Abstract: A high frequency amplifier circuit comprises an amplitude characteristic correction circuit and a phase characteristic correction circuit for compensating the non-linearity of the input-output characteristics of the amplifier. The amplitude characteristic correction circuit varies the drain voltage or the collector voltage of the amplifier in accordance with the envelope level of an input signal in such a manner that the relationship between the amplitude of the output of the amplifier and the amplitude of the input signal has linearity. On the other hand, the phase characteristic correction circuit provides a quantity of phase shift to the input signal in accordance with the envelope level of the input signal, and the phase-shifted input signal is applied to the amplifier in such a manner that the phase of the output of the amplifier and that of the input signal coincide with each other.

Abstract: A linear amplifier includes a variable attenuator and a phase shifter for modifying the amplitude and phase of an input signal to compensate for amplitude and phase distortion caused by non-linear characteristics of a high-powered amplifier utilized in a microwave band communications system. An amplitude comparator and a phase comparator compare the amplitudes and phases of input and output signals of the linear amplifier circuit to develop control signals for controlling the operation of the variable attenuator and phase shifter. The elimination of digital signal processing circuitry allows increased speed of operation that is essential for use in the microwave bands.

Abstract: In a modulation system using an amplitude and a phase of a carrier wave as information such as a QPSK system, a modulation device modifies an input signal series to compensate the nonlinear characteristics of an amplifier located at a later stage, and provides a carrier wave modulated by the modified signal series to the amplifier. A first arithmetic circuit obtains an amplitude and a phase of an input signal by calculation. A ROM is set with correction data corresponding to the calculated amplitude so as to compensate the nonlinearity of the amplifier. A modification value generating circuit and a RAM output an amount of compensation so as to further modify the correction data according to part of an output signal from the amplifier to compensate amplifier characteristic changes due to temperature variations and the like. A second arithmetic circuit provides a signal series produced from the modified amplitude and phase to a quadrature modulator.

Abstract: An amplifier circuit suitable for use in various types of communication devices, radar systems and the like, wherein a fundamental-wave signal extracted from an input side is converted into a second order signal and the second order signal is shifted so as to be opposite in phase and equal in amplitude to a second order signal produced by an amplifier such as an FET or multistage operational amplifier. The phase shifted signal is applied to the amplifier output, whereby the second order signal produced by the amplifier can assuredly be equivalently short-circuited and the operation efficiency of the amplifier can be improved.

Abstract: A field effect transistor amplifer has a high gain in a plurality of microwave frequency bands. In a field effect transistor with the gate terminal and the drain terminal thereof connected to a matching circuit on the input side and a matching circuit on the output side, respectively, a resonance circuit which is composed of a series circuit including at least one second inductor and a capacitor and connected in parallel to a resistor, is connected between at least one of the gate terminal of the field effect transistor and the ground and between the drain terminal of the field effect transistor and the ground. When a series circuit including the first inductor, at least one second inductor and the capacitor is resonated and short-circuited, the gain at the resonance frequency is dropped and a gain in the range outside of the desired bands is suppressed.

Abstract: A non-linearity compensating circuit for a high frequency amplifier includes a first divider for dividing a high frequency input signal into two signals, a distortion generating amplifier for non-linearly amplifying the first output of the first divider, a linear amplifier for linearly amplifying the second output from the first divider, a second divider for dividing the output of the linear amplifier into first and second signals, a first combiner for combining the output of the distortion generating amplifier with the first signal to extract the distortion component of the distortion generating amplifier, and a second combiner for combining the second signal with the distortion component.

Abstract: An antenna system in which primary radiators are disposed on the radiation side of beams from a main reflector and in opposition to a subreflector and in which the subreflector and the primary radiators are disposed in positions offset from beam blocking positions.

Abstract: An earth station antenna is employed for telecommunicating with a satellite in combination with an automatic tracking apparatus. The antenna is a dual reflector antenna which comprises a main reflector, a sub-reflector and a primary radiator, and the used frequency band of the antenna is at least 1.8 octaves. A parameter t of the antenna, defined by a configuration of the primary radiator is less than 0.3 at the lowest operating frequency. The phase center of the primary radiator, at a low frequency within the operating frequency range, is made to correspond with the focus of the sub-reflector.The above parameter t is defined by: ##EQU1## where: .lambda.: wavelength in free space,D.sub.h : aperture diameter of the primary radiator,L.sub.h : center axial length from the radiator apex to the radiator aperture plane, andL.sub.s : length from the radiator aperture plane to the bottom surface of the sub-reflector.

Abstract: A reflector antenna used for radar, etc, has a subreflector so as to give a relatively large aperture diameter for a primary radiator, and to decrease the effect of the outer atmosphere.A subreflector having a different curvature in a vertical plane than a curvature in a horizontal plane is provided whereby an antenna having a different beam width in the vertical plane to that in the horizontal plane is provided even though a primary radiator having a rotationally symmetrical beam is employed.