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A bicone telemetry and command antenna is a stack of two physical antennas with toroidal patterns which have radiation patterns which are omnidirectional in the azimuth plane, perpendicular to the transfer orbit spin axis of the satellite, but are directional in the elevation plane. Each of the two physical antennas,, which operate at different frequencies and polarizations to avoid feedback, has two independent RF inputs (for redundancy) making it actually a four antenna configuration. Each physical antenna consists of three components, which are the feed input section with dual RF inputs, a circular polarizer and a radiation structure comprised of slots, in the circumference waveguide structure, which feed the circumferential conical horn necessary to obtain the required directivity in the elevation plane. The procedures and the problems encountered in constructing and testing each of these parts, as well as the components necessary to permit their testing as independent units is discussed. Because of the broad radiation patterns which characterized these omnidirectional C-Band and K-Band antennas, special consideration had to be given to the measurement of the antenna patterns. These problems and their solutions are highlighted in the paper.
Prior to 1965, there were no geostationary communications satellites. But since the success of Early Bird (INTELSAT I), in 1965, an explosion has occurred in the number of communication satellite (communication channels) in the geostationary orbit (GSO). Because of this increase of satellites in the fixed satellite service (FSS), coupled with the even greater demand for the more desirable positions above land masses and additional channels in the 4/6 GHz band, the FCC and CCIR are attempting by every possible means to increase the number of satellites and channels available. Interchannel interference, of course, must not be increased. Besides enlarging the frequency spectrum available, the use of orthogonal polarizations and closer inter-satellite spacings are under consideration as a means of increasing channel capacity. In 1981, the FCC proposed a decrease from 4 degrees to 2 degrees spacing for satellites operating at 4/6 GHz in the FSS. While many current users prefer larger "close" spacings (2.5 to 3 degrees), 2 degrees will probably become the required inter-satellite spacing for the FSS and is the currently accepted antenna design requirement. When satellites are more closely spaced, their ground terminal antennas must not only have narrow main beams but must also have very low side lobe levels to avoid interference with adjacent satellites. The CCIR has established a new reference pattern, 29-25*log(phi) (ref. CCIR Recommendation 465-1), shown as the overlay in Figure 5. Ground terminal antennas with a diameter to wavelength ratio greater than 100 must comply. This study set out to determine whether this specification could be applied to a carefully designed antenna with a diameter to wavelength ratio as low as 50, 3.5m for the 4/6 GHz band. The future market for such an antenna would be in a low cost earth terminal (LCET) intended for the 'smaller users', who require rapid, reliable communications. The small users may lease channels until the time when their increase in data transmission requirements and the decrease in the cost of earth terminals justifies acquiring their own small earth terminal.
The calibration of gain standards for antenna measurements requires path loss measurements between three antennas if the assumption of identical antennas is not made. The equipment finds the insertion loss for pairs of antennas as if the combination of the antennas and the free space between them were a two port network. The usual setup uses a network analyzer to measure the insertion loss. The Scientific Atlanta 2020 system can be operated as a network analyzer and used for these measurements. Part of the system is a synthesized signal source which allows frequency stepping, and along with leveling, enables the repetition of both amplitude and phase of the signals. The computer control of the equipment provides for rapid stepping through the frequencies, control of the receiver, ability to read amplitude and phase, and means of data storage for off-line analysis.
A method is presented for making fast multi-frequency high accuracy polarization measurements using a digital computer. This paper will provide a brief review of the IEEE standard polarization definitions, their applicability to the three antenna method, and finally a fast two antenna method. [1] The fast two antenna method uses a dual polarized orthomode sampling antenna along with a standard antenna whose polarization is known. The dual polarized sampling antenna is calibrated before the test data is acquired using the polarization standard in two different orientations 90 degrees apart. Once the calibration data is acquired the dual polarized orthomode antenna is used as a sampling antenna for the AUT. Since the sampling antenna is dual polarized the AUT polarization data can be obtained rapidly for many frequencies since neither antenna is required to rotate. This method has been used to acquire polarization data for over 500 frequencies in less than 20 seconds.
An automated antenna measurement system using the HP8510 is described. The system controls the HP8510, associated signal source, and antenna positioner, to provide a fully integrated, automated test facility. Automation speeds and enhances testing by implementing the following features: - Multiple frequency pattern measurements in a single cut of the pedestal. - Patterns with rotating linear polarization - Automatic pedestal control - Storage and presentation of fully documented test data. - Storage and recall of test routines These features complement the premier microwave receiver available today, the HP8510 which offers: - Continuous frequency coverage from .045 to 26.5 GHz - Unparalleled measurement accuracy - 80 dB dynamic range - Time domain gating These features are integrated through software developed using modern software management techniques to form a system which is state of the art in measurement performance, operator interface, and software life cycle supportability.
Near-field testing was conducted on the 30 GHz TRW proof-of-concept (POC) Multibeam Antenna (MBA). The TRW POC MBA is a dual offset cassegrain reflector system using a 2.7 m main reflector. This configuration was selected to assess the ability to create both multiple fixed and scanned spot beams. The POC configuration investigated frequency reuse via spatial separation of beams, polarization selectivity and time division multiple access scanning at 30 GHz.
Near field ranges have been used extensively to measure antenna parameters. These ranges have been shown to be very accurate for measuring absolute gain, polarization, and gain patterns. Most antennas are intended to be used with a receiver, a transmitter, or both. In many cases, it is important to characterize the antenna and active electronics as a system.
Flam & Russell, Inc. has developed a short pulse radar cross section measurement system (Model 8101) which operates from VHF up to L band. This paper describes operation of the system, with emphasis given to the design considerations necessary to minimize susceptibility to a number of problems that have imposed serious limitations on achievable sensitivity at lower frequencies in pulsed RCS outdoor measurement systems. These problems have been, to a great extent, solved in the current system design. The system has been designed for use in outdoor range facilities with a variety of target sizes. A w ideband, high power transmitter is capable of producing pulses 50-350 nanoseconds wide at peak levels of up to several kilowatts. A phase coherent wide bandwidth receiver provides amplitude and phase information at video for sampling. A maximum of four independently located range gates may be selected and set with a resolution of one nanosecond. The data collection system features a three-tier processor structure for dedicated position data processing, target data processing, and system I/O and control, respectively. A real time display of RCS versus position coordinate is available to the operator, as well as a real time indication of the presence of radio frequency interference (RFI). A 60 foot reflector antenna equipped with a duo polarized feed provides full scattering matrix capability with 30 dB of polarization isolation and better than 50 dB of "ghost" suppression. Careful antenna structure and transmission line design has eliminated reverberation or "pulse ringing" problems. A radar "figure of merit" (ratio of peak transmitted power to receiver noise floor for the required pulse bandwidth) of better than 150 dB has been achieved.
The advent of improved compact ranges has promoted the development of a test body, named the almond, to facilitate the measurement of scattered fields from surface mounted structures. A test body should at least have the following three features: (1) provide a very small return itself over a large angular sector, (2) provide an uncorrupted and uniform field in the vicinity of the mounted structure and (3) have the capability to be connected to a low cross-section mount. The almond satisfies the first two requirements by shaping a smooth surface which is continuous in curvature except at its tip. The name almond is derived from its surface similarity to the almond nut. The surface shaping provides an angular sector where there is no specular component. Hence, only low level tip and creeping wave scattering mechanisms are present resulting in a large angular quiet zone. The third requirement is accomplished by properly mounting the almond to a low cross-section ogival pedestal. The mount entails a metal column between the almond and the pedestal covered with shaped absorbing foam. These contoured pieces hide the column and form a blended transition from the almond to the pedestal and yet allow an unobstructed rotation of the almond. Backscatter pattern and swept frequency measurements performed in our compact range illustrate the scattering performance of the almond as a test body. The almond body alone has a backscatter level of -55 dB/m(squared) in its quiet zone. Comparisons of measured hemisphere backscattered returns on the almond are made with those calculated of a hemisphere over an finite ground plane for both principal polarizations for a verification performance test. * This work was supported in part by the National Aeronautics and Space Administration Langley Research Center, Hampton, Virginia under Grant NSG 1613 with the Ohio State University Research Foundation.
The paper describes a simple feed horn designed to illuminate an antenna test range used to measure broad bandwidth antenna patterns with rotating linear polarization. Principal requirements of the feed are equal E and H plane beamwidths with minimal sidelobes in all planes. These characteristics are required to avoid undesirable pattern modulation caused by varying specular scatter and unequal beamwidth vs rotation angle. A survey of pyramidal, conical, and diagonal feed horn patterns revealed that each configuration has high sidelobes in at least one plane making it undesirable for the intended application. Both the pyramidal and conical horns have high side lobes in the E plane. The diagonal horn has very good sidelobe characteristics in the principal planes, but has 13 to 16 dB sidelobes in the diagonal plane.
In this paper we present a three-antenna measurement procedure which yields the polarization of an unknown antenna to an accuracy comparable to that of the improved method of Newell. The complete method is based on step-scan motion of the two polarization axes on which the antenna pairs are mounted. As a special case this step-scan procedure includes the usual single axis polarization pattern method of polarization measurement. This three antenna polarization measurement method can be readily automated and is carried out straightforwardly with the assistance of a minicomputer for data acquisition and data reduction. The data reduction method is based on conventional digital Fourier transform techniques and has the advantage of inherent noise rejection. It utilizes a large number of sample points which greatly overdetermine the parameters to be measured. The method has been verified experimentally with measurements made on multiple overlapping sets of three antennas, as is conventional for this kind of procedure. The data are presented for broad-beam antennas of the type used as near field probe horns.
This paper briefly discusses the calibration techniques used in the Sandia National Laboratories Radar Cross-Section Test Range (SCATTER). We begin with a discussion of RCS calibration in general and progress to a description of how the range, electronics, and design requirements impacted and were impacted by system calibration. Discussions of calibration of the electronic signal path, the range reference used in the system, and target calibration in parallel and cross-polarization modes follow. We conclude with a discussion of ongoing efforts to improve calibration quality and operational efficiency. For an overview description of the SCATTER facility, the reader is referred to the article Sandia SCATTER Facility, also in this publication.
The RF characteristics of a four-element diagonal array configured to yield low sidelobes, dual circular polarization with low axial ratio and high front-to-back ratio are described. The array was designed for use as source antenna in a VHF test range, where the test antenna is nearly omnidirectional and ground multipath effects are a major problem. To achieve broadband performance, crossed open-sleeve dipoles were used as array elements. The array is capable of operation over a 1.66:1 band with a VSWR of <2:1. Experimental studies were made by means of scale model antennas in the 240 to 400 MHz band. The axial ratio is <1 dB, and the sidelobe/backlobe levels vary from –25 dB to –30 dB over the measurement frequency range.
The design of a multipurpose Antenna/RCS range at GTRI is described. A novel approach to design of the far-field antenna range utilizes the bottom 40-foot section of a 130-foot windmill tower. The top 90-foot section is used as the main support for a slant RCS measurement range offering a maximum depression angle of 32º. A 100-tom capacity turntable, capable of rotating an M1 Tank, is located 150 feet from the 90-foot tower. The rigidity and stability of the tower should allow accurate phase measurement at 95 GHz for wind speeds up to 10 mph. In addition, a 500-foot scale-model range uses the ground plane effect to enhance target signal-to-noise and is designed to be useful at frequencies up to 18 GHz. Initially, the radar instrumentation to be utilized with the ranges includes several modular instrumentation systems and associated digital data acquisition equipment at frequency bands including C, X, Ku, Ka, and 95 GHz. The properties of these systems, which include coherence, frequency agility, and dual polarization, are discussed.
A dual offset shaped reflector compact range is described. Improvements over the traditional single reflector, apex-fed compact range are outlined and discussed. A design plan for a dual offset shaped reflector compact range for EHF antenna measurement is presented.
Millimeter wave antenna measurements are hampered by a lack of cost effective automated test equipment and the necessity of using unwieldy waveguide set-ups. This paper describes some practical considerations in using readily available test equipment to perform accurate, repeatable antenna measurements. Experimental results of gain, polarization and sidelobe level measurements will be discussed and compared with calculated results.
This paper describes the equipment, mechanics and methods of one of the outdoor ranges at Teledyne Micronetics. A computer controlled microwave transceiver uses pulsed CW over a frequency range of 2-18 GHz to measure the amplitude, phase and polarization of the signal reflected off the target. The range geometry, calibration and analysis techniques are used to optimize measurement accuracy and characterize the target as a set of subscatterers.
This paper describes the relationship of probe polarization correction to probe-pattern corrected and non-probe-pattern-corrected spherical near-field measurements. A method for reducing three-antenna polarization data to a form useful for polarization correction is presented. The results of three-antenna measurements and the effects of polarization correction on spherical near-field measurements are presented.
The purpose of an instrumentation radar is to characterize the Radar Cross Section (RCS) of a target as a function of target aspect and radar frequency. In addition, an instrumentation radar may be used to produce a high resolution radar image of a target which is useful in target identification work and as a diagnostic tool in radar cross section reduction. These purposes differ from those of a conventional radar, in which the objective is to detect the presence of a target and to measure the range to the target. Several different radars are currently used to perform radar cross section measurements. Common instrumentation radars may be classified as CW, Pulsed CW (Low-Bandwidth IF), Linear FM (FM-CW), Pulsed (High-Bandwidth IF) and Short Pulse (Very High-Bandwidth IF). These radars accomplish the measurement task in distinct manners, and it is sometimes difficult to determine where the strength or weakness of each radar lies. In this paper, a set of performance criteria is proposed for RCS measurements. The proposed criteria can be applied uniformly to any instrumentation radar independent of the type of radar design employed. The criteria are chosen to emphasize those performance characteristics that relate directly to RCS measurements and thus are most important to the user. Two instrumentation radars which have been designed at Scientific Atlanta, namely the Series 2084 (Linear FM) and the Series 1790 (Pulse), are used to illustrate the application of the performance criteria.
End-to-end testing of electronic warfare (EW) equipment at the organizational or flight lines level is accomplished by use of an antenna coupler which is placed over the EW system antenna. The coupler is used to inject a stimulus signal simulating a signal emanating from a distant radar, and to receive and detect the EW system response (EW transmit) signal. The coupler is used to determine the EW receiver sensitivity over a swept frequency coverage and the EW transmit gain and effective radiated power (ERP) versus frequency characteristics, as well as to determine the operating integrity of the EW antenna and transmission lines.