Communications: directive radio wave systems and devices (e.g. – Return signal controls radar system – Receiver
Reexamination Certificate
2001-06-07
2002-08-13
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls radar system
Receiver
C342S093000, C342S099000, C342S197000
Reexamination Certificate
active
06433730
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates generally to detection of radar signals and, more specifically, to apparatus and methods for detecting radar signals with high pulse repetition frequency and high duty cycles.
(2) Description of the Prior Art
While radar uses different pulse repetition frequencies and duty cycles, in some cases it is desirable that the pulse repetition frequency and/or duty cycle be relatively high. For instance, high pulse repetition frequencies may be used for those situations when the radar is detecting relatively close but fast moving objects, with respect to the transmitter, to thereby provide more up to date information about those objects and/or the relative movement therebetween. The closer proximity of the object from which radar reflections occur readily allows use of a higher pulse repetition frequency because the reflection return time of the transmitted pulses is shorter.
Noise riding threshold controls are presently used in wideband crystal video early warning receivers to automatically detect the noise level of the radar receiver and to automatically set and control a signal detection threshold above the noise level. However, the existing noise riding threshold control designs are not immune to signals with high pulse repetition frequencies and/or high duty cycles. When a high pulse repetition frequency, high duty cycle signal is received, prior art noise riding threshold controls may detect the signal as noise and raise the signal detection threshold by some amount related to the signal's pulse repetition frequency, duty cycle, and detected power. Thus, one problem with prior art noise riding threshold controls is that the signal to be detected contains components that are considered to be noise by the noise riding threshold circuit, which therefore sets too high a threshold with respect to the actual noise components.
The following patents disclose various radar receivers and components thereof.
U.S. Pat. No. 3,805,267, issued Apr. 16, 1974, to Collot Gerard, discloses an aircraft radar receiver for searching and for tracking a target through one or more telemetry windows. In the search phase, the receiver carries out distance scanning and, on receiving a target echo, locks onto the same in order to supply telemetric information. The receiver comprises means for, during the search phase, desensitizing the radar receiver for the distance, which corresponds to the altitude of the aircraft above the ground so that the altitude return signal does not cause the radar to switch to tracking state. The desensitization means are inoperative when the altitude return signal occurs in the radar tracking state.
U.S. Pat. No. 3,825,930, issued Jul. 23, 1974, to Eric Davies, discloses that in order to reduce the effect of jamming pulses or spurious noise on the operation of a radar, incoming signals are attenuated to below a threshold level. Only those pulses, which on integration over a number of pulse repetition periods exceed the threshold level, are utilized. Additional information concerning a radar target is obtained from the degree of alternation to which each incoming signal is subjected in order to bring it below the threshold level.
U.S. Pat. No. 4,542,382, issued Sep. 17, 1985, to Will A. Hol, discloses a search radar apparatus containing an MTI video processing unit provided with a canceler for generating video signals of moving targets; a zero-velocity filter for generating clutter video signals; a conditional circuit connected to the canceler and the filter for generating, per range quant of each radar scan, a clutter switching signal, if, for the range quant, the signal value obtained with the filter is greater than the signal value obtained with the canceler; a combination circuit connected to said filter and the conditional circuit for selecting the clutter video signals present with the clutter switching signals and for determining therefrom a temporary clutter level in each clutter cell and each antenna revolution period; and clutter level indication means connected to the combination circuit for determining a standard clutter level per range-azimuth clutter cell of the radar range with the application of clutter video signals.
U.S. Pat. No. 4,700,191, issued Oct. 13, 1987, to Dan Manor, discloses a radar warning receiver for detecting and analyzing radar signals which comprises a plurality of RF heads each tuned to a predetermined frequency band and connected to an antenna covering a preselected sector of reception of radar signals. Each of the heads includes a frequency converter converting the received signals to a common frequency based-band and producing an output signal in the base-band corresponding to the signal received by its antenna. The radar receiver also includes a central receiver unit receiving the signals from the RF heads, the central receiver unit comprising a plurality of channels, one for each RF head, for receiving and processing the signals from the respective head; and mode selector means for selectively switching the central receiver unit to operate according to: (a) an Acquisition Mode, wherein the plurality of channels are connected to cover contiguous sub-bands of the base-band; or (b) an Analysis Mode, wherein the plurality of channels are connected in parallel to cover the same sub-band of the base-band.
U.S. Pat. No. 4,806,933, issued Feb. 21, 1989, to Halsey and Gasser, discloses a crystal video receiver having CW and pulse detection capability which includes a threshold signal generator which switchably provides fixed and noise riding threshold signals, used to determine initial signal detection. Track and hold circuits provide a second threshold, derived from the peak received signal level, for establishing the termination of received video pulses. A pulse width counter is coupled to determine the time a received pulse signal is between the two thresholds and is set to overflow at a predetermined time after the reception of a signal to establish a pulse representative of a received Cw signal and to prevent receiver lock up.
U.S. Pat. No. 5,280,289, issued Jan. 18, 1994, to George R. Root, discloses an automatic thresholding target detection system operable in high clutter, noisy environments providing target recognition through the generation of automatic signal thresholds. Infrared and radar detectors scanning an environment detect radiant energy from manmade and natural sources. The energy received is converted to electrical signals representative of the varying energy intensities, which are filtered and compared with a computed target signal threshold. Signal spikes having amplitudes greater than the automatically generated threshold are then evaluated using a shape parameter test. Finally, an automatic region clutter recognition processor confirms that the spike is a true target, clutter or noise.
U.S. Pat. No. 5,451,956, issued Sep. 19, 1995, to Donald L. Lochhead, discloses a method and apparatus for processing the log video output of a receiver that can measure multiple time overlapped pulses on a nearly instantaneous basis. The receiver measures frequency, pulse modulation, time of arrival, amplitude, pulse width and phase difference when simultaneous pulses are present. To detect pulse parameters a given voltage threshold must be exceeded and M out of the last N data samples must fall within a given voltage window that is above the threshold voltage. Pulse detection is initiated by establishing a dynamic noise threshold that is above the random noise level. When a pulse arrives, the value of the amplitude samples is measured and when the successive differences between the amplitude samples are small enough then a pulse presence is declared. Following detection of a pulse, amplitude samples are continuously taken and processed to detect the end of the pulse or a pulse-on-pulse condition. A pulse-on-pulse condition is detected when the difference between successive amplitude samples again starts to increase after initially stabilizing. As soon
Lall Prithvi C.
McGowan Michael J.
Oglo Michael F.
Sotomayor John B.
The United States of America as represented by the Secretary of
LandOfFree
Noise riding threshold control with immunity to signals with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Noise riding threshold control with immunity to signals with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Noise riding threshold control with immunity to signals with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2891679