Abstract:
There is provided a small size phase shifter which can shift a phase by 180 degrees wherein the accuracy of preset phase is less dependent on frequency. The phase shifter comprises first to fourth switches provided between a first line pair and a second line pair. By turning the first and second switches ON and the third and fourth switches OFF, a signal inputted to the first line pair is outputted from the second line pair in phase. By turning the first and second switches OFF and the third and fourth switches ON, a signal inputted to the first line pair is outputted from the second line pair out of phase. A small-size phase shifter which has the accuracy of preset phase less dependent on frequency can then be obtained.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a phase shifter for shifting a phase of a microwave signal by forming switches such as FETs and slot lines on a semiconductor substrate made of silicon, gallium-arsenic (hereinafter referred to as GaAs), etc. and changing the slot lines over with such switches. 
     2. Description of the Related Art 
     FIG. 1 illustrates an example of the structure of a conventional line change-over phase shifter. In this figure, the reference numeral 1 designates a semiconductor substrate; 3a to 3d drain electrodes; 4a to 4d gate electrodes; 5a to 5d source electrodes; 6a to 6d FETs having drain electrodes 3a to 3d, gate electrodes 4a to 4d and source electrodes 5a to 5d; 7a to 7d bias resistances; 8a to 8d bias pads; 9a to 9d bias circuits comprising bias resistances 7a to 7d and bias pads 8a to 8d; 83a and 83b input/output microstrip line patterns; 84 a reference-phase microstrip line pattern; 85 a phase-preset microstrip line pattern; 86 a ground pattern formed on the bottom surface of semiconductor substrate 1. A bias voltage is impressed to gate electrodes 4a to 4d of FETs 6a to 6d from bias circuits 9a to 9d to operate FETs 6a to 6d as switches. Drain electrodes 3a to 3d and source electrodes 5a to 5d are usually grounded through bias circuits (not illustrated) in order to cause the drain voltage and source voltage of FETs 6a to 6d to have the same DC potential. 
     FIG. 2 is a diagram which explains the operations of the line change-over phase shifter illustrated in FIG. 1. In FIG. 2, reference numerals 16a and 16b designate input/output line pairs; 87a and 87b single-pole double-through switches (hereinafter referred to as SPDT switch); 88a reference-phase line pair; and 89 a phase-preset line pair. 
     Next, the operations will be explained. The circuit between drain electrodes 3a to 3d and source electrodes 5a to 5d of FETs 6a to 6d are turned ON and OFF to turn on and off a microwave signal by equalizing the potential of DC component of the drain and source voltages, for example, 0 V and switching the gate voltages between 0 V and the pinch-off voltage. Therefore, first FET 6a and second FET 6b are used as a pair and 0 V is applied to any one of gate electrodes 4a, 4b, while the pinch-off voltage to the other. When the bias voltages are changed over simultaneously, first and second FETs 6a and 6b operate as a SPDT switch. This SPDT switch corresponds to first SPDT switch 87a of FIG. 2. Similarly, third FET 6c and fourth FET 6d are used as a pair and 0 V is applied to any one of gate electrodes 4c and 4d, while the pinch-off voltage is applied to the other. When the bias voltages simultaneously are changed over, third and fourth FETs 6c, and 6d operate as a SPDT switch. This SPDT corresponds to second SPDT switch 87b of FIG. 2. Similarly input/output microstrip line patterns 83a, 83b of FIG. 1 respectively correspond to input/output line pairs 16a, 16b of FIG. 2. Reference-phase microstrip line pattern 84 of FIG. 1 corresponds to reference phase line pair 88 of FIG. 2, while phase-preset microstrip line pattern 84 of FIG. 1 to phase-preset line pair 89 of FIG. 2. 
     In FIG. 2, a microwave signal inputted from first input/output line pair 16a passes through first SPDT switch 87a, reference-phase line pair 88 and second SPDT switch 87b and is then outputted from second input/output line pair 16b. The phase of the microwave signal can be shifted by the difference in electrical length between the propagation paths by switching between SPDT switches 87a, 87b and changing the propagation path of the microwave signal to phase-preset line pair 89. Assuming that the difference in electrical length is defined as ΔL, microwave signal frequency as f and the velocity of light as C, the amount of phase shift θ can be given by the formula: θ=2πf ΔL/C. 
     Since the conventional line change-over phase shifter operates on the basis of the principle explained above, if a large phase shift is required, phase-preset microstrip line pattern 85 illustrated in FIG. 1 is elongated, as can be understood from the above formula (θ=2πf ΔL/C) to obtain the phase shift. As a result, the conventional line change-over phase shifter is disadvantageous in that a circuit structure becomes larger in size and that a preset phase changes greatly with frequency as signal transmission line becomes longer. 
     SUMMARY OF THE INVENTION 
     The present invention has been proposed to overcome the problems described above and it is therefore an object of the present invention to provide a small-sized 180-degree phase shifter wherein the accuracy of the preset phase is less dependent on frequency. 
     A phase shifter of the present invention comprises a first input/output line pair, a second input/output line pair and first to fourth switches provided between these first and second line pairs. By turning ON and OFF these first to fourth switches, a line conductor of the first input/output line is switched between line and ground conductors of the second input/output line pair and a ground conductor of the first input/output line pair is switched between the line and ground conductors of the second input/output line pair. Consequently, the phase of the AC voltage transmitted can be phase-shifted by 180 degrees and a line for presetting the amount of phase shift can be omitted, and any change in frequency resulting from line length can be reduced. 
     In order to embody a phase shifter of the present invention, there is provided on a semiconductor substrate a first input/output slot line pattern pair, a second input/output slot line pattern pair and first to fourth FETs provided between those input/output line pairs and having gate electrodes formed in a direction parallel or perpendicular to the first and second input/output slot line pattern pairs, and a connection is switched between the first input/output slot line pattern pair and the second input/output slot line pattern pair by the first to fourth FETs. 
     The phase shifter can be reduced in size by arranging the first to fourth FETs in the shape of a ladder in a direction perpendicular to the first and second input/output slot line pattern pairs. 
     Each FET can be designed more freely by arranging the width of the first to fourth FETs in a direction perpendicular to the first and second input/output slot line pattern pairs. 
     The phase shifter can further be reduced in size by arranging the first to fourth FETs, having the gate electrodes formed in a direction perpendicular to the first and second input/output slot line pattern pairs, in the shape of a ladder in a direction parallel to the first and second input/output slot line pattern pairs. 
     The gate electrodes of the first to fourth FETs are connected to bias circuits each having a resistance or a line pattern. 
     The first to fourth FETs may respectively be replaced with a plurality of parallelly connected FETs, thereby reducing signal loss. 
     In order to embody the phase shifter of the present invention, a first input/output slot line pattern pair, a second input/output slot line pattern pair and first to fourth diodes provided between the pattern pairs are provided on one surface of the semiconductor substrate, and the connection is switched between the first input/output slot line pattern pair and the second input/output slot line pattern pair by the first to fourth diodes. This structure allows for more freedom of design and ensures a minimal signal loss. 
     In the phase shifter of the present invention, the first and second input/output coplanar line patterns can respectively be connected to the first and second input/output slot line pattern pairs, whereby on-wafer evaluation can be performed by means of an on-wafer prober. 
     In the phase shifter of the present invention, the first and second input/output microstrip line patterns can respectively be connected to the first and second input/output slot line pattern pairs, whereby the possibility of connection to other devices can be increased. 
     Ground patterns may be provided on the bottom surface of the semiconductor substrate in such a manner as to be opposite the first and second input/output coplanar line patterns and each return pattern of the coplanar line patterns may be connected to the ground patterns via holes, whereby on-wafer evaluation can be performed by using an RF prober. 
     In the phase shifter of the present invention, a ground pattern may be formed on the entire bottom surface of the semiconductor substrate. In this case, a first slot line pattern pair having one of the patterns narrower than the other can be provided between the first and second input/output slot line pattern pairs and the first input/output microstrip line pattern, and a second slot line pattern pair having one of the patterns narrower than the other can be provided between the second input/output slot line pattern pair and the second input/output microstrip line pattern. Such a structure ensures a stable operation of the phase shifter even if a ground pattern is formed on the entire bottom surface of the semiconductor substrate. 
     In the phase shifter of the present invention, a ground pattern may be provided on the entire bottom surface of the semiconductor substrate and the return pattern pairs of the first and second input/output coplanar line patterns may be connected to the ground pattern. In this case, a first slot line pattern pair having one of the patterns narrower than the other can be provided between the first input/output coplanar line pattern and the first input/output slot line pattern pair and a second slot line pattern pair having one of the patterns narrower than the other can be provided between the second input/output coplanar line pattern and the second input/output slot line pattern pair. 
     The phase shifter can operate stably by setting a total length of each microstrip line comprising each of the first and second slot line pattern pairs and the ground pattern to substantially a quarter of the wavelength of an operating frequency. 
     In the phase shifter of the present invention, a first capacitor one electrode of which is grounded can be connected to a junction point of the first input/output microstrip line pattern and the narrower pattern of the first slot line patterns and a second capacitor one electrode of which is grounded can be connected to the junction point of the second input/output microstrip line pattern and the narrower pattern of the second slot line patterns. This ensures that the phase shifter can operate stably even if a ground pattern is formed on the entire bottom surface of the semiconductor substrate. 
     In the phase shifter of the present invention, similar advantages can be drawn by connecting a first capacitor, one electrode of which is grounded, to the junction point of a signal line pattern of the first input/output coplanar line pattern having a grounded return pattern pair and the narrower pattern of the first slot line patterns and by connecting a second capacitor, one electrode of which is grounded, to the junction point of a signal line pattern of the second input/output coplanar line pattern having a grounded return pattern pair and the narrower pattern of the second slot line patterns. 
     In the phase shifter of the present invention, the series connection of the first capacitor and the fifth FET may be connected in parallel to the junction point of the first input/output microstrip line pattern and the first slot line pattern pair and a series connection of the second capacitor and sixth FET may be connected in parallel to the junction point of the second input/output microstrip line pattern and the second slot line pattern pair. This ensures that the phase shifter can operate stably by turning ON and OFF the fifth and sixth FETs even if a ground pattern is formed on the entire bottom surface of the semiconductor substrate. 
     In the phase shifter of the present invention, the influence of the ground pattern formed on the bottom surface of the semiconductor substrate can be reduced by connecting the series connection of the first capacitor and the fifth diode in parallel to the junction point of the first input/output microstrip line pattern and the first slot line pattern pair, by connecting the series connection of the second capacitor and the sixth diode in parallel to the junction point of the second input/output microstrip line pattern and the second slot line pattern pair and by changing the capacitances of the fifth and sixth diodes. 
     In the phase shifter of the present invention, the first microstrip line pattern having a ground pattern on the upper surface of the semiconductor substrate can be disposed between the first slot line pattern pair and the first input/output microstrip line pattern and the second microstrip line pattern having a ground pattern on the upper surface of the semiconductor substrate can be disposed between the second slot line pattern pair and second input/output microstrip line pattern. The ground patterns formed on the upper surface of the semiconductor substrate can reduce any influence of the ground pattern formed on the entire bottom surface of the semiconductor substrate. 
     In the phase shifter of the present invention, it is possible that the first microstrip line pattern having a ground pattern on the upper surface of the semiconductor substrate is disposed between the first input/output coplanar line pattern having a grounded return pattern pair and the first slot line pattern pair and that the second microstrip line pattern having a ground pattern on the upper surface of the semiconductor substrate is disposed between the second input/output coplanar line pattern having a grounded return pattern pair and the second slot line pattern pair. 
     In the phase shifter of the present invention, a ground pattern is provided between the first slot line pattern pair and the first input/output microstrip line pattern, the first parallel-plate capacitor uses a part of the ground pattern as the lower electrode thereof, the narrower pattern of the first slot line patterns is connected to an upper electrode of the first parallel-plate capacitor and the first input/output microstrip line pattern through air bridges, a ground pattern is provided between the second slot line pattern pair and the second input/output microstrip line pattern, the second parallel-plate capacitor uses a part of the ground pattern as the lower electrode thereof, and the narrower pattern of the second slot line patterns is connected to an upper electrode of the second parallel-plate capacitor and the second input/output microstrip line pattern through air bridges. Such a structure ensures that the influence of the ground pattern formed on the bottom surface of the semiconductor substrate can be reduced and that T-shaped low-pass filters having the desired characteristics can be constituted with the air bridges and the parallel-plate capacitors. 
     In the phase shifter of the present invention, similar advantages can be drawn by providing a ground pattern between the first input/output coplanar line pattern having a grounded return pattern pair and the first slot line pattern pair, providing a first parallel-plate capacitor using a part of the ground pattern as the lower electrode, and connecting the narrower pattern of the first slot line patterns to the upper electrode of the first parallel-plate capacitor and the signal line pattern of the first input/output coplanar line pattern through air bridges and by providing a ground pattern between the second input/output coplanar line pattern having a grounded return pattern pair and the second slot line pattern pair, providing a second parallel-plate capacitor using a part of the ground pattern as the lower electrode, and connecting the narrower pattern of the second slot line patterns to the upper electrode of the second parallel-plate capacitor and the signal line pattern of the second input/output coplanar line pattern through air bridges. 
     The phase shifter of the present invention may connect DC-cut capacitors to via holes formed to connect one of the input/output slot line patterns and the ground pattern. If positive voltages are applied to the gate and source electrodes of the first to fourth FETs, the gate electrodes thereof can be controlled by positive voltages. Further, voltages for controlling the diodes can be set freely to the desired values regardless of the ground voltage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a schematic view of the structure of a conventional line switching type phase shifter. 
     FIG. 2 is a diagram for explaining operations of the phase shifter illustrated in FIG. 1. 
     FIG. 3 illustrates a schematic view of the structure of the first embodiment of a phase shifter according to the present invention. 
     FIGS. 4 and 5 are diagrams for explaining operations of the phase shifter illustrated in FIG. 3. 
     FIG. 6 illustrates a schematic view of the structure of the second embodiment of a phase shifter according to the present invention. 
     FIG. 7 illustrates a schematic view of the structure of the third embodiment of a phase shifter according to the present invention. 
     FIG. 8 is a diagram illustrating a modification to the phase shifter of the third embodiment according to the present invention. 
     FIG. 9 is a diagram illustrating another modification to the phase shifter of the third embodiment according to the present invention. 
     FIG. 10 illustrates a schematic view of the structure of the fourth embodiment of a phase shifter according to the present invention. 
     FIG. 11 is a diagram for explaining operations of the phase shifter illustrated in FIG. 10. 
     FIG. 12 illustrates a schematic view of the structure of the fifth embodiment of a phase shifter according to the present invention. 
     FIG. 13 illustrates a schematic view of the structure of the sixth embodiment of a phase shifter according to the present invention. 
     FIG. 14 illustrates a schematic view of the structure of the seventh embodiment of a phase shifter according to the present invention. 
     FIG. 15 illustrates a schematic view of the structure of the eighth embodiment of a phase shifter according to the present invention. 
     FIG. 16 illustrates a schematic view of the structure of the ninth embodiment of a phase shifter according to the present invention. 
     FIG. 17 illustrates a schematic view of the structure of the tenth embodiment of a phase shifter according to the present invention. 
     FIG. 18 is a diagram illustrating a modification to the phase shifter of the tenth embodiment according to the present invention. 
     FIGS. 19 and 20 illustrate elevation and bottom views of the structure of the eleventh embodiment of a phase shifter according to the present invention. 
     FIGS. 21 and 22 illustrate elevation and bottom views of a modification to the phase shifter of FIG. 19. 
     FIGS. 23 and 24 illustrate elevation and bottom views of the structure of the twelfth embodiment of a phase shifter according to the present invention. 
     FIGS. 25 and 26 illustrate elevation and bottom views of a modification to the phase shifter of FIGS. 23 and 24. 
     FIG. 27 illustrates a schematic view of the structure of the thirteenth embodiment of a phase shifter according to the present invention. 
     FIG. 28 illustrates a schematic view of the structure of the fourteenth embodiment of a phase shifter according to the present invention. 
     FIGS. 29 to 32 are diagrams for explaining operations of the phase shifter illustrated in FIGS. 27 and 28. 
     FIG. 33 illustrates a schematic view of the structure of the fifteenth embodiment of a phase shifter according to the present invention. 
     FIG. 34 is a diagram for explaining operations of the phase shifter illustrated in FIG. 33. 
     FIG. 35 illustrates a schematic view of the structure of the sixteenth embodiment of a phase shifter according to the present invention. 
     FIG. 36 illustrates a schematic view of the structure of the seventeenth embodiment of a phase shifter according to the present invention. 
     FIGS. 37 and 38 are diagrams for explaining operations of the phase shifter illustrated in FIG. 36. 
     FIG. 39 illustrates a schematic view of the structure of the eighteenth embodiment of a phase shifter according to the present invention. 
     FIGS. 40 and 41 are diagrams for explaining operations of the phase shifter illustrated in FIG. 39. 
     FIG. 42 illustrates a schematic view of the structure of the nineteenth embodiment of a phase shifter according to the present invention. 
     FIG. 43 is a cross-sectional view taken along the line A--A of FIG. 42. 
     FIG. 44 illustrates a schematic view of the structure of the twentieth embodiment of a phase shifter depending on an embodiment 20 of the present invention. 
     FIG. 45 illustrates a schematic view of the structure of the twenty-first embodiment of a phase shifter according to the present invention. 
     FIG. 46 is an equivalent circuit of the portion B illustrated in FIG. 45. 
     FIG. 47 illustrates a schematic view of the structure of the twenty-second embodiment of a phase shifter according to the present invention. 
     FIG. 48 illustrates a schematic view of the structure of the twenty-third embodiment of a phase shifter according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will be explained hereunder with reference to the accompanying drawings. FIG. 3 illustrates the structure of an embodiment of a phase shifter of the present invention. In this figure, the reference numeral 16 designates an input/output line pair; 17a, 17b, 17c and 17d switches; 18 a line pair and 19 a crossing line pair. The remaining reference numerals designate elements like those illustrated in FIGS. 1 and 2. FIGS. 4 and 5 are diagrams for explaining operations of the phase shifter illustrated in FIG. 3. 
     In FIG. 3, when first and second switches 17a, 17b are turned ON and third and fourth switches 17c, 17d are turned OFF, a microwave signal inputted from first input/output line pair 16a is outputted from second input/output line pair 16 through first switch 17a, second switch 17b and line pair 18. The current path in the above operation is illustrated in FIG. 4. Next, when first and second switches 17a, 17b are turned OFF and third and fourth switches 17c, 17d are turned ON in FIG. 3, a microwave signal inputted from first input/output line pair 16a is outputted from second input/output line pair 16b through crossing line pair 19, third switch 17c and fourth switch 17d. A current path in the above operation is illustrated in FIG. 5. It is noted that, in FIG. 5, the relationship between the line and the ground conductors forming first input/output line pair 16a is the reverse of that between the line and ground conductors forming second input/output pair 16b, in FIG. 4. Therefore, the polarity of an AC voltage propagated is reversed with respect to crossing line pair 19. This fact is equivalent, if attention is paid to the phase of the AC signal, to a phase inversion, that is, to a phase shift of 180 degrees. Such an operation occurs regardless of frequency. Consequently, if all the phase shifts which occur at the first to fourth switches when those switches are ON in FIG. 4 are equal to those in FIG. 5 and electrical lengths of line pair 18 and crossing line pair 19 in FIG. 4 are equal to those in FIG. 5, the phase of the microwave signal outputted to second input/output line pair 16b in the case of FIG. 4 is different from that of the microwave signal outputted to second input/output line pair 16b in the case of FIG. 5 by 180 degrees at any frequency. 
     FIG. 6 illustrates the structure of the second embodiment of a phase shifter according to the present invention. In the second embodiment, of the first embodiment is integrally formed on a semiconductor substrate, as shown in FIG. 6. In this figure, the reference numeral 2a and 2b designate input/output slot line pattern pairs; 10a and 10b connecting line patterns; 11 a line pair constituted of line connecting patterns 10a, 11b; 12a, 12b, 12c and 12d line connecting patterns; 13 an air bridge; 14 a crossing line pair constituted of line connecting patterns 12a, 12b, 12c and air bridge 13; 15, an air bridge. The remaining reference numerals define like elements of the conventional phase shifter shown in FIG. 1. 
     As illustrated in FIG. 6, gate electrodes 4a to 4d of first to fourth FETs 6a to 6d are formed to be in parallel to input/output slot line pattern pairs 2a, 2b. One of the patterns of first input/output slot line pattern pair 2a is connected to drain electrode 3a of first FET 6a and source electrode 5d of fourth FET 6d, and the other of the patterns of first input/output slot line pattern pair 2a is connected to drain electrode 3b of second FET 6b and source electrode 5c of third FET 6c. Further, one of the patterns of second input/output slot line pattern pair 2b is connected to drain electrode 3c of third FET 6c; the other of the patterns of second input/output slot line pattern pair 2b is connected to drain electrode 3d of fourth FET 6d; source electrode 5a of first FET 6a is connected to drain electrode 3c of the third FET 6c; and source electrode 5b of second FET 6b is connected to drain electrode 3d of fourth FET 6d. 
     In FIG. 6, gate bias voltages are applied to gate electrodes 4a to 4d of FETs 6a to 6d from bias circuits 9a to 9d to cause FETs 6a to 6d to perform switching operations. Drain electrodes 3a to 3d and source electrodes 5a to 5d of FETs 6a to 6d are grounded through grounding circuits (not illustrated) so that these electrodes are placed at the same DC potential. 
     If the drain and source electrodes are at the same DC potential, for example, 0 V, each FET performs a switching operation for passing and stopping a microwave signal between the drain electrode and the source electrode by switching the gate voltage between 0 V and the pinch-off voltage. Therefore, first FET 6a, second FET 6b, third FET 6c and fourth FET 6d in FIG. 6 respectively correspond to switches 17a, 17b, 17c, 17d in FIG. 3. Line pair 11 in FIG. 6 corresponds to line pair 18 in FIG. 3; crossing line pair 14 in FIG. 6 to crossing line pair 19 in FIG. 3; and first input/output slot line pattern pair 2a and second input/output slot line pattern pair 2b in FIG. 6 to first input/output line pair 16a and second input/output line pair 16b in FIG. 3, respectively. 
     FIG. 7 illustrates the structure of the third embodiment of a phase shifter according to the present invention. In this figure, 21a, 21b define air bridges. In FIG. 7, a drain-source common electrode 20a operates as source electrode 5a of first FET 6a and drain electrode 3c of third FET 6c shown in FIG. 6, and a drain-source common electrode 20b operates as source electrode 5b of second FET 6b and drain electrode 3d of fourth FET 6d. Drain electrode 3d of first FET 6a and source electrode 5d of fourth FET 6d are connected to air bridge 21a, while drain electrode 3b of second FET 6b and source electrode 5c of third FET 6c are connected to air bridge 21b. 
     With this structure, line pair 11 and crossing line pair 14 illustrated in FIG. 6 can be omitted and first to fourth FETs 6a to 6d can be arranged in the shape of a ladder in a direction perpendicular to input/output slot line pattern pair 2 whereby the phase shifter of the third embodiment can be formed smaller than the structure of FIG. 6. Modifications to the third embodiment are illustrated in FIGS. 8 and 9. In FIG. 8, third FET 6c and FET 6d of figure are interchanged in comparison with FIG. 7. In FIG. 9, first FET 6a and second FET 6b are interchanged in comparison with FIG. 8. Both modifications provide similar advantages. 
     FIG. 10 illustrates the structure of the fourth embodiment of a phase shifter according to the present invention. In this figure, 22a to 22d define gate electrode connecting line patterns. FIG. 11 is a diagram for explaining operations of the phase shifter illustrated in FIG. 10. In FIGS. 10 and 11, first FETs 6a1, 6a2 correspond respectively to first switches 17a1, 17a2; second FETs 6b1, 6b2 to second switches 17d1, 17d2; third FETs 6c1, 6c2 to third switches 17c1, 17c2; and fourth FETs 6d1, 6d2 to fourth switches 17d1, 17d2. Transmission loss of the phase shifter of the present invention substantially depends on a series resistance between the drain and source electrodes when the FET is ON. In order to lower the transmission loss, the series resistance must be reduced, and it is effective to lower the series resistance by connecting a couple of FETs in parallel as in the fourth embodiment. The fourth embodiment illustrated in FIG. 10 forms the respective switches with a couple of parallel FETs (FIG. 11) on the basis of the third embodiment and operates in the same manner as the second and third embodiments reducing size and transmission loss. 
     FIG. 12 illustrates the structure of the fifth embodiment of a phase shifter according to the present invention. In FIG. 12, gate electrodes 4a to 4d of FETs 6a to 6d in the structure illustrated in FIG. 6 are arranged in the direction perpendicular to input/output slot line pattern pairs 2a, 2b. The phase shifter according to the fifth embodiment can provide advantages similar to the second embodiment and reduce the width perpendicular to the direction interconnecting the input/output pattern pairs. 
     FIG. 13 illustrates the structure of sixth embodiment of a phase shifter according to the present invention. In this figure, 23a to 23d define line connecting patterns. In FIG. 13, a drain-source common electrode 20a serves as in the case of FIG. 12, as source electrode 5a of first FET 6a and drain electrode 3c of third FET 6c, and a drain-source common electrode 20b serves as source electrode 5b of second FET 6b and drain electrode 3d of fourth FET 6d. Drain electrode 3a of first FET 6a is connected to source electrode 5d of fourth FET 6d through air bridge 21a and line connecting pattern 23a, while drain electrode 3b of second FET 6b is connected to source electrode 5c of third FET 6c through air bridge 21b and line connecting pattern 23b. Structured such, first to fourth FETs 6a to 6d are arranged in the shape of a ladder in parallel to input/output slot line pattern pairs 2a, 2b and the phase shifter of the sixth embodiment can be formed to be smaller than the structure of FIG. 12. 
     FIG. 14 illustrates the structure of the seventh embodiment of a phase shifter according to the present invention. In this figure, the reference numeral 24 designates an air bridge; and 25a1, 25a2, 25b1, 25b2, 25c1, 25c2 define gate electrode connecting patterns. In FIG. 14, first FETs 6a1, 6a2 respectively correspond to first switches 17a1, 17a2; second FETs 6b1, 6b2 to second switches 17d1, 17d2; third FETs 6c1, 6c2 to third switches 17c1, 17c2; and fourth FETs 6d1, 6d2 to fourth switches 17d1, 17d2. As is already explaining above, transmission loss of the phase shifter according to the present invention substantially depends on a series resistance between the drain and source electrodes when each FET is ON. In order to reduce such a transmission loss, it is required to reduce the series resistance. To this end, it is effective to connect a couple of FETs in parallel. The seventh embodiment is structured to have an equivalent circuit illustrated in FIG. 11 by forming each switch with a couple of parallel FETs on the basis of the sixth embodiment and therefore the phase shifter of the seventh embodiment operates in the same manner as the fourth and fifth embodiments and reduces size and transmission loss. 
     FIG. 15 illustrates the structure of the eighth embodiment of a phase shifter according to the present invention. In this figure, the reference numerals 26a to 26d define anode electrodes of diodes 28a to 28d; 27a to 27d cathode electrodes of diodes 28a to 28d which are, for example, Schottky barrier diodes and PIN diodes; 29a to 29d bias resistances; and 30a to 30d bias pads. These bias resistances and bias pads form bias circuits 31a to 31d. 
     In operation, diodes 28a to 28d perform the switching operations for passing and cutting off a microwave signal by changing the voltages between anode electrodes 26a to 26d and cathode electrodes 27a to 27d between the forward and backward voltages, and thus first, second, third and fourth diodes 31a, 31b, 31c, 31d in FIG. 15 respectively correspond to switches 17a, 17b, 17c, 17d in FIG. 13. The eighth embodiment therefore functions on the basis of the same principle as that of the first embodiment and exhibits advantages similar to that of the first embodiment. 
     FIG. 16 illustrates the structure of the ninth embodiment of a phase shifter according to the present invention. In this figure, the reference numerals 32a and 32b define gate electrode connecting patterns. In FIG. 16, gate electrode 4a of first FET 6a is connected to gate electrode 4b of second FET 6b through gate electrode connecting pattern 32a, while gate electrode 4c of third FET 6c is connected to gate electrode 4d of fourth FET 6d through gate electrode connecting pattern 32b. This embodiment has been proposed to eliminate bias circuits 9a and 9c for the purpose of size reduction by noticing the fact that first and second FETs 6a and 6b operate at the same gate bias and that third and the fourth FETs 6c and 6d operate at the same gate bias. The ninth embodiment can be considered to be a modification to the phase shifter illustrated in FIG. 8. The phase shifters illustrated in FIG. 6, FIGS. 8 to 10 and 12 to 14 can also be modified in the same manner to exhibit a similar effect. 
     FIG. 17 illustrates the structure of the tenth embodiment of a phase shifter according to the present invention. In this figure, the reference numeral 33 defines one of the phase shifters explained in the second to ninth embodiments 34a, 34b signal line patterns for coplanar lines; 35a, 35b return pattern pairs for coplanar lines; 36a, 36b input/output coplanar line patterns comprising signal line patterns 34a, 34b and return pattern pair 35a, 35b; and 37a, 37b air bridges for connecting return pattern pairs 35a, 35b. The type of input/output line can be converted from the slot line to the coplanar line by connecting one of input/output slot line patterns 2a to signal line pattern 34a and the other of input/output slot line patterns 2a connects to one of the return patterns 35a. Similarly, input/output slot line pattern pair 2b, signal line pattern 34b and return pattern pair 35b are interconnected. The tenth embodiment enables an on-wafer test using a microwave on-wafer prober which mainly utilizes coplanar lines. It is noted that similar advantages can be brought about by interconnecting input/output coplanar line pattern 36b and input/output slot line pattern pair 2b as illustrated in FIG. 18. 
     Elevation and bottom views of a phase shifter of the eleventh embodiment according to the present invention are respectively shown in FIGS. 19 and 20. In these figures, the reference numerals 38a and 38b define input/output microstrip line patterns; 39a and 39b ground patterns; 40a and 40b ground patterns formed on the rear surface of semiconductor substrate 1; 41a and 41b via holes for interconnecting ground patterns 39a and 49b and ground patterns 40a and 40b. One of input/output slot line patterns 2a is connected to input/output microstrip line pattern 38a, while the other of input/output slot line patterns 2a is connected to ground pattern 40a through ground pattern 39a and via hole 41a. In the same manner, one of line patterns 2b is connected to line pattern 38b, while the other of line patterns 2b to ground pattern 40b through ground pattern 39b and via hole 41b. This enables the type of input/output line to be converted from the slot line to the microstrip line, thereby facilitating the connection to other microwave integrated circuit which mainly utilizes microstrip lines. It is noted that similar advantages can be attained by interchanging input/output microstrip line pattern 38a and ground pattern 39a connected to input/output slot line pattern pair 2a, as illustrated in FIGS. 21 and 22. 
     Elevation and bottom views of a phase shifter of the twelfth embodiment according to the present invention are respectively shown in FIGS. 23 and 24. The phase shifter of this embodiment has been proposed to modify the phase shifter shown in FIG. 17 in such a manner that ground patterns 40a, 40b formed on the rear surface opposite to input/output coplanar line patterns 36a, 36b which are connected to return pattern pairs 35a and 35b through via holes 41a1, 41a2, 41b1 and 41b2. Air bridges 37a and 37b may be eliminated. This enables signal line patterns 34a, 34b to be used as input/output microstrip line patterns 38a, 38b, and the phase shifter of the twelfth embodiment can exhibit advantages similar to those of the tenth and eleventh embodiments. It is noted that similar advantages can be brought about by modifying the arrangement illustrated in FIGS. 23 and 24, such as to connect one of return patterns 35b to one of input/output slot line patterns 2b as illustrated in FIGS. 25 and 26. 
     FIG. 27 illustrates the structure of the thirteenth embodiment of a phase shifter according to the present invention. In this figure, 42a to 42d define slot line pattern pairs; and 43 a ground pattern formed on the entire bottom surface of semiconductor substrate and connected to ground patterns 39a and 39b through via holes 41a and 41b. This embodiment is different from the structures illustrated in FIGS. 19 and 20 in that slot line pattern pairs 42a and 42b are arranged between input/output slot line pattern pairs 2a and 2b and input/output slot microstrip line patterns 38a and 38b, that ground pattern 43 is formed on the entire bottom surface of semiconductor substrate 1 in place of partial ground patterns 40a and 40b, and that one of slot line patterns 42a, 42b not connected to ground pattern 43 is formed sufficiently narrow so that there is substantially no capacitive coupling with ground pattern 43. Since the area between first slot line pattern pair 42a and second slot line pattern pair 42b has a small capacitive coupling with ground pattern 43 thereby avoiding any influence thereof, desired electrical characteristics can be obtained even if the ground pattern is formed on the entire bottom surface of semiconductor substrate 1, whereby the bottom surface of the phase shifter can be mounted by a soldering process or a conductive bonding agent. It is noted that such a structural modification as introduced in the thirteenth embodiment can also be applied to the structure illustrated in FIGS. 21 and 22 and similar advantages can be drawn. 
     FIG. 28 illustrates the structure of the fourteenth embodiment of a phase shifter according to the present invention. This embodiment is different from the structure illustrated in FIGS. 23 and 24 in that slot line pattern pairs 42a and 42b are arranged between input/output slot line pattern pairs 2a and 2b and input/output coplanar line patterns 36a and 36b, that ground patterns 40a and 40b are replaced with ground pattern 43 formed on the entire bottom surface of substrate 1 and that one of slot line patterns 42a and 42b not connected to ground pattern 43 is formed sufficiently narrower so that there is substantially no capacitive coupling with ground pattern pairs 42a, 42b. Since the area between first slot line pattern pair 42a and second slot line pattern pair 42b has a small capacitive coupling with ground pattern 43 thereby avoiding any influence thereof, desired electrical characteristics can be obtained even if the ground pattern is formed on the entire bottom surface of semiconductor substrate 1, whereby the bottom surface of the phase shifter of the present invention can be mounted by a soldering process or a conductive bonding agent. In addition, a microwave on-wafer test can be made by using an on-wafer prober in which coplanar lines are mainly utilized. The structural modification introduced in the fourteenth embodiment can be applied to the structure illustrated in FIGS. 25 and 26 and similar advantages can be drawn. 
     FIGS. 29 and 31 are diagrams for explaining the operations of the phase shifters illustrated in FIGS. 27 and 28, while FIGS. 30 and 32 respectively show equivalent circuits thereof. In these figures, the reference numeral 44 designates a slot line formed by first slot line pattern pair 42a and second slot line pattern pair 42b when first and second FETs 6a and 6b (FIGS. 27 and 28) are ON and third and fourth FETs 6c and 6d are OFF; 45 a microstrip line comprising the microstrip line formed by the narrower pattern of first slot line pattern pair 42a and ground pattern 43 and the microstrip line formed by the wider pattern of second slot line pattern pair 42b and ground pattern 43; 46 a microstrip line comprising the microstrip line formed by the wider pattern of first slot line pattern pair 42a and ground pattern 43 and the microstrip line formed by the narrower pattern of second slot line pattern pair 42b and ground pattern 43; 47a and 47b input/output terminals; 48 a ground level; 49 a line corresponding to slot line 44; 50 a line corresponding to microstrip line 45; 51 a line corresponding to microstrip line 46; 52 a slot line formed by first slot line pattern pair 42a and second slot line pattern pair 42b when first and second FETs 6a and 6b (FIGS. 27 and 28) are OFF and third and fourth FETs 6c and 6d are ON; 53 a microstrip line comprising the microstrip line formed by the narrower pattern of first slot line pattern pair 42a and ground pattern 43 and the microstrip line formed by the narrower pattern of second slot line pattern pair 42b and ground pattern 43; 54 a line corresponding to slot line 52; and 55 a line corresponding to microstrip line 53. Resistances of first to fourth FETs 6a to 6d when they are ON are eliminated for simplicity&#39;s sake. 
     In operation, when first and second FETs 6a and 6b are ON and third and fourth FETs 6c and 6d are OFF, microstrip lines 45 and 46 formed by slot line pattern pairs 42a and 42b and ground pattern 43 are considered to be equivalent to lines 50 and 51 one end of which is connected to ground pattern 48 as illustrated in FIG. 30. Meanwhile, when first and second FETs 6a and 6b re OFF and third and fourth FETs 6c, 6d are ON, microstrip line 53 formed by slot line pattern pairs 42a and 42b and ground pattern 43 is considered to be equivalent to line 55 parallel to line 54 as illustrated in FIG. 32. Since one of slot line patterns 42a and 42b is the narrower pattern, line 50, 51 and 55 are respectively high-impedance lines whereby the influence thereof can be reduced. If the electrical lengths of these lines are too short, since input/output terminals 47a and 47b can be considered to be substantially short-circuited typically in FIG. 30, the VSWR between the input and output terminals remarkably deteriorates. The VSWR can be improved by setting the length of lines 50 and 51 to one quarter of the wavelength of the operating frequency. 
     FIG. 33 illustrates the structure of the fifteenth embodiment of a phase shifter according to the present invention. FIG. 34 is a diagram for explaining operations of the phase shifter of the fifteenth embodiment. In these figures, the reference numeral 56a and 56b define upper electrodes of parallel-plate capacitors 59a and 59b; 57a and 57b dielectric materials; 58a and 58b the lower electrodes of parallel-plate capacitors; 59a and 59b, and 60a and 60b, capacitors. 
     In operation, when first and second FETs 6a and 6b are ON and third and fourth FETs 6c and 6d are OFF, lines 50 and 51 connected to ground pattern 48 (FIG. 34) are considered to correspond to the microstrip line formed by slot line pattern pair 42a and 42b and ground pattern 43. Capacitors 60a and 60b (FIG. 34) correspond to parallel-plate capacitors 59a and 59b. It is noted that any deterioration in VSWR due to the existence of lines 50 and 51 can be avoided by obtaining a capacitance C 1  of capacitor 60a and a shunt inductance L 1  formed by line 50 and ground pattern 48 from the formula f=1/2πL 1  C 1  making a parallel resonance at a predetermined frequency and by obtaining a capacitance C 2  of capacitor 60b and a shunt inductance L 2  formed by line 51 and ground pattern 48 from the formula f=1/2πL 2  C 2  making a parallel resonance at a predetermined frequency. In this embodiment, a parallel-plate capacitor is used, but similar advantages can be brought about by utilizing an inter-digital capacitor in such a case that a small capacitance value is required. 
     FIG. 35 illustrates the structure of the sixteenth embodiment of a phase shifter according to the present invention. In FIG. 35, a capacitor constituted by parallel-plate capacitors 59a1 and 59a2 corresponds to capacitor 60a in FIG. 34, while a capacitor constituted by parallel-plate capacitors 59b1 and 59b2 corresponds to capacitor 60b in FIG. 34. Therefore, this embodiment operates on the same principle as the fifteenth embodiment and brings about similar advantages. 
     FIG. 36 illustrates the structure of the seventeenth embodiment of a phase shifter according to the present invention, while FIGS. 37 and 38 are diagrams for explaining operations of the same. In these figures, the reference numerals 61a and 61b respectively define inductor patterns loaded between drain electrodes 3e and 3f and source electrodes 5e and 5f of fifth FET 6e and sixth FET 6f; 62a and 62b, ground patterns; 63a and 63b, via holes; 64a and 64b drain-source capacitors when FETs 6e and 6f are OFF; and 65a and 65b inductors of inductor patterns 61a and 61b, respectively. 
     Operations will then be explained hereunder. FIG. 37 is a diagram for explaining the operations when first and second FETs 6a and 6b are ON, third and fourth FETs 6c and 6d are OFF and fifth and sixth FETs 6e and 6f are ON. In this case, any deterioration in VSWR due to the existence of lines 50 and 51 can be suppressed by selecting the capacitance of capacitor 60a and the shunt inductance formed by line 50 and ground 48 to make a parallel resonance in an operating frequency band and by selecting the capacitance of capacitor 60b and a shunt inductance formed by line 51 and ground pattern 48 to effect a parallel resonance in the operating frequency band. 
     FIG. 38 is a diagram for explaining operations when first and second FETs 6a and 6b are OFF, third and fourth FETs 6c and 6d are ON and fifth and sixth FETs 6e and 6f are OFF. In this case, the capacitors 60a and 60b can be neglected and any deterioration in VSWR due to capacitors 60a and 60b can be suppressed by selecting the capacitances of capacitors 64a and 64b and inductances of inductors 65a and 65b to make a parallel resonance in the operating frequency band. 
     FIG. 39 illustrates the structure of the eighteenth embodiment of a phase shifter according to the present invention and FIGS. 40 and 41 are diagrams for explaining operations of the same. In these figures, the reference numerals 66a and 66b define variable capacitors which are formed between anodes 26e and 26f and cathodes 27e and 27f of fifth and sixth diodes 28e and 28f and are varied in accordance with the bias voltages applied thereto. 
     Operations of the phase shifter will be explained. FIG. 40 is a diagram for explaining operations when first and second FETs 6a and 6b are ON, third and fourth FETs 6c and 6d are OFF and the capacitances between the anodes and cathodes of fifth and sixth diodes 28e and 28f are at a maximum (when, for example, the voltage across the anode and the cathode is 0 V). In this case, any deterioration in VSWR due to lines 50 and 51 can be suppressed and advantages similar to those of the seventeenth embodiment can be achieved by selecting the total capacitances of capacitor 60a and variable capacitor 66a and a shunt inductance formed by line 50 and ground pattern 48 to make a parallel resonance in an operating frequency band and by selecting the total capacitances of capacitor 60b and variable capacitor 66b and the shunt inductance formed by line 51 and ground pattern 48 to make a parallel resonance in the operating frequency band. 
     FIG. 41 is a diagram for explaining operations when first and second FETs 6a and 6b are OFF, third and fourth FETs 6c and 6d are ON and the capacitances between the anodes and cathodes of fifth and sixth diodes 28e and 28f are at a minimum (when, for example, an inverse bias which is close to the breakdown voltage is applied across the anode and the cathode). Since the capacitances of variable capacitors 66a and 66b can be made smaller, the total capacitances of capacitors 60a and 60b and variable capacitors 66a and 66b can also be made smaller. Accordingly, any deterioration in VSWR due to capacitors 60a and 60b can be suppressed and advantages similar to those of the seventeenth embodiment can be achieved. 
     FIG. 42 illustrates the structure of the nineteenth embodiment of a phase shifter according to the present invention and FIG. 43 illustrates a cross section of the phase shifter taken along the line A--A in FIG. 42. In the figures, the reference numerals 67a and 67b define ground patterns; 68a and 68b dielectric materials; 69a and 69b microstrip line patterns; and 70a and 70b microstrip lines formed by ground patterns 67a and 67b, dielectric materials 68a and 68b and microstrip line patterns 69a and 69b. This embodiment is constituted by modifying the structure shown in FIG. 27 in such a manner that microstrip lines 70a, 70b are disposed between input/output microstrip line patterns 38a and 38b and slot line pattern pairs 42a and 42b and that ground patterns 67a and 67b of microstrip lines 70a and 70b are connected to microstrip line patterns 69a and 69b as illustrated in FIG. 42. 
     In any of the microstrip lines, coplanar lines or slot lines, an AC signal generally propagates as an electro-magnetic wave between a couple of conductors (signal pattern and ground pattern). If the phase shifter illustrated in FIG. 42 is connected to a microstrip line, an input signal first propagates through a transmission line comprising ground pattern 43 and input/output microstrip line patterns 38a and 38b. In order that the signal propagates with a low loss to slot line pairs 42a and 42b, a total return current has to flow from ground pattern 43 through via holes 41a, 41b to the upper side of the semiconductor substrate. Since ground pattern 43 exists below slot line pattern pairs 42a and 42b, a microstrip line is formed by signal patterns of slot line pattern pairs 42a and 42b and ground pattern 43. Consequently, a part of the return current also flows through ground pattern 43 at the portions opposite to slot line pattern pairs 42a and 42b. The provision of ground patterns 67a and 67b between microstrip line patterns 69a, 69b and ground pattern 43 as illustrated in FIG. 43 effectively reduces any capacitive coupling between microstrip line patterns 69a and 69b and ground pattern 43, prevents the return current from flowing through the portions of ground pattern 43 opposite slot line pattern pairs 42a and 42b and further reduces any influence of ground pattern 43 between first microstrip line 70a and second microstrip line 70b. 
     FIG. 44 illustrates the structure of the twentieth embodiment of a phase shifter according to the present invention. This structure is constituted by modifying the structure shown in FIG. 28 in such a manner that microstrip lines 70a and 70b are disposed between input/output coplanar line patterns 36a and 36b and slot line pattern pairs 42a and 42b and that ground patterns 67a and 67b of microstrip lines 70a and 70b are connected to microstrip line patterns 69a and 69b as illustrated in FIG. 42. As a result, advantages similar to those of the nineteenth embodiment can be derived. 
     FIG. 45 illustrates the structure of the twenty-first embodiment of a phase shifter according to the present invention and FIG. 46 shows an equivalent circuit of part B surrounded by a broken line in FIG. 45. In the figures, the reference numerals 71a and 71b define dielectric materials; 72a and 72b upper electrodes formed on dielectric materials 71a and 71b; 73a and 73b parallel-plate capacitors formed by ground patterns 67a and 67b, dielectric materials 71a and 71b and upper electrodes 72a and 72b; 74a and 74b air bridges connecting input/output microstrip line patterns 38a and 38b, upper electrodes 72a and 72b and the narrower patterns of the slot line pattern pairs 42a and 42b; 75 a capacitor corresponding to parallel-plate capacitor 73a; and 76a and 76b inductors corresponding to air bridges 74a and 74b. 
     In the embodiment illustrated in FIG. 42, microstrip lines 70a and 70b are disposed between input/output microstrip line patterns 38a and 38b and slot line pattern pairs 42a and 42b. If dielectric materials 68a and 68b are as thin as thousands of angstroms, the pattern width of the microstrip line patterns 69a and 69b must be externally narrow in order to obtain the predetermined characteristic impedance (for example, 50Ω), and such a narrow pattern is unachievable. The phase shifter illustrated in FIG. 45 has such a structure that small parallel-phase capacitors 73a, 73b are formed by ground patterns 67a, 67b, dielectric materials 71a, 71b and upper electrodes 72a, 72b and that connections are made by means of the air bridges. Therefore, part B surrounded by the broken line equivalently forms a T-shaped low-pass filter comprising capacitor 75 and inductors 76a and 76b as illustrated in FIG. 46 to achieve a desired characteristic impedance, thereby bringing about advantages similar to those of the nineteenth embodiment. 
     FIG. 47 illustrates the structure of the twenty-second embodiment at a phase shifter according to the present invention. In the embodiment illustrated in FIG. 44, microstrip lines 70a and 70b are disposed between input/output coplanar line patterns 36a and 36b and slot line pattern pairs 42a and 42b. If dielectric materials 68a and 68b are as thin as thousands of angstroms, a pattern width of microstrip line patterns 69a and 69b must considerably be narrow in order to obtain a predetermined characteristic impedance (for example, 50Ω), and such a narrow pattern is unachievable. The phase shifter illustrated in FIG. 47 is structured to form small parallel-plate capacitors 73a and 73b by ground patterns 67a and 67b, dielectric materials 71a and 71b and upper electrodes 72a and 72b and to make connections by the air bridges. Therefore, these portions equivalently constitute T-shaped low-pass filters each comprising capacitor 75 and inductors 76a and 76b (FIG. 46) to achieve a desired characteristics impedance, thereby bringing about advantages similar to those of the twentieth embodiment. 
     FIG. 48 illustrates the structure of the twenty-third embodiment of a phase shifter according to the present invention. In the figure, the reference numerals 77a and 77b define dielectric materials; 78a and 78b, upper electrodes formed on the upper surfaces of dielectric materials 77a and 77b; 77a and 77b parallel-plate capacitors formed by ground patterns 39a and 39b, dielectric materials 77a and 77b and upper electrodes 78a and 78b; 80a to 80d bias resistances; 81a to 81d bias pads; and 82a to 82d bias circuits comprising bias resistances 80a to 80d and bias pads 81a to 81d. Upper electrodes 78a and 78b are connected, as illustrated in the figure, to any one of input/output slot line patterns 2a and 2b. If a positive voltage AV (A&gt;|pinch-off voltage|) is applied to bias pads 81a to 81d, drain voltages and source voltages of first to fourth FETs 6a to 6d become positive. Therefore, each of the FETs performs a switching operation to pass and cut off a microwave signal by switching the gate voltage between 0 V and AV. Since the gate voltage can thus be controlled in a positive voltage range, control, for example, in a TTL become possible. In addition, the phase shifter and an external drive circuit can be considerably reduced in size. 
     In the second to twenty-third embodiments, an FET or a diode is used as a switching element, but a transistor such as bipolar transistor, high electron mobility transistor (HEMT) and heterojunction bipolar transistor (HBT) may be used in accordance with such requirements as switching speed and electrical power resistance.