Abstract: The present invention relates to coherent optical heterodyning receivers which mix a received optical signal, including an arbitrary polarization state, and a local oscillator signal, including a fixed polarization state, while providing a performance which is independent of the polarization direction of a received signal. In one receiver version, the received signal is heterodyned using only a portion of the local oscillator signal, while in a second receiver version, the entire local oscillator signal is used. The combined polarized signals are split in a polarizing beam splitter between the two orthogonal polarization axes for propagation in separate branches. Each branch includes a photodetector and means for processing the resulting photodetector output signal to retrieve the modulation information from the processed signal. The sum of the two demodulated signals from the two branches provides a baseband signal independent of the polarization state of the received optical signal.

Abstract: The present invention relates to an optical heterodyne mixer providing image-frequency rejection which (a) detects a desired signal at frequency f.sub.L.O. .+-.f.sub.IF while rejecting interference from any signal at the image frequency f.sub.L.O. .-+.f.sub.IF, and (b) provides performance which is insensitive to fluctuations in the optical dimensions of the circuit. More particularly, the mixer receives both a local oscillator input signal and a received input signal comprising one or more optical signals, one of the input signals being linearly polarized and the other being circularly polarized. The two signals are merged by an optical device and transmitted to a polarizing beam splitter which has its polarization axes oriented at 45 degrees to the polarization direction of the linearly polarized signal. Each of the two beams from the polarizing beam splitter is detected by a separate photodetector and the resulting two currents from the two photodetectors are added by means of a 3 dB 90 degree IF coupler.

Abstract: The present invention relates to a very fast acquisition phase-lock loop arrangement comprising means for generating an error signal between an input signal to the loop and an output signal of a voltage controlled oscillator (VCO). The generated error signal, over its possible range of phase differences, is transformed by a transforming means into an output signal comprising a predetermined nonlinear response. The output signal from the transforming means is integrated in an integrating means to generate a control signal for appropriately changing the output signal of the VCO. Noise performance can be significantly improved by cascading two or more of the present phase-lock loop arrangements.

Abstract: A metal gate field effect transistor has its source and drain located on one major surface of a gallium arsenide layer, while its gate electrode forms a Schottky barrier contact to an opposed major surface of the layer in a self-aligned relationship to the source and drain.

Abstract: The present invention relates to a time-division radio transmission technique which uses a modified full-duplex arrangement where two channels are assigned to each two-way link. Simultaneous two-way transmission includes sequential digital symbol bursts between two remote transceivers which alternate between a first and a second channel centered on a first and a second radio frequency, respectively, with each transceiver using a different one of the channels at any instant of time.

Abstract: The present invention relates to a mobile radio base station (14) capable of communicating with a large number of mobile stations by implementing space diversity and time-division retransmission techniques in a digital communication system. The digital base station contains a plurality of antenna elements (16.sub.1 -16.sub.M) and a plurality of retransmission branches (18.sub.1 -18.sub.M) associated in a one-to-one relationship. When the base station receives a digital communication signal from a mobile station, each antenna element receives the signal with a unique random phase (.theta..sub.1 -.theta..sub.m) due to the effects of the environment on signal transmission. The signal is then processed through the plurality of retransmission branches, where each branch adapts to compensate for the random phase of the signal received by its associated antenna element.

Abstract: Frequency stabilization of an oscillator by compensating for slow frequency variations due to ambient temperature variations is achieved by diverting a fraction of the oscillator output to a waveguide line section having a coefficient of thermal expansion/.degree. C which is greater than the coefficient of relative frequency drift/.degree. C of the oscillator comprising, in sequence, a variable attenuator and a movable short. The variable attenuator is used to primarily adjust the amplitude of the diverted signal by one-half the desired amount preferably without varying the phase of the diverted signal. The movable short is primarily used for signal phase adjustment while simultaneously reflecting the attenuated signal back through the attenuator and towards the oscillator output.