesis is reduced by inserting phase shifters into paths other than a path used as a reference to adjust the phases. Thus, in the power synthesizing type of power amplifier, phase shifters corresponding in number to (the number of distributions—1) are required. Therefore, in order to make the power amplifier small and sufficiently reduce the loss, a phase shifter which is small and inexpensive and can relatively easily and precisely adjust the phase shift amount is desired.

SUMMARY OF THE INVENTION

An object of this invention is to provide a microwave phase shifter in which the circuit configuration is simple and can be easily made small, and as a result, the manufacturing cost can be lowered, and which can relatively easily and precisely adjust a phase shift amount, and a power synthesizing type of power amplifier using the microwave phase shifter.

A microwave phase shifter of this invention comprises a semi-insulating substrate having an operating layer partly formed thereon, a signal conductor formed on the operating layer of the semi-insulating substrate, a grounding conductor formed on the same surface as the signal conductor on the semi-insulating substrate, and a bias power supply which applies a bias voltage to the signal conductor.

DETAILED DESCRIPTION OF THE INVENTION

There will now be described embodiments of this invention with reference to the accompanying drawings.

FIG. 1is a configuration view showing the configuration of a microwave phase shifter according to a first embodiment of this invention. InFIG. 1, reference label11denotes a circuit board of the microwave phase shifter. The circuit board11is a semi-insulating substrate having a semi-insulating layer111formed of a semi-insulating material such as GaAs. On one surface side (front surface side of the substrate) of the semi-insulating layer111, an active layer112is formed in at least a transmission line forming portion, and on the other surface side (rear surface side of the substrate), a first conductive layer113of a metal material is formed. The active layer112is formed by ion-implanting an impurity into the semi-insulating layer111, for example.

On the upper side of the active layer112, a transmission line114of a metal material is formed. Further, on the surface of the semi-insulating layer111on which the transmission line114is formed, a second conductive layer115having an end portion formed to extend along and in close proximity to one side (right side in the drawing) of the transmission line114is formed.

In the circuit board11with the above configuration, the first conductive layer113and second conductive layer115are connected to a ground terminal116(the first conductive layer and second conductive layer are hereinafter referred to as a first grounding conductive layer and second grounding conductive layer, respectively), and the transmission line114is connected to a bias voltage input terminal117. To the terminal117, bias voltage Vp of negative polarity is applied from a bias power supply12on the external portion of the phase shifter. In this case, reverse bias is applied to the active layer112which lies directly under the transmission line114. As a result, a depletion layer is formed in the active layer112and capacitance is equivalently connected to the transmission line114. Further, if the value of the bias voltage is changed, the extent of the depletion layer varies. Therefore, the capacitance value caused by forming the depletion layer varies based on the function of the bias voltage.

FIG. 2is a circuit diagram showing the equivalent circuit of the microwave phase shifter with the above configuration for unit length. The transmission line114and the first and second grounding conductive layers113,115formed on the front surface and rear surface of the semi-insulating layer111configure a micro-coplanar strip line utilizing the proximity effect. As shown inFIG. 2, the configuration can be expressed by an equivalent circuit configured by inductors and capacitors. InFIG. 2, reference label1indicates inductance of the transmission line114per unit length, reference label c indicates parasitic capacitance caused between the transmission line114and the first and second grounding conductive layers113,115, and reference label c1indicates a capacitance caused by formation of the depletion layer. As is clearly seen fromFIG. 2, the capacitance c1caused by the depletion layer is formed in parallel with the parasitic capacitance c.

In this case, the characteristic impedence Z0of the micro-coplanar strip line is determined by the equation (1).
Z0=[l/(c+c1)]1/2(1)

Therefore, the phase θ of a microwave signal (angular frequency ω) which propagates along the transmission line114with line length L is given by the equation (2) if β=ω·Z0.
θ=βL=ω[l/(c+c1)]1/2×L(2)

As described before, the value of the capacitance c1varies if the bias voltage Vp applied to the transmission line114is changed. Therefore, as is clearly seen from the equation (2), it becomes possible to change the propagation phase θ of the transmission line114by changing the bias voltage Vp.

For example, if a reference phase (θ1) is obtained when the bias voltage Vp is 0 [V] and a phase is set to θ2when the bias voltage Vp is v, phase difference Δθ indicated by the equation (3) can be obtained.
Δθ=θ2−θ1(3)

In this case, it is operated as a phase shifter with the phase shift amount Δθ.

From the above description, according to the configuration of the present embodiment, since a switch circuit to switch transmission lines becomes unnecessary and the phase shift amount can be set only by the bias voltage applied to the transmission line, the circuit configuration is made simple. Further, since the phase difference Δθ is determined by the value of the bias voltage Vp, the phase shift amount can be controlled in a continuous or stepwise fashion by changing the bias voltage in a continuous or stepwise fashion.

FIG. 3is a configuration view showing the configuration of a microwave phase shifter according to a second embodiment of this invention. InFIG. 3, the same portions as those ofFIG. 1are denoted by the same reference symbols and different portions are taken up and explained here.

A circuit board11shown inFIG. 3includes a liquid crystal dielectric layer118instead of the semi-insulating layer ofFIG. 1. Like the first embodiment, a transmission line114and first and second grounding conductive layers113,115formed on the front surface and rear surface of the liquid crystal dielectric layer118configure a micro-coplanar strip line utilizing the proximity effect.

However, in the present embodiment, no active layer is formed.

With the above configuration, if bias voltage Vp is applied to the transmission line114, voltages are applied to the liquid crystal dielectric layer118between the transmission line114and the first grounding conductive layer113and between the transmission line114and the second grounding conductive layer115. As a result, in the liquid crystal dielectric layer118, the directivity of an anisotropic dielectric is changed. The directivity is changed according to the value of the bias voltage Vp. Therefore, if the value of the bias voltage Vp is changed, values of parasitic capacitances caused between the transmission line114and the first grounding conductive layer113and between the transmission line114and the second grounding conductive layer115vary.

FIG. 4is a circuit diagram showing the equivalent circuit of the microwave phase shifter with the above configuration for unit length. InFIG. 4, reference label1indicates an inductance of the transmission line114per unit length and reference label c indicates parasitic capacitance caused between the transmission line114and the first and second grounding conductive layers113,115. As clearly seen fromFIG. 4, in the present embodiment, the capacitance caused by the depletion layer in the first embodiment is not present and the value of the parasitic capacitance c itself is changed.

In this case, the characteristic impedance Z0of the micro-coplanar strip line is determined by the equation (4).
Z0=(l/c)1/2(4)

Therefore, the phase θ of a microwave signal (angular frequency ω) which propagates along the transmission line114with line length L is given by the equation (5) if β=ω·Z0.
θ=βL=ω(l/c)1/2×L(5)

As described before, if the bias voltage Vp applied to the transmission line114is changed, the dielectric constant of the liquid crystal dielectric layer116varies and the value of the capacitance c varies. Therefore, as is clearly seen from the equation (5), it becomes possible to change the propagation phase θ of the transmission line114by changing the bias voltage Vp.

For example, if a reference phase (θ1) is obtained when the bias voltage Vp is 0 [V] and a phase is set to θ2when the bias voltage Vp is v, phase difference Δθ indicated by the equation (6) can be obtained.
Δθ=θ2−θ1(6)

In this case, it is operated as a phase shifter with the phase shift amount Δθ.

From the above description, also, according to the configuration of the present embodiment, since a switch circuit to switch transmission lines becomes unnecessary and the phase shift amount can be set only by the bias voltage applied to the transmission line, the circuit configuration is made simple. Further, since the phase difference Δθ is determined by the value of the bias voltage Vp, the phase shift amount can be controlled in a continuous or stepwise fashion by changing the bias voltage in a continuous or stepwise fashion.

FIG. 5is a block circuit diagram showing the configuration of a power amplifier according to a third embodiment of this invention. InFIG. 5, a microwave transmission signal is supplied to an input terminal21. The signal is distributed into two paths. One of the paths is used as a reference path and the distributed signal thereof is supplied to an amplifier23and power-amplified. The distributed signal of the other path is phase-adjusted by a phase shifter24so that the phase thereof will correspond to the signal of the reference path and is then supplied to an amplifier25and power-amplified. The distributed signals power-amplified by the respective amplifiers23,25are synthesized in a synthesizer26and output from an output terminal27.

The power amplifier of the above configuration is a so-called power synthesizing type, and it evenly matches the phases when power-amplifying the distributed microwave signals and adds and synthesizes the power-amplified outputs. In the present embodiment, as the phase shifter24to make a phase adjustment, the microwave phase shifter with the configuration of the first or second embodiment is used.

The power value of the synthesis signal supplied to the output terminal26is monitored by a power monitoring device28and the monitoring result is supplied to a control device29. The control device29controls the phase shift amount of the phase shifter24so that the monitoring power value is maximum. The control is to supply the bias voltage Vp to a bias voltage input terminal of the phase shifter24and change the bias voltage Vp according to the phase shift amount.

Since the power amplifier with the above configuration uses the microwave phase shifter of the first or second embodiment in the phase shifter24, it can be made small and the cost can be lowered. Further, since the phase shift amount of the phase shifter24can be adjusted continuously or in fine steps, it can be adjusted with high precision in comparison with the conventional line switching system.

In the power amplifier of the above embodiment, the phase shifter24is incorporated in the preceding stage of the amplifier25in each distribution path, but since the configuration of the phase shifter of this invention is excellent in the power-resistance characteristic, it can be arranged in the succeeding stage of the amplifier25as shown inFIG. 6. In this case, since it becomes unnecessary to take the processing delay time of the amplifier25into consideration, phase matching with higher precision can be attained.

Further, in the above embodiment, the amplifier25and the phase shifter24are explained as different units, but the configuration of the phase shifter24can be incorporated into the amplifier25itself. With this configuration, the size can be further reduced.

Further, in the above embodiment, the number of distribution paths is two, but when the number of distribution paths is increased, the phases of transmission signals of the respective paths can be similarly matched by using one path as a reference path and arranging phase shifters in other paths. Of course, the same operation can be performed even when a phase shifter is arranged in the reference path.