Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
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.
This paper discusses the configuration and performance of the HP 8510B Network Analyzer for antenna range measurements. Both manual and automated pattern measurements can be performed. The HP 8510B, introduced in May of 1987, adds several key new features to the HP 8510A which improves its performance in antenna test applications. The HP 8510B now supports an external mixer configuration which provides significant improvements in measurement sensitivity. An analog output has been added to the HP 8510 which allows manual antenna measurements to be made conveniently and quickly. A "FAST CW" mode has also been implemented in the HP 8510 which provides automated data acquisition rates in less than one millisecond per measured point.
The AM Broadcast service area depends on the radiation pattern of the antenna employed. The approach used here to compute the service area requires the radiation pattern of the monopole antenna mounted on a perfectly conducting plane earth. The effects of the ionosphere and the finitely conducting earth can then be calculated and the service area determined. The use of the theoretical thin monopole radiation pattern for the determination of the actual service area is not very accurate. The best solution is to use the measured radiation pattern. But due to the large dimensions of the antenna it is more practical to use a scale model for the measurement.
A general theoretical approach is formulated to describe the complex electromagnetic environment of an N-element array. The theory reveals the element-to-element interactions and multiple reflections within the array. To experimentally verify some features of the theory, measurements on experimental array panels in various configurations were made. These array panels consisted of 256 microstrip radiating elements. In each of the configurations both the near-field and portside signals were measured to study the interactions between these panels. In particular, the effects of open-circuited array panels on the radiation pattern of a single panel are observed both in the near field and in the far field. It is found that internal scattering is the main mechanism of interaction between panels, rather than reradiating of signals received from adjacent panels. The effects of scattering are observable at the -50 dB level.
Enhanced accuracy in antenna pattern measurements using the HP-8510 is possible by using a novel calibration procedure. By circumventing antenna dispersion, this procedure leads to better resolution of multipath responses and thus increases the effectiveness of gated measurements. Measured patterns of a dipole antenna are presented to illustrate the effectiveness of this procedure.
This paper addresses two major issues that impact long-range outdoor antenna measurements with the HP 8510 network analyzer: using a radiated reference signal to provide phaselock reference, and using harmonic mixers with a phase locked local oscillator (LO). The measurements were made at microwave frequencies on a 700 ft outdoor antenna range using a reference antenna in antenna test configurations with the HP 8511A frequency converter and with a harmonic mixer configuration using the new HP 8510 "Remote Phaselock" option developed by Hewlett-Packard. In addition to CW antenna patterns, the use of time domain and gating to reduce the effects of ground reflections was investigated. Measurement considerations and results are discussed. The favorable outcome of this investigation is applicable to a broad variety of antenna measurements.
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.
Conventional pattern measurements are difficult to apply when the aperture is very large (250 lambda or more), particularly in the case of a relatively fragile antenna structure intended for a space application. Near field techniques can offer a solution, but may need a relatively large R.F. enclosure and custom instrumentation. This paper examines various alternative approaches in the case of the 15 m planar array under development at CAL for Radarsat. Specifically, the techniques under consideration include planar probing, cylindrical probing, planar cylindrical probing, intermediate range spherical probing, and some special variants. It is shown that the fact that the Radarsat antenna generates shaped beams as opposed to pencil beams impacts the relative accuracies achieved by these techniques to a very significant extent. The data collection and processing time, the size of the anechoic chamber needed, and the instrumentation requirement are also important considerations.
Spar Aerospace, along with other aerospace companies, have experienced an evolution in the development of spacecraft antennas over the past 20 years. Spacecraft antennas originated as either simple antennas providing figure of revolution patterns for spin stabilized communication satellites or simple monopoles for telemetry and command purposes. Communication satellite antennas later evolved to shape beam reflector type configurations. Spaceborne antennas are now moving to even larger reflector antennas and to planar arrays for radar applications. This evolution in spaceborne antennas has been followed by a parallel evolution in antenna test facilities and facilities requirements.
Near-field measurement techniques are widely used today for antenna far-field pattern characterization. Since the 60's, much has been done concerning accuracy. The three main coordinate systems, planar, cylindrical, and spherical have been investigated. probe corrections have been introduced [1] - [6].
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.
Measurements of the Electromagnetic Field in the quiet zone of Scientific-Atlanta's Model 5753 Compact Range are presented. The Model 5753 is believed to be the largest high frequency compact range yet built and measurements demonstrate a quiet zone exceeding 8 ft. high by 12 ft. wide. Both field probe measurements and pattern comparison measurements are presented in the operating frequency range of 1-94 GHz.
The planar scanning system is commonly used in the near field testing of high gain antennas, where the rectangular measurement grids are used. The polar grids are also used, which are more convenient when the antenna aperture is circular. In the planar scanners the measurements are carried out in the x-y plane in increments of both x and y. The result of the measurement is an mxn matrix of the near field data consisting of m cuts with n data points per each cut. The far field patterns may then be calculated, using the near field data, by the aperture field integration or the modal expansion methods [1]. In this paper the aperture field integration method is studied, where the far field components can be calculated from [1] - [2].
The geometry of a dual parabolic cylindrical reflector system and its projection on the plane of symmetry are shown in Fig. 1. It consists of a point source f and two parabolic cylindrical reflectors S1 and S2 with curvatures in two orthogonal planes and of focal lengths F1 and F2, respectively. Alpha is the angle between the generator of the sub-reflector and the main beam direction. It is considered positive if the generator of S1 rotates towards the main reflector and negative if it rotates in the other direction. The feed orientation is specified by the angle gamma which is the angle between the feed axis and the normal from the feed point f to S1. The feed angle is 2f , which is the angle subtended by the sub-reflector in the principal planes. The sub-reflector geometry is selected such that it subtends equal angles from the feed in two orthogonal planes. The main reflector geometry is selected to intercept all reflected rays from the sub-reflector. The projected aperture of the main reflector is rectangular in shape, the sides of which are denoted as A and B. The ratio between these aperture sides is given by [1]. The separation between the two reflectors may be increased by any value delta which results in reducing the aperture dimensions. The feed radiation pattern is assumed to be rotationally symmetric and its electric field distribution in the feed coordinates is represented by cos??. If the feed is vertically polarized in the asymmetric plane (along y-axis), the y and x-components of the aperture field are the co-polar and cross-polar components, respectively. The feed may also be horizontally polarized along the unit vector [sin (?+a) i + cos (?+a) k] in the symmetric plane. In this case the co-polar and cross-polar components of the aperture field are the opposite of the above case.
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.
It is sometimes necessary to tolerate a narrow vertical obstacle in proximity to an antenna system. This study quantifies the effects on the antenna horizontal pattern of an obstruction with vertical dimension large compared to the antenna and horizontal dimension small compared to the antenna. Both dimensions are large compared to wavelength.
Electronic scanning phased arrays are being used more and more in radar, EW and communication systems. The development of such an array can be divided into two separate parts: development of the radiating elements and development of the beam forming network. The development of these two parts is often done in parallel and the radiating elements should always be developed taking into consideration the whole array and not only single elements.
This paper presents data from facility evaluation tasks on current projects. The data were obtained on outdoor free-space pattern test facilities, and in anechoic chamber RCS test facilities.
This paper describes the mechanical as well as electrical measurement of doubly curved reflector antennas. The techniques developed for measurement of the new Canadian RAMP Primary Surveillance Radar antenna are described. Instead of a conventional full size template fixture to measure the antenna contour accuracy, an optical twin-theodolite method is used. The problems of the method are discussed and a new simplified analysis for calculating reflector error of doubly curved antennas is presented. Reflector errors are calculated and displayed concurrent with the actual measurements. The measurement of primary and secondary patterns for such antennas are described. Included are brief descriptions of the improved Andrew pattern test range and anechoic chamber facilities.
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.