Gordon Woodington

Target discrimination technique utilizing noise waveforms

Noise waveforms generated using low cost diodes are a simple way for radars to transmit a wideband (> 4 GHz) multi-bit 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 targets 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.

Direct digitization of ultra-wideband (UWB) noise signals using frequency band folding

Frequency spectrum responses of targets are of importance in UWB radar for target identification and recognition. As technologys digitization rate of analog sources increases, direct acquisition of wider bandwidths is becoming possible. Through conversion to the frequency domain, wider bandwidth spectral responses for targets can be produced. However, to directly digitize higher frequencies with UWB signals directly (i.e., ≥ 4 GHz), the technology is somewhat limited. This paper will present a technique which utilizes both hardware and software to produce a lower bandwidth signal (e.g., 1.5 GHz), which contains larger spectral bandwidth information (e.g., 6 GHz). The technique utilizes a double band folding methodology implemented in hardware, or software, to translate larger bandwidths into lower bandwidths for direct digitization. The generated lower bandwidth will have a unique spectral response containing the superimposed amplitudes of the larger bandwidth transmitted signal. This folded spectrum can then be used in applications such as target recognition and identification. Simulated and experimental results will be presented to evaluate the advantages and disadvantages of such an approach.