A concept is being developed to upgrade the permeability of a homogenous, isotropic magneto dielectric material by inserting metamaterial macro-cells to produce a hybrid composite material of much higher permeability than that of the host material. The new material will be anisotropic or bi-anisotropic. The analysis and simulation show the multiplicative effect of the hybrid structure, operating at high frequencies using specially designed host materials. In this paper, we take the first step in proving the concept of permeability upgrading by performing experimental verification of a hybrid structure that uses commercially available host material at low frequency. Measuring the S-parameters of thin layers of the host material, followed by using documented parameter retrieval algorithms, we calculate the host material's permeability, permittivity, and loss tangent versus frequency. The measurements are repeated for the metamaterial-inserted hybrid structure to obtain the same parameters and observe the permeability upgrading, or multiplication.

In this paper, we compare the first principle homogenization theory (FPHT) with the Nicolson-Ross-Weir (NRW) approach for determining the complex permittivity and permeability of periodic metamaterials from the measurement of S-parameters. We show that the FPHT overcomes the anti-resonant behavior associated with the wrong sign for the imaginary part and negative slope for the real part versus frequency, for permittivity or permeability in the NRW method. A homogenous slab and a slab embedded with metamaterial inserts formed by U-spiral-pair resonators are then used as examples to prove the accuracy and robustness of the FPHT.

Today’s military radars are being challenged to satisfy multiple mission requirements and operate in complex, dynamic electromagnetic (EM) environments. They are simultaneously constrained by practical considerations like cost, size, weight and power (SWaP), and lifecycle requirements. Tomorrow’s radars need to be resilient to changing operating environments and capable of doing more with fewer resources. Radar research supports this shift toward more agile and efficient radar systems, and current trends include modular hardware and software development for multi-purpose, scalable radio frequency (RF) solutions. Software-defined radios (SDRs) and other commercial-off-the-shelf (COTS) technology are being used for flexible waveform generation, signal processing, and nontraditional radar applications. Adaptive RF technology, including apertures and other front-end components, are being developed for multi-purpose functionality and resiliency. Together, these research trends will result in a technology framework for more robust future systems that are capable of implementing cognitive processing techniques and adapting their behavior to meet the demands of a congested and contested EM environment.

The Army Research Laboratory is in partnership with the University of Florida - Electronics Communications Laboratory to develop compact radar technology and demonstrate that it is scalable to a variety of ultra-lightweight platforms (< 10 lbs.) to meet Army mission needs in persistent surveillance, unattended ground sensor (UGS), unmanned systems, and man-portable sensor applications. The advantage of this compact radar is its steerable beam technology and relatively long-range capability compared to other small, battery-powered radar concepts. This paper will review the ongoing development of the sensor and presents a sample of the collected data thus far.

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.

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.

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 synthesizer's flexible waveform control provides a means for motion compensation, reducing ambiguities, and correction of nonlinearities in the transceiver's 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 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.<>

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.

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.<>

ABSTRACTAnacousto-optic (AO) correlator is being constructed that offers a small, lightweight solution to detectingand analyzing widebandwidth, spread-spectrum signals. The processor is being inserted into an existingelectronic support measure (ESM) test-bed under the Defense Advanced Research Projects Agency (DARPA)Transition of Optical Processors into Systems (TOPS) program. The correlator has a processing bandwidth of500 MHz and will be used to detect direct-sequence, phase-modulated signals, frequency-hopped signals, chirps,and impulses. A description of the processor is provided along with experimental results obtained from aninterim developmental breadboard. Subsequent digital processing, which includes nonlinear detection andFourier transformation, is used to determine center frequencies, bandwidths, and band shape. Theoreticaldescriptions of the post-processing are provided and simulation results are discussed.1. INTRODUCTIONSignal environments are becoming increasingly complex in both signal density and emitter sophistication.Future battlefield systems are expected to increase the use ofwideband impulse, direct-sequence, and frequency-hopped signals. To more readily intercept and classif' these signals, additional receiver sophistication isrequired. Current ESM receivers work very well at detecting and characterizing narrowband and pulsed signals;however, wide-bandwidth and spread-spectrum signals are not as readily handled. As an example in some ESMreceivers, a frequency-hopped signal may be reported as a multitude of individual, narrowband signals insteadof a single wideband, spread-spectrum signal.