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A microwave power combiner with waveguide ports is proposed and its design method is described. It can combine a large number of inputs at the same time and its voltage tolerance is high. On the side wall of a circular TM0m0 (m = 2, 3, 4,…) mode resonator, rectangular waveguides are connected as the input terminal while a circular waveguide is connected at the bottom surface of the resonator as the output port. The output is transformed into a rectangular waveguide via a TM 01ô‐TE 10□ mode transformer. Slits on the side of the output circular waveguide prevent propagation of the modes that do not contribute to the power combining. In the design method, the Y parameters are computed from the equivalent circuit seen from the output side. Thus, the matching condition is obtained from the image parameters. Actual dimensions of the iris for adjustment of the coupling between the input and output waveguides and the resonator can be found from this procedure. The insertion loss of a 14‐GHz four‐way combiner with a TM020 mode resonator was 0.25 dB.

Presently, realization of a high‐output FET amplifier with more than several tens of watts at microwave frequencies requires power combining. This paper proposes a low loss and broadband power combiner with a simple structure in which a cylindrical TMOmO mode (m × 2, 3, …) cavity with coaxial input and output lines is used. The effects of modes m and the number of devices to be combined are studied by means of an equivalent circuit. Since the spurious modes in the resonator degrade the reliability of the power‐combined FET amplifier, a structure is proposed in which slits and subcavity are attached to the TMOmO mode cavity for suppression of spurious modes. To verify the effectiveness of these structures, the spurious modes are excited and their reflection characteristics are measured. The insertion losses of the 4‐ and 8‐way combiners designed with m × 2 and 4 in the 12‐GHz band are 0.25 and 0.45 dB, respectively. An FET amplifier with a maximal output of 40 W is realized with the present power combiner.

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A transmission system suitable for a small Hi-Vision wireless camera is proposed and a small transmitter and receiver for the 42-GHz band is developed. In the present system, no signal processing is performed on the camera output which is directly frequency modulated. Orthogonal circular polarizations are co-used for transmission.By means of this system, miniaturization and weight reduction of the equipment (with a transmitter of 5 kg) are attained. At the same time, the transmission bandwidth is reduced to 80 MHz. Also, as the key 42-GHz devices for realization of the present equipment, a direct FM modulator (modulation sensitivity of 20 MHzi V), an HEMT power amplifier, an orthogonal circular polarization feed system (with a cross-polarization discrimination ratio of more than 23 dB), a low-noise downconverter (with a noise figure of less than 5 dB) and a simple IF cross-polarization interference equalizer are developed.The antenna for the transmitter automatically adjusts its direction by means of the signal returned from the receiver at 10 GHz. The present equipment has a transmission distance of about 250 m with a transmitter output of 25 m W and the signal-to-noise (SN) ratio is 48 dB (Y signal). Also, the equipment can be unified with the Hi-Vision two-thuds inch small CCD camera developed in our laboratory and can be operated for close to one hour with one battery.