This paper provides radar test results of an optical processor for sidelobe jamming reduction. Using a Rome Laboratory C-Band phase array radar and jammer testbed, numerous realistic test scenarios were performed. These tests were conducted with the radar in a receive-only mode, with target and jammer signals provided externally. The sum beam from the C-band array served as the main channel input to the adaptive canceller, and one of eight subarrays provided the auxiliary channel. Targets and jammers consisted of both barrage noise and pulsed continuous tone signals produced by stationary jamming and target sources located in the far field of the phase array radar. Closed loop testing, sidelobe jamming reduction, and multipath signal considerations were all integral parts of the test scenarios. The processor is designed to cancel 10 MHz wide bandwidth jamming signals and to work at the radar intermediate frequency of 80 MHz. A processor overview, cancellation results for a variety of test conditions, and future hardware enhancements and test plans will be summarized.
An acousto-optic (AO) range-Doppler processor is being developed to interface to an advanced ground-based radar system developed by the U.S. Army Missile Command (MICOM). The AO processor will replace the function of several digital processor boards currently in the radar. The primary objective of this program is the real-time demonstration of an optical processor in the MICOM radar. This paper provides an overview of the MICOM radar system, discusses the design of the AO range-Doppler processor, and describes the radio frequency and digital electronic interfaces required to achieve real-time operation in the MICOM radar. Upcoming integration and test activities are then described.
Over the past few years, we have been continually upgrading and testing an acousto-optic (AO) multichannel adaptive optical processor, the anti-jamming optical beam-nuller (AJOB), with the ultimate goal of mitigating multipath jamming interference in advanced surveillance applications. Multipath signal considerations are often crucial to successful operation and utilization of adaptive interference cancellation radar hardware. Relative time of arrival and signal strength detection are necessary for accurate placement of the necessary nulls. Presented in this paper are the initial test results and the preliminary test plans for conducting simulated multipath jamming cancellation. Thus, the AJOB represents a potential solution to the problem of multisource multipath jamming interference.
We present the continuing development of an anti-jamming optical beamformer (AJOB) at Rome Laboratory's Photonics Division. Developments include live radar tests and new system designs. The purpose of the AJOB system is the cancellation of multipath jamming interference in advanced surveillance radars. AJOB is a multichannel adaptive optical system which performs cancellation of multiple wideband (10 MHz) interference sources in the presence of multipath. The live radar test consisted of using a downconverted 80 MHz received signal from the main and subarrays of a C-band radar to correlate jamming signals produced by stationary jammers. The correlation parameters fed a tapped delay line filter to form an estimate of the noise, which was subtracted from the main antenna signal. For the scenarios tested, the long integration time for the correlation data provided accurate estimates of the jammer delays, and therefore single-step convergence was achieved.
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.
The primary objective of this program is to perform pulse compression in an existing military system using an optical processor. To achieve this objective, an acousto-optic (AO) range- Doppler processor is being developed to interface to an advanced ground-based radar system developed by the U.S. Army Missile Command (MICOM) and replace the function of several digital processor boards currently in the radar. This paper provides an overview of the MICOM radar system, describes the AO range-Doppler processor, the rf and digital electronic interfaces required to achieve real-time operation in the MICOM radar, and system integration issues.
In this paper it is shown that the reference beam for true time delay operation of a heterodyne system must be carefully chosen to achieve proper signal time delay behavior. True time delay is defined here as an equivalent delay of the envelope and carrier frequency of a carrier-modulated waveform, resulting in no apparent phase shift of the envelope. For acousto-optic (AO) tapped delay lines, or more complex AO systems utilized for tapped delay line filters, signal excisors, or beamformers, the reference beam must be equivalent to the undiffracted beam exiting the AO device in order to achieve true time delay. Two examples are used to demonstrate the application of the time delay concepts described in the paper. The first example is a heterodyne transform architecture that uses an external reference beam to select a tap position within an AO cell. The second example is an AO tapped delay line filter that employs the undiffracted beam from the AO interaction as the reference beam.
The acousto-optic (AO) module described in this paper is an in-line, time- integrating correlator architecture that detects and analyzes inherently wide bandwidth signals in a small and lightweight package. The correlator processes a 500 MHz instantaneous bandwidth to provide enhanced detection capability for broadband signals. The existing electronic support measures (ESM) testbed processes a wide bandwidth but can only detect the presence of narrowband signals. This paper will describe the AO correlator design and the radio frequency and digital interface required for the insertion into the ESM testbed.
An acousto-optic (AO) range-Doppler processor is being developed to interface to an advanced ground-based radar system developed by the U.S. Army Missile Command (MICOM). The AO processor will replace the function of several digital processor boards currently in the radar. The primary objective of this program is the demonstration of an optical processor in the MICOM radar. This paper provides an overview of the MICOM radar system, discusses the design of the AO range-Doppler processor, and describes the RF and digital electronic interfaces required to achieve real-time operation in the MICOM radar.
An acousto-optic (AO) range-Doppler processor is interfaced to an advanced ground-based radar system developed by the U.S. Army Missile Command (MICOM). Demonstration of this optical processor in the MICOM radar is the primary objective of this program, part of the DARPA-sponsored Transition of Optical Processors into Systems (TOPS) program. This paper reviews the MICOM radar system, describes the design of the AO range-Doppler processor, and details the digital electronic interfaces required to achieve real-time operation in the MICOM radar. Experimental results for the AO processor are also provided.
An Acousto-Optic (AO) Range-Doppler Processor is described that is designed to interface to an advanced ground-based radar system developed by the U.S. Army Missile Command (MICOM). Demonstration of this optical processing technology in the MICOM radar is the primary objective of this DARPA-sponsored Transition of Optical Processors into Systems (TOPS) program. This paper presents a description of the MICOM radar system, highlights the design of the AO Range-Doppler Processor, and describes the required radio frequency (RF) and digital electronic interfaces to achieve real-time operation in the MICOM radar. Insertion plans for this TOPS program are also summarized.
Optical signal processing architectures have been designed which offer potential solutions to Air Defense Initiative (ADI) radar signal processing requirements for low radar cross-section target detection and noncooperative target recognition (NCTR). A rack-mounted engineering development model of a wide-bandwidth acousto-optic correlator has been developed to provide high range resolution for target feature extraction and discrimination. A wideband acousto-optic range-Doppler processor brassboard has also been designed to provide simultaneous high range resolution and Doppler filtering. Design and fabrication of a test radar subsystem is in progress, and will be utilized as an ADI clutter suppression test-bed for integration and testing of the high resolution acousto-optic correlator engineering development model and the acousto-optic range-Doppler processor brassboard. In this paper, the designs and status of the optical processors and test-bed are described.
Hardware implementation of the steepest descent algorithm, as applied to multichannel adaptive jamming cancellation, requires the realtime correlation of wide bandwidth signals from multiple input channels. The described optical system uses a single-channel acousto-optic (AO) deflector as an input device for the adapted main antenna signal, where multiple jamming sources mask the target return, and a multichannel AO deflector as the input device for an array of auxiliary antennas, each receiving jamming energy. A time-integrating correlation between the main and auxiliary channels is calculated optically and produces an update to each weight function (stored in computer memory) in accordance with a steepest descent algorithm. The updated weight functions are optically reconstructed and used to tap a multichannel AO delay line, which carries the information from the array of auxiliary channels. A spatial sum of the output from the weighted delay line yields an estimate of the noise in the main channel. The multichannel optical time-integrating correlator has demonstrated realtime parallel computation of the correlation between two wide bandwidth auxiliary channels and the adapted main channel.
A novel optical architecture is presented that is based on the Hartley transform implementation of the classical adaptive least mean square (LMS) algorithm. The Hartley transform is employed to transform the time-domain signal of interest into the frequency domain, where filtering is performed via multiplication by the adaptively controlled filter transfer function. The inverse Hartley transform is then applied to this product resulting in the desired signal estimate, which is then subtracted from the desired signal to obtain the error to be used to update the filter transfer function. In addition to the presentation of this algorithm and the optical implementation, performance assessments based on the number of calculations required for the digital and optical approaches are provided.
A wideband signal processor based on a common module concept is presented that has applications to both radar and signal-intercept applications. This processor is suitable for the coherent pulse compression of wideband radar signals, the intercept/characterization of spread-spectrum radar and communication signals, and the generation of the radar ambiguity function. This paper describes the theory, operation, and application of the processor, which is composed of several modules, including a 1-GHz-bandwidth wideband correlator module, a 200-MHz four-product correlator module, a radio frequency receiver and waveform/transmitter module, and a digital processing and operator interface module for use in field demonstrations.
A novel acoustooptic architecture that implements linear least-mean square adaptive filtering and prediction and has the potential for very wide bandwidth signal processing is described and analyzed in this paper. This architecture maintains coherent operation (providing complex weights) and employs a single acoustooptic device, a photodiode, and a laser diode. The application of a multichannel acoustooptic processor to multiple antenna adaptive interference cancellation is then presented.