Abstract: In a feed forward amplifier, an RF amplifier is supplied with an input RF signal at an input terminal for amplifying the same; a distortion extraction loop supplied with the input RF signal and further with the output RF signal from the RF amplifier is for extracting non-linear distortion components formed in the output RF signal as a result of amplification in the RF amplifier; a variable phase shifter is provided in the distortion extraction loop for varying a phase of the input RF signal; a variable attenuator is provided in the distortion extraction loop for attenuating an amplitude of the input RF signal that has been supplied to the distortion extraction loop; and a distortion extraction circuit is provided in the distortion extraction loop for producing a distortion output signal that includes non-linear components; further, a control circuit is supplied with the input signal and with the distortion output signal for extracting a main signal component contained in the distortion output signal.

Abstract: In a space diversity reception system, a plurality of receiving circuits, each of which is connected to respective antenna, outputs a first type signal having a level which varies in accordance with the radio frequency signal level input to the receiving circuit. An automatic gain-controlled amplifier amplifies the first type signal so as to output a second type signal having a substantially constant level. A phase control circuit detects a phase difference between the second type signal output from each of the automatic gain-controlled amplifiers and controls the phase difference in each of the first type signals to be null. A combining circuit combines the signals, whose levels are respectively following the input radio frequency signal levels, picked up from each of an inter-stage in the receiving circuits, an output of the combining circuit is the output of the space diversity system.

Abstract: A band pass filter is comprised of one or more filter units each having a V-shaped microwave strip line provided with two variable capacity elements at its two open ends and a high frequency elimination element connected to the apex thereof through which a control voltage for the variable capacity elements is applied.

Abstract: A high frequency generator including a frequency generator and a multiplier, the multiplier including a diode, which multiplies the output frequency of the frequency generator, and shuts off or reduces an output by suspending or suppressing the multiplying operation through the control of a bias voltage applied to the diode used in the multiplier. The system for cutting off the output by controlling the multiplier is very effective for simplifying the circuit structure and reliably turning off the output.

Abstract: A frequency conversion unit comprising a local oscillator, first and second mixers, first and second hybrid circuits. The mixers receive, via the first hybrid circuit, local oscillation outputs from the local oscillator, and the second hybrid circuit receives outputs from the first and second mixers, producing a frequency conversion output signal therefrom. Intermediate frequency signals used in the first and second mixers are .pi. radians out of phase with each other. The first hybrid circuit produces outputs for the first and second mixers having a predetermined phase difference of .phi..sub.1 therebetween. The second hybrid circuit receives outputs from the first and second mixers and combines them after making a phase difference of (.pi.-.phi..sub.1) therebetween.