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Measurements of antenna prototypes are a critical component of the development cycle for antennas, arrays, and other radiating structures. Benchtop tests to characterize the circuit performance of such devices are generally available to engineers and scientists, but the ability to capture the space (radiating) characteristics is often lesser available. This is not only due to the need for a vector network analyzer but also the necessity for mechanical infrastructure to sample the fields in a scan volume around the antenna (i.e., antenna range). Moreover, the software capable of any data manipulation is needed to obtain the far-fields either directly or from the sampled near-fields. Herein, we describe the initial exploratory development of a low-cost, bench-top, custom spherical range. The system consists of a phi-stage turntable where the antenna under test (AUT) is mounted, a theta-stage swing arm that sweeps the probe antenna in an arc about the center of rotation, and a polarization stage turntable on the probe antenna side. An adjustable scan radius of 30-40 cm is built into the theta-stage. The bulk of the range is fabricated using standard fused deposition modeling (FDM) 3D printing and inexpensive commercial off-the-shelf (COTS) components are used for the motors and controllers to keep cost of the system (excluding the network analyzer and RF cables) to around 500 US dollars, in accordance with the restrictions for an advanced antennas course class project. Development, fabrication, and assembly took place over the course of approximately a month. The drawbacks of the utilized materials, however, primarily manifest in the oscillations of the theta-stage due to the low-infill ratio (~10%) of the 3D printed plastic in conjunction with the weight of the probe antenna. Additionally, a basic spherical near-field to far-field transform code is developed. The measurement results of a wideband horn antenna are performed to validate the range performance and will be shown and discussed at the conference. Thoughts on future development and potential are also shared.
Ultra-Wideband (UWB) calibration of RCS measurement radar systems, particularly outdoor, ground-to-air dynamic signature measurement radars, are conventionally accomplished using calibration devices (CD) attached to static towers, tethered from balloons, dropped from helicopters or other air vehicles, or with active RF repeater systems. These methods all contain errors from background-target interactions, or are operationally compromised, or are expensive. For high accuracy RCS radar calibration, a revolutionary methodology and architecture is mandatory to support demanding new radar metrology requirements. Within this paper, an update of ongoing efforts toward developing an autonomous, airborne drone-based CD is provided. The radar reflectivity of such a device must have a highly reproducible RCS, as manifested by a narrow, well defined probability distribution function (PDF), and should be independent of viewing aspect. Computational electromagnetic simulations were used to predict the RCS of a 60.9-cm diameter autonomous Spherical Passive/Active Calibration Device (SPARCS) with periodic, hexagonal “honeycomb” electromagnetic screens for inlet/outlet ports of the propulsion system. Three methods were used to predict the RCS, including Large Element Physical Optics (LE-PO), Physical Optics (PO) and Method of Moments (MoM) using the Adaptive Cross-Approximation (MoM-ACA). All methods show reduced cross section at angles centered on the periodic hexagonal RF screens. LE-PO resulted in a 30-fold decrease in computational expense relative to PO, but had a higher standard deviation. MoM-ACA calculations are ~57-fold more computationally expensive than PO results, but provide the full wave solution. PDFs determined from UWB RCS measurements have a narrow distribution and show reasonable agreement with calculations. These results validate the RCS signatures of the autonomous, airborne, spherical CD incorporating inlet/outlet RF screens as a valid calibration target.
Phased array antennas are often built from sub-arrays with identical or symmetrical layout. At an early project stage, performance verification measurements of the sub-array are valuable to proof the single module design. However, the characteristics of the final antenna are questionable without further processing. This work presents a concept that is based on far-field measurements of a sub-array in a Compact Antenna Test Range (CATR) in conjunction with planar near-field (PNF) processing to synthesize the entire phased array antenna characteristics. The procedure is explained with an example of a dual linear polarized L-band planar phased array antenna for an airborne synthetic aperture radar application. It is shown that the measured sub-array can be complemented by the synthesized twin to evaluate the characteristics of a final antenna that is not yet available in this form. The resulting performance of the synthesized entire phased array is presented and compared with simulations. The presented post-processing method would be beneficial to characterizing radiation patterns of large phased arrays by measuring only sub-arrays in a limited test-zone with any measurement principle.
While the size of the parabolic reflector in general determines the usable area of the quiet zone of a compact antenna test range (CATR) inside which a pseudo plane-wave condition is produced, the reflector edge treatment also plays a significant role in terms of overall quality and electromagnetic field distribution & uniformity, and especially so at mm-wave frequencies. Using modern powerful digital computational simulation technology in combination with genetic optimization, the edge treatment can be evolved for a specific CATR application as part of the design process. This is crucial as it attempts to maximize the performance of a given solution while ensuring efficient use of the available space which correspondingly provides an economical implementation. This is particularly important in 5G production test applications where, in many instances, multiple systems are required to be collocated within a given host building and in which case, the savings become multiplicative. In this paper the novel design methodology is introduced for the genetic optimization (GO) of blended rolled edge single offset reflector CATRs. Several edge blends and treatments are considered with the genetically optimized design parameter. For each variation the quiet-zone performances are compared and contrasted.
This paper presents a novel method using multiple compact antenna test range (CATR) reflectors to simulate the Radio Resource Management (RRM) measurements required for 5G devices capable of beam-forming in the millimeter wave frequency range (i.e. FR2). Four CATR reflectors are arranged on a semi-circle with the device under test (DUT) on a dual axis positioner in the center of the intersection of four planar waves in order to generate five sets of two Angles of Arrival (AoA), thereby capable of simulating multiple basestations from different directions for the 5G device to monitor and perform handovers. The reflectors create far-field conditions at the device under test (DUT) such that quiet zones of up to 20-30cm in size can be achieved. Absorber baffles are strategically placed as to reduce scattering from adjacent reflectors. In addition to RRM measurements, one reflector can be used to also perform in-band RF beam characterization[JMFL2] while additional reflectors can measure out of band emissions at the same time, thereby decreasing total measurement times by a factor of 2-3 times.
Direct far-field (DFF) testing has become the standard test methodology for sub-6 GHz over the air (OTA) testing of the physical layer of radio access networks with the far-field multi-probe anechoic chamber (FF-MPAC) being widely utilized for the test and verification of massive multiple input multiple output (Massive MIMO) antennas when operating in the presence of several users. The utilization of mm-wave bands within the 5th generation new radio (5G NR) specification has necessitated that since the user equipment should, preferably, be placed in the far-field of the base transceiver station (BTS) antenna, excessively large FF-MPAC test ranges are required or, the user equipment is paced at range-lengths shorter than that suggested by the classical Rayleigh criteria or, a modified compact antenna test range geometry must be developed and utilized. This paper presents a novel design for a new compact antenna test range (CATR) design that uses a parabolic toroid as the main reflector. The folded optics utilized within this design possesses superior pseudo-plane wave scanning capabilities than those available from equivalent, classical, point source offset parabolic reflector CATR designs. This wide-angle scanning capability is a crucial feature for successful over-the-air testing and measurement of mm-wave 5G NR Massive Multiple Input Multiple Output (MIMO) antenna systems within multi-user applications providing 60 degrees of azimuth scan and 15 degrees of elevation scan to the incoming plane wave at the AUT. CATR quiet-zone results are presented, compared and contrasted with more classical designs before results of the effects of the CATR test channel on a number of commonly encountered communication system figures of merit in wide scanning cases are presented.
A method to solve the far-field distance problem is the usage of reflectors in order to transform the spherical wave from the feed antenna into a plane wave which ultimately leads to the same far-field condition but in a more compact way. Therefore, these facilities are called compact antenna test ranges (CATRs). However, the finite size of the reflector(s), despite edge treatment, is the main cause of erroneous signals impinging into the test zone in which an antenna under test (AUT) is characterized. Especially at lower frequencies, every further structure inside the test chamber, although covered with absorbers, is an additional source of scattered signals. One method of correcting stray signals and to improve the AUT measurement accuracy is to compensate the non-ideal test-zone field (TZF) via spherical wave expansion (SWE). For this technique, a complete description of the TZF, i.e. measurements on a closed surface around the test zone, is required. The most convenient approach is to use a spherical scanning surface. In ranges with a roll-over-azimuth positioning system, the spherical scanning can be realized by an additional measurement arm. Using the chamber positioning system, thus, strongly reduces the required additional hardware and makes spherical scanning of the test zone a practical approach. With the knowledge of the incident unwanted field components, AUT measurements carried out in the corresponding test zone are correctable. Spherical near-field measurements of the test zone created by the CATR installed at the Institute of High Frequency Technology, RWTH Aachen University are performed at a frequency of 2.4 GHz using a simple scanning arm. Reliability of the results is ensured by comparing the measurements to full-wave simulations of the CATR. The radiation pattern of a base transceiver station antenna serves as a test case and is subsequently corrected for the erroneous signals using the SWE.
Advanced driver assistance systems (ADAS), such as blind spot warning and braking assistants, have been in use for years to improve road security. ADAS are currently further promoted through the autonomous driving trend. Due to their cost / performance trade-off, the automotive industry perceives 4-D high-resolution radar sensors, as one of the backbones of autonomous driving. With human safety being at stake, the topic of calibration of these sensors is obviously of the utmost importance. Performing an accurate calibration requires a test condition where the target is in the far-field of the radar under test (RUT). Due to the requirements for angular resolutions, 77 / 79 GHz radars with 15 cm radiation aperture or more are quite common. Applying Fraunhofer formula then results into a necessary measurement range length of 11.5m. Because of the high cost of ownership of an adequate anechoic range, radar manufacturers usually limit their measurements to the strict minimum and try to simplify the calibration process. A typical approach is to go for a diagonal calibration where the target is always at boresight for each beam-formed pattern of the RUT. This technique however delivers a sub-optimal compensation of the RUT biases. In particular, it creates high peak-to-side-lobe ratios (PSLR), where energetic echoes are observable in directions of side lobes of each beam. This paper introduces a new system for radar measurements, made of a short-size focal length offset-fed compact antenna test range (CATR), interfaced with an analog echo generator. With a chamber size of only 0.9 m x 2 m x 1.6 m, the setup has been designed to test apertures up to 30 cm size. The quality of the quiet zone achieved is discussed in the paper, as well as various uncertainty contributions relating to radar measurements. Tests are presented which involve a latest generation 4-D imaging radar on chip (RoC). Results obtained in the CATR are compared to a reference 7 m far-field range. Diagonal and full angular calibrations of the RoC are carried out and analyzed, demonstrating an improvement of 10 dB PSLR when the target is swept over the complete azimuth region.
Time and Direction of Arrival (TADOA) analysis of field probe data has been an accepted method for characterizing stray signals in an antenna measurement range for many years ([1], [2]). Recent uncertainty investigations at the OneRY range have shown a need for increased resolution to isolate and characterize energy in TADOA images so that resources can be carefully applied to reduce the uncertainty from these stray signals. This is accomplished by modeling the TADAO image as the solution to a Basis Pursuit (BP) l1 minimization problem. This paper outlines the model development and shows concrete examples from OneRY field probe data where BP allows for the identification of stray energy which was previously difficult to find. We also show how the BP optimization context can be using to remove contamination from the data through the inclusion of additional basis functions ([3]). I.J. Gupta, E.K. Walton, W.D. Burnside, “Time and Direction of Arrival Estimation of Stray Signals in a RCS/Antenna Range,” Proc. of 18th Annual Meeting of the Antenna Measurement Techniques Association (AMTA '96), Seattle WA, September 30-October 3, 1996, pp. 411-416. I.J. Gupta, T.D. Moore, “Time Domain Processing of Range Probe Data for Stray Signal Analysis,” Proc. of 21st Annual Meeting of the Antenna Measurement Techniques Association (AMTA '99), Monterey Bay CA, October 4-8, 1999, pp. 213-218. B.E. Fischer, I.J. LaHaie, M.H. Hawks, T. Conn, “On the use of Basis Pursuit and a Forward Operator Dictionary to Separate Specific Background Types from Target RCS Data,” Proc. of 36th Annual Meeting of the Antenna Measurement Techniques Association (AMTA '14), Tucson AZ, October 12-17, 2014, pp. 85-90.
In this contribution we demonstrate a method to measure the absolute Group Delay (GD) of a high gain dual feed offset reflector antenna for circular polarized signals in Ku- and S-band by which we reach a measurement accuracy better than 10 picoseconds. At first we discuss the definition and different possible measurement methods of GD. We specifically show that the utilization of the antennas phase centre does not lead to the demanded measurement accuracy. Instead we propose a measurement method that uses an electrically small Reference Antenna (RA). We use the measurement of the GD of the RA as a reference for the GD of the Antenna Under Test (AUT). Therefore the exact positions of the reference planes of the corresponding wave guide ports have to be ensured. For this we made use of a theodolite. These measurements must be performed in a Compensated Compact Range to meet the strict requirements of plane waves. Here the CCR of the Lab for Satellite Communication, Munich University of Applied Sciences was used. The GD of the (electrically small) RA is determined by measuring the GD of two identical RAs separated by an exact known free space distance and by referencing these measurements to the measured GD of the same arrangement, where the free space is bypassed by a long high precision rectangular wave guide with well-known dimensions. We demonstrate that by using a soft gating method the accuracy of the measurement results can be tremendously improved. Measurement results parametrized by the width of the gate window in the time domain are discussed. We further discuss the accuracy of the measurement results quantitatively and we especially show, that the influence of an antenna misalignment is negligible, as long the alignment error is smaller than the one dB power beam width. The measurement campaign was commissioned by the European Space Agency (ESA) to meet the requirements of the project Atomic Clock Ensemble in Space (ACES). By ACES a microwave link is used to compare the times given by different atomic clocks in space and on earth, so three ACES ground terminals were tested.
Among different measurement techniques for the wall reflectivity, an RCS_based technique has been implemented and test results are reported. For most of the anechoic chambers, the factory acceptance test and a quality-control check is sufficient for the customers to be sure that the absorbers used to line their chamber are good enough. In some cases, a quiet-zone reflectivity measurement will certify that the chamber yields the quietness as needed for the specific application of the customer. This last technique is mostly used in the far-filed ranges. However, in some anechoic chambers, e. g. some compact ranges, the customer wants to know the effect of the installation and the shipment on the final absorber installed in the room. That is why, they ask for a wall reflectivity measurement to see the reflectivity of the absorbers after being installed. The main problem to be solved when talking about wall reflectivity is the un-wanted clutter in the room which needs to be compensated for. Last year at AMTA 2016, we have introduced a clutter-removal technique to reduce the unwanted shattering levels. That was supported by some lab implementations and accordingly some limitations in the implementation. This paper, explains the result of the first practical on-site test done in an anechoic chamber. Many different points in the chamber have been tested and a detailed discussion of the results are brought to view.
The portable antenna measurement system PAMS was developed for arbitrary and irregular near-field scanning. The system utilizes a crane for positioning of the near-field probe. Inherent positioning inaccuracies of the crane mechanics are handled with precise knowledge of the probe location and a new transformation algorithm. The probe position and orientation is tracked by a laser while the near-field is being sampled. Far-field patterns are obtained by applying modern multi-level fast multipole techniques. The measurement process includes full probe pattern correction of both polarizations and takes into account channel imbalances. Because the system is designed for measuring large antennas the RF setup utilizes fiber optic links for all signals from the ground instrumentation up to the gondola, at which the probe is mounted. This paper presents results of the Ka-band test campaign in the scope of an ESA/ESTEC project. First, the new versatile approach of characterizing antennas in the near-field without precise positioning mechanics is briefly summarized. The setup inside the anechoic chamber at Airbus Ottobrunn, Germany is shown. Test object was a linearly polarized parabolic antenna with 33dBi gain at 33GHz. The near-fields were scanned on a plane with irregular variations of over a wavelength in wave propagation. Allowing these phase variations in combination with a non-equidistant grid gives more degree of freedom in scanning with less demanding mechanics at the cost of more complex data processing. The setup and the way of on-the-fly scanning are explained with respect to the crane speed and the receiver measurement time. Far-fields contours are compared to compact range measurements for both polarizations to verify the test results. The methodology of gain determination is also described under the uncommon near-field constraint of coarse positioning accuracy. Finally, the error level assessment is outlined on the basis of the classic 18-term near-field budgets. The assessment differs in the way the impact of the field transformation on the far-field pattern is evaluated. Evaluation is done by testing the sensitivity of the transformation with a combination of measured and synthetic data.
Abstract— Tilting the receive end wall of a compact range anechoic chamber to improve Radar Cross-Section (RCS) measurements has been a tool of the trade used since the earliest days of anechoic chambers. A preliminary analysis using geometrical optics (GO) validates this technique. The GO approach however ignores the backscattering modes from the reflected waves from a field of absorber. In this paper, a series of numerical experiments are performed comparing a straight wall and a tilted wall to show the effects on both the quiet zone and the energy reflected back towards the source antenna. Two Absorber covered walls are simulated. Both walls are illuminated with a standard gain horn (SGH). The effects of a wall tilted back 20° are computed. The simulations are done for 72-inch long absorber for the frequency range covering from 500 MHz to 1 GHz. The ripple on a 10 ft (3.05 m) quiet zone (QZ) is measured for the vertical wall and the tilted wall. In addition to the QZ analysis a time-domain analysis is performed. The reflected pulse at the excitation antenna is compared for the two back wall configurations Results show that tilting the wall improves measurements at some frequencies but causes a higher return at other frequencies; indicating this method does not provide a broadband advantage. Keywords: Anechoic Chamber Design, Radar Cross Section Measurements, Geometrical Optics
Equivalent Isotropically Radiated Power (EIRP), Saturating Flux Density (SFD) and Group Delay (GD) are three system level parameters often measured during the characterization of spacecraft systems. EIRP is of interest for transmitters, SFD for receivers and GD for the entire up/down link. A test methodology for EIRP and SFD was first presented in [1] and [2] and a detailed procedure presented in [3]. To date GD has only been measured under far-field (or simulated far-field) conditions. In [4], a concept for measuring GD in a planar near-field (PNF) range is described, but no methodology is presented. In this paper, we present a method for measuring GD in a planar near-field range. The technique is based on a set of three antenna pairs, measured sequentially, from which the insertion phase of the measurement system and the near-field probe [5] can be resolved. Once these parameters are known, insertion phase for the device under test (i.e. a Tx or Rx antenna) can be measured and GD calculated as the negative frequency derivative of the insertion phase. An added complexity in the case of a near-field measurement is the near-field probe is in close proximity to the device under test (not far-field condition) for which compensation is needed. We show through simulation and measurement, that the plane wave expansion allows us to compute a correction factor for the proximity of the probe to the device under test; thus allowing correction of the measured insertion phase. The final step in measuring payload GD through both uplink and downlink channels is to set up a fixed Tx probe in close proximity to the Rx antenna and an equivalent Rx probe in close proximity to the Tx antenna and performing a through measurement as one would do on a far-field range. Correction factors for compensating for the proximity of both probes are then applied, based on independent a-priori Rx and Tx case measurements performed on the antennas. Simulated and measured data will be presented to demonstrate the process and to illuminate some of the finer nuances of the correction being applied. Index Terms— Group Delay, Planar Near-Field, Antenna Measurements, Three Antenna Method. [1] A. C. Newell, R. D. Ward and E. J. McFarlane, “Gain and power parameter measurements using planar near-field techniques”, IEEE Trans. Antennas &Propagat, Vol 36, No. 6, June 1988 [2] A. C. Newell, “Planar near-field antenna measurements”, NIST EM Fields Division Report, Boulder, CO, March 1994. [3] D. Janse van Rensburg and K. Haner, “EIRP & SFD Measurement methodology for planar near-field antenna ranges”, Antenna Measurement Techniques Association Conference, October 2014. [4] C. H. Schmidt, J. Migl, A. Geise and H. Steiner, “Comparison of payload applications in near field and compact range facilities”, Antenna Measurement Techniques Association Conference, October 2015. [5] A. Frandsen, D. W. Hess, S. Pivnenko and O. Breinbjerg, “An augmented three-antenna probe calibration technique for measuring probe insertion phase”, Antenna Measurement Techniques Association Conference, October 2003.
Cellular Base Stations require efficient performance validation methods. One performance criterion is the Station radiation pattern. In directive pattern measurements, it is well documented that the Compact Antenna Test Range (CATR) and the Spherical Near Field (SNF) methods produce equivalent patterns. However, Base Station radiation patterns are not necessarily directive to the extent necessary for equivalent patterns among CATR and SNF methods. In deploying a number of Spherical Near Field and point source Compact Antenna Test Range (CATR) test facilities, we have observed the radiation pattern of base station antennas are more sensitive to the mount in a CATR than in a Spherical Near Field Antenna Test Range. This fact conflicts with intuition and theory. A barbeque spit positioner has been deployed in both spherical near field and point source compact ranges. Recently the point source compact range has been observed to yield patterns noticeable different depending on the antenna mount to the spit. On the other hand, the Spherical Near field implementation, in at least two deployments to Germany, has NOT manifested such a dependence on the mount, or, perhaps, such a dependency exists and yet has not been recognized. Measured Data will be presented showing radiation dependencies upon the mount in a CATR and SNF implementation. Explanations as to the Root Cause will be stated.
As part of the Lockheed Martin (LM) Additive Manufacturing (AM) Initiative, the Rotary Mission System antenna group has been developing a new and improved Additive Spiral Antenna (ASA) for both transmit and receive applications. This is a collaboration effort between LM engineering and LM manufacturing for a low cost and high performance antenna for manyultra-wide band(UWB) applications in both military and commercial market sectors. Unlike other conventional spiral designs, thisrecently emerging Additive Manufacturing capabilities allow extra spiral antenna miniaturizations without additional gain bandwidth performance penalties. This is achieved by leveraging unique low cost AM abilities to form complex and thus much more efficient 3D shapes to increase spiral antenna radiation efficiency, approaching the Chu’s gain bandwidth limitation. An initial prototype ASA was designed and tested in 2016 and showed very encouraging results. The measured ASA performance indicated nearly the same antenna performance as our current conventional production spiral antenna having multi-decade frequency band performance. More importantly, the ASA aperture size was significantly reduced by more than 50% with excellent transmit and receive gain efficiency and power handling capabilities. This paper will describe this ASA prototype design approaches and antenna near field and far field compact range measurement results along with material characterizations to demonstrate Additive Manufacturing technology can enhance antenna performance that otherwise not realizable with conventional fabrications. In addition, an integrated optimum balun length electromagnetic band gap (EBG) cavity design further reduces the antenna depth by over 70% will be presented. This is realized by use of high power and high temperature honeycomb absorbers in conjunction to electromagnetic band gap (EBG) cavity design for achieving high efficiency and low cavity profile, with total antenna volume reduction by nearly 3x. Some discussions will be provided for solving high thermal issues associated with ASA’s transmit capabilities.
A detailed study of several analytic methods for the simulation of compact antenna test range (CATR) quiet zone field is presented. The focus of the present paper is to develop a fast simulation model suited to an optimization process of the CATR geometry in order to minimize the desired quiet zone parameters, such as amplitude taper and ripple, phase variation and crosspolar level, for a wide range of frequencies. The algorithms introduced are based on physical optics (PO) which provides accurate results at high frequencies, when the reflector size is very large in wavelengths. Unlike conventional PO algorithms where the surface current integration is performed with a finite integral, here the problem is addressed by modeling the reflector surface as a set of equivalent radiating planar triangles. Comparisons between the developed method and the direct integration are given to justify the computational savings. A Fast Physical Optics algorithm is implemented for evaluating the quiet zone field to further reduce computational times.
Raytheon, El Segundo, CA chamber #2 is a dual reflector, indoor compact range that is the largest facility of its kind within the company. A series of tests were performed to characterize the measured transfer function of the chamber because of a recent capital upgrade of the range measurement system. The purpose of this paper is to document and discuss the results of the characterization testing, review how the measured transfer function of the range was determined, and compare the current results with both past data and analytical predictions, and demonstrate how this transfer function is used for antenna and radar cross section (RCS) measurement characterization. The measured transfer function of the range is used for both antenna and RCS measurement characterization. For antenna measurements, the transfer function is used in the Friis transmission equation to determine, for example, the expected power at the receiver given the transmit power and gain of both the transmit antenna and the antenna under test. Appropriate amplification and/or attenuation can determined as part of the test planning process saving time during test setup and test execution. For RCS measurements, the transfer function was recently utilized to study the benefits and challenges of relocating our instrumentation radar from a smaller compact range to this large compact range. The motivation for the study was enhanced measurement capability for larger targets and lower frequencies. This study utilized noise equivalent RCS (NERCS) as the metric and transmit power, pulse width, and pulse integration as the study parameters to find a practical solution for optimizing NERCS.
Compact Antenna Test Range (CATR) provide convenient testing, directly in far-field conditions of antenna systems placed in the Quiet Zone (QZ). Polarization performance is often the reason that a more expensive, complex, compensated dual reflector CATR is chosen rather than a single reflector CATR. For this reason, minimizing the QZ cross-polarization of a single reflector CATR has been a challenge for the industry for many years. A new, dual polarised feed, based on conjugate matching of the undesired cross polar field in the QZ on a full wave-guide band, has recently been developed, manufactured and tested. The CXR feed (cross polar reduction feed) has shown to significantly improve the QZ cross-polar discrimination of standard single reflector CATR systems. In previous papers, the CXR feed concept has been discussed and proved using a limited scope demonstrator and numerical analysis. In this paper, for the first time, the exhaustive testing of the dual polarised feed operating in the extended WR-75 waveguide band (10-16 GHz) is presented. Accuracy improvements, achieved in antenna cross-polar testing, using this feed is also illustrated by measured examples.
A high quality antenna feed is an essential element of a compact antenna test range (CATR) in order to ensure the range can achieve the necessary stability in beam width, phase center and the necessary purity of polarization throughout the range’s quiet zone. In order to maintain the requisite quality, such feeds are typically 1) single-port and 2) cover a relatively limited band of frequencies. It is desirable to have a single dual ported, broadband feed that covers multiple waveguide bands to eliminate the need for a polarization positioner and avoid the difficulty associated with changing feeds for a single antenna measurement. Though some such feeds exist in the market, with such feeds, we often see a reduction in polarization purity across the band of interest relative to the more band limited feeds. Previous attempts to utilize dual-port probes and/or extend the bandwidth of the feed have resulted in degraded performance in terms of beam pattern and polarization purity. In an attempt to overcome some of the deficiencies above, the authors have applied polarization processing to dual-pol antennas to correct for the impurity in polarization of the antenna as a function of frequency. We present here a broadband CATR feed solution using a low-cost, dual-port sinuous feed structure combined with polarization processing to achieve low cross-pol coupling throughout the quiet zone. In the following paper, the feed structure, polarization theory, and processing algorithm are described. We also present co- and cross-pol coupling results before and after correcting for the polarization distortion using data collected in two CATRs in Atlanta, GA and Asia.