Abstract: A block code decoding method finds the highest path metric path in a forward direction of a trellis diagram from an initial state of the trellis diagram to a final state. Next, the highest path metric path is found in a backward direction from the final state back to the initial state. The metrics of these two highest path metric paths are compared and the path having the absolute highest metric, in either direction, is chosen as a most likely path through the trellis diagram.

Abstract: A method is described for performing fast Fourier transforms (FFTs) of various sizes simultaneously in one pipeline processor. The processor consists of several stages of butterfly computational elements alternated with delay-switch-delay (DSD) modules that reorder the data between the butterfly stages. The sequence of the DSD operations in the pipeline is made arbitrary. This flexibility in choosing the DSD sequence enhances the fault tolerance operation of the pipeline in case of a partial failure in one or more of the DSD modules. If one of the DSDs is no longer capable of operating in its prescribed mode, it is assigned a different operating mode. All the required changes are performed by software control without the need to physically remove or interchange any components. By properly ordering the input data to the pipeline and the butterfly twiddle factors, and by bypassing some butterfly elements for the smaller size transforms, it is shown that any mixture of FFT sizes can be performed.

Abstract: A monolithic gallium arsenide (GaAs) phased array using integrated gold (Au) posts for interconnecting multiple substrate layers. The phased array includes a GaAs substrate having transmit/receive modules fabricated on one side and radiating elements etched on the backside of the same substrate. The conductive gold posts are integrated on the same side with the transmit/receive modules and interconnect the transmit/receive modules with a distribution network which is printed on a second substrate. Gold posts are also used to interconnect DC bias and control lines of the two substrates.

Abstract: A method for rejuvenating Ni-H.sub.2 battery cells suffering a voltage anomaly providing an improved cell output voltage and capacity. After the battery containing the cells suffering the voltage anomaly is removed from service, the battery is discharged. Discharging the battery reduces the hydrogen pressure within the cells, thereby increasing the rate of mass transport of free water back to the electrode stacks of the cells. The cells are then left to stand for a period sufficient to allow any free water to diffuse back to the electrode stacks. If gravity is available, the cell can simply be rotated to return the free water to the stack.

Abstract: A printed-circuit antenna array having broadband linear polarization, and circular polarization with high polarization purity, feedlines of the array being capacitively coupled to feeding elements at a single feedpoint or at multiple feedpoints, the feeding elements in turn being electromagnetically coupled to corresponding radiating elements. The radiating elements may be patches, disposed on a dielectric board which is contactlessly coupled to another board containing the feeding elements, in accordance with a first embodiment of the invention. Alternatively, the radiating elements may be slots, formed by an absence of material in ground planes which are formed on the same dielectric board as the feeding elements. Still further, both radiating patches and radiating slots may be used. The exclusively contactless coupling enables simple, inexpensive multilayer manufacture.

Abstract: A coherent phase and frequency recovery method capable of rapidly recovering the phase and frequency of bursts of received signals from plural sources. The received signal is applied to a first input of a mixer, the output of which is amplified and applied to two feedback paths, one for frequency and the other for phase. The frequency path contains a loop filter driving a voltage-controlled oscillator, and the phase path a loop filter and amplifier. Initial estimates of the phase and frequency of the present burst are derived and injected into the respective feedback paths. The output of the phase path is applied to correct the phase of the output of the frequency path, which is then applied to a second input of the mixer.

Abstract: An attenuator element has a reference path and a relative attenuation path. The reference path is formed by a T-network of two FETs operated in the passive mode and a shunt path and the attenuation path is formed with a similar structure, with the FETs in the shunt path having a different channel width. Instead of a T-network, a Pi-network of transistors can be used. The respective gates of the FETs along the reference path are connected to a first control input corresponding to either zero volts or the pinch-off voltage and the respective gates of the transistors on the attenuation path are connected to a complementary control input having a voltage corresponding to the other of zero volts and the pinch-off voltage. Another type of attenuator element is formed with a reference path having a transmission line and an attenuation path formed by a resistive T-network, with the attenuation and reference paths being alternately selectable by two single pole, double throw switches.

Abstract: An analog TV system includes a transmitter which produces a horizontal unique pulse sequence during each horizontal blanking interval. The pulse sequence is amplitude modulated between two levels to define a horizontal unique word for horizontal synchronization. The frequency of the pulse sequence is selected for use by the receiver section as the color subcarrier phase reference. The average level of the pulse sequence is set at the transmitter and used at the receiver for DC restoration in a clamping circuit. The peak amplitude of the pulses of the pulse sequence define a reference level against which a receiver produced local reference is compared for AGC.

Abstract: In a system for transmitting analog video signals, the luminance and chrominance components are each subjected to different bandwidth reduction processes. In addition, the high and low frequency portions of the luminance component are subjected to different bandwidth reduction signal processes.

Abstract: A microstrip antenna array having broadband linear polarization, and circular polarization with high polarization purity, feedlines of the array being capacitively coupled to feeding patches at a single feedpoint or at multiple feedpoints, the feeding patches in turn being electromagnetically coupled to corresponding radiating patches. The contactless coupling enables simple, inexpensive multilayer manufacture.

Abstract: On-board satellite switching is performed in three stages, an outer stage of switching on the up-link side for routing the received signals to either demodulators or frequency translators, a first inner stage of switching, preferably a baseband switch and processor, for routing and processing the outputs of the demodulators, a second inner stage of switching, e.g., a microwave switch matrix, for routing the outputs of the frequency translators, and an outer stage on the down-link side for assembling and routing the down-link spot beams. For a multiple hopping-beam system, the outer stages are microwave switch matrices, and for a hybrid scanning-hopping system the outer stages are beam forming matrices. A general purpose modified rearrangeable switch matrix is also disclosed.

Abstract: A printed-circuit antenna enabling two signals to be received simultaneously. Two layers of radiating elements and corresponding power dividers are provided, one set of power dividers being disposed orthogonally with respect to the other, so as to enable reception of two signals with orthogonal senses of polarization. Either dual linear or dual circular polarization may be achieved through suitable selection of radiating elements. Alternatively, a quadrature hybrid may be coupled, either externally or as an integral part of the antenna, to enable dual circular polarization.

Abstract: A gridded radiating element for printed circuit antennas employing capacitive coupling of radiating elements to feedlines. The radiating element is formed of a grid wherein a metallization region is etched selectively to yield a plurality of metal strips disposed parallel to each other with a predetermined separation. This element, in contrast to known elements which employ solid metallization regions, finds particular application in dual polarization geometries, and enables improved performance over a wide bandwidth.

Abstract: An apparatus for detecting the modulation rate of voice-band data signals. The detector determines the level occupancy L.sub.p, the partial entropy E.sub.p, and the zero-crossing count N.sub.zc for the input signal and compares these values with threshold values to determine the data rate.

Abstract: In encrypting a video signal for communications security, the horizontal synchronization pulses are removed, the active signal portions of each line in a field are delayed according to psuedorandom sequence of delays, and the reference color burst is moved to a position in the horizontal blanking interval which is constant for all lines irrespective of their individual delays. The process is reversed for decryption.

Abstract: In antenna arrays having normally unexcited or little-excited elements, a technique for configuring the array to provide both global and spot beam coverage, wherein the normally unexcited or little-excited elements are excited at a higher level, together with other normally excited elements to provide spot beam coverage, the normally unexcited elements being left unexcited to provide global beam coverage. Ring redundancy configurations for amplifiers in a transponder provided in the configuration are optimized to minimize additional hardware requirements. The specific example of the INMARSAT II satellite system is discussed.

Abstract: The invention relates to a circular polarization (CP) technique and a microstrip array antenna implementing this technique. Using four microstrip radiating elements with proper phasing of the excitation in a 2.times.2 array configuration, the technique averages out the cross-polarized component of the radiation, generating circular polarization of high purity. The technique is broadband and capable of dual-polarized operation. The resultant 2.times.2 array can be used either independently as a CP radiator or as the building subarray for a larger array.

Abstract: Linear and nonlinear bits are logically combined to form each of at least three sequences, one of which is selectively used to couple either one of the others to the output of the sequence generator.

Abstract: A symbol timing recovery circuit with a clock synchronization loop for variable rate data signals utilizes a frequency synthesizer for setting the frequency of the recovered clock signal. The received data signal, representing the modulating waveform of a transmitted modulated wareform, is estimated by passage through a data filter and sampling comparator sampled by the recovered clock. The received data signal is also delayed and multiplied by the time derivative of the estimated data signal to produce an error signal representing the difference between the incoming data rate and the output of a narrow pull range voltage controlled oscillator, VCO. The error signal is input to the VCO to correct the VCO output. A programmable frequency synthesizer provides timing signals having a range of the symbol rate divided by n.

Abstract: In a secure communications system, a key number which is changed periodically, e.g. monthly, and a random number from a random number generator are combined and used as a seed to reset a PN sequence generator, with the output of the generator being used to control encryption of transmission data in a signal processor. The key is also provided to a first encipherer to encipher the random number for transmission with the encrypted data. At the receiver, the key is provided on common to a decipherer for deciphering the random number and a PN sequence generator which is periodically reset by the combination of the key and random number in the same manner as in the transmitter. The PN sequence is then used to decrypt the information. User identification codes are stored in the transmitter and are used to encipher the key, with each employing its ID code to decipher the key. The user ID codes are known only to the system operator, so that not even a particular user can know the key.