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 proposed method is based on fiber-optic link connected to the antenna under test in order to measure the radiation pattern of electrically small antennas without any metallic cable effects. The experimental radiation characterization of electrically small antennas reveals significant effects of the RF cable strongly disturbing the antenna gain and radiation patterns for both polarization components. With a very simple use and a low cost, the presented systems can characterize radiation of both narrow and UWB compact antennas in the 0.1-4 GHz frequency band. The proposed test-bench is firstly validated then its performances are compared to classical cable measurements and antenna simulation results. Both measured and simulated results are compared and the agreement is excellent (±1 dB) for co polarisation in the different cut planes. Limitations of the proposed method are also addressed. For very low gain levels (for the presented antennas at 950 MHz and 473 MHz, a cross polarization level below -30 dBi) the 42 x 20 x 23 mm3 autonomous optical receiver is too large and alters the antenna under test radiation. In this last case, and for a using at higher frequency, it is recommended to miniaturize the optical receiver whose size is mainly governed by battery performances (6 hours).
G/T is a standard figure of merit describing the sensitivity of receive, active, microwave antenna systems. It is therefore critical to have an accurate test technique for measuring the G/T of systems with varying levels of sensitivity. The Yfactor method is a commonly used and wellunderstood technique for characterizing receive microwave systems. While the concepts behind the Yfactor measurement techniques are generally understood, little quantitative work has been done establishing limits and rules regarding selection of measurement hardware and design of the measurement system. This paper seeks to provide examples of test systems and quantify the error induced into the measurement due to mismatched standard hardware. The variables and techniques involved in a G/T test are examined using simulated results of measurement systems performed in VSS (Visual System Simulator).
RF guided missile developers require flight simulation of their target engagements to develop their RF seeker. This usually involves the seeker mounted on a Flight Motion Simulator (FMS) as well as an RF target simulator that simulates the signature and motion of the target. Missile defense developers, whose job it is to defend against guided missiles, require a similar test environment adding the ability to insert decoy RF targets that can spoof the seeker. Both seeker development and counter-measure development can benefit from an RF test facility that can provide RF targets and decoys controlled by a real-time simulation. This paper addresses an RF Target and Decoy Simulator developed by MI Technologies that provides this test capability. The direction of the target and decoy emitters is independently controlled such that the centerlines of their radiated main antenna lobes are always directed at the RF seeker. Each emitter can be independently and simultaneously commanded along a spherical surface. High rates of acceleration and velocity are achieved all the way out to the ends of the test area to simulate the high line of sight rate that occurs at missile closure. The simulator is capable of safely stopping a decoy racing to the ends of the target area with minimal over-travel. Collision avoidance provisions prevent target and decoy from damaging each other during the simulation. The paper presents a description of the simulator, pertinent tradeoffs considered in the design and accuracy data of the simulator’s performance.
Fig. 1: Cylindrically conformal antenna array system This paper discusses an example of a unique cylindrical conformal array design approach. This exemplary design is composed of six subarrays of series-fed microstrip patch antenna operating in X-band. The diameter of the conducting cylinder is 7.5 inches in diameter. Each subarray contains seven patch antennas connected in series configuration and is connected to a single coaxial probe located at the center element. Such feed arrangement greatly reduces the number of feeding cables, increases the feed-line isolations, and minimizes the feed-line radiation. The elevation pattern of each subarray is controlled by the number of patches and impedance matching tapering via varying the width of connecting microstrip lines. The azimuth pattern is controlled by the subarray height above cylinder surface, substrate width, cylinder radius, and surface treatments between subarrays. Measurement results exhibited good impedance matching and broad antenna coverage in X-band.
The Enhanced Antenna Subsystem (EAS) is a 12 beam, receive only antenna which uses a combination of switched elements and phase delay to accomplish independent beam steering. The upper portion of the domeshaped antenna is populated with 45 circularly polarized antenna elements in an icosahedron pattern along with 15 additional circularly polarized elements along the cylindrical skirt extension. The antenna was tested in our 35’ by 35’ by 65’ compact range. Pattern testing was accomplished by mounting the antenna to a roll positioner atop a high load tower, which was then mounted to an azimuth turntable. The range has a 20’ by 20’ reflector providing an 8’ quiet zone. Using a switching network, we simultaneously characterized 11 statically pointed beams while tracking the range source antenna with the 12th beam. Post processing of the data was performed to separate the beam data and calibrate out losses through the switching network.
In this paper, a beam-steering computer design is explored for a large space-fed phased-array antenna. GTRI previously developed a beam-steering computer for a smaller phased-array antenna which accomplished spherical propagation focusing and multiple phase-only beam-broadening modes. In a subsequent effort, the beam-steering computer design was scaled for a large phased-array antenna to accomplish similar tasks. To verify the design, a series of far-field measurements was initiated to characterize the performance of the antenna by comparing with past measured near-field data and modeled results. One of the primary responsibilities of the beam-steering computer was the focusing of the spherical propagation wave front. A measurement technique is discussed to accomplish this focusing for the large space-fed phased-array antenna by correcting measurement errors in the spherical propagation routine of the beam-steering computer. Additional patterns were taken using the updated feed horn focal point for spherical propagation correction. By correcting the phase errors caused by spherical propagation defocusing in the original beam-steering computer, significantly better antenna performance was obtained, including higher peak gain, reduced nearby sidelobe levels, and removal of beam-pointing errors. Another important responsibility of the beam-steering computer was the ability to realize multiple antenna modes, including a focused pencil beam as well as defocused broadened-beam modes. A stochastic gradient descent algorithm was utilized to obtain several phase tapers to accomplish beam-broadening for the antenna modes. These modes were implemented in the beam-steering computer and tested on a far-field range. The antenna patterns were compared with modeled results and with previous measured data to ensure validity of the implementation.
Calibration of probes for planer near field range measurements is generally required to obtain accurate cross-polarization (xpol) data; however, probe calibration is costly and time consuming. Using analytical models in place of calibration is generally much more cost effective, but may result in larger measurement errors. In a previous paper [1], we showed that simple models of copol probe patterns with zero xpol can give accurate measured results, provided that the probe xpol is much better, generally 10-15 dB better, than the Antenna Under Test (AUT). The next question is “Can a lower performing (and cheaper) probe be used if both the copol and xpol probe patterns are modeled?” In this paper, we compute AUT xpol measurement errors that result from probe xpol errors, and we compare far field AUT patterns processed using probe models with patterns processed with calibrated probe files.
One of the most promising bands for long-range radiocommunications is the Ka-band (25-40 GHz). This is due to the existence of a natural radio transmission window around 30 GHz. Both terrestrial and satellite transmission systems are planned on this frequency band. For satellite applications, circular polarization is needed and the antennas or antenna arrays must frequently exhibit specially tailored radiation patterns. This paper proposes an efficient planar element for Ka-band telecom and remote sensing applications. The element has reduced losses (and hence good efficiency), while providing circular polarization (AR better than 3 dB) and good matching (better than 10 dB) in the 25.5-27.0 GHz frequency band. The element is fed by an integrated low loss transmission line (suspended strip line, SSL). This modular design allows an easy grouping into high efficiency subarrays, which include beam forming networks (BFNs) built in the same SSL technology and an innovative transition to the final standard waveguide feeder.
A spherical near-field measurement range at Nearfield Systems Inc. has recently been used to measure gain, pattern and polarization of a multi-element helix array operating in the UHF band. Verification of gain performance over the operating band was of primary importance and so major efforts were made to obtain the best possible gain results and to quantify the gain uncertainty through a complete error analysis. A single element helix gain standard was first calibrated and the estimated uncertainty in this calibration was 0.35 dB. A double ridged horn was to be used as the probe for the spherical near-field measurements and so the patterns of the horn at all test frequencies were measured on the spherical range using identical horns as the AUT and the probe. From these measurements, probe pattern files were generated that could be used to perform the probe correction in the measurements of the helix gain standard and the multi-element array. The helix gain standard was then installed in a new spherical near-field range at NSI with the double ridged horn as the probe. The range used a specially designed phi-over theta rotator that could support and rotate the array and maintain the required position accuracy. The chamber was lined with 36 inch absorber. Spherical measurements were then performed and the data processed to provide the far-field peak amplitudes at each frequency that were necessary for gain measurements. The far-field peak values are equivalent to the far electric field for the gain standard and are compared to the same parameter for the multi-element array to produce the final gain results. The helix array was then installed in the spherical range and a series of measurements were performed to produce the far-field gain, pattern and polarization results and also to provide the data for the complete 18 term uncertainty analysis. The uncertainty in the gain measurements was 0.45 dB and the axial ratio uncertainty was 0.11 dB.
Pattern distortion due to finite range measurement of antennas in close proximity to electrically large metallic media is examined. The ubiquitous yet arbitrary 2D2/. distance requirement cannot be blindly applied to scenarios where antennas couple to nearby structures. A C-band standard gain horn antenna is analyzed near a circular metallic plate at 6 GHz using the commercial software FEKO. The near-fields are computed at various radii, which are set to multiples of D2/., where D is defined as the largest dimension of the complete structure. The radiating near-field patterns are normalized and compared to the far-field pattern. Results indicate that measurement at 2D2/. may not be necessary. Increasing fractions of D2/. results in a diminishing measurement error that may be tolerable, depending on the intended application.
Alignment of the axis of range positioner systems can be performed using modern laser tracking equipment. An approach to the alignment of the radome measurement range at the Raytheon McKinney, Texas facility will be presented. Key words, range alignment, laser tracking, laser alignment
ABSTRACT A comparison of the planar, spherical, and cylindrical near-field techniques was completed at the National Institute of Standards and Technology (NIST) for a Ku-band Cassegrain reflector antenna. This paper discusses measurement results and reports on the sources and magnitudes of the uncertainties for the three near-field techniques. We conclude that measurement results from the three different near-field methods agree within the expected uncertainties.
This paper elaborates on certain aspects of a new measurement process that permits an assessment of spherical near-field (SNF) measurement errors based on a set of practical tests that can be done as part of any SNF measurement. It provides error bars for a measured radiation pattern in an automated fashion.
– far-field transformation with cylindrical scanning are efficiently determined by using an optimal sampling interpolation algorithm. The comparison of the far-field patterns reconstructed from the acquired irregularly distributed measurements with those obtained from the data directly measured on the classical cylindrical grid assesses the effectiveness of the approach.
This paper presents a hybrid analysis algorithm, which is used at Radiation Group (UPM) to carry out the design of a conformal serrated-edge reflector for the mm-Wave compact range UPM facility. Main features of this algorithm involve its capability of handling conformal serrated rim parabolic reflectors, accuracy and computational efficiency.
The overall measurement system details are presented, along with mechanical accuracies achieved for the scanner system. Details of the chamber and host facility are described. Finally, the paper concludes with measurements of a UHF-band Standard Gain Horn using the system. The challenges and benefits of such a system will be highlighted.