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This paper discusses the design, fabrication, installation, and testing of a Scientific-Atlanta Model 5702 Compact Range used for radar system testing. The unique feature of this compact range is that it provides a plane wave target source for automated closed loop radar system testing. Techniques employed for meeting and verifying stringent specifications such as phase and amplitude gradients over the quiet zone are discussed. Results from closed loop testing of radar systems in the compact range are also presented.
The Wright Laboratory at WPAFB, OH, operates an advanced compact range facility (ACRF) for RCS measurements. The ACRF employs a dual chamber compact range system to generate a plane wave in the target zone. The main reflector, which is a blended rolled edge paraboloid, is housed in the main chamber; whereas, the feed assembly and the subreflector, which is a serrated edge ellipsoid, is housed in the sub chamber. The two chambers are electromagnetically coupled through a small opening near the focal point of the main reflector. The compact range system was originally designed to perform RCS measurements at frequencies above 1 GHz. Recently, there has been some interest in us ing the ACRF to perform RCS measurements at lower frequencies, from 100-1000 MHz. In fact, the ACRF facility has been successfully used to measure small targets at these lower frequencies, but one would like the target zone to be as large as possible. In order to accommodate a larger target zone, the first step was to evaluate the performance of the ACRF at lower frequencies. The performance evaluation revealed that the subreflector edge diffraction was leaking through the coupling aperture into the target zone. Some feed spillover was also observed in the target zone. To control these stray signals in the target zone, an absorber fence was designed for the ACRF. The absorber fence sits near the focal point of the main reflector. A prototype absorber fence has been built and installed in the ACRF. The performance of this absorber fence is discussed in terms of the improvement in the target zone fields.
Recently, we designed two doubly periodic curved pyramidal absorbers using Rantec absorber material. One of the pyramidal absorbers is 4011 high and is designed to operate at frequencies as low as 300 MHz; whereas the second pyramidal absorber is 6011 high and is designed to operate at frequencies as low as 200 MHz. The design goal was to achieve at least 45 dB attenuation for normal incidence. Based on our design, Rantec built the new pyramidal absorbers. The back-scattered fields of the new pyramidal ab sorbers were measured in the Wright Laboratories' (WL) advanced compact range facility (ACRF) us ing a 12' x 12' panel. In this paper, the measured data is presented and compared with the theoretical predictions. For reference, the scattered fields of a 72" pyramidal absorber are also included. The 72" pyramidal absorber was built by Ray Proof.
Sanders, A Lockheed Martin Company, measures radar cross section (RCS) and antenna performance from 2 to 18 GHz at the Com pany's Compact Range. Twelve feed horns are used to maintain a constant beam width and stationary phase centers, with proper gain. However, calibration with each movement of the feed tower is required and the feed tower is a source of range clutter. To Improve data quality and quantity, Sanders and The Ohio State University ElectroScience Laboratory designed, fabricated, and tested a new wide band feed. The design requirement for the feed was to maintain a constant beam width and phase taper across the 2 - 18 GHz band. The approach taken was to modify the design of the Ohio State University's wide band feed [1]. This feed provides a much cleaner range which reduces the dependence on subtraction and other data manipulation techniques. The new feed allows for wide band images with increased resolution and a six fold increase in range productivity (or reduction in range costs). This paper discusses this new feed and design details with the unique fabrication techniques developed by Ohio State and its suppliers. Analysis and patterns measured from the feed characterization are presented as well. This paper closes with a discussion of options for further improvements in the feed.
A new edge treatment approach using resistive cards (R-cards) for compact range reflectors is introduced in this paper. This new treatment has proven to be successful in achieving the design goal of reducing the diffracted fields from the reflector edges in the quiet zone. The design key of this new treatment relies on the proper choice of both the resistance distribution and placement of the R-cards in front of the reflector edge. Preliminary analysis and design studies show the potential of this new treatment in reducing the ripple level in the target zone over a wide range of frequencies. The simplicity, flexibility and the low cost of this new approach provide a viable alternative approach to the other edge treatments, such as serrated or blended rolled edges.
Leader in the field of space environment simulation (vibrations, thermal vacuum, acoustics, EMC), INTESPACE company has built a new compact range for antenna measurement called MISTRAL with a view to providing an overall satellite test service. The purpose of this new full-scale test facility is to determine the radioelectric characteristics of integrated satellite antennas covering : - classic antenna tests such as radiation pattern and gain measurement, - payload-specific end-to-end tests such as EIRP, SFD, GIT, Gain/Frequency, etc. The aim of this paper is : - first, to present the main and extra features of the MISTRAL compact range, - second, to show the major improvements and system optimization achieved through the study and development phases of MISTRAL, - third, to present the results of the intensive acceptance tests (quiet zones probing and antennas measurements) confirming the high quality of the test facility.
Scientific-Atlanta has recently begun work on a large 55 ft.(W) x 45 ft.(H) compact range reflector. The reflector is a Model 5738 with a 45 ft. focal length and a 38 ft. diameter by 38 ft. long cylindrical quiet zone. Due to the large size of the reflector, it is necessary to form the surface as several large, independent sections and assemble and align the reflector at the installation site. The 5738 reflector is shown in Figure 1 with the 38 ft. quiet zone superimposed. Figu re 1. Front View of 5738 Reflector Showing Sections The independent and predictable behavior of large sections proves to be very beneficial for performing an electrical alignment of the reflector based on field probe phase data. This paper discusses the required alignment tolerances and analytic tools developed to predict the effects on quite zone performance due to alignment errors in the sections of the reflector.
The measurement of the characteristic antenna data by means of conventional far-field ranges in frequencies up to 200 GHz requires measurement distances of some kilometers. The high atmospherical attenuation and the low available transmit power limit the dynamic range of the measurements considerably. The DASA Compensated Compact Range (CCR) /1/ is a high precision test facility; which avoids these disadvantages and allow measurements with considerably higher accuracy under controlled environmental conditions. The precision reflectors have an extremely high surface accuracy of 25 µm RMS, which allow their use even in the mm-wave range. For the frequency band of about 200 GHz, the relative roughness is in the order of N/60. This results in considerably lower degradation for the DASA CCR compared to the typical degradation on far-field ranges (N/16). For mm-wave application the test facility is equipped with broadband transmit and receive moduls, which covers the frequency range from 75 to 220 GHz. The basic transmit frequency is generated in a tunable Gunn oscillator, which is phaselocked to an externally supplied I 0 MHz reference signal. This optimized concept allows measurements with a dynamic range of more than 60 dB at 200 GHz. For a cost efficient solution the complete equipment for the transmit and receive moduls consists of commercial components. Keywords: MM-Wave Antenna Measurement, Compensated Compact Range, MM-Wave Transmit Module Tracking Converter
Recently, we proposed a new method for the testing of antennas or the measurement of RCS in submillimeter wave region. A specific feature of this technique resides in that investigated object or its scaled model is mounted inside a quasi-optical waveguide in the form of a circular hollow dielectric waveguide (HDW) so as to determine the scattering parameter of the waveguide dominant HE11 mode which is certainly related to the wanted RCS of the object under study. In this paper, we intend to theoretically substantiate the proposed method for measuring RCS inside a circular HDW by using geometrical optical ray representation of guided modes and "virtual" waveguide concept. Then, a correspondence between RCS of an object inside a HDW and in a free space is established. Also, RCS of reference objects such as a perfectly conducting square flat plate inside a circular HDW are measured and compared with predicted returns in free space.
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.
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.
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.
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.
Absorbing material can suppress unwanted reflections in a compact range chamber to some extent. The simultaneous use of time-domain filtering (gating) to extract only the desired signal from measurements, serves to improve measurement results. There are two types of time-domain gating, namely software and hardware gating. This paper discusses time-domain filtering performed using hardware gating. The concept of a test zone, as created by the hardware gates in a down-range sense, is introduced. This test zone is explored through measurement as well as through computer simulation of the hardaware gating process.
For indoor antenna measurements, compact ranges or near-field/far-field techniques are most frequently used. One of the major problems is the handling of physically large antennas. Compact ranges will in general provide test-zone sizes up to approximately 5 meters in diameter. Applying the planar NF/FF technique, even larger test-zone sizes can be realized for certain applications. On the other hand, requirement of real-time capability, for instance in production testing, will exclude NF/FF techniques. It has been shown previously that single-plane collimators have a pseudo real-time capability which makes these devices comparable to compact ranges. Furthermore, the physical test-zone sizes which can be realized when compared to compact ranges are approximately 2-3 times larger for the same size of the anechoic chamber. Finally, it will be shown that the accuracy in sidelobe level determination, gain and cross polarization is considerable higher than with other indoor techniques, even at frequencies below 1 GHz.
A fully-polarimetric compact range operating at 160 GHz has been developed for obtaining X-band RCS measurements on 1:16th scale model targets. The transceiver consists of a fast switching, stepped, CW, X-band synthesizer driving dual X16 transmit multiplier chains and dual X16 local oscillator multiplier chains. The system alternately transmits horizontal (H) and vertical (V) radiation while simultaneously receiving H and V. Software range-gating is used to reject unwanted spurious responses in the compact range. A flat disk and a rotating circular dihedral are used for polarimetric as well as RCS calibration. Cross-pol rejection ratios of better than 40 dB are routinely achieved. The compact range reflector consists of a 60” diameter, CNC machined aluminum mirror fed from the side to produce a clean 20” quiet zone. A description of this 160 GHz compact range along with measurement examples are presented in this paper.
A folded compact range configuration has been developed at the Sandia National Laboratories’ compact range antenna and radar-cross-section measurement facility as a means of performing indoor, environmentally-controlled, far-field simulations of synthetic aperture radar (SAR) measurements of distributed target samples (i.e. gravel, sand, etc. ). In particular, the folded compact range configuration has been used to perform both highly sensitive coherent change detection (CCD) measurements and interferometric inverse-synthetic-aperture-radar (IFISAR) measurements, which, in addition to the two-dimensional spatial resolution afforded by typical ISAR processing, provides resolution of the relative height of targets with accuracies on the order of a wavelength. This paper describes the development of the folded compact range, as well as the coherent change detection and interferometric measurements that have been made with the system. The measurements have been very successful, and have demonstrated not only the viability of the folded compact range concept in simulating SAR CCD and interferometric SAR (IFSAR) measurements, but also its usefulness as a tool in the research and development of SAR CCD and IFSAR image generation and measurement methodologies.
In 1993, we presented the newly completed compact range and tapered chamber facility [1]. As part of this presentation, the issue of “range certification” was presented. This paper will discuss the work that we have done with the compact range for radar cross section (RCS) measurement acceptance. For customer acceptance, we had to “prove” that the compact range made acceptable measurements for the fixtures and apertures involved. Schedule and funding did not permit the full exploitation of the uncertainty analysis of the chambers, not was it felt to be necessary [2]. The determination of our range capabilities and accuracy was based on system parameters and target measurements. Targets that were calculable either in closed form solutions (spheres) or by numerical methods (cylinders and rods) were used. Finally, range to range comparisons with the Rye Canyon Facility [3] of a standard target was used. The range to range comparison proved especially difficult due to customer exceptions, feed differences, and target mounting. This paper will discuss the “success” criteria applied, the procedures used, and the results. The paper will close with a discuss of RCS standards and the range certification process.