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An investigation of the use of array mutual coupling measurements, to evaluate displaced phase center antenna (DPCA) performance, is made. The details of a subscale space based radar (SBR) DPCA phased array and the array mutual coupling technique are discussed. DPCA results are quantified experimentally under a number of test conditions. It is shown that the test array beam decorrelation computed from array mutual coupling data, is in good agreement with both theoretical predictions, planar near field measurements and direct far field measurements.
For many years, rain impact and erosion failures to aircraft radomes have been a recurring problem. Impingement upon rain droplets by aircraft traveling at velocities of 300 mph, or greater, may be destructful to radomes and jeopardize the function of associated antennas, unless sufficient rain erosion resistant materials are employed in the construction. Changes to the surface of a radome due to rain erosion, such as porosity and structural failure, will affect electrical performance. Other material properties that must be considered besides rain erosion are dielectric constant and lost tangent.
It is often desirable to measure antenna impedance during an operational state. In applications such as experimental studies of ionospheric properties it is desirable to determine the instantaneous impedance. Most applications will involve adaptive tuning such as in antenna filter or multicoupler systems to maintain resonance despite other operations being conducted on the system. Adaptive tuning of HF whip antennas will provide compensation for environmental conditions such as ice load, or proximity to various objects. In cases where the antenna, or its surrounding, is affected by the power level, it is also desirable to measure the impedance over the power range as well as frequency. Two methods of determining impedances will be discussed in this paper. The first method is that of voltage and current probes and the second that of directional couplers for measuring forward and reflected waves.
This paper presents results of an on-going research program at Georgia Tech into the theory and technique of antenna measurements. Specifically this paper presents the results of an investigation into sampling requirements for electromagnetic measurements performed on a surface enclosing an antenna under test (AUT).
Lessons learned in the design of large, planar near field ranges used at millimeter wavelengths are described. Specific issues include facility design, RF equipment, scanner design, dynamic position measurement, servo control and software requirements.
This paper describes the Harris Corporation, Broadcast Group, Outdoor, Cylindrical, Near-Field Antenna Range. The range is located on a bluff overlooking the Mississippi River flood plain near Quincy. IL and is used for the alignment and testing of UHF-TV transmitting antennas.
During the last year ERICSSON RADIO SYSTEMS in Moelndal, Sweden, has had a near-field test facility in operation in a clean-room environment. It was been used for spherical near-field testing but during the next year a large planar scanner will be installed in the room.
The Electromagnetic Engineering Section of the National Research Council of Canada maintains a variety of pattern ranges and associated instrumentation to serve the needs of Canadian industry, government departments and universities. An extensive review of the facilities in 1983 revealed the need for significant modifications to maintain the current state-of-the-art level in antenna measurement technology.
A number of analytical efforts, but relatively fewer experimental results, have been published on the effects of rain on radome losses at microwave frequencies (1-9). Further, the development of analytical models becomes more difficult as the development of “hydrophobic” (non-wetting) surfaces progresses, because the effect to be modeled becomes increasingly random and statistical.
This paper presents some current measurement results obtained as part of a research program to investigate the theory, technique, apparatus and practicality of monostatic near-field radar cross-section measurement (MNFRCSM).
Review of a computational technique used in the design of anechoic chambers is presented. Details of an interactive computer program to predict fields inside anechoic chambers are discussed. Use of the program in (a) computing change in field distribution due to reflections from the walls of the chamber and (b) optimizing cost/performance ratio of the chambers is illusterated.
A great deal of effort has gone into the optimum design of anechoic chambers over the years, however little attention is generally given to the choice of the source antenna used to illuminate these chambers. Typically, any antenna which operates at the desired frequency and that happens to be available in the antenna laboratory is commandeered for us as a source.
A method for calibrating an automated network analyzer for antenna impedance measurements through a long interconnecting transmission line is developed. The transmission line is non-precision and of nominal characteristic impedance, loss, and dispersion
Modern fighter aircraft carry dozens of transmitting and receiving antennas for purposes of electronic countermeasures (ECM), communications, threat warning, fire control, navigation, etc. As new antenna systems are added or changed, it is important to measure the intersystem and intrasystem antenna coupling (or isolation) to insure compatibility and effectiveness of onboard systems.
The matrix of scattering coefficients which describes the transfer of excitation between the port of an antenna and free space forms a fundamental description of that antenna. In carrying out the spherical near-field to far-field transforms for a probe-corrected measurement one is required to utilize the scattering coefficients of the probe antenna. An essential feature of any software system which supports probe-corrected measurements is the capability of analyzing and storing these coefficients.
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.
Two alternative sampling techniques for planar near-field measurements are discussed. The first technique reduces the number of data points taken by 50% by measuring the field and its differential in one direction at each point. The second technique samples the field on a hexagonal lattice and allows reduction in the number of samples taken by up to 25%. Far-field patterns for an X-band antenna calculated from these alternative near-field sampling schemes are presented and compared with the far-field patterns calculated using conventional planar near-field techniques.
Over the long periods of time needed to acquire spherical near-field data, thermal drift of the system can cause errors in the measurement. The effect of thermal-drift can be removed, if it is monitored during the scanning process. This is accomplished by periodically returning the probe to the near-field peak during acquisition. The same point is re-measured upon each return; and the variations in phase and amplitude are used to produce a correction factor which is applied to each point in the near-field data file. This paper describes the return-to-peak method and the correction algorithm. Experimental results will also be presented.
A novel technique for improved accuracy of sidelobe measurement by planar near field probing has been developed and tested on the modified near field scanner at the National Bureau of Standards. The new technique relies on a scanning probe which radiates an azimuth plane null along the test antenna’s mainbeam steering direction. In this way, the probe acts as a mainbeam filter during probe correction processing, and allows the sidelobe space wavenumbers to establish the dynamic range of the near field measurement. In this way, measurement errors which usually increase with decreasing near field signal strength are minimized. The probe also discriminates against error field which have propagation components in the direction of mainbeam steering, such errors may be due to multipath or scanner Z-position tolerances. Near field probing tests will be described which demonstrate measurement accuracies from tests with two slotted waveguide arrays—the Ultralow Sidelobe Array (ULSA) and the Airborne Warning and Control System (AWACS) array. Results show that induced near field measurement error will generate detectable far field sidelobe errors, within established bounds, at the –60dB level. The utility of te probe to detect low level radar target scattering will also be described.
The compact range has been used for many years to measure directive antenna patterns. More recently, however, there has been increased interest to use the compact range for scattering measurements. In order to provide the proper field illumination for such measurements, the traditional designs must be improved in terms of the stray signals coming from the reflector termination. One attempt to improve the field quality in the measurement zone was to use a rolled edge structure added to the basic parabolic reflector. This improved the system performance but required excessively large structures to meet the system requirements. Thus, a novel blended surface was developed which satisfies the measurement requirements without adding large structures. This new design can provide ripple levels no larger that 1/10th of a dB across the target zone as will be shown in the oral presentation.