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ORBIT/FR has recently installed and qualified a combined microwave (2-18 GHz) and millimeter wave (92.5-95.5 GHz) RCS system in an existing compact range based chamber. The facility is used for scale model reflectivity measurements on a wide variety of targets. The system features a unique, high power hardware gating system at the millimeter wave band that contains an integrated compact range feed assembly specifically designed to optimize RCS performance. Changeover between the microwave and millimeter wave bands is possible by placement of the appropriate compact range feed assembly on the feed stand, with locating pins being utilized to assure repeatable performance of the feeds in the compact range system. The system utilizes the FR959 RCS Measurement Workstation and HP 8530/85330 "turbo" based receiver system. Appropriate upconversion and downconversion hardware is integrated into the millimeter wave gating system to allow a common set of HP 8360 series sources and the HP 8530 IF receiver to be utilized for operation in both bands. The system is capable of producing high quality ISAR images at the millimeter wave frequencies, as well as in the microwave band.
ORBIT/FR has recently delivered an integrated facility capable of being used for Antenna, Radar Cross Section (RCS), and EMI measurements to the Naval Underwater Warfare Center in Newport, RI. The facility includes a shielded anechoic chamber, a compact range system capable of producing a 6 foot diameter quiet zone, multi-axis positioning equipment, and a complete complement of Antenna, RCS, and EMI measurement instrumentation and data collection hardware/software. The facility is capable of operation over a frequency range of 100 MHz to 50 GHz, with compact range operation feasible above 2 GHz. The facility can be reconfigured to go between antenna and RCS measurements in any band using both frequency band and antenna/RCS mode switching. In addition, automatic positioning of the appropriate compact range feed to the reflector focal point is available. EMI measurements require minimal relocation of absorber in an isolated area of the chamber floor. Performance of the system is optimized by location of critical RF equipment on the compact range feed carousel or on the positioning system rail carriage. This system offers a unique combination of performance and convenience for making all three types of measurements.
This paper discusses Radar Cross Section (RCS) measurement capability at Very High Frequencies (VHF) in the Boeing 9-77 Range in Seattle, Washington. This indoor facility provides a unique asset to the RCS measurement community. Initially operational in 1989, the 9-77 Range was upgraded in 1995 to include a VHF measurement capability. This was achieved using a 56 foot square array of 256 elements, for RCS measurements at frequencies from approximately 140 to 220 MHz, with a 40 foot quiet zone. In this paper, we discuss results from the characterization process used to verify the initial capability and ongoing operation of the RCS measurement system at VHF. We include data demonstrating the sensitivity, stability and dynamic range of the system. We also present samples of recent field probes, and background subtraction and stability measurements. A comparison is made between calculated and measured canonical target signatures.
Range characterization is becoming a very important topic for the operators of RCS measurement ranges. Techniques for characterization can be expensive and time consuming. We present a top down approach that recognizes that the range construction and optimization is the responsibility of the range operators. Once the range is operating satisfactorily from the point of view of the range operator, then characterization of t he range performance as achieved can be done. Measurements are proposed that perform this characterization rapidly and inexpensively.
Recently, several deployable, ground-to-ground col lection systems have been developed for the assessment of aircraft RCS on the flight-line. The majority of these systems require bulky rail or scanning hardware in order to collect diagnostic imaging data. The measurement technique described in this paper, while not a "cure-all", does eliminate the need for bulky hardware by allowing the collection system to move freely around the target while collecting radar backscattering data. In addition, a nearfield-to-farfield transformation (NFFFT) algorithm is incorporated in the process to allow the collection of scattering data collected in the near field to be processed and evaluated in the far field. The techniques described in this paper are a part of a data conditioning process which improves the data quality and utility for subsequent analysis by an automated diagnostic system described elsewhere in this proceedings [1]. The techniques are described and demonstrated on numerically simulated and experimentally measured data.
The RATSCAT radar cross section (RCS) measurement facility at Holloman AFB, NM is working to satisfy DoD and customer desires for certified RCS data. This paper discusses the low frequency characterization of the RATSCAT VHF/UHF Measurement System (RVUMS). The characterization was conducted on a portable pit with a 30' foam column at the RAMS site. System noise, clutter, backgrounds and generic target measurements are presented and discussed. Potential error sources are examined. The use of background subtraction and full polarimetric calibration are presented. Potential errors, which can occur from using certain cross-pol calibration techniques, are discussed. The phase relationship between each polarization components of the scattering matrix and cross-pol validation techniques are considered.
The Ohio State University ElectroScience Laboratory (OSU/ESL) has built a series of radars that transmit UWB random noise. On receive, the signal is cross correlated with a delayed version of the transmitted signal. When the response of the system is taken as a function of the delay time, the result is proportional to the impulse response of the system. After background subtraction and calibration, the impulse response of the target results. We will present a description of the variable delay line system and show an example ISAR image made from measurements taken in the OSU compact range.
A time domain near-field far-field transformation technique based on a non redundant plane-polar sampling representation of the field is presented. The method allows to obtain the far-field with a minimum number of samples and/or a reduction of the scanning area. Various computational schemes are presented.
Compact range technology has been used to measure the reflection properties of sea-ice. It is also being applied to detect anti-personnel (A-P) mines. The antenna configuration and its field in the vicinity of the scatterer are discussed.
A new holographic technique for array diagnosis is discussed. Numerical and experimental results are shown in case of linear arrays and compared with the performance of the “classical” holographic approach based on FFT. Furthermore, the working progress on a sub-optimal algorithm specifically developped for diagnosis of large arrays is presented.
This paper will address the design and verification procedures for an Elevated Far Field antenna measurement facility at the Naval Explosive Ordinance Disposal Technical Center, Indian Head, MD for operation at 30 MHz – 1000 MHz.
A display scheme is explored that may be of diagnostic value in interpreting scatterer interactions in ISAR imagery. It relies on the non-coherent sum of several images, and thus traces the motion of all scatterers across the range-crossrange plane. The scheme is demonstrated by means of a very simple geometric optics model involving only two scatterers.
A technique of measuring the mutual capacitance per unit length of a shielded twisted pair transmission line is developed and used to verify a finite difference model developed previously by the authors. Attempts to measure the very small capacitance values using a capacitance bridge were unsuccessful. The phase technique presented here is easily performed and gives good results.
We describe an imaging technique which allows the isolation of sources of unwanted radiation on an antenna/RCS range. The necessary data may be collected by using a roll-over azimuth mount to scan a probe over a spherical measurement surface.
This paper describes the status of NASA’s Inflatable Antenna Experiment (IAE) and a brief discussion on potential future applications. The space experiment of a 14-meter diameter reflector antenna was flown and deployed successfully aboard the Space Shuttle, STS-11, launched May 19, 1996. Since the flight data is still being processed and reduced, only preliminary results can be presented at this time. The development of the IAE will be discussed along with the results of ground test measurements which were conducted to determine the overall mechanical and projected electrical performance characteristics of this inflatable concept. Large, space-deployable antennas are needed for numerous applications which include mobile communications, Earth remote sensing, and space-based radar systems. Due to the traditionally high cost to develop and launch such large antennas, new technology must be developed which is cheaper, faster, and better. Inflatable antenna technology provides the opportunity to accomplish these objectives.
Antennas that are integrated with system electronics extend the measurement scope of conventional, passive antenna designs. At a minimum, the dynamic range of the antenna system as limited by the electronics must be established. Array antennas with active electronics pose additional challenges because unit to unit variations in the array element electronics affect array performance. Other challenges are presented when digital electronics are incorporated into the antenna. Measurement techniques and instrumentation issues are discussed.
Antennas with integrated RF or microwave sources are becoming more prevalent as the wireless explosion continues to evolve into specific programs and products. These types of antenna modules span several different business areas such as communication satellites, radars, and collision warning systems and cellular or wireless systems. In order to evaluate a device’s true performance parameters, it is desirable to test the device in its actual operating environment. There are a number of different tradeoffs that must be considered when configuring an antenna measurement system to test antennas with integrated sources or transceiver based products. This paper will discuss the tradeoffs available in the antenna measurement system design for a test range that can measure antennas with integrated sources. Several antenna test ranges will be presented and the advantages and disadvantages of each configuration will be discussed.
We describe a technique which employs amplitude-only measurements of an unknown antenna combined with a synthetic reference wave to produce a hologram of a near-field antenna distribution. The hologram, which may be recorded by amplitude-only receiving equipment, is digitally processed using an enhanced theory which allows complete removal of the spurious images normally encountered with optical hologram reconstruction. The recovered near-field data are then processed using standard algorithms to calculate antenna far-fields. We present the theoretical formulation and results of measurements obtained on an 1.2 m reflector antenna.
Use of a compact range for testing high power antennas is generally limited to testing the antennas at low power levels. In most cases, this is adequate, but for antennas where the management and dissipation of power is a key test parameter, the antenna and transmitter must be tested at the design power level. If this testing is to be performed in a compact range, it is important that the energy be captured and safely dissipated because allowing the energy to be incident on the absorber could result in destruction of the facility. The chamber under construction for Hollandse Signaalapparaten in Hengelo, Netherlands is designed to receive this energy in a specific region of air cooled absorber and to dissipate the heat into the chamber as an added load on the HVAC system.
This paper addresses some of the practical considerations and numerical consequences of using the Advanced Antenna Pattern Comparison (AAPC) method to improve the accuracy of antenna measurements in compact ranges. Two main issues are of particular importance: 1. Appropriateness of circle-fitting algorithm results to the measured data. 2. Ambiguous circles due to the crowding of data. These issues deal specifically with Kasa’s circle-fitting procedure—an essential part of the AAPC method—and provides useful checks for conditions commonly met with the use of this technique. In addition, we consider the problem of data distribution along the fitted circle, another important element of the AAPC method. Simulation results are submitted in support of the proposed methods.