A flexible test bed radar architecture is described which includes an integrated RF electronics package that can support multiple radar applications, including surveillance, fire control, target acquisition, and tracking. This type of architecture can significantly reduce the cost, power, size, and weight of electronics on future weapon delivery platforms. The Army Research Laboratory (ARL) is developing technology to support multimode radar requirements. These requirements include the detection and location of moving or stationary low radar cross section targets in heavy ground clutter and the classification and/or recognition of these targets. We address these requirements with commercial-off-the-shelf (COTS) products and the integration of several enabling technologies. The test bed radar includes a direct digital synthesizer (DDS) for frequency-diverse waveform generation, a flexible wideband transceiver for bandwidth extension and frequency translation, and an open architecture signal processor with embedded wideband analog-to-digital converters for real-time acquisition and processing. Efficient signal processing algorithms have been developed to demonstrate multimode radar capability. This paper discusses the various subassemblies, algorithm efficiency, and field experiment results.

A flexible test bed radar architecture is described which includes an integrated RF electronics package that can support multiple radar applications, including surveillance, fire control, target acquisition, and tracking. This type of architecture can significantly reduce the cost, power, size, and weight of electronics on future weapon delivery platforms. The Army Research Laboratory (ARL) is developing technology to support multimode radar requirements. These requirements include the detection and location of moving or stationary low radar cross section targets in heavy ground clutter and the classification and/or recognition of these targets. We address these requirements with commercial-off-the-shelf (COTS) products and the integration of several enabling technologies. The test bed radar includes a direct digital synthesizer (DDS) for frequency-diverse waveform generation, a flexible wideband transceiver for bandwidth extension and frequency translation, and an open architecture signal processor with embedded wideband analog-to-digital converters for real-time acquisition and processing. Efficient signal processing algorithms have been developed to demonstrate multimode radar capability. This paper discusses the various subassemblies, algorithm efficiency, and field experiment results

Waveform requirements for a ground penetration ultra-wideband exciter (UWBE) include generating a frequency spectrum over a wide bandwidth, with a low-start frequency. A scripted linear-frequency-modulated waveform is used for the frequency coverage, with the added ability of arbitrarily notching-out portions of the transmitting spectrum in which radio frequency interference (RFI) exists. This exciter uses an arbitrary waveform generator (AWG), which scripts waveform packets with notches in the spectrum. The AWG is coupled to a frequency synthesizing architecture (FSA) device for waveform packet placement to create a phase-continuous broad-band response.

The Army Research Laboratory is evaluating ultra-wide-band radar imaging techniques for subsurface target detection. Of importance in this effort is the generation of an appropriate waveform and the development of an ultra-wide- band exciter (UWBE). A critical requirement for ground penetrating (GPEN) radar is to identify near-surface or subsurface targets in sufficient detail to allow unambiguous identification. For example, a subsurface mine must be distinguishable from benign subsurface soil strata or other man-made objects (e.g., decoys). To optimize the measured signal-to-clutter ratio requires high cross-range and down- range resolution. High cross-range resolution is achieved by collecting radar returns while the radar is in motion and using synthetic aperture techniques to process those returns. High down-range resolution is achieved by the transmission of wide-bandwidth waveforms. The UWBE design uses a wide-bandwidth (approximately 3 GHz) linear frequency modulated (LFM) waveform. Another critical requirement for GPEN radar is the need for efficient propagation of the radar waveform into the soil, which enhances the detection and recognition of subsurface objects. Since low frequencies (approximately 10 MHz) propagate better into soils than do high frequencies, a low chirp start frequency is desired. The use of a LFM waveform that spans from HF to S Band presents another problem of co-site interference with commercial communication equipment (FM, TV, and cellular radio). Since broadcasting in these bands is restricted, a method has been developed to arbitrarily notch out portions of the transmitting bandwidth. This paper will discuss the use of an arbitrary waveform generator (AWG) from Tektronix with a switching local oscillator (LO) architecture to generate the low start frequency wideband LFM waveform required. The AWG with its 1 GHz clock is bandwidth limited to approximately 400 MHz by Nyquist sampling and filter design constraints. The longer LFM waveform is generated by frequency offsetting and concatenating multiple LFM waveform packets from the AWG. The frequency offset is controlled by the switching LO architecture, where the switching time is on the order of a few nanoseconds. Each AWG output can be pre-programmed with notches in the band for interference suppression, as well as a phase offset to maximize the phase continuity of the desired LFM waveform.

A test target simulator (TTS) based on a fiber-optic delay line (FODL) has been designed for realistic testing and characterizing of wideband pulsed Doppler radars. The TTS can simulate one or two targets at different radar cross sections (RCS's), different Doppler, and different ranges in the presence of uncorrelated noise or interference. With one target, clutter and multipath effects can also be simulated. In a closed-loop test of a pulsed Doppler radar transceiver, the variable control of the RCS can be used to test the radar's dynamic range. Simulating two targets and varying the range and Doppler of each target in the closed-loop test can evaluate the radar's range and Doppler resolution, respectively.<>