Abstract: A receive frequency band interference protection system includes an input terminal for receiving an input signal and a dividing coupler coupled to the input terminal. The dividing coupler is configured to divide the input signal into a first signal and a second signal. The system further includes a first signal path and a second signal path. The first signal path includes a delay, and it is coupled to the dividing coupler and configured to receive the first signal. The second signal path is coupled to the dividing coupler and configured to receive the second signal. The second signal path includes an attenuator coupled to the dividing coupler and a predistortion linearizer coupled to the attenuator. The system further includes a combining coupler and an output terminal. The combining coupler is coupled to the first signal path and the second signal path. The combining coupler is configured to obtain a sum of the respective outputs of the first signal path and the second signal path.

Abstract: A horn antenna includes a conducting horn having an inner wall and a first dielectric layer lining the inner wall of the conducting horn. The first dielectric layer includes a metamaterial having a relative dielectric constant of greater than 0 and less than 1. The horn antenna may further include a dielectric core abutting at least a portion of the first dielectric layer. In one aspect, the dielectric core includes a fluid. A waveguide including a metamaterial is also disclosed.

Abstract: A horn antenna includes a conducting horn having an inner wall and a first dielectric layer lining substantially the entire inner wall of the conducting horn. The first dielectric layer includes a metamaterial having a dielectric constant of greater than 0 and less than 1. The horn antenna may further include a dielectric core abutting at least a portion of the first dielectric layer. In one aspect, the dielectric core includes a fluid. A waveguide and a power combiner assembly, each including a metamaterial, are also disclosed.

Abstract: A horn antenna includes a conducting horn having an inner wall and a first dielectric layer lining the inner wall of the conducting horn. The first dielectric layer includes a metamaterial having a relative dielectric constant of greater than 0 and less than 1. The horn antenna may further include a dielectric core abutting at least a portion of the first dielectric layer. In one aspect, the dielectric core includes a fluid. A waveguide including a metamaterial is also disclosed.

Abstract: A horn antenna includes a conducting horn having an inner wall and a first dielectric layer lining substantially the entire inner wall of the conducting horn. The first dielectric layer includes a metamaterial having a dielectric constant of greater than 0 and less than 1. The horn antenna may further include a dielectric core abutting at least a portion of the first dielectric layer. In one aspect, the dielectric core includes a fluid. A waveguide and a power combiner assembly, each including a metamaterial, are also disclosed.

Abstract: Methods and apparatus provide vibration-free steered-beam antennas using a module to accommodate segregated de and rf signals. A phase-shifter element is disposed within an interior of the module. A radiating element is provided, and an rf interface is adapted to couple energy between the phase-shifter element and the radiating element. The rf interface is disposed entirely within the interior of the module and is adapted to provide an rf interface with the module substantially only through the radiating element. A dc interface is adapted to couple energy between the phase-shifter element and an electrical connection element disposed exterior to the module.

Abstract: An RF amplifier includes a FET output stage and a driver. The FET is subject to long-term degradation in multiple-carrier use if its average gate current often exceeds a predetermined value. The random superposition of signal peaks of the multicarrier signal may cause such peaks to occur. The driver stage is selected to provide a range of four dB or less between the single-signal 1 dB compression point and the hard compression point, as measured by driver input signal level. This prevents application of excessive input signal to the output stage in a multicarrier situation, and prevents degradation of the FETs of the output stage. In one embodiment, a predistortion equalizer or linearizer is placed before the driver stage, to tend to linearize the characteristic of the driver and output stage combination at signal levels below those at which the driver is limited.

Abstract: A travelling-wave tube (TWT) for a satellite communication system includes a cathode current regulator which compares a sensed I.sub.K signal with a cathode current reference to form an cathode current error signal, and controls the cathode current in response to the cathode current error signal. Helix arc protection is provided by a helix current shut-down, which compares the helix current with a particular reference, and shuts the TWT supply down when helix current flows. Desirable high efficiency TWTs have a small input drive range between maximum TWT output and a defocussed condition, in which beam current flows in the helix. Sudden changes in path attenuation may result in an RF overdrive condition, and cause helix current flow, and undesirably shut down the TWT. A helix current limiter senses the helix current, and compares it with a reference which represents less helix current than that which causes shutdown, to produce a helix current error signal.

Abstract: For use in a spacecraft for correcting amplifier distortion, a wideband distortion corrector avoids the need for directional couplers. The corrector includes a FET mounted in a miniature microwave-type housing. Signal flows through the source-to-drain channel. A gate impedance selected to be inductive at the operating frequency is coupled from the FET gate to the platform of the package, and may be simply a loop of bond wire. The channel connects by a strip transmission line to an amplifier, the distortion of which is to be corrected. For enhanced bandwidth, an inductor is coupled between the FET source and drain electrodes within the miniature housing. The platform of the package is coupled to the reference conductor of the transmission line. In one embodiment, direct bias voltage is applied by way of a bias tee across a strip transmission line and ground, and galvanic connections cause the bias to appear between the FET gate electrode and the channel.

Abstract: A FET is operated without source-to-drain bias, with the source-to-drain conductive path coupled in series with a transmission line. A gate-to-ground impedance is selected in conjunction with a gate voltage near pinchoff to impress nonlinear distortion or gain and/or phase of signals traversing the source-to-drain conductive path. The nonlinear distortion can compensate for the amplitude distortion of a following amplifier, but the phase distortion may not be suitable for correcting that of the following amplifier. An inductor is bridged from source to drain, and corrects the phase without excessive effect on the amplitude. The magnitude of the inductor may be adjusted to minimize nonlinear amplitude change without affecting the phase change, whereupon the phase change may be made independent of amplitude change. A resistor in series with the bridging inductor can be selected to render amplitude change independent of phase change. Two such independent amplitude and phase correctors may be cascaded.

Abstract: A communications system includes a transmission channel in which, for efficiency, a processor such as an amplifier is operated in a nonlinear mode. When the signal is modulated in a manner which is affected by the nonlinearity of the processor, such as a multicarrier modulation, a distortion linearizer is used. The distortion linearizer incluees the source-to-drain conductive channel of a FET. The gate of the FET is coupled to ground by an impedance which may be a low inductance, and the gate is biased relative to the channel, possibly near pinchoff, to cause the channel to exhibit desirable gain expansion and phase shifts in response to signal input level, which are selected to compensate the distortion of the nonlinear processor. When the signal is modulated in a manner which is not significantly affected by the nonlinearity of the processor, as for example frequency modulation, the distortion linearizer is switched to a linear or ON mode, in which the amplitude and phase are invariant with signal level.

Abstract: A nonlinear processor for use as a signal limiter or predistortion equalizer includes a four-port, 3dB directional coupler. Signal to be distorted is applied to a first port of the coupler, and is coupled by second and third ports to a pair of nonlinear circuits. Each nonlinear circuit includes the source-to-drain transmission path of a FET. Each nonlinear circuit is grounded or short-circuited, to form a nonlinear reflective circuit which reflects the energy back to the associated port of the coupler. The nonlinearly reflected energy is received at the two coupler ports, and is combined and made available at the fourth coupler port. The input return loss of the processor is improved by matching the nonlinear circuits to each other.

Abstract: A distortion generator uses the source-to-drain conductive path of a FET as the nonlinear element, in either a reflective or transmissive mode. In the reflective mode, the signal is applied across the source-to-drain conductive path, and in the transmissive mode the source-to-drain conductive path is in series with the transmission path. The FET may be biased, and the gate impedance to reference potential aids in selecting the nonlinearity characteristic. Reflective embodiments of a predistortion equalizer include a circulator version and a 3 dB hybrid splitter version. Transmissive embodiments include a direct series embodiment, and another with a 3 dB splitter and a separator combiner. Limiter and log-amp uses are described.

Abstract: A predistortion equalizer for a power amplifier includes a linear channel and a nonlinear channel. A phase shifter is associated with the linear channel and an attenuator is associated with the nonlinear channel. A resistive power divider divides the received signal which is to be predistorted and divides it into two parts, each of which is applied to one of the channels. The two parts may be equal in magnitude. The linear and nonlinear signals at the outputs of the linear and nonlinear channels, respectively, are combined out-of-phase in a resistive combiner to produce a predistorted signal for appication to a power amplifier. The resistive combiner and divider maximize bandwidth.

Abstract: A feedforward predistortion equalizer includes a first loop with a signal divider for dividing signals into first and second portions, and a distortion generator for distorting the second signal. The first loop is completed by a signal combiner which combines the undistorted first signal and the distorted second signal. The phase and amplitude of the signals in the loop are controlled so that the linear or carrier signal component is cancelled, leaving at the output of the first combiner only the distortion component of the distorted signal. A second loop includes phase and amplitude controls for combining the pure distortion and undistorted signals to produce the desired predistorted signals. In a particular embodiment, the phase and amplitude controls of the first loop are automatically adjusted for a null.

Abstract: A paralleled amplifier arrangement includes a plurality of amplifier modules, the output ports of which are coupled to a common combining node. Switches are coupled to the output ports for selectively decoupling one or more of the amplifier modules from the combining node during those intervals in which the amplifier modules are held in reserve or are nonfunctional. Each amplifier module is associated with an isolation resistor which is coupled to all the isolation resistors. In order to reduce losses attributable to the isolation resistors when the decoupling switches are operated, the isolation resistors are each coupled to a switched network which decouples the isolation resistors associated with the decoupled amplifier modules.

Abstract: An active or translating device having distortion is associated with a controllable predistortion circuit or linearizer. A filter sampler arrangement samples the desired fundamental-frequency signal and its second harmonic. A control circuit forms the ratio of the amplitude of the second harmonic divided by the amplitude of the fundamental-frequency signal, and controls the linearizer to minimize the ratio.

Abstract: An N.times.M signal routing matrix has low loss. The N input ports are connected to N input transmission lines, and the M output ports are connected to M output transmission lines. A plurality of interconnects interconnect the input and output transmission lines at their crossing points. The points of connection of the interconnects to any one of the input or output transmission lines are spaced .lambda./2 (or multiples thereof) apart along the transmission line. Each interconnect includes a transmission line at least .lambda./2 long, and each includes a short-circuiting switch arrangement capable of short-circuiting the inteconnecting transmission line at point(s) .lambda./4 (or odd multiples thereof) from the ends of the interconnecting transmission line.

Abstract: A composite amplifier includes a plurality of signal amplifiers. The amplified signals are coupled by transmission lines to node points for combination. In order to achieve a reduction in power below full output power, some of the amplifiers are deenergized. Shorting switches at selected points along the transmission lines are selectively rendered conductive to adjust the impedances to maintain impedance match. Short- or open-circuited transmission lines may also be switched in-circuit to aid in maintaining impedance match.

Abstract: The tuning of a coaxial cavity resonator to match the characteristics of the diode is achieved by changing the amount of the dielectric in the cavity resonator. The diode is heat sunk to a short in the cavity. The cavity is of fixed length. A washer-like dielectric ring is added in the cavity to adjust the cavity reactance to match the diode for maximum power output.