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A procedure to design blended rolled edges for arbitrary rim shape compact range reflectors is presented. The reflector may be center-fed or offset-fed. The design procedure leads to continuous and smooth rolled edges and ensures small diffracted field from the junction between the paraboloid and the rolled edge. The performance of a compact range reflector designed using the prescribed procedure is also presented.
Over the years formulations have been developed which provide an implicit measure of transfer efficiency of the compact range. Reasonable accuracy has been demonstrated for both antenna and RCS measurement applications. In general, however, these formulations require specific design details pertaining to the collimating reflector. In this note a more general formulation is examined in which efficiency is explicitly expressed in terms familiar to antenna engineers and which do not directly involve reflector parameters. Applications of this formulation are presented.
The radar cross section of large targets has previously been measured on large outdoor far field ranges. Due to environmental and security limitations of outdoor ranges, low cost indoor compact ranges are preferred. To optimize compact range performance and to minimize size, careful attention must be paid to the design of feeds which are required for the proper illumination of the reflector. This paper describes a new polarization diversified parasitic multimode/corrugated (PMC) feed for a compact range reflector. The performance attributes of the PMC feed are presented. The PMC feed provides several advantages over other known commercially available compact range feeds.
This paper describes how corrugated feed horns are designed for compact ranges with tight pattern control. Both the amplitude and phase of the horn pattern must be invariant over a wide frequency band. A horn synthesis computer program has been developed using the JPL HYBRIDHORN computer program as the analysis module which is driven by a Harris developed synthesis code (OPTDES). This paper also discusses launching techniques used to generate the HE(11) hybrid mode in the corrugated horn as well as design methods to eliminate ringing effects observed in both the input waveguide circuits and corrugated horns when used for RCS measurements.
The design, fabrication, and testing of a high directivity, constant beamwidth feed horn is presented in this paper. The subject feed horn is designed to illuminate a shaped reflector compact range operating from 140 to 170 GHz. Design considerations related to pattern control and VSWR are discussed. Fabrication challenges are also considered. Primary pattern test results are presented and compared to predictions. Integration (into the reflector system) considerations are reviewed and quiet zone performance is discussed.
The development of a small compact range facility that has been integrated into an existing laboratory space is described. This facility uses a commercially available offset reflector with a 6 ft projected diameter and has sufficiently precise construction for operation at EHF frequencies. The edge diffraction degradation of the quiet zone is controlled by reducing the reflector edge illumination rather than using a complex edge treatment or a dual reflector design. Measured values of the quiet zone fields compare very well with calculated values. The facility can be used to measure antennas and radar targets whose dimensions do not exceed 20 in at high microwave and millimeter-wave frequencies. The low cost and simplicity of this compact range design are key features.
The utility of absorber-lined tunnels to control the sidelobe levels of horns has previously been demonstrated. The use of such a tunnel gives the designer the option of designing a broadband feed, for example, and later tailoring the sidelobe level to meet a given specification. In this paper, a technique for calculating the radiation characteristics of a horn in an absorber-lined tunnel will be presented. The analysis is based on an absorbing phase screen approximation which has been used by one of the authors in analyzing the diffraction of signals around rocket plumes. Propagation through the tunnel is treated as if the wave travels through a sequence of layers in which the absorption depends on the transverse coordinates. The absorbing phase screen model will be developed, and then applied to the analysis of a Narda standard gain horn in a square tunnel which is lined with wedge absorbing material. For the determination of E and H-plane pattern cuts, a two dimensional model can be utilized. In order to determine the radiation pattern over the full range of theta and phi as is required for illuminating a reflector, a three dimensional model is needed. All calculations were implemented in Fortran on an IBM personal computer.
The development of the Harris 1640 compact range required significant technical advances in developing a method of constructing a 70 foot reflector to a 0.005 inch RMS operational surface accuracy. A panelized approach is believed to be the only practical way to achieve this level of accuracy. Four technology areas had to be developed, adapted to this use, or have their current limits extended. A method was required for reducing the RF shaping data to individual panel contours. The reflector has no axis of symmetry thus each panel has a unique contour and the description of each contour requires complex mathematical interpolation. A new fabrication technique was needed to produce 0.002 inch RMS panels. Positioning and initially aligning the panels would require the adaptation of multiple theodolite techniques. The final setting of the panels would then require the use of a photogrammetric measurement system, the most accurate method available.
When Harris first undertook to produce large compact ranges made up of multiple panels, a significant capability to be developed was the production of precision panels (< 0.002 inch RMS). Sandwich construction was chosen as the fabrication technique due to its excellent stiffness to weight ratio and the ability to support the reflective skin over its entire surface. A number of studies were then conducted to determine the optimum skin thickness, honeycomb core thickness and the number of adjustment points. An adjustable bonding fixture was also designed to accommodate the shaped reflector characteristic of each panel having a different shape. The results of those studies provided a fabrication process that has yielded 0.001 inch RMS panels. The process and the monitoring guidelines have yielded 224 acceptable panels of 225 fabricated to date.
A variety of positioner control systems are available for making antenna and RCS measurements, but few can be upgraded economically as test facilities are expanded. Positioner control system components may include a controller, positioner motor drive unit, and a position indicator. Integration of these functional components into a single modular unit to operate the desired number of axes provides the basis for a positioner control system. Other desired features may include programmability, remotability, operation outdoors, and expansion capability. This paper will address the development of a modular positioner control system that can economically be upgraded as changing test requirements dictate. Functional capabilities such as remotability, expansion capability, and programmability will be highlighted. System configuration and integration will also be discussed.
The capabilities of micro computer systems have jumped dramatically in the last few years; their performance now rivals that of mini computers, which have traditionally been used for acquiring and processing antenna measurement data. This paper discusses the significant advantages of using new-generation micro computers for antenna data processing, and provides specific, practical examples of how to use advanced features to process antenna measurement data efficiently.
A far-field antenna range has been assembled on the roof of the Electrical Engineering building at Virginia Tech. Antenna radiation patterns and polarization patterns can be measured. The system consists of two Scientific-Atlanta azimuth positioners, a Scientific-Atlanta 1711 receiver, a Scientific-Atlanta 1832A amplitude display unit, a DC motor controller, a synchro-to-digital converter, an IBM PC, and signal sources. The DC motor controller has been interfaced to the PC along with the synchro-to-digital converter, forming a closed loop positioning control system that can be used with either of the azimuth positioners. One of the positioners is used for the antenna under test while the other positioner controls the polarization of the transmit antenna. The receiver and amplitude display provide a 60 dB dynamic range for antenna measurements. The PC has been programmed in TURBO Pascal to control the antenna positioner, record antenna patterns, store pattern data on disk, and provide antenna pattern plots. This modular approach provides permanent storage on PC disk of all measurements as well as allowing many plot combinations including linear or logarithmic form and rectangular or polar format.
Precision measurements of antenna gain to accuracies of 0.1-0.2 dB is usually a rather challenging task. A major limitation at microwave frequencies around 10 GHz and higher is the difficulty in achieving the high stability of the antenna measurement system for such precision. An alternative approach for measuring antenna gain is to measure the backscatter cross section of the antenna. Historically, very few antenna gain measurements have been reported that use the backscatter approach. A new method is presented here for implementing the backscatter approach.
This paper reports on a project carried out at Georgia Tech to reduce forward scattering from the top edge of far-field range diffraction fences over a wide frequency band. It is shown that the addition of serrations with length greater than ten wavelengths and a flower petal shape reduce the stray radiation in the quiet zone by as much as 10 dB. Several variations on the basic shape are investigated and computed results are shown.
This paper first presents an overview of the types of errors present in phase length measurements. Next, a minimum-error test method is formulated. The first test results using the test method are included, demonstrating accuracies on the order of plus-or-minus 3 electrical degrees at 18 GHz. Measurement time using currently available ANAs is accomplished in less than 1/2 minute when run in the reflective, time-domain mode.
The National Bureau of Standards (NBS) has been measuring antennas and dealing with the problems of leakage for the past twenty years. This paper will discuss the various methods of detecting leakage, typical sources of leakage, how to correct leakage problems, and the effects that leakage can have on calibration.
The Systems and Techniques Laboratory (STL) of the Georgia Tech Research Institute is upgrading their measurement capabilities by developing a planar nearfield range. The new range incorporates a Microvax Workstation II, an Hewlett Packard 8510B, and an automated planar scanner designed and developed by STL. The scanner is automated using an IBM compatible personal computer while Microvax serves as system controller on the IEEE 488 bus which interconnects the system.
The Systems and Techniques Laboratory of the Georgia Tech Research Institute is producing a PC-controlled near-field planar scan system which will allow phase measurements more accurate than one degree at 10 GHz in a 10 foot by 12 foot plane. This high degree of accuracy will be accomplished with microstep motors, absolute linear encoders, and a helium neon laser compensator. The probe positioning system consists of a tower traveling across a set of linear rails. A probe moves vertically on the tower, allowing operator pre-described measurements to be taken. The system is designed to accept data as the probe moves vertically, then indexed horizontally for complete plane coverage.
For the past two years the National Bureau of Standards (NBS) has been developing the capability to perform on-axis gain and polarization measurements at millimeter wave frequencies from 33-65 GHz. This paper discusses the error analysis of antenna measurements at these frequencies. The largest source of error is insertion loss measurements. In order to make accurate insertion loss measurements, flanges on antennas need to be flat and perpendicular to the waveguide axis to within approximately 0.001 cm (0.0005 in). In addition, waveguide screws need to be tightened with a device that supplies constant torque. For antennas with gains less than about 25-30 dB (probes) we can measure on-axis gains within an uncertainty of 0.14 dB in the 33-50 GHz frequency band and within 0.16 dB in the 55-65 GHz frequency band using the three-antenna technique on the extrapolation range. For antennas with larger gains we can measure on-axis gains within an uncertainty of 0.21 dB in the 33-50 GHz frequency band and within 0.24 dB in the 55-65 GHz band using the planar near-field technique. NBS in continuing development of its measurement capabilities, including measuring probe correction coefficients required in planar near-field processing, in order to provide accurate pattern measurements at these frequencies.
While near field antenna test techniques are well understood, published methods for high volume testing are rare. This paper addresses special requirements for production testing of satellites at the Hughes Aircraft Company Space and Communications Group facility in El Segundo, California. The El Segundo facility has the capability of testing antennas which employ multiple beams and polarization isolation for frequency spectrum reuse. It is required that the measurement techniques and equipment be able to test this type of antenna during a single traverse of the planar near field scanner. Serious demands are placed on the system to meet these requirements: * Maximum dynamic range and linearity must be maintained in an environment of rapidly shifting signal levels. * Isolation of signals must be maintained while allowing rapid switching for beam and polarization sampling. * Equipment settling time must be minimized to maintain scan rate at the highest possible speed. * RF interfaces must be repeatable, and capable of rapid reconfiguration. * Calibration and system checkout techniques must be accurate, quick, and capable of detecting malfunctions and costly setup errors. * Data transfer and processing must not be a limitation to the availability of the system for measurement. * System growth capability must be maintained, but not allowed to interfere with 'old and valued' customers. Some of the trades and pitfalls in meeting these requirements will also be presented.