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.)
Techniques for measuring G/T have been previously presented at AMTA; however, there are very few papers that discuss how to measure G/T in a near-field antenna range. One recent paper discussed such a method and gave a brief description within the larger context of satellite payload testing [1]. The paper's treatment of G/T was necessarily brief and gives rise to several questions in relation to the proposed method. Other papers that treated this topic required the antenna aperture to be separable from the back-end electronics, which may not be possible in all cases [2-3]. In this paper, we discuss in great detail a slightly modified version of the G/T measurement method presented in [1]. A signal and noise power diagram is presented that can be useful for understanding how system signal-to-noise ratio (SNR) relates to G/T, and a few common misconceptions concerning the topic of G/T are addressed. The CW-Ambient technique for computing G/T of a Unit Under Test (UUT) from measurements in a planar near-field system is described in detail, and a list of assumptions inherent to the CW-Ambient technique is presented. Finally, the validity of the CW-Ambient technique is assessed by analyzing measured data collected from a separable UUT.
In this paper, a 3D metal printed dual circular-polarized horn antenna operating in the V-band is proposed, built and tested. This antenna consists of a horn and a circular waveguide, a single groove polarizer and is side-fed by orthogonally placed rectangular waveguide ports. The groove is placed at 45° with respect to the input ports and provides a phase delay of 90° to generate right-or left-hand circular polarization (RHCP or LHCP). The proposed antenna provides symmetric patterns for all planes and exhibits polarization isolation of more than 30 dB at broadside. This antenna is analyzed to realize wide impedance matching bandwidth and wide 3dB axial ratio (AR) bandwidth. A prototype of the horn antenna has been fabricated using 3D metal printing technology. Metal material with finite surface roughness is considered when modeling this antenna.
Accurately measuring the polarization of an antenna is a topic that has garnered much interest over many years. Methods abound including phase-referenced measurements using two orthogonal polarizations, phase-less measurements using two or three pairs of orthogonal polarizations, spinning linear probe measurements, and the rigorous three-antenna polarization method. In spite of the many publications on the topic, polarization measurements are very challenging and can easily lead to confusion, particularly in accurately determining the sense of polarization. In this paper, we describe a method of accurately and rapidly measuring the polarization of an antenna with the aid of a multi-channel measurement receiver and a dual-polarized probe. The method acquires phase-referenced measurements of two orthogonal polarizations. To enable such measurements, we describe a methodology for calibrating the probe. We also describe a tool for automating the polarization measurement and display of the polarization state. By automating the process, it is hoped that the common challenges and confusions associated with polarization measurements may be largely obviated.
An extended long object usually gives rise to a bright reflection (a glint) when viewed near its surface normal. To take advantage of this phenomenon and as a new concept, a discrete Fourier transform (DFT) on the RCS measurements, taken within a small angular range of broadside, would yield a spectrum of incident wave distribution along that object; provided that the scattering is uniform per unit length, such as from a long cylinder [1, 2]. In this report, we examine the DFT spectra obtained from three horizontal long objects of different lengths (each of 60, 20, and 8 feet). Aside from the end effects, the DFT spectra looked similar and promising as an alternative to the conventional field probes by translating a sphere across a horizontal path. Keywords: RCS measurements, compact range, field probes, extended long objects 1. The Boeing 9-77 compact range The Boeing 9-77 indoor compact range was constructed in 1988 based on the largest Harris model 1640. Figure 1 is a schematic view of the chamber, which is of the Cassigranian configuration with dual-reflectors. The relative position of the main reflector and the upper turntable (UTT) are as shown. The inside dimensions of the chamber are 216-ft long, by 80-ft high, and 110-ft wide. For convenience, we define a set of Cartesian coordinates (x: pointing out of the paper, y: pointing up, z: pointing down-range), with the origin at the center of the quiet zone (QZ). The QZ was designed as an ellipsoidal volume of length 50-ft along z, height 28-ft along y, and width 40-ft along x. The back wall is located at z = 75 ft, whereas the center of the roll-edged main reflector (tilted at 25 o from vertical) is at z =-110 ft. It is estimated that the design approach controls the energy by focusing 98% of it inside the QZ for target measurements. The residual field spreading out from the main reflector was attenuated by various absorbers arranged in arrays and covering the chamber walls.-, Tel. (425) 392-0175 2. Anechoic chamber In order to provide a quiet environment for RCS measurements, the inside surfaces of an anechoic chamber are typically shielded by various pyramidal and wedged-shaped absorbers, which afford good attenuation at near-normal incidence for frequencies higher than ~2 GHz. At low frequencies and oblique angles [3], however, Figure 1. A schematic view of the Boeing 9-77 compact range with dimensions as noted. insufficient attenuation of the radar waves by the absorbers may give rise to appreciable backgrounds. Figure 2 shows a panorama view inside the compact range, as viewed from the lower rear toward the main reflector and the UTT. With the exception of the UTT, all other absorbers are non-moving or stationary. A ring of lights on the floor shows the rim around the lower turntable (LTT), prior to the installation of absorbers. In order to minimize the target-wall interactions, the surfaces facing the QZ from the ceiling, floor, and two sidewalls are covered with the Rantec EHP-26 type of special pyramidal absorbers.
A reliable technique for antenna array characterization and calibration is demonstrated for two state-of-the-art antenna measurement systems, a near-field system and a compact antenna test range system. Both systems are known to reduce the measurement distance between device under test and the probe antenna in comparison to classical far-field systems, which need to provide at least the Fraunhofer distance as minimum range length. Equivalent magnetic surface currents are derived from measurements, which represent the electric field on the applied Huygens surface. The calculated equivalent magnetic currents are utilized for characterizing two completely different antenna arrays in the millimeter-wave region. Magnitude and phase calibration opportunities of antenna arrays are discussed, as well as the accuracy provided by the proposed calibration technique.
As the wireless industry continues the move to 5G, the development and subsequent testing of mmWave radios for both base stations and user equipment still face numerous hurdles. The need to test most conformance and performance metrics through the antenna array at these frequencies poses significant challenges and has resulted in excessively large measurement uncertainty estimates to the point where the resulting metrics themselves may be useless. A large contribution to this measurement uncertainty is the impact of the over-the-air (OTA) test range used, driving the industry towards expensive compact range reflector systems in order to overcome the path loss considerations associated with direct far-field measurements. However, this approach necessitates the use of a combined axis measurement system, which implies the need for considerable support structure to hold the device under test and manipulate it in two orthogonal axes. This paper explores some of the limitations and considerations involved in the use of traditional "RF transparent" support materials for mmWave device testing.
The IEEE Standards Association Standards Board (IEEE-SASB) approved the IEEE Std 1720™ "Recommended Practice for Near-Field Antenna Measurements" in 2012 [1]. More than forty dedicated people from industry, academia and other institutions contributed to the creation of this new document. The main motivation for a new standard dedicated to near-field measurements was to complement the existing IEEE Std 149-1979™ "Test Procedures for Antennas" [2]. According to the IEEE-SA policies, the existing standard IEEE Std 1720-2012™ is approaching expiration in 2022. A working group of the APS Standard Committee has been formed to review the current document. Most of the current standard is still relevant and useful for individuals designing and evaluating near-field antenna measurement facilities and other people involved in antenna measurements. However, the standard needs update and renewal in areas in which new developments and technologies have matured. This paper gives an overview of the current standards and discusses the suggested potential changes.
Delivering on the promise of 5G measurements requires the adoption of new RF system technologies that encompass both the mobile user equipment and the active base station. Keeping pace with the impact of new wireless system test parameters such as: Data throughput, Error Vector Magnitude, Symbol Error Rate, and technologies such as mm-wave Massive MIMO, OFDM, and QAM presents significant challenges to antenna test community. For the most part, the market has attempted to react by adapting traditional test equipment to the wireless market however 5G testing presents an ever-greater challenge and demands the incorporation of simulation effects when designing and optimising an antenna test system, especially as these systems have increased in complexity with the adoption of the indirect far-field method and specifically the compact antenna test range (CATR). This paper discusses how 5G communication system parameters affect the design of the CATR and how newly developed simulation capabilities have been incorporated to optimize the CATR design for 5G test applications.
The publication of CISPR 16-1-6 [1] in 2107 marked a significant change in the CISPR documents, for the first time the consideration of how to perform antenna pattern measurements in and determine the associated estimate of the uncertainty of those measurement. This is a look at that technique and presentation of how that helps and relates to measurement traceability.
The calibration of the antenna measurements system is a fundamental step which directly influences the accuracy of any power-related quantity of the device under test. In some types of systems, the calibration can be more challenging than in others, and the selection of a proper calibration method is critical. In this paper, the calibration of the truncated spherical near-field ranges typically used for automotive tests is investigated, considering both absorbing and conductive floors. The analyses are carried out in a 12:1 scaled multi-probe system, allowing access to the "true", full-sphere calibration which is used as reference. It will be demonstrated that the substitution (or transfer) method is an excellent calibration technique for these types of systems, if applied considering the efficiency of the reference antenna.
The Compact Antenna Test Range (CATR) was initially conceived as an efficient way of testing electrically large antennas at very much reduced, fixed, range lengths than would otherwise be the case. However, when testing lower gain, physically smaller antennas, the measurements can become susceptible to inhomogeneities within the CATR QZ including phenomena associated with edge diffraction effects, feed spill-over, chamber multipath etc. Whilst it has been demonstrated experimentally that many of these measurement artefacts may be effectively mitigated using standard and modern more sophisticated post-processing techniques. This paper supports those findings through simulation of the direct and indirect far field ranges and by careful examination of the data processing chain. Results are presented, the relative success of the various techniques examined and the utility of this is set, and expounded, in the context of modern, i.e. 5G, communications systems.
Radiating performances of vehicle-installed antennas are typically performed in large spherical near-field systems able to accommodate the entire car. Due to the size and weight of the vehicle to be tested, such spherical systems are often nearly hemispherical, and the floor is conductive or covered with absorbers. The main advantage of the first is the ease of the accommodation of the vehicle under test. Conversely, the latter is more time consuming in the setup of the measurements because the absorbers need to be moved in order to be placed around the vehicle. On the other hand, the absorber-covered floors emulate a free-space environment which is a key enabling factor in performing accurate measurements at low frequencies (down to 70 MHz). Moreover, the availability of the free-space response allows easy emulation of the cars' behaviors over realistic automotive environments (e.g. roads, urban areas etc.) with commercially available tools. Such emulations are instead much more challenging when a conductive floor is considered. Furthermore, the raw measurements over conductive floors are a good approximation of realistic grounds (such as asphalts) only in a limited number of situations. For these reasons, when PEC-based automotive measurements are performed, it is often required to retrieve the free-space response, or equivalently, to remove the effect of the conductive ground. In this paper two spatial-filtering techniques (the spherical modal filtering and the equivalent currents) will be experimentally analyzed and compared to verify their effectiveness in removing the effect of the conductive floor. For this purpose, a scaled automotive PEC-based measurement setup has been implemented considering a small spherical multi-probe system and a 1:12 scaled car model. The two techniques will be analyzed considering two different heights of the scaled car model with respect to the conductive floor.
We present a novel, non-contact characterization technique for simultaneous characterization of conventional antenna parameters, including the antenna port input impedance, antenna gain and its radiation pattern, without requiring a network analyzer connection to the antenna port. The test antenna and the network analyzer are considered as a 2-port open-air fixture whose network representation corresponds to the desired antenna parameters. The unknown network parameters of the 2-port open-air fixture are determined via a novel calibration process using 4 offset-short termination standards. The error parameters determined by the calibration are then related to the test antenna port impedance and its gain as a function of frequency. Furthermore, the radiation pattern of the test antenna can also be characterized using measured reflection coefficient at the network analyzer port for two offset-short terminations of the test antenna port, while rotating the test antenna over the desired angular range. This novel technique is particularly attractive for installed-antenna applications where an active connection to the test antenna port is either difficult or undesirable, such as on-chip antennas and implanted antennas, to name a few. To demonstrate the efficacy our new method, we present the measured impedance, gain and radiation pattern of a diagonal-horn antenna operating over 360-450 GHz, and a lens-integrated planar butterfly antenna for the 220-325GHz band.
Over-the-air (OTA) performance evaluation requires large investments in anechoic environments. The question of minimizing the test distance is hence critical, and even more in this time where millimeter-wave technologies are about to be largely deployed in 5G devices. A recent publication has identified that direct far-field measurements can be accurately carried out at a much shorter range length than the well-known Fraunhofer distance. This paper introduces a further validation of this reduced distance, by employing an innovative method to simulate spherical measurements with arbitrary DUT, test probes and range lengths. The studies carried out confirm the relevance of this shorter distance, not only for the evaluation of the peak equivalent istropic radiated power (EIRP) or sensitivity (EIS), but also for the total radiated power (TRP) or sensitivity (TIS). In addition, it is demonstrated that the usual assumption that the TRP or TIS measurement is almost independent from the range length is flawed. Two main reasons relating to the test antenna are established which create this dependence: (i) OTA test probes have a finite resolution, and (ii) the probe and instrumentation typically captures the magnitude of two components of the E-field, which are not straightforwardly related to the power density in the near-field.
Antenna measurement errors occur due to reflections and diffractions within the measuring chamber. In order to extract and correct the undesired signals, a technique based on test-zone field compensation and spherical wave expansion is applied to Compact Antenna Test Range (CATR) and Spherical Near-Field (SNF) measurements of a base transceiver station antenna. The required spherical test-zone field is acquired by simulating the corresponding measurement environment with the multi-level fast multipole method. Due to the numerical complexity of the problem, only the parts of the chamber with a significant influence on the measurement results are modeled. Comparing the determined directivities after applying the correction method, an exact overlap is achieved between the SNF and CATR solution.
The Plane Wave Generator (PWG) is an array of elements generating an approximately plane wave over a finite volume in the test area called Quiet Zone (QZ). The plane wave condition can be achieved in close proximity to the array with suitably optimized complex coefficients. The PWG thus achieve far-field testing conditions in a manner similar to the Compact Antenna Test Range (CATR) but with a reduced distance to the QZ [1-2]. As a complete system the PWG has the advantage of reduced physical size compared to the a CATR with equivalent testing capabilities, in particular at lower frequencies. In [3-4], the concept of a high performance, dual polarized PWG supporting up to 1:10 bandwidth was presented. A prototype of a dual polarized PWG has been designed, manufactured and tested in the 600MHz to 6GHz frequency range. This paper presents the initial verification of the prototype PWG. The testing is performed using a representative analog beam forming network with narrow bandwidth. The QZ uniformity of the PWG is verified by spherical near-field measurements and back-propagation. The peak gain of a low directivity antenna is measured at different distances in the QZ and compared to reference measurements in a spherical near-field system. The aim of the comparison is to access the measurement accuracy of the PWG.
In this paper, the experimental validation of a micro-probe fed reference antenna targeting the upcoming 5G applications (24.25-29.5GHz band) is presented. The main purpose of these reference antennas is to serve as "gold standards" and to perform gain calibration of 5G test facilities through the substitution method. The outline of these antennas is based on a square array of four printed patches enclosed in a circular cavity. The RF input interface is a stripline-to-coplanar waveguide transition and allows for feeding the device with a micro-probe. Performance obtained by high-fidelity modeling is reported in the paper and correlated to experimental data. Interaction and unwanted coupling with the test equipment are discussed. The use of echo-reduction techniques and spatial filtering is investigated to mitigate these effects.
This paper introduces the new Portable Laser Guided Robotic Metrology (PLGRM) system at the National Aeronautics and Space Administration's (NASA) Glenn Research Center. Previous work used industrial robots in fixed facilities to characterize antennas and required fixtures that do not lend themselves to portable applications. NASA's PLGRM system is designed for in-situ antenna measurements at a remote site. The system consists of a collaborative robot arm mounted on a vertical lift and a laser tracker, each on a mobile base. Together, they enable scanning a surface larger than the robot's reach. To accomplish this, the robot first collects all points within its reach, then the system is moved and the laser tracker is used to relocate the robot before additional points are captured. The PLGRM implementation will be discussed including how safety and planning are combined to effectively characterize antennas. Software defined triggering is a feature, for flexible integration of vector network analyzers and antenna controllers. Lastly, data will be shown to demonstrate system functionality and accuracy.
The Three-antenna polarization measurement technique is used to determine the axial ratio, tilt angle and sense of polarization of three antennas from measurements on each of three antenna pairs. The three antennas are generally nominally linearly polarized and the measurement data consists of the change in amplitude from the initial antenna orientation where they are co-polarized to the orientation where one of the antennas is rotated about its axis to the null amplitude position. The sign of the phase change is also noted and the phase change at the null position is known from theoretical calculations to be either plus or minus 90 degrees. The correct sign is determined from the sign of the phase change. For antennas with axial ratios in the range of 50 to 80 dB that will be used as near-field probes or as feeds for reflector antennas, it is imperative to measure the polarization parameters as accurately as possible. The primary source of uncertainty in the measurement is due to scattered signals in the measurement range that arise from multiple reflections between the two antennas and from the absorber on the chamber walls. For antennas with very large axial ratios, the scattered signals can be larger than the true measurement signal. These scattered signals can change the sign of the phase and produce large errors in the amplitude at the null. If the separation distance between the antennas is adjusted after rotating to the null to produce a maximum amplitude, the scattered signal is in phase with the true measurement signal. If the distance is adjusted for the minimum at the null, the scattered and true signals are out of phase. Measurements at these two positions will produce the best measurement of the phase sign and the true amplitude. But if measurements are being performed at a number of frequencies, the maximum and minimum amplitude positions will be different for each frequency, and this will complicate automated multifrequency measurements. New improvements have been developed in the details of the measurements that greatly improve the determination of the phase sign and the amplitude at the null for multiple frequency measurements and these will be described and illustrated in the following paper. With these improvements, the estimated uncertainty of a 60 dB axial ratio is on the order of 1.8 dB. A new technique has also been developed to improve the source correction of the pattern data for probes with large axial ratios that guarantees that the on-axis polarization of the pattern data will be identical to the results of the Three-antenna measurement. The probe correction processing will then produce the highest accuracy results for the polarization of the AUT.
In this paper, we will discuss the impact of mounting structures on the installed performance of phased arrays. In particular, performance data for the Conformal, Lightweight Antennas for Aeronautical Communications Tech-nology (CLAS-ACT) antenna will be presented. Performance data from a series of mounting configurations will show that null depth and location is particularly susceptible to change while the main beam steering angle remains relatively stable. In addition, the Portable Laser Guided Robotic Metrology (PLGRM) system will be discussed as a suitable instrument for measuring antenna patterns in complex or difficult locations that are challenging for traditional ranges. The PLGRM system was recently developed at the National Aeronautics and Space Administration's (NASA) Glenn Research Center (GRC) and deployed to measure in situ antenna patterns.