AMTA Paper Archive
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Brief history of anechoic chambers for antenna measurements
A review will be made of advances in anechoic chamber technology from the precursors of World War II to the huge complex chamber of today. A glimpse of the technology of the 80’s will be offered.
Polarimetric calibration of reciprocal-antenna radars
We discuss how RCS target depolariza tion enhances cross-polarization contamination, and we present a graphical study of measurement error due to depolarization by an inclined dihedral reflector. Error correction requires complete polarimetric RCS measure ments. We present a simple polarimetric calibration scheme that is applicable to reciprocal antenna radars. This method uses a dihedral calibration target mounted on a rotator. Because the calibration standard can be ro tated, there is no need to mount and align multiple sepa rate standards, and clutter and noise may be rejected by averaging over rotation angle.
Flexible high speed antenna measurement data acquisition system for the outdoor antenna range, A
Rome Laboratory has recently designed and implemented a state of the art automated antenna measurement data acquisition system at the Rome Lab/Newport antenna test facility. A generalized approach to the antenna data acquisition hardware and software was implemented which allows sequencing, control and measurement of test variables in virtually any order without test specific software modifications. The hardware design is based on distributed computers in which real-time data acquisition tasks and near real-time operator control and data analysis tasks are performed independently. The computers operate in a remote client/server configuration in which control information and data are transferred via fiber optic local area network. In this paper, the fundamental approach to the data acquisition system design is discussed and the antenna measurement hardware and software that comprises the final system are described.
ISAR RCS editing via modern spectral estimation methods
ERIM is investigating the use of modem spectral esti mation techniques for extracting (editing) desired or undesired contributions to RCS and ISAR measurements in two ways. The first approach involves using parametric spectral estimators to perform frequency sweep range compression and signal history editing, while the second involves using the associated stabilized linear prediction filters to extrapolate sweep data and perform "enhanced resolution" Fourier image editing. This paper summarizes our editing algorithms and illustrates RCS editing results using measurements of a conesphere target contaminated by a metal rod and foam support. The reconstructed "clean" conesphere measurements are compared quantitatively against numerically simulated ground truth. Editing was performed using three bandwidths at two center fre quencies to provide insight into the impacts of nominal resolution and scatterer amplitude variation with fre quency on editing efficacy, and to assess the degree to which superresolution algorithms can offset reduced nominal resolution.
Ultra-wideband transient antenna measurement techniques
In the past few years there have been new application of transient, ultra-wide band microwaves include cooperating aircraft identification and ground penetration Radar's, high power microwave weapons and others. These applications typically require the use of ultra-wideband antennas with characteristics suitable to radiate transient pulses. This paper describes the capabilities of the USAF Phillips Laboratory's new Transient Antenna Range. The antenna range can measure the radiated characteristics of sources/antennas wave forms with risetimes in the 75 ps regime, and with greater than 50 ns pulse width. The antenna range incorporates a hardware suite controlled by a powerful software data acquisition system that runs on a PC. Automatic data reduction can yield values of wave form peak electric field, risetime and waveform spectrum at a single point, or across an azimuthal scan. This paper will also describe a unique wave form splicing technique used in the data processing algorithms of the Transient Antenna Range. This splicing technique allows test personnel to record the (typically) very fast early time history of the radiated waveform with an SCD-5000 scan converter (operating at a maximum bandwidth, 5 ns of record available), and the long time history of the waveform with a DSA-602 transient digitizer.
RF techniques for gauging antenna repair processes
The antenna repair shop of McClellan Air Force Base near Sacramento, California has been involved in the repair of military high frequency antennas for many years. With the acquisition of precision microwave measurement equipment, in the last five years, the antenna shop has developed innovative methods of gauging its antenna material repair processes. This paper will focus on the work done on a LS-band phased-array, satellite ground station antenna. Specific processed examined will be radome-point selection, phased-array receive element cleaning, and radome bonding. The history of the problems that required the repairs will be discussed. Several antenna/radome repair processes and RF test methods will be described. Manufacturer specifications will be examined where available. Included in this paper will be RF test data and data analysis.
Parametric signal history editing techniques for removal of additive support contamination in narrowband RCS measurements
ERIM has developed techniques, based on parametric spectral estimators, for removing additive target support contamination from narrowband RCS measurements . These techniques allow target and support returns to be extracted from frequency sweep data with much greater accuracy and resolution than that afforded by conventional Fourier techniques. These algorithms have recently been enhanced to incorporate scattering mechanism frequency dependence in the underlying signal model. Specifically, damped exponential and power-of-frequency sweep data with much greater accuracy and resolution than that afforded by conventional Fourier techniques. These algorithms have recently been enhanced to incorporate scattering mechanism frequency dependence in the underlying signal model. Specifically, damped exponential and power-of-frequency signal models have been used. The modification substantially improves algorithm performance in measurement situations where there is small absolute bandwidth, but relatively large fractional bandwidth, which can lead to appreciable variation in scattering mechanism amplitude. The paper will demonstrate the technique’s ability to remove target support contamination using numerical simulations and compact range measurements of canonical targets mounted on pylon supports. It will be shown that the algorithm can remove the additive pylon contamination even for situations where the pylon return dominates the target return and cannot be resolved from the target in conventional Fourier range profiles.
RCS Data Improvement Using Two-Dimensional Parametric Signal History Editing (PSHE)
Target support and clutter contamination can be a limiting factor in radar cross section (RCS) measurements of signature controlled targets. Conventional ISAR image editing methods can be used to remove contamination, but their performance degrades rapidly when the available resolution is insufficient to identify and separate the support returns from those of the target. ERIM International, Inc. (EI) has developed and successfully demonstrated data post-processing techniques based on 1-D parametric spectral estimators for removing additive contamination from low resolution swept frequency measurements [1, 2]. To further enhance performance and take advantage of the cross-range resolution afforded by target aspect information, EI has investigated the use of coherent 2-D spectral estimation techniques for improved identification and mitigation of measurement contamination in frequency and angle diverse data. In particular, parametric signal history editing (PSHE) algorithms based on 2-D TLS-Prony  and 2-D MEMP  have been developed and exercised on numerical simulations and measured data. The paper demonstrates 2-D spectral estimation in representative measurement situations, identifies strengths and limitations, and quantifies mitigation algorithm performance. In addition, automated filtering of spectral representations using energy level ordering, Cramer Rao Bounds (CRBs), and spatial filtering are discussed.
Helicopter Based RCS Measurements
A helicopter-based radar cross section (RCS) measurement system was designed and demonstrated during the past year. The system was a novel combination of modified and un-modified commercial off the shelf (COTS) equipment and software, a minor amount of new hardware, and extensive prior experience. Validation was accomplished using known calibration standards and existing test practices relevant to this type of system, and data were collected and processed for a number of targets of opportunity. The primary subsystems include the measurement radar, the helicopter, antennas and associated mount, boresighted video and recorder, and the calibration tools. The SCI1000 radar was employed because of the combination of its excellent performance at the desired test target range and its minimal physical and power demands. The Bell 500 helicopter was chosen for its size and its wide availability on the world market. Data products were RCS vs. aspect, downrange profile history, and two-dimensional imaging following pre-processing by a robust motion compensation algorithm.
A History of Antenna Testing at BATC
From the earliest days of antenna development, the need for measurement of performance and function has been present. Some characteristics of antennas, such as radiation pattern, are measured by moving one antenna with respect to another. In early antenna testing, outdoor ranges were used to provide a close approximation to the pattern. However, due to the challenges of weather and other environmental effects, antenna testing moved indoors with a number of methods used to compensate for the lack of available space. This paper presents an overview of the history of testing at BATC, from the early days of outdoor testing to the transition to conventional anechoic chambers and nearfield probe facilities. During this time, a variety of techniques have been used to augment standard methods for special requirements, and this paper seeks to communicate some of these methods to the testing community as well as providing a general history of antenna measurement.
The History of NBS/NIST in Boulder, Part 3 - Everything Else
Although the original reason for creating the Boulder Laboratories of NBS (later known as NIST) was to accommodate the radio program, as described by Dennis Friday and Allen Newell at this conference, the first major program in Boulder was in Cryogenics, which was created in response to a perceived emergency in national security and went on to provide basic cryogenic data to serve the national space program. It was also the origin of programs continuing to the present in the reliability of materials, the thermophysical properties of fluids, and cryoelectronics. The early work at NBS on radio propagation led to the development of new tools for meteorology and became an essential part of the newly formed National Oceanic and Atmospheric Administration. The Joint Institute for Laboratory Astrophysics was formed in collaboration with the University of Colorado and quickly exceeded the field of activity suggested by its name. The Time and Frequency program created a series of radical innovations in frequency standards and the dissemination of time, including a new definition of the meter and an experimental frequency standard based on a single mercury ion.
The Blue Airborne Target Signatures (BATS) Database
This paper discusses the Blue Airborne Target Signatures (BATS) database. BATS is the United States Air Force central repository for US and allied signature data. It resides at and is maintained by the Signatures Element, 453rd Electronic Warfare Squadron, Air Force Information Warfare Center, Lackland AFB TX. BATS contains radar cross section (RCS), infrared (IR), and antenna pattern (AP) data, both measured and simulated. The history and background of BATS is also presented, as well as current activities.
Computation and Use of Characteristic Frequency Modes for Patch Antenna Design
The use of characteristic modes or eigenmodes in arbi-trary electromagnetic geometries for a variety of ap-plications has a long history (, , ). This work introduces a means for numerically computing these modes over frequency in a Finite Element Boundary Integral (FE-BI) prediction code framework for arbi-trary patch antenna geometries. Manipulation of modes using material texturing is demonstrated as an effective means for adjusting lossless patch antenna performance. Mode visualization aids in understand-ing material texture requirements for a particular wideband optimization condition.
RCS Measurement Facilities Certification Program Update
The National Radar Cross Section Measurement Facilities Certification Program seeks to raise collectively the quality bar across the community. A program to accomplish this goal was initiated in 1995. It continues with facilities joining the program every year. The program has now entered the recertification phase for facilities that achieved certification five or more years ago. This paper will briefly cover the history of the program, the participants, the certification process and criteria, the recertification process, status, and the way ahead.
A Standalone RF System for Solid-State Phased Array Antenna Measurements
Lockheed Martin MS2 has a long history of utilizing antenna ranges for calibration, test and characterization of the phased array antennas. Each range contains an integrated RF receiver subsystem for performing antenna measurements, typically on the full array. For solid-state phased array testing, what is often needed, however, is a test station capable of performing complex S-parameter measurements on a subarray or subset of the full antenna system without incurring the expense of a test chamber. To address this requirement, Lockheed Martin, working with Nearfield Systems, has developed a portable standalone RF measurement system. The standalone system consists of an Agilent PNA, automated transmit/receive unit (TRU) and a waveform generation (WFG) subsystem for interfacing to the phased array beam-steering computer. This paper will discuss the capabilities of the Standalone RF System including the TRU and WFG subsystems. The TRU is used to tailor the RF signal by automated switching of amplifiers and programmable step attenuators for various test scenarios. The WFG is an automated pattern generator used to present many digital waveforms in arbitrary sequences to the phased array beam steering computer. The design features of the standalone RF system will be presented along with the COTS hardware utilized in assembling the station.
On the Use of Basis Pursuit and a Forward Operator Dictionary to Separate Specific Background Types from Target RCS Data
RCS measurements are often comprised of a combination of the coherent summation of many things in addition to the desired target. Those other things contribute to error in RCS measurements and include noise, clutter and background, which can be further characterized according to specific types. An approach has been developed that is capable of capturing and separating certain types of noise, clutter and background based on specific forward models to include RFI, target support (e.g., pylon), and many others, such that engineers can clearly see the separated components and selectively choose to include, exclude, or edit as the case may be. This approach affords far more flexibility than classic image edit reconstruct (IER), and offers more editing accuracy than Fourier-based approaches including entire phase history based approaches. This paper describes the basic approach and shows examples with measured data.
Distinguishing Localized and Non-Localized Scattering for Improved Near-Field to Far-Field Transformations
Historically, the inverse synthetic aperture radar (ISAR) reflectivity assumption has been used in the implementation of Image-Based Near Field-to-Far Field Transformations (IB-NFFFT) to estimate monostatic far field radar cross-sections (RCS) from monostatic near field radar measurements. The ISAR assumption states that all target scattering occurs at the location of the incident field excitations, i.e., the target is composed entirely of non-interacting localized scatters. Certain non-localized scattering phenomenon cannot be effectively handled by the IB-NFFFT approach with the ISAR assumption. Here we have used the adaptive Gaussian representation, which is a joint time-frequency decomposition technique, to coherently decompose near field measured data into two subsets of scattering features: one subset of localized scatterers and the other of non-localized scatterers. The localized scattering features are processed through the IB-NFFFT as typical, which includes compensating for the R4 fall-off present in the near field measured data. The non-localized scattering features, more appropriately scaled, are then coherently added back in to the post-NFFFT localized scattering phase history. Although this does not properly transform the non-localized scattering features into the far field, it does avoid the over-estimation error associated with improperly compensating distributed non-localized scattering features by a R4 power fall off based strictly on downrange position.
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