Hughes Aircraft Company

Hughes Electronics Corporation

Stephen D Taylor

Steve I Hsu

Howard S Nussbaum

William P Posey

Paula I Tanaka

Paul I Tanaka

Timothy E Kuo

A phase shifter using digital counters allows extremely accurate phase shifts. In a parallel circuit arrangement of a number of basic phase shift units, which each includes a dual modulus counter and phase control circuitry for controlling the counter modulus, the outputs of several units are combined in parallel. With the divider ratios of all the dividers of the units consisting of roots of pairwise relatively prime numbers, the total number of phase states is equal to the multiplication of its divider ratios.

Digital frequency divider phase shifter

Discrete phase modulation for modulating the transmit and receive radar signal waveforms in order to control distortion. The signal is modulated by discrete phases which change from pulse-to-pulse. A digital frequency division circuit accurately generates the modulation signals, and allows the discrete phases to be generated with precise accuracy. The discrete phase changes can be a quadratic phase progression for target Doppler and range detection.

Discrete phase modulator

A phase shifter that employs digital circuitry to achieve arbitrarily fine phase control of reference signals at frequencies extending to the Gigahertz region. The phase shifter includes a cascade of identical phase shift units that provide progressively finer phase control resolution over a full 360 degree range. The phase precision is set by the number of stages used.

Precision digital phase shifter

A precision digital phase shift element for achieving precise phase shift of an input pulse train signal. The output is a pulse train at a frequency equal to the input signal frequency divided by N, and having N equally spaced phase states. The relative phase state of the output signal is reliably controlled by selective deletion of pulses from the input signal pulse train. The selective deletion can be achieved by selectively gating the input pulse train, or by use of a dual modulus frequency divider circuit.

Precision digital phase shift element

The frequencies of N oscillators are summed to provide a signal generator output signal. Because the phase noise power spectral densities of the oscillators add as power, the frequency summed output exhibits a noise degradation over a single oscillator of only 10 log(N). The signal generator is implemented to assure independence of the oscillator noise contributions, with phase locking the oscillators to a common frequency for ease of spurious signal control.

Ultra low noise frequency generator producing the sum of plural signal

Unique stretch and chirp waveform formats are described which allow significant simplification of radar signal generation and receive processing hardware. The new formats produce a non-zero intermediate frequency (IF) to facilitate in-phase and quadrature (I/Q) processing but allows the use of a homodyne type of receiver architecture. That architecture greatly simplifies the receiver hardware because the first local oscillator (LO) signal is simply a sample of the transmitter drive signal and no second LO is required. The non-zero IF is achieved by control of the timing and start frequency of the first LO waveform for stretch processing and timing of the transmit signal gating for chirp processing.

Stretch and chirp waveform format for reduced generating and receiving

A wideband frequency synthesized, fault-tolerant microwave signal generator is described, which can generate the spectrally pure transmitter or antenna drive and receiver first local oscillator (LO) signals needed for advanced tactical airborne radar systems. Separate generation of the transmitter drive (TD) and first LO minimizes spurious signal generation over a wide operating band, typically 45% or greater. Extensive fault tolerance is provided without resort to redundant hardware. The sharing of two internal signal generators limits the frequency generation needs to just the operating band for economy of required hardware.

Fault-tolerant, wideband radar microwave signal generator

A frequency synthesized, microwave signal generator is disclosed that provides multiple channel frequency selection capability with rapid channel change time and low levels of spurious signals and noise. The generator uses a microwave harmonic phase locked loop to lock a microwave VCO to a programmable harmonic of a VHF reference crystal oscillator to provide coarse frequency control in steps equal to that reference frequency. The phase lock loop includes an offset mixer for injecting an offset signal frequency to achieve fine frequency control. A harmonic detection and counting scheme is used to rapidly sweep the harmonic loop and obtain phase lock at the desired harmonic.

Frequency agile microwave signal generator

A system is disclosed for measuring and correcting for waveform modulation errors in a radar system employing FM signals and a digitally controlled waveform generator. The system relies on the assumption that the transmitter and other waveform phase and amplitude error contributions are slowly varying with respect to the radar mode data collection time and that instantaneous pulse-by-pulse correction is not necessary. During a calibration mode, a small portion of the transmitter output is input into the receiver and mixed with the waveform generator signal, with the waveform modulation being removed from the mixer signal, such that the mixer signal is at a constant IF but with phase and amplitude variations that result from the distortions. The radar digital processor measures these distortions, and during normal radar operation predistorts the waveform generator signal with phase distortions in antiphase with the measured distortions to compensate for the measured distortions. Amplitude distortions are compensated by control of a variable attenuator device. As a result, the system compensates for the exciter and transmitter distortions as well as distortions introduced by the receiver input circuitry.

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Agoura, CA, United States of America

Stephen D Taylor