Abstract: An improved calibration system for a receiver is configured to calibrate the I and Q paths to correct for gain mismatch and quadrature phase errors. In a preferred embodiment, the calibration system calibrates the I and Q paths by using a calibration signal and a reference signal coherently generated from the same single frequency source. The calibration signal is input into the receiver and propagated along the I and Q paths of the receiver simultaneously with a received signal. The reference signal coherently extracts the calibration signal from the I and Q paths. The resulting calibration signals include a component at zero frequency that can be used to measure the phase and gain error. The calibration system is configured to adaptively calibrate the gain and phase error by iteratively measuring the gain and phase error and reducing it to the desired level or eliminating it altogether.

Abstract: An adaptive antenna is implemented using a modular array element module. The array element module comprises an antenna element of the adaptive antenna. The antenna element has a weighting circuit which is coupled to a previous weighting circuit within a previous array element module in a concatenated manner. The weighting circuit is configured to apply a complex weight to antenna samples and to add the result to the output of the previous weighting circuit. The antenna element is also coupled to a cross-correlation measurement circuit configured to cross-correlate antenna samples with adaptation error samples to provide cross-correlation measurement samples to a controller which determines a weight applied by the weighting circuit.

Abstract: An adaptive antenna is implemented using a plurality of modular array element modules. Each array element module comprises an antenna element of the adaptive antenna. Each antenna element is coupled to a weighting circuit is also coupled to a previous weighting circuit within a previous array element module in a concatenated manner. Each weighting circuit is configured to apply a complex weight to the antenna samples and add the result to the output of the previous weighting circuit. Each antenna element is also coupled to a cross-correlation measurement circuit configured to cross-correlate antenna samples with adaptation error samples to provide cross-correlation measurement samples to a controller which determines a weight applied by the weighting circuit.

Abstract: An improved calibration system for a receiver is configured to calibrate the I and Q paths to correct for gain mismatch and quadrature phase errors. In a preferred embodiment, the calibration system calibrates the I and Q paths by using a calibration signal and a reference signal coherently generated from the same single frequency source. The calibration signal is input into the receiver and propagated along the I and Q paths of the receiver simultaneously with a received signal. The reference signal coherently extracts the calibration signal from the I and Q paths. The resulting calibration signals include a component at zero frequency that can be used to measure the phase and gain error. The calibration system is configured to adaptively calibrate the gain and phase error by iteratively measuring the gain and phase error and reducing it to the desired level or eliminating it altogether.

Abstract: A digital equalizer and equalization method for a spread spectrum communication link that has a dispersive channel and other systems that process signals having a sufficient degree of redundancy in time and/or phase. No training signal is required, except for an initialization bit sequence. The receiver incorporating the equalizer uses correlation over a bit time between a received signal, that includes data modulation, and a locally generated spreading signal that does not. The output of the correlator is a set of complex digital samples (I and Q-channel) taken at the spreading sequence bit rate. In the absence of multipath dispersion, there is perfect cross-correlation function, and hence only one large sample per transmitted data symbol. With multipath dispersion, the received energy is spread over two or more samples of the correlation.

Abstract: A spread spectrum transmitter uses simultaneous pseudorandom shifts of the transmitted carrier phase and receive local oscillator phases by 90 or 45 degrees and/or pseudorandom time shifts of the transmitted and receiver chip timing by half a chip duration to limit the coherent integration of carrier and chip rate detectors at an intercept receiver attempting to detect the transmissions. Direct sequence spread spectrum signals are intercepted and identified using an intercept receiver by recovering a spectral line corresponding to their carrier frequency or to their direct pseudo-noise chip rate. The conventional use of a phase shift with a fixed carrier frequency and/or a chip time shift with a fixed chip rate simplifies the design of the intercept receiver because the receiver is optimized to a single carrier frequency and chip rate.

Abstract: A precision satellite tracking system incorporating a novel smoothing processor. The satellite tracking system estimates an angle between an antenna boresight and a desired line of sight to a moving satellite. The smoothing processor receives a sequence of pointing error measurements and using a Taylor series mathematical model of the satellite motion, the processor utilizes the sequence of measurements to generate the coefficients of the Taylor series model. The processor then executes a sequential, discounted least mean square algorithm to estimate the satellite's angular position, velocity, and acceleration as a function of time. Based on these estimates, the processor determines incremental adjustments to azimuth and elevation pointing angles of the antenna to maintain the center of an antenna beam on the moving satellite. The information is used in a program track mode to continually update the pointing of the antenna beam during the measurement process.

Abstract: A high frequency (HF) communications buoy that employs HF surface wave, and sky wave, communication and spread spectrum modulation to suppress multipath fading and to decrease the undesired detectability of transmitted signals. The buoy comprises a water-tight floatable enclosure that may be deployed from a flying vehicle or a submerged vessel. An HF communications transceiver is disposed within the enclosure that is capable of transmitting and receiving signals employing high frequency (HF) band surface wave and sky wave propagation. The transceiver further comprises spread spectrum modulation and demodulation circuitry for modulating transmitted signals utilizing spread spectrum modulation and for demodulating received signals encoded by means of spread spectrum modulation. The spread spectrum modulation and demodulation circuitry is provided to suppress multipath fading and decrease the probability of detection of transmitted signals.

Abstract: A planar constrained lens (bootlace lens) antenna is disclosed capable of providing a large one or two dimensional field of view with either a scanning feed or with multiple feeds. This planar constrained lens antenna is of the type which can replace both narrow field of view and wide field of view lenses in multiple beam communications satellite and in limited scan radars using focal plane scanning or with a two element lens system and a scanning phased array feed.