Abstract: A direction-finding interferometer (100) includes a novel autocalibration subsystem using bi-directional transmissions at a common frequency. The interferometer determines direction using a primary phase comparator (15) to assess the phase differences in signals transmitted by signal channels (13) from multiple antennas (11). The signal channels may include RF amplifiers (17), mixers (19) coupled to a local oscillator (23), IF amplifiers (21), and transmission lines.The autocalibration subsystem employs a frequency synthesizer (25) as a calibration signal source. The calibration signal path is directed between reversing switches (40) and couplers (33) in alternating directions via transmission lines (57 and 59). In either direction, the calibration is split so that part of the signals are coupled into the signal channels, and the remaining part is directed to a secondary phase comparator (131). The outputs of the primary and secondary comparators provide the data necessary for autocalibration.

Abstract: An internal calibration system is provided for use with a direction finding interferometer which comprises a plurality of receiving antenna elements (A.sub.1, A.sub.2), a local oscillator (20), a master receiving channel means (41), a receiving channel means (42), and a phase meter (92). The internal calibration system comprises a master switch (22), a master power divider and switch assembly (31), a power divider and switch assembly (32), two transmission lines (M.sub.1, M.sub.2) connected to the master switch assemblies (31, 32), an inter-channel transmission line (T.sub.12) connected to the master power divider and switch assembly (31) and to the other power divider and switch assembly (32), and a plurality of couplers (51, 52).

Abstract: An improved optical heterodyne receiver is disclosed. Novel control circuitry is utilized in the receiver to provide compensation and tracking for undesired phase and frequency excursions of both the received and the local oscillator signals. An optical heterodyne receiver such as that disclosed is especially useful in optical communications systems having wideband variations in the frequency of the received signal caused by Doppler shifts and angle-modulated noise components.

Abstract: An improved homodyne receiver for use in wideband optical communications systems is disclosed. The receiver utilizes dual channelization of the optical input signal in the manner of a Costas two-phase synchronous receiver. A novel beam-splitting/phase-splitting optical assembly is used to channelize the received and the local oscillator beams and insure the desired phase relationships. The receiver is capable of phase-locked operation in the presence of noise and frequency variations in the received and local oscillator signals.

Abstract: A laser oscillator circuit is disclosed which allows the operating frequency of the laser to be tuned over a wide range of frequencies in response to a wideband control signal. A laser oscillator such as that disclosed is useful in optical communications systems and especially in optical receivers utilizing a phase-locked control loop for tracking out frequency variations due to noise and the Doppler shifts.

Abstract: An improved homodyne receiver for use in wideband optical communications systems is disclosed. The invention provides phase-locked homodyne reception of non-suppressed carrier or suppressed carrier input signals. Novel means are provided in the receiver for generating an error signal to provide phase-locked operation in the presence of noise and frequency excursions of the received signal.