A CAVITY RESONATOR COUPLING-TYPE POWER DISTRIBUTOR/POWER COMBINER

Abstract: A cavity resonator coupling-type power distributor/power combiner consisting of a first cavity resonator (2) operatively resonating with a cylindrical T 0,n,0 mode, and a plurality of second cavity resonators (4) arranged on the periphery of the first cavity resonator and extending radially and symmetrically with respect to the first cavity resonator, the second cavity resonators having the same shape and size as each other, whereby magnetic-field coupling is established between the first cavity resonator and each of the second cavity resonators, for distributing or combining microwave power in a microwave amplifier.

Description: The present invention relates to a cavity resonator coupling-type power distributor/power combiner. More particularly, it relates to a distributor/combiner of a cavity resonator coupling-type for distributing or combining microwave electric power between a single coupling terminal and a plurality of coupling terminals. In recent years, attempts have been made to use semiconductor amplifier elements such as gallium-arsenide (GaAs) field effect transistors (FET's) instead of conventional travelling-wave tubes, in order to amplify signals in the microwave band. The semiconductor amplifier element, however, has an output power of several watts at the most , and when it is necessary to amplify a high frequency signal of a large electric power, such elements must be operated in parallel. Because of this, it is accepted in practice to distribute input signals in the microwave band into a plurality of channels by a microwave distributor, to amplify the signals of each channel by the above-mentioned semiconductor amplifier elements, and to combine the amplified output signals of each of the channels into a signal of one channel by a microwave combiner, thereby obtaining a high frequency large electric power. Some electric power, however, is lost when the phases and the amplitudes of the microwave electric power distributed by the microwave distributor are not in agreement, or when the microwave electric power is not combined in phase and in equal amplitude by the microwave combiner. It is, therefore, desirable that the phases and the amplitudes of microwave signals should be uniformly distributed in the microwave distributor and in the microwave combiner. It is also necessary that the distributor and the combiner themselves lose as little electric power as possible. Hybrid junction circuits are conventionally used for distributing or combining microwave electric power. Some hybrid junction circuits, however, have disadvantages in that they cause considerable insertion loss and require a considerably large area due to the microstrip lines constituting the hybrid junction circuits. A cavity resonator may be effectively used as a distributor or a combiner because it can provide a high coincidence of both phase and electric power between the input and the output thereof. Conventionally, only a single cavity resonator is normally used. A single cavity resonator, however, has by its character, a too narrow bandwidth to be used as a distributor or a combiner. Therefore, a single cavity resonator cannot be practically used as a distributor or a combiner. US-A-2 770 778 discloses a cavity resonator apparatus in which a cylindrical main cavity resonator is surrounded by a plurality of smaller cylindrical auxiliary resonators, each arranged tangentially with its axis inclined to the axis of the main cavity resonator. Each auxiliary resonator is coupled to the main resource by a specially shaped slot. The apparatus can be used to combine high frequency electromagnetic waves generated by oscillators in each of the auxiliary resonators. All the auxiliary resonators are designed to operate at a single fixed frequency. Moreover, this apparatus has the drawbacks that the physical configuration of the resonators is complex, it is difficult to mechanically couple auxiliary resonators to the main resonators, and the mechanical strength of the assembly is poor. It is therefore desirable to provide a cavity resonator apparatus capable of distributing or combining microwave power over a wide bandwidth, with a simple physical configuration which is easy to manufacture and mechanically strong. According to the present invention, there is provided a cavity resonator coupling-type power distributor/power combiner comprising: a first cavity resonator having a symmetric, cylindrical shape with respect to an axis thereof and operatively resonating with a cylindrical TM O,n,O mode, where n is a positive integer; first conducting means having an input/output end for receiving or providing input/output signals of microwave electric power, an electric-field coupling operatively being established between said first conducting means and said first cavity resonator through an antenna; and a plurality of second cavity resonators arranged on the periphery of said first cavity resonator, said second cavity resonators having the same shape and size as each other, magnetic-field coupling operatively being established between said second cavity resonators and said first cavity resonator; characterised in that: and each of said plurality of second cavity resonators is formed as a rectangular waveguide, said second cavity resonators extending radially with respect to said axis of said first cavity resonator; a plurality of second conducting means are provided having output/input ends, respectively for conducting output/input signals of microwave electric power between said second cavity resonators and said output/input ends of said second conducting means; and in that said first cavity resonator and said second cavity resonators are formed as one body by milling. An embodiment of the present invention can provide a cavity resonator coupling-type power distributor/power combiner which can distribute or combine microwave electric power in a wide bandwidth and with a small insertion loss. An embodiment of the present invention can also provide a cavity resonator coupling-type power distributor/power combiner in which a single cavity resonator and a plurality of cavity resonators are magnetically coupled. An embodiment of the present invention can also provide a microwave power amplifier consisting of a cavity resonator coupling-type power distributor, a plurality of amplifying units for amplifying the outputs of the distributor, and a cavity resonator coupling-type power combiner for combining the outputs of the amplifying units, the distribution and the combination being carried out in a wide bandwidth and with a small insertion loss. Reference is made, by way of example, to the accompanying drawings in which:- Figure 1 is a block circuit diagram showing a conventional microwave power amplifier employing hybrid junction circuits; Fig. 2 is a block circuit diagram showing a conventional microwave power amplifier employing cavity resonators; Fig. 3 is a partially cut top plan view of a cavity resonator coupling-type power distributor/power combiner, according to an embodiment of the present invention; Fig. 4 is a side view of the portion between the arrows IV-IV' in Fig. 3; Fig. 5 is a partially cut top plan view of a cavity resonator coupling-type power distributor/power combiner, according to another embodiment of the present invention; Fig. 6 is a partial cross-sectional view taken along line IV-IV' in Fig. 5; Fig. 7 is a partial cross-sectional view of a cavity resonator coupling-type power distributor/power combiner, according to still another embodiment of the present invention; and Fig. 8 is a block circuit diagram of a microwave power amplifier employing a cavity resonator coupling-type power distributor and a cavity resonator coupling type power combiner of any one of the embodiments shown in Figs. 3, 5 and 7. Before describing the preferred embodiments of the present invention, conventional microwave power amplifiers will first be described with reference to Figs. 1 and 2. Figure 1 shows a block circuit diagram of an example of a conventional microwave power amplifier employing hybrid junction circuits. In Fig. 1, a hybrid circuit H₁ receives microwave input signals at its input terminal IN₁ and branches them two ways. The signals on one branch and on the other are received by hybrid junction circuits H₂ and H₃ , respectively. The hybrid junction circuits H₂ and H₃ further branch the input signals two ways, respectively. Amplifying units AMP₁ through AMP₄ receive the branched signals from the hybrid junction circuits H₂ and H₃ and amplify them. The amplified signals from the amplifying units AMP₁ and AMP₂ are combined by a hybrid junction circuit H₄. The amplified signals from the amplifying units AMP₃ and AMP₄ are combined by a hybrid junction circuit H₅. The combined signals from the hybrid junction circuits H₄ and H₅ are further combined by a hybrid junction circuit H₆. Thus, a desired microwave power is output from an output terminal OUT₁. To obtain a higher microwave power, a larger number of amplifying units should be operated in parallel. To achieve this, a larger number of stages of hybrid junction circuits are necessary. There are disadvantages in the conventional microwave power amplifier employing hybrid junction circuits. One disadvantage is that each hybrid junction circuit has a high insertion loss so that a number of stages of hybrid junction circuits have a considerably large insertion loss. Another disadvantage is that each hybrid junction circuit is usually constructed by microstrip lines which occupy a large area, so that a number of stages of the hybrid junction circuits occupy a considerably large area, resulting in a large size of the microwave power amplifier. Figure 2 shows another example of a conventional microwave power amplifier employing cavity resonators. In Fig. 2, two amplifying units AMP₅ and AMP₆ are connected between a first cavity resonator CR₁ and a second cavity resonator CR₂. The first cavity resonator CR₁ receives microwave input signals at its input terminal IN₂ , and functions as a distributor. The second cavity resonator CR₂ provides desired output signals at its output terminal OUT₂ , functioning as a combiner. Between the input terminal IN₂ and the first cavity resonator CR₁ , electric-field coupling is established by means of a disk-type antenna A₁. Also, between the second cavity resonator CR₂ and the output terminal OUT₂ , electric-field coupling is established by means of a disk type antenna A₂. Between the outputs of the first cavity resonator CR₁ and the inputs of the amplifying units AMP₅ and AMP₆ , and between the outputs of the amplifying units AMP₅ and AMP₆ and the inputs of the second cavity resonator CR₂ , magnetic-field coupling is established. By forming a plurality of magnetic-field coupling loops in the first and the second cavity resonators CR₁ and CR₂ , it is easy to distribute or to combine microwave signals with a small insertion loss. However, since the first cavity resonator CR₁ or the second cavity resonator CR₂ is a single cavity resonator, and since a single cavity resonator can, by its character, deal with only a very narrow bandwidth of microwave electric power, the conventional amplifier in Fig. 2 cannot be used for distributing and combining a wide bandwidth of microwave electric power. Embodiments of the present invention will now be described. Figure 3 is a partially cut top plan view of a cavity resonator coupling-type power distributor/power combiner, according to an embodiment of the present invention. Fig. 4 is a side view from the direction of the arrows IV-IV' in Fig. 3. In Figs. 3 and 4, the cavity resonator coupling-type power distributor/power combiner distributes input signals into eight outputs or combines eight inputs into one output, and comprises a resonator body 1 having an octagonal cross section with a cylindrical cavity, a first cavity resonator 2 formed by the cylindrical cavity, windows 3 for establishing magnetic-field coupling, second cavity resonators 4, windows 5 for establishing magnetic-field coupling, output/input waveguides 6, an input/output part 7, an input/output waveguide 8, a coaxial line 9 combined with the input/output waveguide 8, and an antenna 10 for establishing electric field coupling. The first cavity resonator 2 is formed by the cylindrical cavity formed within the central portion of the resonator body 1. The antenna 10 is provided in the first cavity resonator 2 and at the central portion of the upper surface of the first cavity resonator 2. The antenna 10 is connected to the inner conductor of the coaxial line 9 and operatively establishes an electric-field coupling with the first cavity resonator 2. The first cavity resonator 2 operatively resonates with a cylindrical TM 0,n,0 mode, where n is a positive integer, resulting in a circular magnetic field MF₁ as indicated in Fig. 3 by a circle. Each of the eight second cavity resonators 4 is formed by a corresponding window 3, a corresponding window 5, and a cavity formed between them. The second cavity resonators 4 are arranged on the periphery of the first cavity resonator 2 and extend radially and symmetrically with respect to the axis of the cylindrical shape of the first cavity resonator 2. The second cavity resonators 4 have the same shape and size as each other. In this embodiment and in the other embodiments, the cavity in each of the second cavity resonators 4 has a rectangular cross section, and is part of a waveguide. Each of the windows 3 and 5 is formed, in this embodiment, by two opposite projections 31 and 32, and 51 and 52 on the inner wall of the waveguide forming each of the second cavity resonators 4. Therefore, the area of each window 3 or 5 is smaller than the cross-sectional area of the waveguide. Magnetic-field coupling is operatively established between the first cavity resonator 2 and each of the second cavity resonators 4, by means of the windows 3 between the first cavity resonator 2 and the second cavity resonators 4, resulting in a magnetic field MF₂ in each of the second cavity resonators 4. Thus, each of the second cavity resonators 4 having a rectangular cross-section resonates with, for example, TE₁₀₁ mode, TE₁₀₂ mode, or other modes. If the cavity in each of the second cavity resonators 4 has a circular cross- section, the resonating mode will be, for example, TE₁₁₁ mode. Magnetic-field coupling is operatively established between each of the second cavity resonators 4 and the corresponding one of the output/input waveguides 6, by means of the windows 5 between the second cavity resonators 4 and the corresponding waveguides 6. Electric-field coupling may alternatively be established by appropriately forming the windows 5. When the device illustrated in Figs. 3 and 4 is used as a power distributor, the output/input waveguides 6 act as output waveguides, and the input/output waveguide 8 acts as an input waveguide. That is, microwave power supplied to the input waveguide 8 is supplied through the coaxial line 9 to the antenna 10. The input microwave power is transferred to the first cavity resonator 2 by the electric-field coupling between the antenna 10 and the first cavity resonator 2. The microwave power in the first cavity resonator 2 is divided and transferred to the eight second cavity resonators 4 by the magnetic-field coupling between the first cavity resonator 2 and the second cavity resonators 4 by means of the windows 3. The divided microwave power in the second cavity resonators 4 is transferred through the windows 5 to the output waveguides 6. The output power from the output waveguides 6 is supplied to the respective amplifying units (not shown in Figs. 3 and 4). On the contrary, when the device in Figs. 3 and 4 is used as a power combiner, the output/input waveguides 6 act as input waveguides, and the input/output waveguide 8 acts as an output waveguide. That is, when microwave signals respectively amplified by eight amplifying units (not shown in Figs. 3 and 4) are applied to the input waveguides 6, the microwave power in these input waveguides 6 is transferred through the windows 5, and through the second cavity resonators 4, and combined in the first cavity resonator 2 by the magnetic-field coupling. The combined microwave power in the first cavity resonator 2 is then transferred through the coaxial line 9 to the output waveguide 8 by the electric-field coupling between the first cavity resonator 2 and the coaxial line 9 by means of the antenna 10. Thus, a combined microwave signal is obtained at the end of the output waveguide 8. Since the first cavity resonator 2 has a cylindrical shape, it can be easily manufactured by milling. Also, since the second cavity resonators 4 are formed in one body with the first cavity resonator 2 and on the periphery of the first cavity resonator 2 so as to extend radially and symmetrically with respect to the center of the circular cross-section of the first cavity resonator 2, that is, with respect to the axis thereof, the second cavity resonators 4 can be manufactured easily. Figure 5 is a partially cut top plan view of a cavity resonator coupling type power distributor/power combiner, according to another embodiment of the present invention, and Fig. 6 is a partial cross-sectional view taken along line VI-VI' in Fig. 5. The difference between the embodiment shown in Figs. 3 and 4 and the embodiment in Figs. 5 and 6 is that, in place of the windows 3 and 5 shown in Figs. 3 and 4, a first set of electrically conductive posts 11 and a second set of electrically conductive posts 12 are provided at respective ends of each second cavity resonator 40. These sets of conductive posts also function to establish a magnetic-field coupling between the first cavity resonator 2 and the second cavity resonators 40, and between the second cavity resonators 40 and the output/input waveguides 6. The embodiment shown in Figs. 5 and 6 has an advantage over the first embodiment shown in Figs. 3 and 4 in that, since none of the second cavity resonators 40 need to be provided with projections for forming the windows 3 and 5 as in Figs. 3 and 4, the second cavity resonators 40 can be easily manufactured because the size of the cross-section of each of the second cavity resonators 40 is the same as the size of the cross-section of each of the waveguides 6 at any place in the second cavity resonators 40. Figure 7 is a partial cross-sectional view of a cavity resonator coupling-type power distributor/power combiner, according to still another embodiment of the present invention. The difference between the embodiment shown in Figs. 5 and 6 and the embodiment in Fig. 7 is that, in place of the conductive posts 11 in Figs. 5 and 6, opposite projections 31 and 32 for forming windows 3 are formed between the first cavity resonator 2 and each of the second cavity resonators 41, as in the first embodiment shown in Figs. 3 and 4, and a conductive wire 13 is provided between the first cavity resonator 2 and each of the second cavity resonator 41 through each window 3. The conductive wire 13 is used to adjust the coupling coefficient between the first cavity resonator 2 and each of the second cavity resonators 41. Figure 8 is a block circuit diagram of a microwave power amplifier employing a cavity resonator coupling-type power distributor and a cavity resonator coupling-type power combiner of any one of the embodiments shown in Figs. 3, 5, and 7. In Fig. 8, eight amplifying units AMP₁₁ through AMP₁₈ are connected between cavity resonators CR₁₁ through CR₁₈ and cavity resonators CR₂₁ through CR₂₈. The former cavity resonators CR₁₁ through CR₁₈ are in magnetic-field coupling with a cavity resonator CR₁₀. The cavity resonators CR₂₁ through CR₂₈ are in magnetic-field coupling with a cavity resonator CR₂₀. The cavity resonator CR₁₀ and the cavity resonators CR₁₁ through CR₁₈ constitute a divider (distributor) D for dividing microwave power applied to an antenna A₃ provided in the cavity resonator CR₁₀ , into eight microwave outputs. The outputs of the divider D are amplified by the amplifiers AMP₁₁ through AMP₁₈ , respectively. The outputs of the amplifiers AMP₁₁ through AMP₁₈ are combined by a combiner C consisting of the cavity resonators CR₂₁ through CR₂₈ and the cavity resonator CR₂₀. Thus, a combined output is obtained at an output terminal OUT₃ through an antenna A₄ in the cavity resonator CR₂₀. The amplifiers AMP₁₁ through AMP₁₈ are provided by a microwave integrated circuit (MIC) having input lines 81 through 88 and output lines 91 through 98. These input lines and output lines are formed by microstrip lines. Electromagnetic-field coupling between the cavity resonators CR₁₁ through CR₁₈ and the input microstrip lines 81 through 88 can be easily established by those skilled in the art. For example, by connecting additional waveguides to the output waveguides 6 (Fig. 3), and by bending the additional waveguides toward the MIC including the amplifying units, the additional waveguides can be electromagnetically coupled with the input microstrip lines 81 through 88 by means of MIC antennas provided at the boundary ends of the input microstrip lines between the output waveguides 6 and the input microstrip lines. Similarly, between the output microstrip lines 91 through 98 and the cavity resonator CR₂₁ through CR₂₈ , electromagnetic-field coupling can also be established easily. In place of using the input/output waveguides 6 for establishing electromagnetic-field coupling between the cavity resonators CR₁₁ through CR₁₈ and the input microstrip lines 81 through 88, or between the cavity resonators CR₂₁ through CR₂₈ and the output microstrip lines 91 through 98, coaxial cables may alternatively be employed. That is, by introducing antennas connected to coaxial cables into the second cavity resonators 4 (Fig. 3), the second cavity resonators 4 can be coupled with the coaxial cables. Thus, the input/output microwave power can be transferred through the coaxial cables and through the input/output microstrip lines into or from the amplifying units AMP₁₁ through AMP₁₈. From the foregoing description, it will be apparent that, according to the present invention, since only cavity resonators are employed and no hybrid junction circuit is employed, insertion loss can be greatly decreased in a power distributor/power divider. Also, since the first cavity resonator and the second cavity resonators are coupled in a magnetic field to form a double cavity resonator, the power distributor/power combiner can distribute or combine microwave electric power in a wide bandwidth in comparison with the prior art employing a single cavity resonator. Further, by forming the windows 3 as small as possible or by providing an appropriate number of posts 11 and 12, any undesired mode in the second cavity resonators can be limited so that the distribution or combination of microwave electric power can be stably carried out. Still further, a cavity resonator coupling-type power distributor/power combiner according to the present invention has a simple structure and a small size. As will be apparent, the cavity resonator coupling-type power distributor/power combiner can be effectively used with a number of amplifying units so as to constitute a microwave amplifier. It should be noted that the present invention is not restricted to the foregoing embodiments. Various changes and modifications are possible without departing from the spirit of the present invention. For example, the number of second cavity resonators may be more or less than eight.

Claims: A cavity resonator coupling-type power distributor/power combiner comprising: a first cavity resonator (2) having a symmetric, cylindrical shape with respect to an axis thereof and operatively resonating with a cylindrical TM O,n,O mode, where n is a positive integer; first conducting means (7,8,9) having an input/output end (8) for receiving or providing input/output signals of microwave electric power, an electric-field coupling operatively being established between said first conducting means (7,8,9) and said first cavity resonator (2) through an antenna (10); and a plurality of second cavity resonators (4,40,41) arranged on the periphery of said first cavity resonator (2), said second cavity resonators having the same shape and size as each other, magnetic-field coupling operatively being established between said second cavity resonators and said first cavity resonator; characterised in that: each of said plurality of second cavity resonators (4,40,41) is formed as a rectangular waveguide, said second cavity resonators extending radially with respect to said axis of said first cavity resonator; a plurality of second conducting means (16) are provided having output/input ends, respectively for conducting output/input signals of microwave electric power between said second cavity resonators (4,40,41) and said output/input ends of said second conducting means; and in that said first cavity resonator (2) and said second cavity resonators (4,40,41) are formed as one body by milling. A cavity resonator coupling-type power distributor/power combiner as set forth in claim 1, wherein each of said second cavity resonators (4) comprises a cavity formed by a waveguide, a first window (3) formed between said first cavity resonator (2) and said cavity, for establishing magnetic-field coupling therebetween, and a second window (5) formed between said cavity and a corresponding one of said second conducting means (6), for establishing electromagnetic-field coupling therebetween. A cavity resonator coupling-type power distributor/power combiner as set forth in claim 2, wherein each-of said second conducting means (6) is formed by said waveguide, the size of said first window (3) and the size of said second window (5) being smaller than the size of the cross-sectional area of said waveguide. A cavity resonator coupling-type power distributor/power combiner as set forth in claim 1, wherein each of said second cavity resonators (40) comprises a cavity formed by a waveguide, a first set of electrically conductive posts (11) arranged between said first cavity resonator (2) and said cavity, for establishing magnetic-field coupling therebetween, and a second set of electrically conductive posts (12) arranged between said cavity and a corresponding one of said second conducting means (6), for establishing electromagnetic-field coupling therebetween. A cavity resonator coupling-type power distributor/power combiner as set forth in claim 4, wherein each of said second conducting means (6) is formed by said waveguide. A cavity resonator coupling-type power distributor/power combiner as set forth in claim 1, wherein each of said second cavity resonators (41) comprises a cavity formed by a waveguide, a window (3) formed between said first cavity resonator (2) and said cavity, for establishing magnetic-field coupling therebetween, and a set of electrically conductive posts (12) arranged between said cavity and a corresponding one of said second conducting means (6), for establishing electromagnetic-field coupling therebetween. A cavity resonator coupling-type power distributor/power combiner as set forth in claim 6, further comprising a conductive wire (13) between said first cavity resonator (2) and each of said second cavity resonators (41) through said window (3), for adjusting said magnetic-field coupling. A microwave power amplifier, comprising: a first cavity resonator coupling-type power distributor/power combiner as claimed in any preceding claim, providing a power distributor (D); a plurality of amplifying units (AMP₁₁...AMP₁₈), having input terminals (81...88) connected to the output ends of the second conducting means of said power distributor (D), and having output terminals (91...98); and a second cavity resonator coupling-type power distributor/power combiner as claimed in any preceding claim, providing a power combiner (C), the input ends of the second conducting means of said power combiner (C) being connected to said output terminals (91...98) of said amplifying units (AMP₁₁...AMP₁₈).

Inventors: KANEKO, YOSHIAKI, OKUBO, NAOFUMI, SAITO, TOSHIYUKI
Applicants: FUJITSU LIMITED
Application year: 1984
Main classification: H01P5
IPC codes: H01P5