A signal receiver employing constant false alarm rate (CFAR) circuitry is disclosed. The CFAR circuitry includes a dispersive delay line for stretching received echo signals, means for limiting the stretched echo signals and an inverse dispersive delay line for finally processing the stretched and limited echo signals. With delay lines of proper characteristics, the just-outlined processing of echo signals results in reconstituted signals, the amplitude of each one of such reconstituted signals being indicative of the source of a corresponding echo signal.
CROSS-REFERENCE TO RELATED CASES
This is a continuation of application Ser. No. 549,585, filed Feb. 13, 1975, now abandoned, which is a continuation of Ser. No. 329,239 filed Feb. 2, 1973, now abandoned, which is a continuation of application Ser. No. 148,560 filed June 1, 1971, now abandoned.
A chirp signal generator circuit includes a pulse generator PG for generating a single impulse for application to first surface acoustic wave device SAW. This device produces an output signal comprising several cycles of energy at a predetermined frequency. A threshold circuit TH passes only that part of the output signal which second surface acoustic wave device EXP having the predetermined frequency as its center frequency, and this output signal is then amplified. The second device EXP generates a frequency modulated chirp signal.
A digital pulse detector circuit having a selectable false alarm rate receives an analog input signal containing periodic correlation pulses in a background of noise. The input signal is sampled and digitized to produce a series of digital input samples which are taken for regular time slots within a series of time frames. Each of the digital input samples is summed with a previously stored digital summation sample to produce a new summation digital sample that replaces the summation sample read out of memory to produce the new summation sample. The new digital summation sample is compared to a threshold value to produce a signal confirmed signal to indicate detection of the correlation pulse. When a set number of summation steps are carried out for a particular time slot and the summation value for that time slot has not exceeded the threshold value, that time slot is reset to zero to eliminate accumulated noise. The threshold values of the integrated pulses can be set at the threshold detector to enable the operator to select the false alarm rate.
A radar system is disclosed which includes a transmitter which produces a long coded radar pulse. The return of the long coded radar pulse is compressed by a long pulse compression filter to produce a short coded pulse and the short coded pulse is compressed by a short pulse compression filter to produce a return pulse for processing by an existing processor designed to process return coded pulses of a particular format. The long pulse transmitter can also transmit a short coded precursor pulse, to improve radar range coverage, along with the long coded pulse by the provision of a switching bypass device which routes the short coded pulse return signal around the long pulse compression filter.
The present inventive concept for bistatic or monostatic radar utilization discloses a method and a system for unambiguous angle resolution of a sparse wide-band array antenna by utilizing an ultra wide-band signal, generally a wide-band noise signal which may be continuous bandwidth limited white or colored noise. The noise signal is typically generated and radiated by a transmitting antenna covering the entire reception range of a receiving sparse antenna array. An echo signal is received by the sparse receiving array containing n antenna elements, which are generally positioned with separation distances of several wavelengths without creating strong grating lobes due to the type of generated transmit signal. By means of a selected auto-correlation function defining the wide-band noise signal power spectrum, the convolution of the radiated output signal and the received echo input signal will give the target range information, the individual time-delay setting for each antenna element will give an unambiguous angular resolution.
