Abstract: A high spectral purity swept local oscillator including a tracking filter. The output of a swept DDS oscillator may be improved by filtering it with a band-pass filter having an adjustable center frequency, which is adjusted in real time to track the instantaneous frequency of the DDS oscillator. The tracking may be accomplished by comparing, using a phase comparator, the phase at the output of the band-pass filter to the phase at its input, and feeding back to the frequency control input of the band-pass filter a signal corresponding to the phase difference measured by the phase comparator.

Abstract: A Doherty-type power amplifier suitable for satellite telecommunication systems provides linear amplification of noise-like RF signals that have multiple carriers spread over a large instantaneous bandwidth. Efficiencies of 40% to 50% are achieved using PHEMT devices. The power amplifier includes a carrier amplifier that operates a low power levels and a peak amplifier that operates at high power levels. For low power levels, the carrier amplifier delivers its output into twice the optimum load resulting in high efficiency, while the peak amplifier is turned off. At high power levels, both the carrier and the peak amplifier is working into an optimum load and maximum power is delivered. Output matching sections are used to transform the very low optimum load impedance of the PHEMT devices prior to phase shifting and combining.

Abstract: An improved Doherty amplifier for operation at microwave frequencies using microstrip circuit technology and gallium arsenide devices to achieve greater efficiency and linearity. The circuit divides the input power equally between a carrier amplifier and peak amplifier with a quarter-wave delay at the input to the peak amplifier insuring that the output power of the two amplifiers will be in phase at the load. A three-port network combines the phase-delayed carrier amplifier output with the output of the peak amplifier. The outputs of the two amplifiers are connected together by a quarter wave transmission line of impedance R. A load of one-half the optimum load (R/2) is attached to the output of the peak amplifier. A quarter-wave line section provides the transition from R/2 to the desired impedance, R. When the peak amplifier is off, its output impedance is infinite and the output power of the carrier amplifier is delivered entirely to the load.

Abstract: A transmit/receive (T/R) module of an electrically steered phased array antenna having a receiver comprising a T/R switch, an impedance matching and bias feed network, and a low noise amplifier. The T/R switch comprises a .pi. network to provide a matched termination for protecting the receiver in the transmit mode. This .pi. network emulates a one-eighth wavelength transmission line by providing a 45 degree phase delay, but it exhibits the isolation and bandwidth characteristics of a one-quarter wavelength line. The T/R switch effectively isolates the low noise amplifier from an antenna during transmit mode and uses less than half the area on a substrate typically required for a conventional one-quarter wavelength transmission line. In a receive mode the T/R switch has minimal effect on an RF input signal passing through it.

Abstract: An impedance matching and bias feed network for interfacing to a low noise amplifier of a receiver section of an electrically steered phased array antenna. The impedance matching and bias feed network includes an inductor and capacitor network for impedance transformation while providing in shunt with a 50 ohm input side of the network a gate bias path via the inductor to the low noise amplifier thereby substantially reducing the receiver noise figure.