Hughes Aircraft Company

Ditrans IP, Inc.

Robert A Dell-Imagine

Wesley K Masenten

Khiem V Cai

Chinghsiu Shih

Erik C Fountain

John A Carnaghie

Peggy L Escobedo

Millard J Parrish

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.

Systems and methods for coherent adaptive calibration in a receiver

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.

Digital modular adaptive antenna and method

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. The equalizer combines the signal energy contained in the multiple output samples, converting the concatenation of the channel and equalizer into an equivalent nondispersive channel. The equalizer uses the output of its demodulator function to convert the data bearing signals into a known signal structure, which is used to determine the (unknown) channel impulse response. The equalizer employs optimum filtering of the individual correlation samples averaged over many bit times, to determine a set of multiplicative weights that time and phase align the samples so that they are coherently added. The equalizer improves the effective signal to noise ratio to a point that is close to the theoretical nondispersive channel without increasing signal power or reducing data rate.

Digital equalization method and apparatus

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. However, in accordance with the present invention, changing the frequency of the carrier and the chip rate demands complex changes in the intercept receiver design to implement carrier line recovery and chip linear recovery. This strategy accomplishes the desired reduction in the efficiency of the intercept receiver, and hence provides for low probability of detection.

Spread spectrum transmitter for degrading spread spectrum feature

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. The satellite tracking system provides continuous tracking of the antenna, which minimizes the instantaneous error between the reported direction of the line of sight and the actual direction to the satellite.

Precision satellite tracking system

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. An antenna is coupled to the transceiver and supports the transmission and reception of the high frequency (HF) spread spectrum modulated signals. The use of HF surface wave communications in conjunction with the spread spectrum modulation of the transmitted signals provides for networking of a plurality of buoys. The use of HF spread spectrum communications also reduces the probability of exposing the presence and location of the transmitting terminal and eliminates multipath interference between ground wave and sky wave transmissions, or transmissions reflected from different sky wave layers. In addition, utilization of the underwater communication circuitry permits a submerged vehicle to take advantage of the relatively secure communications link provided by the present invention.

Technique for surface to surface communications using high frequency

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.

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Orange, CA, United States of America

Robert A Dell-Imagine