Sanders Associates Limited

Bae Systems Information and Electronic Systems Integration Inc.

Lockheed Sanders, Inc.

Chester E Stromswold

John T Apostolos

Robert P Boland

Robert H Carrier

Harrison W Fuller

Walter J Albersheim

Robert T Martel

A compressive receiver including a dispersive delay line ( ) and a frequency translator ( ) is preceded by signal compressors ( ) that record the incoming signals at one speed and play them back at a higher speed. This increases the frequency spread and provides greater frequency resolution at the output of the receiver.

Compressive receiver with frequency expansion

The input ports (18) of an imaging compressive receiver (20) receive from a tapped delay line (16) progressively delayed versions of a received signal s(t). Because of the delays, a signal component in the received signal appears at least at one of the input ports (18) of the compressive receiver (20) at a time when the compressive receiver (20) will detect it, even if the undelayed version occurs during a time at which the compressive receiver (20) would ordinarily be insensitive to it. Since the compressive receiver (20) is an imaging device, it provides relatively isolated channels between its input terminals (18) and its output terminals (38). The phase relationships between the delays in these channels remain constant despite changes in environmental factors, however, because the various channels are embodied in a common two-dimensional delay line.

Real-time wide-band compressive-receiver system

An electromagnetic dispersive delay line (10) includes a dielectric strip (28) as well as a coupler (24, 34, 36, and 38) for launching surface electromagnetic waves into the dielectric strip. The upper surface of the dielectric strip (28) is left exposed to the air in order to provide an interface with a lower-permittivity medium of propagation. This permits a surface-electromagnetic-wave propagation mode. The thickness of the dielectric strip (28) is varied along its length so as to result in a linear relationship of delay to frequency throughout a predetermined frequency range. Preferably, a conductive strip (26) spaced from the dielectric strip extends along the surface-wave propagation path in the region occupied by the evanescent field external to the dielectric strip (28). This conductive strip (26) modifies the phase relationships between the electric and magnetic fields in the evanescent-field region so as to cause some of the power transmission to occur outside of the dielectric strip. This modifies the dispersion curve so as to extend the bandwidth of significant dispersion.

Compressive receiver

Electromagnetic dispersive delay line

A device for determining the frequency range and chirp rate of chirp radars or other sources of frequency-modulated signals includes a compressive receiver (16, 22, 24) for time-compressing single-frequency signals and a discriminator (26) for generating an output that represents the instantaneous frequency of the compressive-receiver output. For narrow-band signals, the frequency-modulated components in the output of the compressive receiver do not last long enough to cause a response from the discriminator (26). When the input of the compressive receiver is a chirp signal, on the other hand, the resultant compressive-receiver output lasts long enough to cause a discriminator response, and its time of occurrence and rate of frequency change are indications of the frequency range and chirp rate of the compressive-receiver input. The discriminator (26) accordingly generates an output whose slope is an indication of the chirp rate of the compressive-receiver input.

FM/chirp detector/analyzer and method

A signal source in the general form of a phase-locked loop (12, 20, 22, and 24) has its output fed to a phase modulator (32) controlled in response to the output of the phase-locked-loop phase detector (20). This provides feed-forward error correction that gives the signal source a faster response than a conventional phase-locked-loop arrangement would have.

Feed-forward error correction for sandaps and other phase-locked loops

In a spread-spectrum direction-finding system, the outputs of the several antenna elements (10a-d) are progressively translated in frequency by a chirped local oscillator (14) and mixers (12a-d) and applied to a two-dimensional dispersive filter (18), which time compresses the results of single-frequency components in the antenna-element outputs to narrow pulses. Limiters (24a-d) remove any strong narrow-band components that are compressed by the dispersive delay line (18) so that further processing to detect a spread-spectrum signal is not degraded by the presence of narrow-band signals. The use of a common two-dimensional delay line (18) to provide the time compression avoids the need to maintain phase tracking among a plurality of separate parallel one-dimensional dispersive delay lines.

Spread-spectrum detection system for a multi-element antenna

A system for indicating the direction of a source of radio waves received by a circular antenna array (12) includes a Butler matrix (18) that receives the array outputs and feeds the resultant matrix outputs to correction circuits (22) whose transfer functions are the inverses of the direction-independent factors of antenna patterns generated by antenna elements driven at relative phases that advance around the array at rates that complete an integral number of cycles in one circuit of the array. The resultant corrected signals are fed to a compressive receiver (26), which accordingly generates an output on an output port whose position indicates the direction of the source of the signal.

Acquisition system employing circular array

A phase-angle circuit (24) processes the outputs of an antenna array (12) to apply to a compressive receiver (20) an ensemble of signals having components whose spatial frequencies are proportional to the bearing angle of the electromagnetic plane waves that give rise to them. A signal whose phase angle is equal to twice the bearing angle is generated by interconnecting the antenna elements as two quadrupoles offset by 45.degree.. The output of one of the quadrupoles is shifted in phase by 90.degree. and added to the output of the other quadrupole to generate the desired signal, which is applied as an input to the compressive receiver. Other inputs to the compressive receiver are generated in similar ways. The position of the compressive-receiver output port (22) at which a maximum occurs indicates the bearing angle of the electromagnetic plane wave that gave rise to the maximum.

The sweep rate of a linearly swept frequency generator is increased while maintaining strict linearity by artificially increasing the number of zero axis crossings of the output signal from a linearly swept voltage controlled oscillator over those that would naturally occur during a linear sweep. This permits an increased sampling rate which, in turn, permits the oscillator sweep rate to be increased without loss of accuracy. Increasing the number of zero axis crossings is accomplished by introducing phase shifts in the output of the oscillator at calculated sampling times with phase shifting being accomplished indirectly by heterodyning the swept oscillator output with the output from a fixed oscillator whose output signal is phase shifted by discrete amounts during the frequency sweep. Only a small number of phase shifts need be introduced due to the discovery of certain symmetries of phase when sweeping through a frequency range.

Method and apparatus for increasing the sweep rate of a linearly swept

The envelope detector of a compressive receiver is replaced with either a Fourier Transform device or a demodulator such that the output of the dispersive delay line utilized in the receiver is processed to yield the spectrum of the incoming signals and/or the modulation impressed on the incoming signals, thus to permit rapid identification of a signal and its source. In order to permit spectral analysis and/or demodulation of many signals over wide bandwidths, an especially wide bandwidth dispersive delay line is utilized along with a sweep-to-sweep phase coherent variable frequency oscillator.

A dispersive delay line and method for fabricating the delay line is described in which coaxial cable is utilized and in which the dispersive or bandpass characteristic is established by the crimping of the coaxial cable in such a manner that the axial crimp length is small compared to the wavelength, thereby providing a discontinuity which behaves like a simple shunt capacity. A simple fabrication technique is utilized in which the crimps are applied to the line at selected points by use of a four-tooth crimping tool.

Crimped coax reflective dispersive delay line

A spread spectrum detector utilizes compressive receiver techniques and squaring of the incoming signal to detect the presence of a spread spectrum signal and to obtain its center frequency, with the squaring cancelling the pseudo-random code. Once having determined the center frequency, the gated output of the compressive receiver's dispersive delay line may be directly demodulated without resort to code correlation, by applying the output of the dispersive delay line to a narrowband filter set to the detected center frequency. Narrowband interfering signals are rejected by a continuous comb filter, hard limiters for the filter outputs and a summing device. The same narrowband signal rejection can be accomplished by hard limiting the output of the compressive receiver delay line and then returning to the time domain with an additional dispersive delay line having a dispersive characteristic inverse to that of the compressive receiver delay line. Pseudo-random quadrature phase shifts may be cancelled out by raising the incoming signal to the fourth power.

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Nashua, NH, United States of America

Chester E Stromswold