Abstract: A microwave power amplifier/combiner which is composed of .pi./2 hybrid coupler. This microwave power amplifier/combiner is constructed by associating a .pi./2 phase shifter with the .pi./2 hybrid coupler to form a 2-amplifier/combiner having a single input/output port and employing the 2-amplifier/combiner as one unit. 2.sup.N -amplifier/combiner can be constructed by employing a desired number of the unit 2-amplifier/combiner. According to this amplifier/combiner, the microwave power amplifier/combiner which combines the outputs of a large number of power amplifiers can be combined by employing a small number of .pi./2 hybrid coupler.

Abstract: An amplitude modulation circuit for a transmitter has an automatic level controlled circuit (ALC circuit), including in its negative feedback loop a series circuit of a high-pass filter, a rectifier circuit and an eliminator circuit, for modulation degree suppression, thereby avoiding overmodulation. The high-pass filter is so designed that the negative feedback signal level for modulation degree suppression of the ALC circuit is raised as the audio-signal frequency supplied to the transmitter increases. In the modulation circuit having such ALC circuit, a sufficiently high mean modulation degree may be obtained without encountering overmodulation if the main spectrum components of the input audio-frequency signal are distributed in the intermediate range of the audio-signal frequency band.