A multifunction, single platform RF sensor capable of performing target acquisition and tracking, combat identification, high data rate communications, and active protection is of interest to the USA army. The sensor ultimately must tie affordable and the size minimized to meet the demands of a rapidly deployable force. To address these needs, the Army Research Laboratory has built and tested a multifunction radar test bed capable of performing multiple tasks simultaneously at K/sub a/-band. The system has integrated high-end RF components together with commercial-off-the-shelf (COTS) signal processing technology. Key elements of the test bed are a commercial direct digital synthesizer (DDS) for adaptable waveform generation, multiple COTS field programmable gate array (FPGA) processors for real-time data acquisition and signal processing, a COTS FPGA based multi-port input/output (I/O) board programmed for radar timing and control, and an electronically scanned antenna (ESA) based upon a Rotman lens beam-former with active elements for multi-beam generation. The radar is capable of transmitting and receiving two simultaneous and independent beams in azimuth with up to 3 GHz of bandwidth and up to 8 watts of average power. The current configuration uses one beam for a radar target acquisition function and the other for a high data rate communication channel. The emphasis of this paper is on the radar's waveform generation and signal processing capability.

A future goal of the Army is to deploy a highly mobile force that is more survivable and lethal than today's heavy tank centric force structure. These future goals can be met by simultaneously removing some of the tank's armor, significantly reducing the weight, and enabling a millimeter wave (mmW) multifunction sensor that includes an active protection function. With the paramount need of enabling an advanced sensor in mind, the Army Research Laboratory is developing a multifunction RF (MFRF) system with a common electronic scanning antenna (ESA) that will perform the functions of target acquisition and tracking, high data rate communications, combat ID, weapons guidance and active protection. The motivation of this mmW sensor is to mitigate the target acquisition, identification and communication timelines in the complex electromagnetic environments encountered in tactical situations. This paper presents an overview of the ESA and some measured results from a first prototype.

A wide-bandwidth electronic scanning antenna (ESA), based on a Rotman lens beam-former, has been developed for shared aperture applications. The key feature of the Rotman lens is that it allows multiple simultaneous beams to be transmitted in different directions and at different frequencies. Since the Rotman lens is a true time-delay element, it is inherently wide-bandwidth and other components of the antenna were designed to support a bandwidth of 8 to 18 GHz. In the ESA, the input signal to the Rotman lens is controlled by a PIN diode beamswitching network, and the outputs are fed to a two-dimensional array of Vivaldi notches. The ESA performance is characterized, and the results is presented.

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

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.

The modern threat for electronic support measure (ESM) receivers are radars that use exotic wideband modulation waveforms for achieving higher resolution or reducing the probability of intercept. Existing ESM testbeds can receive both narrowband and wide-bandwidth modulations but can only detect the presence of narrowband signals. A wideband acousto-optic (AO) correlator (AOC) has been jointly developed by the Army Research Laboratory and Dynetics, Inc., under the ARPA TOPS program for insertion into an existing ESM testbed. The AO module is an in-line, time-integrating correlator architecture that offers a small, lightweight solution for detecting and analyzing inherently wide-bandwidth, spread-spectrum signals. The correlator processes 500 MHz of instantaneous bandwidth and offers enhanced detection capability of direct-sequence, phase-modulated chirps, and frequency-hopping signals. The ESM testbed, developed by the Intelligence and Electronic Warfare Directorate of the US Army Communications and Electronics Command, is currently being evaluated for integration into existing and future Army platforms. The AOC complements the existing ESM testbed and offers a wideband detection capability as described in this paper. The AOC insertion with the ESM testbed was demonstrated at the International Low Probability of Intercept Trials in Salisbury, australia. Performance results for the AOC against realistic LPI waveforms from this field test will be presented.