Eric D. Adler

Direct digital synthesis applications for radar development

A chirp synthesizer promises to have a great impact on waveform generation and local oscillator (LO) configurations for next-generation radar architectures. The flexibility in waveform control provided by the synthesizer offers the potential for improved radar performance. The synthesizer allows the generation of waveforms with a wide range of carrier frequencies, chirp rate, pulse widths, and pulse repetition frequencies. The variation of these parameters allows the radar to transmit different waveforms to achieve various missions such as target acquisition, tracking, or classification. The synthesizers flexible waveform control provides a means for motion compensation, reducing ambiguities, and correction of nonlinearities in the transceivers frequency response. Waveform distortion due to propagation path and component and signal processor errors can also be reduced by application of the synthesizer to perform certain error correction techniques. These features are realized in a small lightweight package that can be utilized in various radar scenarios. The paper discusses the salient features of the new chirp synthesizer and its application in various radar configurations.

A multifunctional Ka-band electronic scanning antenna (ESA)

A future goal of the army is to deploy a highly mobile force that is more survivable and lethal than todays heavy tank centric force structure. These future goals can be met by simultaneously removing some of the tanks 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.

Waveform generation and signal processing for a multifunction radar system

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 radars waveform generation and signal processing capability.

Low-cost technology for multimode radar

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 test target generator for wideband pulsed Doppler radars

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 (RCSs), 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 radars dynamic range. Simulating two targets and varying the range and Doppler of each target in the closed-loop test can evaluate the radars range and Doppler resolution, respectively.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 (RCSs), 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 radars dynamic range. Simulating two targets and varying the range and Doppler of each target in the closed-loop test can evaluate the radars range and Doppler resolution, respectively.<<ETX>>

Low-cost enabling technology for multimode radar requirements

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.

An ultra-wideband exciter for ground-penetration radar systems

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.

Fiber optic dual delay line for a multi-mode radar test target simulator

A fiber-optic delay line has been designed for a multimode radar test target simulator. This delay line, operating between 3.0 and 3.6 GHz, has a fixed delay of 30 mu s. Low transmission loss has been achieved using reactive matching techniques and a GRIN lens for optical coupling of the laser to the fiber. The transmission gain of a link consisting of the transmitter and the receiver, connected with a short length of single-mode fiber, is -17 dB at 3.3 GHz with 1-dB variation across the band. It is estimated that the gain of the delay line will be -20 dB due to the additional loss of 3 dB from 6.2 km of optical fiber. These results show a significant improvement in transmission gain, and can improve the noise figure and dynamic range characteristics over commercially available wideband delay lines.<<ETX>>

Realization of Rotman's concepts of beamformer lenses and artificial dielectric materials

The Rotman lens as a passive beam former for antenna arrays and the artificial dielectric material, referred to recently as metamaterial, are two of the key concepts that Walter Rotman proposed. They made significant impact in the areas of antenna arrays and antenna and microwave components. This paper goes into the details of the realizations of the Rotman lens over the years, going from the waveguide-based to the printed-circuit configurations. The paper also discusses the results of some of the metamaterial implementations and features of antenna designs that use such materials.

Wideband acousto-optic processor for ESM applications

This paper describes an acousto-optic (AO) processor that offers a small, lightweight solution to detecting and analyzing wide-bandwidth, spread-spectrum signals. The processor is being developed for insertion into an existing electronic support measure (ESM) test-bed. The correlator will have a processing bandwidth of 500 MHz and will be used to detect direct- sequence phase modulated (PM) signals, frequency-hopped signals, chirps, and impulse signals. An in-line AO correlator is the heart of the processor and is used for detecting wideband activity. Subsequent digital processing, including Fourier transformation, will be used to determine center frequencies, bandwidths, and band shape. Theoretical operation of the correlator is discussed along with descriptions of the radio frequency (RF) interfaces and digital post-processing.