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Method and system for radio detection and ranging intrusion detection systemMethod and system for radio detection and ranging intrusion detection system description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080316086, Method and system for radio detection and ranging intrusion detection system. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION
The present disclosure relates generally to intrusion detection systems, and particularly to radio detection and ranging (RADAR) intrusion detection systems. There is a need for indoor security devices to monitor areas subject to penetration by trespassers and also to alert authorities when personnel have entered a hazardous zone. One commonly employed technique is that of electromagnetic RADAR. It is well known in the art that a RADAR system may be used to monitor an area even though there is no direct visible line of sight from the RADAR unit to the area under surveillance, as a RADAR signal may often successfully penetrate and return through common building materials, thereby allowing the RADAR unit to be hidden or inconspicuous. Referring now to FIG. 1, a block schematic diagram of a basic signal processing operation is depicted. A baseline system 100 operates as a simple Pulsed Doppler radar using analog signal processing. A radio frequency (RF) pulse generator 105 produces a first burst and a second burst of microwave energy via an antenna 110, the bursts having a center frequency of 5.8 GHz (+/−75 MHz). As used herein, the term burst shall refer to a short duration portion of a sine wave of microwave energy. This frequency is part of the Industrial, Scientific, and Medical (ISM) band reserved for unlicensed use at limited transmit power levels. In the United States, three of the commonly used ISM bands occupy frequencies from 902-928 MHz, 2400-2483.5 MHz (also herein referred to as the 2.4 GHz band), and 5725-5850 MHz (also herein referred to the 5.8 GHz band). The two bursts are separated by some time interval from about 10 nanoseconds (ns) to about 80 ns, depending on the range of the region to be monitored, thereby defining the range to be monitored. In an embodiment, the duration of the bursts shall be less than the delay between the first and second burst. The burst pairs are generated at a rate of roughly 12 kHz. The first burst illuminates the target and the second burst (also herein referred to as a reference burst) is used to derive a Doppler signal. The RADAR unit 100 transmits the second burst in addition to the first, but the return of the second burst is ignored and has no effect on the processing. If it is desired that the RADAR not actually transmit the second burst, this can be accomplished through the use of a standard RADAR structure, where the reference burst is supplied to the receiver by a separate local oscillator and the antenna is switched back and forth between transmitter and receiver subsections by an analog switch. Such structures are described, for example, in RADAR Design Principles, by F. E. Nathanson (McGraw Hill, 1991). In response to the reception of the reflection of the first transmitted burst at the antenna 110 it is, in effect, added to the second burst, and the sum is processed by a signal processing chain 115, starting with an envelope detector 120. The envelope detector 120 (also herein referred to as a non-linearity or a demodulator) may comprise one or more diodes in series followed by a low-pass filter (LPF) 130. For the duration of that period during which the reflected burst overlaps with the reference pulse, the amplitude of the envelope detector (also herein referred to as a demodulator) 120 output oscillates with a frequency equal to the difference of the frequency of the reference burst and the reflected first burst. If a target is moving at one foot/sec, the Doppler frequency is approximately 12 Hz when using a center frequency in the 5.8 GHz band, so that the output of the demodulator 120 will appear constant over the overlap period for normal walking speeds. The output of the demodulator 120 should be considered a sampled version of a continuous Doppler signal, so that the output of the demodulator 120 is a 12 kHz pulse sequence composed of a static part and a part oscillating at the Doppler frequency. The static part originates in the non-overlapped portions of the reflected and reference pulses and includes a constant part within the overlap interval that is due to the difference in amplitude between the return burst and the reference burst. The oscillating part originates in the pulse overlap region, as described below. If the envelope detector 120 is considered to be a half-wave square law device and the associated low-pass filter 130 has a critical frequency low enough to block a signal of the form cos(2πf0+θ0), where f0 is the transmitted center frequency, and if the input is given by Equation-1:
input
=
{
cos
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