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.)
The Boeing V-22 Osprey tilt rotor aircraft is a candidate platform for use as an airborne surveillance radar system. The impact of radar RF energy scattering from the aircraft's large propellers is a concern due to the potential for interference with an airborne pulse doppler radar where frequency changes are used to discriminate moving targets from ground clutter. In order to ascertain the effects of the scattering, a unique measurement system was devised for recording the time modulated antenna pattern of an array antenna.
We present a method for determining antenna couplings caused by a near field. These couplings often exist between antennas on tactical aircraft, or any other types of airborne platforms. The limited size and peculiar exterior contour of these platforms make a theoretical calculation of near field couplings difficult. High antenna isolation is critically important to proper avionics functioning. To achieve this higher degree of isolation, the causes of antenna couplings need to be identified and corrected. At present, no diagnostic methods are available. Existing methods only measure the degree of isolation between antennas, which is the ration between the power of the transmitting antenna to that of the receiving antenna. These methods do not provide any clues as to what may be causing the couplings. A diagnostic method using a network analyzer is feasible, and the causes of antenna couplings can be identified.
An antenna radiation pattern measurement technique which allows near real time pattern capture is presented. This technique uses relatively simple field probles and detectors to cover a reasonably broad operating band. The captured pattern data is digitized with a resolution of 1.0 degree and has an angular range of 150 degrees. Many captured patterns or snap-shots could be recorded during a given time interval and later viewed for diagnostic evaluations where rapid changes in the pattern are expected.
This paper will discuss the disadvantages of a conventional Earth Station Antenna (ESA) pattern measurement technique compared with an alternative, time-proven technique. These measurement techniques are used to verify that a particular ESA has been properly constructed, focussed correctly and meets or exceeds a manufacturer's pattern envelope and gain specifications. These tests are performed on-site through a satellite link.
Many experimental and analytic studies on travelling waves have been performed in relation to their radiation properties for antenna applications. One common structure that has supported a fast travelling wave is a slotted waveguide. Such structures can also support travelling waves from a scattering viewpoint. This aspect was verified by incorporating a trough in an almond test body to observe its scattering characteristics using aspect angle patterns, frequency spectra and transient signatures from compact range measurements at the ElectroScience Laboratory, OSU. The travelling wave behavior is also correlated to the calculated travelling wave propagation constant for this structure with good agreement.
March Microwave Systems B.V. is manufacturer of the dual cylindrical reflector Compact Antenna Test Range (CATR) that was designed by Vokurka [1] (see Fig. 1). The analysis of the test-zone fields of such a design is necessary to be able to optimize the geometry.
Over the last five years a considerable attention has been paid to further developments of Compact Antenna Test Ranges for both antenna and RCS measurements. For many applications, these devices proved to be more attractive than outdoor ranges or near-field/far-field transformation techniques. On the other hand, accurate operation at very low or very high frequencies can cause considerable difficulties. It is the aim of this paper to describe the theoretical limitation of collimating devices, in particular for low frequencies. For this purpose, an idealized collimator will be defined. Using the spectral components analysis a comparison of achievable accuracy will be made between collimators and outdoor ranges. Theoretical limits in the accuracy for RCS measurements will be computed for all applicable frequencies. Finally, a comparison will be made between the experiments on a dual-reflector Compact Antenna Test Range and theoretically achievable limits. Representative targets, like cylinders and rectangular plates have been used for experimental investigation. These data will also be presented.
Characteristics of the Harris Model 1606 Compact Range are summarized and considered for applicability to RCS measurements. Measured characteristics of quiet zone performance (amplitude and phase distributions) and standard target RCS data are presented. Of particular interest is a comparison of predicted and measured radar cross section versus aspect angle of some familiar standard targets under various conditions.
The development of a high efficiency compact range has made it possible to consider alternative equipment for making radar cross section measurements. Historically, high power radars were required to make measurements on low efficiency, high clutter ranges. Their high power and narrow pulse capability was essential in making precision measurements. Such instrumentation is complex and expensive. There is, however, a relatively inexpensive approach which uses test equipment commonly found in the laboratory. It is centered around an HP8510 network analyzer and an RF switching network.
During the development of the McDonnell Aircraft Corporation (MCAIR) compact range a low back scatter field probe was built to evaluate the range's performance using realistic signal levels. The probe was built using off-the-shelf electronics and a standard Hewlett Packard desk top computer system to drive the probe and record the data. The mechanical components were designed to be easily assembled and quickly mounted upon a low cross section pylon.
Precision rotary vane attenuator calibrations are required in both the planar near-field method for determining antenna parameters and in the extrapolation method for determining on-axis gain of standard gain horns and probes. These attenuator calibrations are used to measure the linearity of the receiving systems and also to provide a precise offset capability used in insertion loss measurements. The Antenna Metrology Group of the National Bureau of Standards has utilized the i.f. substitution method to calibrate millimeter wave precision attenuators using equipment available in their measurement laboratory. The technique will be described along with the problems encountered. Results will be presented. In addition to mm wave attenuator measurements, the first calibrations of mm wave antennas and probes has resulted in tests to determine waveguide flange to flange connection errors for insertion loss measurements where repeated connections are necessary. The effects of these measurements on the overall error budget for the determination of the gain of an antenna will be presented and the effects of methods to reduce these errors will be discussed.
Millimeter band measurements require that care be exercised in the connection and handling of the waveguide flanges and their contact surfaces. When properly connected these flanges can provide many years of reliable and repeatable measurements. Improper use will limit the flange life to just a few connections, and cause measurement errors. These misuses are especially acute in situations requiring repeated connecting and disconnecting of small waveguide flanges, such as in antenna or insertion loss measurements. Some examples of misuse are: 1. using the flange to support heavy devices, 2. rocking the flange to get it on or off, 3. over-torquing multiple sides, and 4. using flanges with non-uniform surfaces. The effect of these misuses is that the flange is no longer usable for measurements requiring repeatability and this results in calibrations with unsatisfactory error bounds. NBS is currently addressing these problems by developing a Mechanical Millimeter Flange Alignment Fixture. The fixture indicates deficiencies in the contact area which need to be corrected. The fixture is then used to ensure that the flanges are mated correctly and repeatably. No twisting, rocking or angular mating of the flanges can occur. The fixture relieves the weight of the device on the flange and makes a versatile mounting fixture for almost any device where repeated connections must be made. The fixture and its use will be discussed in detail.
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.
With the introduction of the HP 8510B vector measurement analyzer with external mixer operation, multiple source control, and external phaselock capability, a variety of new antenna test configurations are now possible. The wide assortment of compatible LO sources (HP8350B family) allows the user to choose between configurations using fundamental mixing and obtain the highest performance over the full RF range, or harmonic mixing and achieve the advantages of operating with a lower frequency LO source.
Scale modeling and its application to antenna measurements has been elaborated many years, though implemented in most cases with much simplification. The foundation for scaling originates from the linearity of Maxwell's equations. However, scaled-down modeling is incompatible with such formulation in authentic applications. The main essence in antenna measurements on models is the simulation of vectorial field configuration, which may be satisfied by so called geometrical scaling, as compared to absolute modeling ~ a quantitative class of modeling, which additionally comprises the simulation of power levels. A set of measurable quantities, adequate for such scaling, is listed. Attention is given to the principle of Electromagnetic Similarities related to geometrically homologous antennas. An algorithm for some distinctive scaling qualifications is developed, and physical aspects of scale modeling are discussed. The relative advantages of scale modeling in antenna measurements are examined, and some remarks for particular technical interests are also presented.
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 novel method for evaluating conductive coatings used for radar cross section (RCS) scale models is presented. The method involves the RCS measurement of a short circuited cavity whose interior is coated with the material under study. The dominant scattering from such a structure occurs from the cavity rim and surface walls internal to the cavity. The method of conductivity testing has excellent sensitivity due to the energy that couples in and out of the cavity. This energy undergoes many reflections with the interior walls and thus very small losses can be detected. Calculations and measurements are shown for several different types of coatings, including coatings of silver, copper, nickel and zinc.
This paper describes the computer system interfaces and hardware additions which provide engineers enhanced capabilities and greater flexibility from their antenna measurement systems. RCA Astro-Electronics has built three outdoor antenna ranges, each equipped with Scientific-Atlanta Antenna Analyzers. Two Series 2020 and one Series 2080 Analyzer are used to perform data acquisition and preliminary data processing for the three antenna ranges. Both S-A 2020 system computers have direct interface capabilities with two remote computer systems, which are primarily used for antenna design and analysis. The S-A 2080 system is interfaced indirectly via one of the S-A 2020 range computers. Direct line and modem interfaces provide user access to remote computer software and allow up and down loading of measured or computed data files. Using RCA software resident in each range computer, measured data files are unpacked, reformatted and downloaded for off-line processing. This process accelerates test schedules and allows analysis software to process data files from three antenna ranges in a single data format. Other enhanced system features include access to remote analysis software, requiring large disc storage space, for real-time evaluation at the antenna analyzer location.
In recent years automatic antenna test ranges have become more commonplace. This has created new particle problems related to the software and data stored. The problems are further pronounced if several test ranges are operated in parallel within the organization and nearfield tests are included.