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Previous AMTA papers have discussed pulsed antenna measurements and the importance of parameters such as pulse width, pulse repetition frequency (PRF) and receiver dynamic range in determining the appropriate technique for performing pulsed measurements. Typically, the pulse width and PRF determine the IF bandwidth required of the instrumentation receiver to achieve a specific level of receiver performance. Less emphasis has been given to the receiver timing and synchronization required to achieve optimum performance for a full pulsed antenna measurement scenario. This paper will discuss receiver timing considerations and show examples of scan time performance during high-speed pulsed measurements. Inter-pulse and intra-pulse measurements will be compared with respect to their impact on measurement time. Pulse profile measurements will be examined to show the importance of a fast synchronous receiver for sub-microsecond pulse characterization. Pulsed antenna pattern results will also be presented and compared with CW measurements.
Currently there is a lack of facilities capable of measuring the full upper hemisphere radiation patterns of antennas mounted on an infinite ground plane. Measurements performed with a finite ground plane suffer diffraction interference from the truncated edges. To circumvent this problem, a new measurement setup was developed at the Ohio State University ElectroScience Laboratory (ESL) for fully characterizing upper hemisphere radiation gain patterns and polarization for antennas up to 4” in diameter from 1-18 GHz. A probe antenna is positioned 46” away from the antenna under test (AUT). The ground plane end diffractions are removed using time-domain gating. The key design consideration is to position the probe antenna in the far-field region and yet shorter than the radius of the ground plane. This paper will present the calibration procedure necessary for the measurement system and it’s limitations due to ground plane probe antenna coupling at low elevation angles. In addition, the complete radiation pattern of a 4” monopole measured from 1-5.5GHz to demonstrate the systems capability for the lower third of the systems operating frequency range.
This paper gives a detailed account of free space Voltage Standing Wave Ratio (VSWR) method. We first review the formulations and terms commonly used in this method. We then discuss errors involved in its direction determination of extraneous signals, contrasting them among plane wave, spherical wave and specular reflection. We highlight issues relating to its application in anechoic chamber electromagnetic performance. Also discussed is the practice of data processing through analyzing a measured VSWR pattern.
An efficient algorithm for calculating the position of the phase center of an antenna from a measurement is derived and implemented in software. Application of the algorithm to actual measurements shows that the success of the algorithm depends on characteristics of the antenna and a weighing parameter derived from the amplitude pattern.
This paper describes the development of a test procedure for OMNI directional antenna pattern measurements in Compact Antenna Test Facility (CATF). This study is also of importance as it was presumed that OMNI directional antennas can not be tested in ISAC-CATF due to reflections coming from high-rise metallic structure of DUT positioner. As in ISAC-CATF, DUT positioner is not at all covered with the RF absorbers. Further, effect of Spacecraft body on radiation pattern is also studied. In addition to that effect of high-rise metallic structure of DUT positioner is also presented. It was observed that due to spacecraft body ripples were generated in the radiation pattern of OMNI directional antenna. It was also observed that effect of high-rise metallic structure of DUT positioner was not as significant as of Spacecraft body. At the end of this study, to exactly simulate the integrated spacecraft level condition a 33 dB coupler was connected at antenna output port and measurements were performed with the help of coupled port. Those results are also presented in this paper.
A probe-compensated near-field-to-far-field transform algorithm has been developed that can generate far-field patterns from near-field measurements made on an arbitrary surface. We present the concept, the algorithm, and computer simulated and measured test results for measurements on a conical surface. The prototype conical near-field measurements were made in a planar near-field range on a horn antenna under test (AUT) mounted on an azimuth-over-elevation positioner to produce a conical measurement surface. This system is especially applicable for producing full-hemisphere far-field patterns for antennas mounted on vehicles where other standard measurement systems may not adapt to the profile well, may not provide full-hemisphere coverage, or may require large, mechanically complex systems.
Traditional passive antenna measurements result in well-known quantities like Directivity, Efficiency, and Gain. However, when testing over-the-air (OTA) performance of active devices, there are additional effects that cannot be lumped together as part of the antenna performance. Terms like gain and efficiency are defined based on transmit or receive signal levels at the antenna port relative to the radiation pattern of the device. Thus, OTA performance is often assumed to be equivalent to the conducted performance of the device combined with the passive radiation pattern. However, when that antenna port is attached to an active radio in a typical wireless device, interactions between the circuitry and the antenna can produce results that do not match that predicted by the conducted performance and the passive radiation pattern. The difference between the predicted and actual performance of a device can be quantified in terms of "interaction factors", which represent the often non-linear behavior of the active circuitry when operating in an OTA environment. These factors include such effects as variation in amplifier gain due to heating caused by antenna mismatch, and receiver desensitization due to platform noise that couples through the antenna of the device. This paper will discuss the concept of interaction factors and define a number of sub-components of these factors that may be useful in predicting the level of some interaction factors.
Calibration of planar near field probes is generally required to obtain accurate cross-polarization measurements of satellite antennas; however, probe calibration is costly and time consuming. One way to avoid probe calibration is to ignore the probe cross-polarization and use the probe co-polarized patterns alone for probe correction. Then the probe can be easily characterized by standard, in-house measurements or by analytical models. Of course, if the probe cross-polarization is ignored, additional errors are introduced in the co- and cross-polarized pattern measurements, but the errors can be manageable, depending on the probe and Antenna-Under-Test (AUT) polarization properties. Complete formulas and/or tables for near field measurement errors for three popular measurement configurations are presented, along with experimental verification of the error estimates for one case.
A novel approach using Artificial Neural network (ANN) is proposed to identify the number of faulty elements present in a uniform linear array consisting faults in multiple elements. The input to the neural network is amplitude of deviation pattern and output is the number of faulty elements. In this work, ANN is implemented with three different algorithms; Radial Basis Function neural network (RBF), Generalised Regression neural network (GRNN) and Probabilistic neural network and their performance is compared. The network is trained with some of the possible faulty deviation patterns and tested with various measurement errors. It is demonstrated that the method gives a success rate of 93.4%.
Indoor RCS measurement facilities are usually dedicated to the characterization of only one azimuth cut and one elevation cut of the full spherical RCS target pattern. In order to perform more complete characterizations, a spherical experimental layout has been developed at CEA for indoor near field monostatic RCS assessment. The experimental layout is composed of a motorized rotating arch (horizontal axis) holding the measurement antennas. The target is located on a polystyrene mast mounted on a rotating positioning system (vertical axis). The combination of the two rotation capabilities allows full 3D near field monostatic RCS characterization. Two bipolarization monostatic RF transmitting and receiving antennas are driven by a fast network analyser : - an optimised phased array antenna for frequencies from 800 MHz to 1.8 GHz - a wide band standard gain horn from 2 GHz to 12 GHz. This paper describes the experimental layout and the numerical post processing computation of the raw RCS data. Calibrated RCS results of a canonical target are also presented and the comparison with compact range RCS measurements is detailed.
The present paper introduces a lower frequency design for the open boundary quadridge horn (OBQH) introduced in [1]. This new horn cover the UHF band and it is usable up to 6GHz. It exhibits a fairly uniform radiation pattern at the upper end of its range as well as a fairly flat gain as was the case with the higher frequency design. The increased frequency band up to 6GHz is accomplished by the use of a ferrite filled cavity that maintains a good VSWR even when the feed cavity is reduced to avoid higher order modes that cause the main beam of the pattern to split. As with the higher frequency design this horn can be used as a source in antenna pattern measurement chambers and even reflectors. As a second part to the paper some data is presented on the use of the S to Ku Band OBQH as a feed for reflectors used in Radio-Astronomy [2]. The results show that by placing the OBQH in an absorber lined cavity the pattern improves and the feed becomes more effective.
Boumans [1] has introduced an alternative to the classical (Advanced) Antenna Pattern Correction (A)APC method by moving the range feed in the focal plane of a Compact Antenna Test Range (CATR) instead of moving the Device Under Test (DUT) around in the Quiet Zone (QZ). The advantages are clear: it is easier (cost and accuracy wise) to implement a feed scanner than a DUT scanner; the method can be used for azimuth and elevation patterns and it can even be implemented using multiple feed horns to get to the same measurement time as with a single range feed. The capabilities of defocused measurements in the Compact Payload Test Range (CPTR) at ESA/ESTEC have been previously assessed [2] and they revealed a triply reflected ray [2] and a QZ ripple induced by periodic surface inaccuracies [3]. This paper focuses on verifying the performance of the Focal Plane AAPC method for these effects. Use has been made of the well known DTU-ESA VAST-12 antenna [3].
A new antenna diagnostics technique has been developed for the DTU-ESA Spherical Near-Field Antenna Test Facility at the Technical University of Denmark. The technique is based on the transformation of the Spherical Wave Expansion (SWE) of the radiated field, obtained from a spherical near-field measurement, to the Plane Wave Expansion (PWE), and it allows an accurate reconstruction of the field in the extreme near-field region of the antenna under test (AUT), including the aperture field. While the fundamental properties of the SWE-to-PWE transformation, as well as the influence of finite measurement accuracy, have been reported previously, we validate here the new antenna diagnostics technique through an experimental investigation of a commercially available offset reflector antenna, where a tilt of the feed and surface distortions are intentionally introduced. The effects of these errors will be detected in the antenna far-field pattern, and the accuracy and ability of the diagnostics technique to subsequently identify them will be investigated. Real measurement data will be employed for each test case.
Accurate antenna measurements at sub-millimeter frequencies are very challenging. Especially the phase measurement accuracy is usually limited by the mechanical accuracy of the measurement equipment. The measurement techniques used, and the measurement results of a dual reflector feed system (DRFS) at 650 GHz are presented in this paper. Planarity error compensation technique was used that enabled accurate correction to the measured phase pattern without accurate pre-existing information of the planarity error of the planar near-field scanner. The measured DRFS beam agrees well with the simulated and the achieved measurement accuracy is good.
In this paper we present and evaluate a method for estimation of in-network performance of mobile terminal antennas developed by the Swedish telecom operator Telia. The Telia Scattered Field Measurement (TSFM) Method is intended to give a better estimate of the performance of the mobile terminal antenna as in an in-network fading scenario. The parameter measured from the TSFM method is referred to as the Scattered Field Measurement Gain, SFMG, i.e. the Mean Effective Gain, MEG, measured relative to a half wave dipole antenna. MEG includes the radiation pattern of the mobile terminal antenna as well as an estimate of polarization and directional losses that occur due to the propagation environment. In this study it is found that the TSFM method provides a good measure of the in-network performance of the mobile terminal antenna. Furthermore, it is shown that the SFMG measured with this method is found to be well correlated with the Total Radiated Power Gain, TRPG, or radiation efficiency. This suggests that the Total Radiated Power, TRP, may be a good measure of the in-network performance of mobile terminal antennas if measured with proper adjustment to the antenna and propagation channel mismatch.
This paper presents a miniature conformal GNSS (Global Navigation Satellite Systems) antenna array with integrated low-profile feed that provides continuous upper hemisphere coverage with good axial ratio. The four element array is comprised of two-arm wire spirals with substrate dielectric loading and termination resistors. The array has a total size of 3.5” x 3.5” and is approximately 0.8” thick. The antenna array can be used to receive signals from all GNSS satellites in various bands. The antenna has a similar footprint as a FRPA-3 (Fixed Reception Pattern Antenna – 3), and thus can easily replace the existing FRPA-3. One can obtain improved performance with the new antenna in that the signals from any GNSS satellite can be received. In addition, the array can be used to null interfering signals by adaptively weighting the signals received by various antenna elements. We have analyzed the performance of the antenna using HFSS, and are in the process of building the antenna. Next, the performance of the antenna will be verified experimentally.
Comparisons of the far-field results from two different ranges are a useful complement to the detailed 18 term uncertainty analysis procedure. Such comparisons can verify that the individual estimates of uncertainty for each range are reliable or indicate whether they are either too conservative or too optimistic. Such a comparison has recently been completed using planar and spherical near-field ranges at Nearfield Systems Inc. The test antenna was a mechanically and electrically stable slotted waveguide array with relatively low side lobes and cross polarization and a gain of approximately 35 dBi. The accuracies of both ranges were improved by testing for, and where appropriate, applying small corrections to the measured data for some of the individual 18 terms. The corrections reduce, but do not eliminate the errors for the selected terms and do not change the basic near-to-far field transformations or probe correction processes. The corrections considered were for bias error leakage, multiple reflections, rotary joint variations and spherical range alignment. Room scattering for the spherical measurements was evaluated using the MARS processing developed by NSI. The final results showed a peak equivalent error signal level in the side lobe region of approximately -60 dB for both main and cross component patterns for angles of up to 80 degrees off-axis.
Now-a-days, far-field ranges are being used to measure antenna radiation patterns. Two main types of ranges used are used for these measurements: direct and indirect illumination. In either case, the accuracy of the measurement is dependent upon the quality of the range quiet-zone fields. In direct illumination, phase and amplitude taper cause discrepancies in the fields. For indirect illumination, only amplitude taper must be accounted for. Additionally, stray signals and cross-polarization will further distort the quiet-zone fields and lead to measurement errors. This new methodology starts with the measured antenna data and a priori knowledge of the incident fields and estimates an Effective Aperture Distribution (EAD). The EAD compensates for these sources of error and can be used to predict the far-field radiation pattern of the antenna under test. Analytical results are presented for taper and stray signal analysis.
The goal of this research is to develop an unconstrained reconfigurable programmable array antenna. The concept is to build patch arrays using individual controllable pixels. The aperture of the system is made up of a large array of small (1/10 .min) pixels. Each pixel is a small piston made up of a metal top, a dielectric shaft, and a metal base. The pistons can be moved up and down under computer control. When all pistons are in the down position, a ground plane is created. When a line of pixels is raised into the up position, a microstrip transmission line (a metal line over a dielectric substrate) is created. A patch antenna is created when multiple pixels are raised into the up position to form a larger rectangle or other shape. In the final design, a set of feed lines and antennas can be created in any pattern within 1 millisecond. Under computer control, it is possible to change the beam direction, the beamwidth, the polarization, and the frequency of operation of the array. Design details, theoretical models, and the behavior of test fixtures and configurations will be discussed during this presentation.
Adaptive antenna has both the amplitude and phase (as weights) which can be adapted optimally to get required multi path arrival estimation or directed beam forming. We had earlier tried to find out errors in adaptive arrays (ULA) and further try to investigate mutual coupling effect in closely spaced antenna elements in rectangular / planar arrangement. It is always desired to place antenna elements closer in order to reduce grating lobes when the main lobe is electrically tilted. In real life when an adaptive array is subjected to multi path and mutual coupling it is necessary to counteract with suitable modeling so as to make it usable for wireless communication. We attempt to study / investigate the mechanism for mutual coupling between antenna elements. In adaptive antenna arrays, mutual coupling can deteriorate the algorithms which try to deal with the direction of arrival (DOA) and beam forming. There is also a need to reduce the size of the antenna aperture and element itself, without degrading the performance and bandwidth of the element. We have simulated in Matlab our planar adaptive array algorithm which mitigates errors and reduces effects of mutual coupling. It was found that Tschebyscheff polynomial distribution was one of the optimum arrangements for antenna synthesis. When aperture length has to be fixed and new antenna elements are introduced we try to find way to deal with this by spacing nulls on unit circle according to Tschebyscheff pattern. We also try to touch issues in implementing the array on FPGA. Key words: ULA, DBF, Tschebyscheff, FPGA.