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A multi-probe array (MPA) spherical near-field antenna measurement system, comprised of COTS equipment, has been developed for testing UHF antennas mounted in an aircraft rotodome. The spherical probe radius is 5 meters, which accommodates a 24 ft. diameter rotodome. The probe array, arranged in a circular arc about the test zone center, provides rapid time multiplexed samples of dual polarized spherical theta angle measurements. These measurements are collected at incremental steps of spherical phi angles, provided by a floor azimuth turntable. The rotodome is mounted on the azimuth turntable, and is rotated 360 degrees during a data collection. During one azimuth rotation, completed in a few minutes, a full set of 3D, dual polarized, multi-frequency near-field pattern data is collected. The data is transformed to full 3D far-field patterns in another few minutes, providing a complete rotodome test time within 15 minutes. The entire system is contained within a room 42’ x 42’ x 25’. This paper will describe the test requirements, physical requirements of the DUT, size constraints of the facility, and measurement speed goals. Alternate solutions and range geometries will be discussed, along with why the MPA solution is best given the requirements and size constraints. The system will be described in detail, including discussion of the room design, RF instrumentation, multi-probe array, positioning equipment, and controllers. Measurement results will be presented for test antennas of known pattern characteristics, along with other performance metrics, such as test times.
We have successfully designed and developed an innovative “CLose-range Antenna Scanner System” (or CLASS) suitable for measuring the far-field radiation pattern of installed antennae at short distances. The system consists of three key components: (1) a uniquely designed lens horn antenna that generates plane waves in close proximity, (2) a mechanical x-y scanner to scan the antenna-under-test, and (3) a customized stitching software to compute the far-field antenna pattern from the measured field information. The developed system has a scan area of 4.6 x 4.6 m, with resolutions of ±0.1mm in both the x and y traverse directions. The scanner structure is designed in a scalable fashion to cater for measurement of antenna installed at various locations (e.g. front and sides) on a platform. The system is capable of measurement from 1 to 18 GHz and generates far-field radiation pattern with a gain accuracy of ±1 dB.
For today's sophisticated antenna applications, the accurate knowledge of 3D radiation patterns is increasingly important. To measure the antennas under far-field conditions over a broad frequency band is hereby hardly impossible. By near-field to far-field transformation, one can overcome the difficulties of limited measurement distances. In common spherical near-field antenna measurement software, the transformation based on spherical mode expansion is typically implemented. These software tools only provide to correct the influence of first order azimuthal probe modes. The influence of the probe’s higher order modes though increases with shorter measurement distances. To measure a broad frequency range in one measurement set-up and to save time, dual ridged horns are popular candidates since they operate over a wide frequency range. The drawback is that they are probes of higher order. In this contribution, we will present an investigation on near-field measurements which are transformed into the far-field deploying the transformation technique based on spherical modes which is extended by a higher order probe correction capability. The resulting diagrams comparing first and higher order probe correction show that a correction is important in particular for the cross polarization In addition, the near-field data is transformed with an algorithm which employs a representation by equivalent currents. In this method, a higher order probe correction based just on the probe’s far-field pattern is integrated. The equivalent currents supported by an arbitrary Huygens surface allows to reconstruct the current densities close to the actual shape of the AUT which is mandatory for precise antenna diagnostics. Another issue needs to be accounted for regarding limited measurement distances and spherical modal expansion. While representing the AUT and the probe in spherical modes the radii of the spheres grow the more modes are included which depends on the sizes of the TX and the RX antennas. It has to be ensured that both spheres do not interfere. All measurements were carried out in the anechoic chamber of our laboratory in which measurements starting at 1 GHz are practicable according to the dimension of the chamber and of the absorbers. Due to our restricted measurement distance of 0.57 m, all the above mentioned rules need to be considered. In conclusion, small anechoic chambers are also capable of delivering precise antenna measurements over a broad frequency range due to algorithms capable of higher order probe correction.
For satellite applications payload measurements are a crucial part of the radio frequency validation campaign before the launch. Parameters like Equivalent Isotropic Radiated Power (EIRP), Input Power Flux Density (IPFD), Gain over Noise Temperature (G/T), Gain over Frequency (G/F), Group Delay, and Passive Intermodulation (PIM) are to be measured in suitable facilities on satellite level. State-of-the-art payload measurements are conducted in compensated compact range facilities which offer a real-time test capability which is easy to setup and use. Closed link tests are straightforward to realize with two compact range feeds employing feed scanning. The measurement techniques as well as the error budgets are well known. Near-field facilities are widely used for antenna pattern measurements. However, there is not much literature available discussing in particular measurements of G/T, G/F, and Group Delay in the near field. Measurements of the above parameters in the near field seem to be feasible, however, the processing of the measured data has to be adapted and further calibration measurements are required. In this paper methodologies for payload parameter measurements in compact range and near field facilities will be described. A comparison of payload measurement campaigns in near field and compact range facilities will be drawn. The techniques will be compared in terms of measurement timing and effort, practicability for satellite applications, and achievable accuracies.
In this paper, a patch antenna has been designed based on the complementary split ring resonator (CSRRs), complementary rose curve resonators (CRCRs) and without using these inclusions. Complementary rose curve resonators (CRCRs) are used in design of patch antenna. The Patch antenna based on the complementary rose curve resonators (CRCRs) are achieved by patterning the ground plane under the conductor trace. The perimeter of the Rose curve can be adjusted by tuning the amplitude of the sine function and the radius of the base circle. With the order of CRCRs, the loading effect of the complementary resonators on the patch antenna is controlled. This works demonstrated that higher order CRCRs allows more compactness of the design and higher miniaturization factor. We proposed a compact patch antenna based on the complementary split ring resonator (CSRRs) and the complementary Rose curve resonator (CRCRs). The proposed patch antenna shows good performances which is designed to operate at 2.4 GHz. The results demonstrate the configurability of the design for a specific size. The results show the effectiveness of using metamaterials in microwave circuit can obtain from n to n+1 of the CRCRs order will result in 0.3 % miniaturization. IndexTerms: Patch Antenna, Metamaterial, Size Reduction, split ring Resonators, Rose Curve Resonators
We have performed spherical and extrapolation scans of two antennas at 118 GHz using a commercial 6-axis robot. Unlike spherical scanning, linear extrapolations do not precisely conform to the natural circular movement about individual robot axes. To characterize the quality of the data, we performed dynamic position and orientation characterization of the robotic systems. A laser tracker is used to measure the probe antenna movement relative to the antenna under test, this information is used to continually update the position and posture of the probe during scanning. We correlated the laser tracker data with the mmWave insertion phase to validate dynamic measurement position results at speeds up to 11 mm/s. We previously demonstrated spherical measurements with this system. The extrapolation measurements presented here require more stringent accuracies for pointing that general pattern analysis
We present experimental results for on platform (in-situ) calibration of an antenna array with signals that are treated as signals of opportunity. In-situ calibration is required for antenna arrays installed on vehicles as platform scattering significantly perturbs the radiation patterns of the antenna elements. In-situ measurement of the array response requires: determining location of the unknown signals; determining the array’s response in the direction of the signals; and synthesizing the array pattern from the measured data. For this work, a seven element L-band antenna array was mounted on a generic aircraft platform. The platform was mounted on a dual rotator setup and emitters were placed nearby. The platform was then rotated while the emitters transmitted, and the signals received by the antenna elements were digitized. The collected data was then post processed to obtain the array calibration. We found that the calibrated array manifold enables more accurate direction of arrival estimation and provides additional gain in direction constrained beamforming. The present work serves as experimental verification of earlier simulation studies on in-situ array calibration.
The Space Communications and Navigation (SCAN) Testbed was a Software Defined Radio (SDR)-based payload launched to the International Space Station (ISS) in July of 2012. The purpose of the SCAN Testbed payload was to investigate the applicability of SDRs to NASA space missions in an operational space environment, which means that a proper model for system performance in said operational space environment is a necessary condition. The SCAN Testbed has line-of-sight connections to various ground stations with its S-Band Earth-facing Near-Earth Network Low Gain Antenna (NEN-LGA). Any previous efforts to characterize the NEN-LGA proved difficult, therefore, the NASA Glenn Research Center built its own S-Band ground station, which became operational in 2015, and has been successfully used to characterize the NEN-LGA’s in-situ pattern measurements. This methodology allows for a more realistic characterization of the antenna performance, where the pattern oscillation induced by the complex ISS ground plane, as well as shadowing effects due to ISS structural blockage are included into the final performance model. This paper describes the challenges of characterizing an antenna pattern in this environment. It will also discuss the data processing, present the final antenna pattern measurements and derived model, as well as discuss various lessons learned.
The single-offset compact antenna test range (CATR) is a widely deployed technique for broadband characterization of electrically large antennas at reduced range lengths [1]. The nature of the curvature and position of the offset parabolic reflector as well as the edge geometry ensures that the resulting collimated field is comprised of a pseudo transverse electric and magnetic (TEM) wave. Thus, by projecting an image of the feed at infinity, the CATR synthesizes the type of wave-front that would be incident on the antenna under test (AUT) if it were located very much further away from the feed than is actually the case with the coupling of the plane-wave into the aperture of the AUT creating the classical measured “far-field” radiation pattern. The accuracy of a pattern measured using a CATR is primarily determined by the phase and amplitude quality of the pseudo plane-wave with this being restricted by two main factors: amplitude taper (which is imposed by the pattern of the feed), and reflector edge diffraction, which usually manifests as a high spatial frequency ripple in the pseudo plane wave [2]. It has therefore become customary to specify CATR performance in terms of amplitude taper, and amplitude & phase ripple of this wave over a volume of space, termed the quiet-zone (QZ). Unfortunately, in most cases it is not directly apparent how a given QZ performance specification will manifest itself on the resulting antenna pattern measurement. However, with the advent of powerful digital computers and highly-accurate computational electromagnetic (CEM) models, it has now become possible to extend the CATR electromagnetic (EM) simulation to encompass the complete CATR AUT pattern measurement process thereby permitting quantifiable accuracies to be easily determined prior to actual measurement. As the accuracy of these models is paramount to both the design of the CATR and the subsequent determination of the uncertainty budget, this paper presents a quantitative accuracy evaluation of five different CEM simulations. We report results using methods of CATR modelling including: geometrical-optics with geometrical theory of diffraction [3], plane-wave spectrum [4], Kirchhoff-Huygens [4] and current element [3], before presenting results of their use in the antenna pattern measurement prediction for given CATR-AUT combinations. REFERENCES [1]C.G. Parini, S.F. Gregson, J. McCormick, D. Janse van Rensburg “Theory and Practice of Modern Antenna Range Measurements”, IET Press, 2014, ISBN 978-1-84919-560-7. [2]M. Philippakis, C.G. Parini, “Compact Antenna Range Performance Evaluation Uging Simulated Pattern Measurements”, IEE Proc. Microw. Antennas Propag., Vol. 143, No. 3, June 1996, pp. 200-206. [3]G.L. James, “Geometrical Theory of Diffraction for Electromagnetic Waves”, 3rd Edition, IET Press, 2007, ISBN 978-0-86341-062-8. [4]S.F. Gregson, J. McCormick, C.G. Parini, “Principles of Planar Near-Field Antenna Measurements”, IET Press, 2007.
Abstract Antenna far field phase pattern is important for some applications. It can be directly obtained in pattern measurement by far field test range (FFTR) or compact range (CR). However, it is found that the antenna far field phase pattern measured by current near field test range (NFTR) is not correct. For a uniform phase feeding plane array, its far field phase pattern should be near constant in 3dB beam width. However, the antenna phase pattern measured by current NFTR looks square curve vs angle. This paper found out that the root cause of the error is due to different reference planes. Both the amplitude pattern and the phase pattern obtained by current NFTR, in fact, refer to the probe scanner plane, not the antenna plane. This shifting of the reference plane has no effect on amplitude pattern, but has effect on phase pattern. After that, a correction method is proposed. One example is used for the root cause finding and correction technique explanation. According to this paper, if one wants to get phase pattern using NFTR, it is necessary to measure the distance between AUT and probe aperture accurately so as to correct it accurately after measurement and obtain accurate phase pattern.
Within the standard scheme for probe-corrected spherical data-processing, it has been found that for an efficient computational implementation it is necessary to restrict the characteristics of the probe pattern such that it contains only azimuthal modes for which µ = ±1 [1, 2, 3]. This first-order pattern restriction does not however extend to placing a limit on the polar index mode content and therefore leaves the directivity of the probe unconstrained. Clearly, when using this widely utilized approach, errors will be present within the calculated probe-corrected test antenna spherical mode coefficients for cases where the probe is considered to have purely modes for which µ = ±1 and where the probe actually exhibits higher order mode structure. A number of analysis [4, 5, 6, 7, 8] and simulations [9, 10, 11, 12] can be found documented within the open literature that estimate the effect of using a probe with higher order modes. The following study is a further attempt to develop guidelines for the azimuthal and polar properties of the probe pattern and the measurement configuration that can be utilized to reduce the effect of higher order spherical modes to acceptable levels. ? [1] P.F. Wacker, ”Near-field antenna measurements using a spherical scan: Efficient data reduction with probe correction”, Conf. on Precision Electromagnetic Measurements, IEE Conf. Publ. No. 113, pp. 286-288, London, UK, 1974. [2] F. Jensen, ”On the probe compensation for near-field measurements on a sphere”, Archiv für Elektronik und Übertragung-stechnik, Vol. 29, No. 7/8, pp. 305-308, 1975. [3] J.E. Hansen, (Ed.) “Spherical near-field antenna measurements”, Peter Peregrinus, Ltd., on behalf of IEE, London, 1988. [4] T.A. Laitinen, S. Pivnenko, O. Breinbjerg, “Odd-order probe correction technique for spherical near-field antenna measurements,” Radio Sci., vol. 40, no. 5, 2005. [5] T.A. Laitinen, O. Breinbjerg, “A first/third-order probe correction technique for spherical near-field antenna measurements using three probe orientations,” IEEE Trans. Antennas Propag., vol. 56, pp. 1259–1268, May 2008. [6] T.A. Laitinen, J. M. Nielsen, S. Pivnenko, O. Breinbjerg, “On the application range of general high-order probe correction technique in spherical near-field antenna measurements,” presented at the 2nd Eur. Conf. on Antennas and Propagation (EuCAP’07), Edinburgh, U.K. Nov. 2007. [7] T.A. Laitinen, S. Pivnenko, O. Breinbjerg, “Theory and practice of the FFT/matrix inversion technique for probe-corrected spherical near-field antenna measurements with high-order probes”, IEEE Trans. Antennas Propag., vol. 58,, No. 8, pp. 2623–2631, August 2010. [8] T.A. Laitinen, S. Pivnenko, “On the truncation of the azimuthal mode spectrum of high-order probes in probe-corrected spherical near-field antenna measurements” AMTA, Denver, November 2012. [9] A.C. Newell, S.F. Gregson, “Estimating the effect of higher order modes in spherical near-field probe correction”, AMTA 34th Annual Meeting & Symposium, Seattle, WA, October. 2012. [10] A.C. Newell, S.F. Gregson, “Higher Order Mode probes in Spherical Near-Field Measurements”, EuCAP, Gothenburg, April, 2013. [11] A.C. Newell, S.F. Gregson, “Estimating the Effect of Higher Order Modes in Spherical Near-Field Probe Correction”, AMTA 35th Annual Meeting & Symposium, Seattle, WA, October. 2013. [12] A.C. Newell, S.F. Gregson, “Estimating the Effect of Higher Order Azimuthal Modes in Spherical Near-Field Probe Correction”, EuCAP, The Hague, April, 2014.
In 2015, the Space Communications and Navigation (SCaN) Testbed project completed an S-Band ground station located at the NASA Glenn Research Center in Cleveland, Ohio. This S-Band ground station was developed to create a fully characterized and controllable dynamic link environment when testing novel communication techniques for Software Defined Radios and Cognitive Communication Systems. In order to provide a useful environment for potential experimenters, it was necessary to characterize various RF devices at both the component level in the lab and at the system level after integration. This paper will discuss some of the lab testing of the ground station components, with a particular focus / emphasis on the near-field measurements of the antenna. It will then describe the methodology for characterizing the installed ground station at the system level via a TDRS satellite, with specific focus given to the characterization of the ground station antenna pattern, where the max TDRS transmit power limited the validity of the non-noise floor received power data to the antenna main lobe region. Finally, the paper compares the results of each test as well as provides lessons learned from this type of testing methodology.
Measurement uncertainty is a vital parameter when assessing the performance of an antenna. Common measurement procedures such as field-probing give performance parameters of the quiet zone, such as amplitude-taper and ripple. However, relating these measurements to the actual measurement uncertainty is difficult at best. Furthermore the gain of the used probe has large influence on the outcome of the performance parameters, making measurement chamber intercomparison based on these parameters difficult. Quiet zone spherical near-field scanning fully describes the field distribution inside the quiet zone. Probe correction can be applied to compensate for the probe influence on the spherical modes. The mode spectrum consists of all electric waves propagating into the quiet zone. From the mode spectrum several performance parameters of the quiet zone can be derived. As an example the main beam power is concentrated in the m=±1 spectrum when aligned with the z-axis. Since other sources, having a different angle, have their mode spectrum spread over the m-spectrum, the power in m=±1 can be divided by the power in m?±1. This provides a signal-to-noise ratio which can be directly related to measurement uncertainty. Using the signal-to-noise ratio a new determination of the measured pattern uncertainty is found. In contrast to parameter derived from field-probing the new parameter is more general and comprehensive. In the paper we will derive new performance parameter and apply them to measured data in a CATR.
In the contemporary world there is high demand for mutual communications and data transmissions. More and more new radio communication systems are developed that require to prepare new types of antennas. Such requirements are satisfied by microstrip antennas. These antennas are characterised by many interesting features, both positive and negative, these attributes have to be taken into account in the design process. These antennas allow to miniaturise antenna system, and by this its highest density. It causes appearance of mutual couplings changing fields distributions on aperture antennas as well currents distributions in linear antennas. A methodology of shaping directional characteristics of microstrip antenna arrays will be presented in the article using phase shifters. Basing on the CST Microwave Studio software, two models of microstrip antenna arrays were designed and done using a method of radiation patterns shaping as well as real models that were put on measurements. Shapes of radiations patterns optimised according to the effects of signal amplitude and phase of particular antenna array radiators were presented in the article. The results were also presented in the tables taking into account values of phase shifts and amplitudes of power supplying system. The results achieved were compared with the results of measurements done on a special measuring position at the anechoic chamber.
Mars rover Direct-to-Earth (DTE) communication is an exciting new development that can maintain transfer of high volumes of scientific data from Mars to Earth. Currently, large orbiting assets are used as a relay to return scientific data, often containing higher data rates than current DTE systems. Therefore, the goal of this paper is to investigate antenna array topologies to augment DTE systems to support high data rates. The antenna design is complex, having to simultaneously support dual-band, high gain, high power handling, and circular polarization capabilities. An exhaustive study of patch elements in literature shows that current geometries are infeasible for a Mars rover DTE system. A CP Half E-shaped patch element is developed, containing important dual band S11/AR performance in the required RX and TX bands while featuring a single-feed single-layer design. Moreover, various subarray architectures are evaluated to determine if the gain requirements can be achieved. To meet this gain requirement, a 4x4 subarray topology is designed which allows a modular, scalable, and high gain design. To feed each of the 4x4 element subarrays, a stripline feed network is developed, consisting of a binomial impedance transformer and a four stage 1:2 power divider. This feed network supported a broadside radiation pattern for the subarray topology. These components are then integrated, first through a full wave simulation in HFSS. This rigorous study showed support for Mars rover DTE communications systems. The integrated subarray design is then fabricated and measured using a spherical near-field chamber in the UCLA Center for High Frequency Electronics (CHFE) facilities where measurements showed a very good comparison to the simulation results. Overall this integrated subarray design was successful, showing dual-band, high gain, high power handling, and CP performance.
It is a common practice when computing radiation patterns from non-uniformly sampled planar fields to interpolate the samples into a regular grid [1], although it might cause inaccuracies due to the interpolation process. The non-uniform fast Fourier transform (NUFFT) has been applied to process near field measurements in non-uniform planar grids with arbitrary precision [2], and also to analyze aperiodic arrays [3]. However, samples are usually treated as punctual sources. In this contribution, an efficient and accurate method to calculate the far field radiated by non-uniformly sampled planar fields which comply the Nyquist theorem using the non-uniform fast Fourier transform (NUFFT) is shown. The method takes into account the amplitude of the unit cell radiation pattern, which allows to compute more accurately the copolar and crosspolar components of the far field with regard to the array factor [3], which models the samples as punctual sources. For measured fields it is assumed that post-processing has been done, for instance, taking into account probe corrections. Because the NUFFT is precision-dependent, a discussion of how its accuracy can affect the computed radiated fields will be carried out. Numerical examples will be provided to show the accuracy and performance of the NUFFT with regard to the FFT and direct evaluation of the far fields. Finally, a study of computing times comparing the FFT, NUFFT and direct evaluation will be presented. References [1] Y. Rahmat-Samii, L. I. Williams, and R. G. Yaccarino, “The UCLA bi-polar planar-near-field antenna-measurement and diagnostics range,” IEEE Antennas Propag. Mag., vol. 37, no. 6, pp. 16–35, Dec. 1995. [2] R. C. Wittmann, B. K. Alpert, and M. H. Francis, “Near-field antenna measurements using nonideal measurement locations,” IEEE Trans. Antennas Propag., vol. 46, no. 5, pp. 716–722, May 1998. [3] A. Capozzoli, C. Curcio, G. D'Elia, and A. Liseno, “Fast phase-only synthesis of conformal reflectarrays,” IET Microw. Antennas Propag., vol. 4, no. 12, Dec. 2010.
Reflectarrays have been widely studied in the past 3 decades and several techniques have been developed for the synthesis of shaped-beam far-field radiation patterns [1]. Also, some near-field applications have been studied, such as imaging [2] or RFID [3]. In this contribution, a near-field synthesis technique is proposed for the reflectarray quiet zone optimization, which can be of interest in the design of probes for compact antenna test ranges (CATR) at high frequencies. The near-field of the reflectarray is characterized by a simple radiation model which computes the near field of the whole antenna as far-field contributions of each element. The reflectarray unit cell is considered the unit radiation element and its far field is computed employing the second principle of equivalence. Then, at each point in space, all contributions from the elements of the reflectarray are added in order to obtain the near field [4]. This simple model has been validated through simulations with GRASP [5] and also through near-field measurements. Then it has been used to optimize the near field of the reflectarray. The Intersection Approach algorithm is used to optimize both amplitude and phase of the near field radiated by the antenna, and uses the Levenberg-Marquardt algorithm [6] as backward projector. This optimization increases the size of the quiet zone generated by the reflectarray. References [1] J. Huang and J. A. Encinar, Reflectarray Antennas Wiley-IEEE Press, 2008. [2] H. Kamoda et al., "60-GHz electronically reconfigurable large reflectarray using single-bit phase shifters," IEEE Trans. Antennas Propag., vol. 59, no. 7, pp. 2524–2531, July 2011. [3] Hsi-Tseng Chou et al., "Design of a near-field focused reflectarray antenna for 2.4 GHz RFID reader applications," IEEE Trans. Antennas and Propag., vol. 59, no. 3, pp. 1013–1018, March 2011. [4] D. R. Prado, M. Arrebola, M. R. Pino, F. Las-Heras, "Evaluation of the quiet zone generated by a reflectarray antenna," International Conference on Electromagnetics in Advanced Applications (ICEAA), pp. 702–705, 2-7 Sept. 2012. [5] "GRASP Software", TICRA, Denmark, http://www.ticra.com. [6] J. Álvarez et al., “Near field multifocusing on antenna arrays via non-convex optimisation,” IET Microw. Antennas Propag., vol. 8, no. 10, pp. 754–764, Jul. 2014.
This paper gives a review of cross-eye (CE) jamming using the retro-directive channel implementation. CE jamming is an electronic warfare self-protection technique in which the phase-front of an electromagnetic wave, transmitted towards a threat radar, is distorted in a way similar to radar glint. A retro-directive channel is used in the implementing of the CE jammer to avoid prohibitive tolerance requirements on the electronic warfare (EW) system. In a practical implementation of the CE jammer in an EW system, active electronically scanned array antennas (AESA) can be used to fulfil effective radiated power requirements. The achievable reciprocity i.e. similarity between the transmission and reception radiation patterns in the AESA is central to the performance of the CE jammer system. Effects of the CE jammer on mono-pulse radar are presented and described. The effects include the mixing of a CE jammer signal and a target echo. The CE jammer can induce false target angles and prevent the radar from finding a stable settling angle. The origin of CE jamming is in the field of radar multipath phenomenon such as glint and reflections from water surfaces. The CE jamming technique has previously been described and analyzed in various literature. This paper summarizes the most recently published results and gives references to the publications.
Antenna range calibration is commonly performed with the goal of obtaining the gain of an antenna under test. The most straightforward calibration procedure makes assumptions about the polarization properties of the range illumination, which can lead to both polarization and gain errors in the measured patterns. After introducing the concept of polarization correction we describe three published range polarization correction techniques and provide an example of polarization correction applied to a compact antenna test range measurement. We then discuss the practical aspects of incorporating polarization correction into the range calibration workflow.
Comparisons are made between far-field patterns of an X-band polarization reference horn obtained using the equally-spaced, latitude, and uniform near-field measurement grids. All of the far-fields were obtained by transforming the measured near-field data. Measurement and data processing times are also presented, such that the reader can understand the benefits and drawbacks of the equally-spaced, latitude, and uniform grids. In addition to these comparisons, the sampling requirements of the latitude grid are investigated. In the past, it has been recommended to thin the uniform grid near the poles of the measurement sphere, which is referred to as latitude sampling. The typical method is to multiply the number of sample points required on the equator by a sin(theta) weighting function to obtain the number of sample points required near the poles. However, it will be shown that the sin(theta) weighting function may lead to aliasing in certain cases, and a new method is proposed which is guaranteed to minimize aliasing for any antenna-under-test. We refer to this new grid as the Maximum Fourier Content (MFC) latitude grid.