Abstract: The fade character of a transmitted radio signal comprising an amplitude or phase modulated double-sideband signal is determined from the algebraic sign of the fade induced modulation and the location of the fade notch (.omega..sub.f) relative to the center (.omega..sub.c) of the double-sideband signal frequency spectrum. In the disclosed embodiment, the algebraic sign of the fade induced modulation is determined (e.g., 402, 403, 404, 405, 406, 409, 410, 411, 412, 413, 417) from the sign of the dc component of the product of the differentiated amplitude modulation and frequency modulation of the received signal. The relative location of the fade notch is determined by comparing the amplitudes (e.g., 402, 404, 405, 406, 415) of corresponding frequency components in each sideband of the received double-sideband signal.

Abstract: The present invention relates to wideband antenna arrangements for suppressing selected sidelobes comprising a main antenna (10) comprising a predetermined aperture (l) and two sidelobe suppression means (12, 14, 40, 42) disposed adjacent and on symmetrically opposite sides of the main antenna in the plane of the sidelobes to be suppressed. The distance between the suppression means preferably approximates the width of the aperture of the main antenna and the aperture size of the suppression means controls the sidelobe suppression region at the aperture of the main antenna. The suppression means can comprise two auxiliary antennas or two sections of the main antenna focusing reflector having apertures (l.sub.1) which are smaller than that of the main antenna.

Abstract: An adaptive multipath fade equalizer is disclosed comprising differencing means (24) for forming a difference between an input equal to said equalizer and a component of the equalizer output signal and a feedback loop (21) for coupling said component of output signal to the differencing means. The feedback loop includes a fixed delay T (22), a variable attenuator (23) and a variable phase shifter (25). A phase control network (30) and an attenuation control network (31) compare selected portions of the frequency spectrum of the signal and adjust the variable controls to minimize the effects of multipath fades upon the signal. It is an advantage of the equalizer that it automatically adjusts for changes in the frequency and depth of the fade notch.

Abstract: A 90 degree phase stepper is described comprising a tandem array of one 90 degree hybrid coupler and one 180 degree hybrid coupler. A phase shifter, capable of introducing either zero or 180 degrees of phase shift, is included in each of the two wavepaths connecting the two couplers. By the appropriate selection of phase shifts, the phase of the output signal can be continuously increased or decreased in 90 degree or 180 degree increments.

Abstract: The problems of high cost, high loss and incomplete distortion compensation are resolved in a distortion generating circuit which employs a nonlinear phase modulator (70, FIG. 7) and a linear phase shifter (71) as a means of generating selected distortion signal components. The circuit includes an output coupler (30) and an output coupler (31) interconnected by means of a pair of wavepaths (32, 33). The nonlinear phase modulator (70), which includes a nonlinear reactive element (37), is disposed in one of the wavepaths (32). The linear phase shifter (71) is included in the other wavepath (33). By the appropriate adjustment of the linear phase shift in wavepath (33) the entire gamut of distortion characteristics can be compensated. Distortion generating circuits of the type disclosed can be employed as either predistorters or as postdistorters to compensate for the nonlinearities in electromagnetic signal devices, such as amplifiers.

Abstract: A complementary distortion circuit for reducing the level of IM products in the output of a TWT amplifier. One embodiment of the invention includes a 3 db, 90.degree. coupler to divide the input signal into two components of equal amplitude but differing phase with an IM generator positioned in the path of each component. The IM generator may comprise non-linear phase modulators or non-linear amplitude modulators. The two components are then re-combined in a second, 3 db, 90.degree. coupler. The non-linear phase-modulators may comprise varactors and the non-linear amplitude modulators may comprise varistors. The unit is intended to operate in the microwave region.

Abstract: Third order IM distortion in a microwave repeater is measured in situ by applying a small amount of low frequency amplitude-modulation to the payload signal while at the same time adding a test-tone of fixed frequency and amplitude. At the repeator's output, a pair of synchronous detectors, driven in phase quadrature by the test-tone generator, measure the modulation depth of the test-tone. This modulation depth is now a measure of the degree of distortion in the repeater.

Abstract: Microwave repeaters and the like are tested for third-order IM distortion by applying two, swept-frequency test-tones to the repeater. The test-tones are offset by a fixed frequency difference .delta.. A detector circuit, connected to the output of the repeater, measures the amplitude of any signal component of frequency 2.delta. which is a direct measure of the repeater's non-linearity. Because a signal component of frequency 2.delta. can be generated by second-order distortion within the detector itself, the detector includes special circuitry to cancel out any such unwanted term.

Abstract: A protection switching system for microwave radio employs a frequency-agile-repeater (FAR) which is automatically re-tuned to the frequency of a failed repeater. A shutter associated with the failed repeater reflects the input signal normally employed by the failed repeater into the FAR, while the output of the FAR is reflected by a second shutter into the transmitting antenna.

Abstract: A feedbackward, distortion-compensating circuit suitable for pre- and post-distortion compensation of non-linear amplifying devices. The circuit taps-off a portion of the output signal of the compensating circuit, cubes it, and combines it with the input signal to that circuit. Appropriate adjustments to the phase and amplitude of the cubed signal ensure that the output signal of the non-linear amplifying device is free from all significant distortion.