Noise waveforms generated using low cost diodes are a simple way for radars to transmit a wideband (> 4 GHz) multibit pseudorandom code for use in a cross correlation receiver. This type of waveform also has the advantage of being difficult to intercept and is less prone to interfere with adjacent systems. Radar designed to operate over this wide frequency range can take advantage of unique target Radar Cross Section (RCS) ripple versus frequency for objects of different materials and sizes. Specifically the periodicity and amplitude of the ripple is dependent on the shape and size of a target. Since background clutter does not display this variation, RCS variation determines whether a known target is present in a return. This paper will present the radar hardware and signal processing techniques used to maximize a target's unique spectral response against a cluttered background. The system operates CW over a 4-8 GHz bandwidth requiring the need to address issues regarding range resolution and far out undesired returns. Lessons learned from field observations and mitigation techniques incorporated in the system are included. This paper also deals with the signal processing technique used for detection, then discrimination. Detection thresholds are set and triggered by a simple correlation peak level. Discrimination involves inspection of the spectral return. A comparison performed in real time to a stored library value determines the presence of known objects. Measured data provided demonstrates the ability of the radar to discriminate multiple targets against multiple backgrounds.
INTRODUCTIONIn the Mie region an object's shape is comparable to wavelength. Spheres and cylinders of this size exhibit a Radar Cross Section (RCS), which varies significant across a relatively large frequency bandwidth. It is possible these RCS variations discriminate one object from another, such as a metallic cylinder from flat plates or rocks 123 . In order to obtain a useful amount of information, this discrimination technique requires a wideband waveform. Typically there are limitations to wideband waveforms in the heavily regulated bandwidths under 6GHz. A low power Noise Band Radar (NBR) provides a means to transmit a wideband noise waveform in a manner that minimizes interference in heavily regulated and crowded frequency bands. Generation of wideband thermal noise through noise diodes with good linearity provides the addition benefit of a low cost transmitter.In order to validate the phenomenology of this discrimination technique, a Noise Band Radar (NBR) prototype test bed was built. The desire for low cost COTs components drove NBR performance. The test bed included bi-static TX/RX horn antennas separated horizontally by a few feet. A noise diode served as transmitter creating an un-Chirped, CW, 4-8GHz waveform. The receive signal was fed directly into an A/D converter. All the testing covered in this paper used a 20GHz A/D converter. The penalty of this simple setup was an inability to range gate. It was difficult to isola...
