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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.
Open-area test site (OATS) is a basic range for measuring omni antennas at VHF/HUF band. Reflections from the trees nearby, from the edge of the metal ground plane of an OATS are researched with the aid of ultra-broadband calculable dipole antennas (CDAs). Usually, these reflections are detrimental to precise antenna measurements from 20 MHz to 1 GHz; however they are very difficult to analyze accurately, since no rigorous theory exists on the relationship between the reflections and the configurations of an OATS. For this difficulty, a pair of very accurate and broadband CDAs are manufactured and verified with a slightly modified near-field method, whose site-insertion-loss deviation (?SIL) between measurements and simulation is less than 0.3 dB over 10 MHz to 340 MHz for a single pair of dipole elements resonated at 90 MHz. Based on the optimized CDAs, the effects of ground plane sizes, wire mesh shapes around the edge of the metal ground plane, trees nearby and especially masts are researched. The research shows that the reflections from the edge of an optimized ground plane is less than 0.1 dB at 10 m range. Finally, the performance of an OATS with these optimizations is verified: for 10 m separation, ?SIL is within 0.26 dB at horizontal polarization (HP) and within 0.34 dB at vertical polarization (VP) for the typical 24 frequencies from 30 MHz to 1 GHz; at 20 m separation, ?SIL is within 0.59 dB (HP) and 0.85 dB (VP) from 20 MHz to 500 MHz. An example for the uncertainty of calibration the free-space antenna factor of tuned dipole antennas are provided, too.
Flexibility and reconfigurability technologies for antenna designs are presented, investigated and merged in this paper to design a flexible and reconfigurable antenna. Prior to designing the proposed antenna, a review was undertaken to choose the best antenna configuration and flexible substrate that meet the flexibility and reconfigurability objectives. It is concluded that planar printed antennas with coplanar waveguide (CPW) feeding are the most attractive designs due to the ease of fabrication for flexible antennas and the ease of integration of active devices for reconfigurability. This paper presents a flexible reconfigurable antenna, which is designed based on the concept of printed folded slot antennas with CPW feeding technique. The High Frequency Structure Simulator (HFSS) is used to design and simulate the proposed antenna. It is designed on a very thin flexible substrate, Polyethylene terephthalate (PET) film, which is chosen since it has a low loss compared to other flexible substrates, such as paper type substrates. Moreover, it is less fragile than other substrates when it is used for high bending applications. From the literature, slot antennas and folded slot antennas are reconfigured by altering the length of the slot to tune the resonant frequency. Here we present an alternate technique to reconfigure folded slot antennas. One PIN-diode is used to redirect the current on the internal stub inside the slot, which results in a radiating stub, acts as a dipole for a second resonant frequency. When the PIN-diode is forward biased (ON), the proposed antenna has a single band due to the slot at 2.42 GHz for Wireless Local Area Network (WLAN) applications. When the PIN-diode is reversed biased (OFF), the proposed antenna is dual-band, linearly polarized with different orientations, one polarization due to the slot at 2.4 GHz and the other due to the stub inside the slot at 3.62 GHz. This provides WLAN and Worldwide Interoperability for Microwave Access (WiMAX) for wireless systems. The proposed flexible reconfigurable antenna is designed and simulated for both curved and flat configurations to ensure that the antenna maintains its radiation characteristics when it is used for wearable conformal applications.
End-of-the-line over-the-air (OTA) testing of fully assembled wireless devices is one of the most important tests done in factories. It is designed to detect defective devices to avoid them being shipped out to the end customers. There are many requirements in designing over-the-air test systems for factory testing, including small factory real estate, measurement repeatability, and fast test time. These requirements prompt to challenges in OTA test system designs. Few existing widely-used test systems exist: near-field coupling systems where the test antenna is located very near the device’s antenna under test, small TEM cells, and shielded enclosures with one or several test antennas. Each technology has advantages and disadvantages, such as system size, defect detection capabilities/limitations, and performance measurement correlation to that from a far-field method. However, they all lack in dealing with improving test time with devices having technologies working with multiple simultaneous antennas/streams. For example, the current test time for a 2-antenna device (MIMO or received diversity capable devices) is doubled because each antenna chain is tested sequentially. Furthermore, possible coupling effect between antennas is not typically tested. The newly proposed OTA test system is an adaptive system with an array of test antenna elements inside a shielded enclosure. It takes advantage of the multi-path environment inside the enclosure to adapt itself and create a static channel environment with the specified requirement needs. For example, to improve test time for a 2-antenna device, the system groups the antenna elements of the system into two arrays to create two signal streams creating a 2x2-matrix channel with the cross-coupled matrix values minimized (e.g. minimization of the matrix condition number). This created static channel environment with optimized isolation between the two direct signal paths enables testing of the two antenna streams concurrently with minimized perturbation between the streams, hence reducing test time by almost half. The system will reconfigure the antenna elements for each test channel. This proposed new method of an adaptive over-the-air test system opens up to new ways of testing fully-assembled wireless devices in factories and also enables testing of certain performance qualities that current existing OTA test systems cannot perform.
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.
Active S-parameters represent reflection coefficients of elements in an active phased array antenna under various element excitations. Active S-parameters can be calculated for any array excitation if the S-parameter matrix is fully characterized. In practice, the entries of this matrix can usually be gathered through measurements with a 2-port vector network analyzer (VNA). However, depending on the number of elements in the phased array, the number of measurements can be extremely large in order to obtain a full S-matrix. For a phased array consisting of N elements, N(N-1)/2 measurements with a 2-port VNA are required to obtain N-by-N S-matrix, assuming the antenna elements are reciprocal. In order to avoid large number of measurements, a scenario consisting of S-parameter measurements for the center element and also some elements located at the edges and corners of the array is proposed under a flexible predefined error criterion. Then, measured S-parameters are used to obtain N-by-N S-matrix via exploitation of the array symmetry and periodicity which is required to calculate the active S-parameters of the whole array. A fabricated uniform planar Vivaldi array with 112 elements is measured with the proposed scenario and calculated active S-parameters are compared with those obtained from full-wave analysis.
For future applications telecommunication satellites are built with increasing antenna sizes thus having high demands on the test volumes in antenna measurement facilities. AIRBUS Defence & Space provides highly accurate Compensated Compact Range facilities (CCRs) for antenna and payload testing. Mainly facilities of type CCR 75/60 with a quiet zone of 5 m diameter and facilities of type CCR 120/100 with a quiet zone size of 8 m diameter are installed in various countries. A quiet zone size of 5 m might become a limiting factor for test campaigns of future satellite generations. Since numerous CCR 75/60 facilities are installed worldwide, a quiet zone extension upgrade has been developed which allows enhancing the performance of existing facilities with relatively little effort. Lightweight extension panels are installed on upper and lower edges of sub and main reflector increasing the vertical quiet zone dimension. The possible enlargement of the quiet zone can be optimized to customer needs and is mainly driven by the available chamber dimensions. Besides the extension of the quiet zone dimension also the performance in the existing quiet zone will improve due to the larger reflector surfaces. The cross-polar purity goes down up to -60 dB. The first quiet zone extension upgrade has been recently performed at the facility of Thales Alenia Space in Cannes. The quiet zone has been extended from 5 m to 6 m in the vertical direction. A potential extension of the quiet zone up to 1.8 m has been analyzed and is feasible. The design, installation, and verification of the quiet zone extension will be presented in this paper. Quiet zone probing measurement results in C- and Ku-band will be shown.
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.
The National Institute of Standards and Technology (NIST) has developed computationally efficient algorithms for probe location and polarization compensation in near- to far-field transformations for use when measurements are not made on the standard canonical grids. A major application of such methods is at higher frequencies, where it is difficult or impractical to locate a probe to required tolerances for the standard transforms. Our algorithms require knowledge of the actual position of the probe at the measurement points. This information can be furnished by state-of-the-art optical tracking devices. Probe position information is routinely obtained by the NIST CROMMA (Configurable Robotic MilliMeter-wave Antenna) Facility. Even at lower frequencies, probe-location compensation techniques allow in principle, the use of less precise and therefore, less expensive scanning hardware. Our approach also provides the flexibility to process data intentionally collected on nonstandard grids (plane-polar, spiral, etc.) or with mixed geometries (such as a cylinder with a hemispherical or planar end cap). We present simulations and actual probe position compensation results at 183 GHz. The possibility of compensating for known variations in the probe pointing is considered.
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.
The Mathematical Absorber Reflection Suppression (MARS) was originally applied in spherical nearfield measurements. [G. Hindman and A. C. Newell, AMTA, Newport, RI, 2005.] One samples the field with the antenna shifted from the rotation axis by about one aperture diameter and mathematically shifts the resulting modal expansion to a new origin centered on the antenna. Subsequently filtering to low order modes limited by the maximum radial extent of the antenna about this origin, reduces the impact of measurement chamber artifacts because it removes modes associated with the artifacts alone. It does not completely remove the effects of the artifacts however because it does not remove all such modes. In this paper it is shown that the effects of MARS can be understood in terms of the equivalence principle of electromagnetic theory and images produced by the artifacts. The treatment begins with a discussion of two spherical nearfield scanning geometries, one in which the antenna under test (AUT) is rotated and the probe is fixed and the other in which the AUT is fixed and the probe moves over a sphere enclosing it. Because MARS has recently been extended to planar nearfield measurements [S.F. Gregson, A.C. Newell, G.E. Hindman, M.J. Carey, AMTA, Atlanta, 2010], analogous planar geometries are proposed and analogies are drawn between the spherical and planar cases. In terms of these geometries, potential artifacts are classified according to their locations relative to the scan surfaces. For those classes of artifact treatable via MARS, the impact of mode filtering is discussed using image theory where applicable. Differences in the fixed probe and fixed AUT geometries are discussed as are the results of commonly applied approximations. Finally, the utility of spherical expansion of the planar measurements is discussed in terms of recent demonstrations of planar MARS and the manner in which the advantageous effects of MARS obtain in these demonstrations is detailed. [Gregson, et al., AMTA, Denver, 2011][L. J. Foged, et al., AMTA, Seattle, 2012]
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.
In antenna measurement, well-established procedures are consolidated to determine the associated measurement uncertainty for a given antenna and measurements scenario. Similar criteria for establishing uncertainties in numerical modeling of the same antenna are still to be established. In this paper, we investigate the achievable agreement between antenna measurement and simulation when external error sources are minimized. The test object, is a reflector fed by a wideband dual ridge horn (SR40-A and SH4000) manufactured by MVG. This highly stable reference antenna has been selected to minimize uncertainty related to finite manufacturing and material parameter accuracy. Two frequencies, 10.7GHz and 18GHz have been selected for detailed investigation. The antenna has been measured by several measurement facilities (spherical, cylindrical and planar near field ranges) across Europe in the frame of the EurAAP/WG5 “Facility Comparison Campaign” activity. The purpose of this intercomparison campaign is the comparison of the different antenna measurement facilities, throughout Europe, considering measurement procedures and uncertainty estimates. The antenna has been simulated using a full CAD model, in step compatible format and using different numerical methods from different software vendors.
Rectangular open-ended waveguide probes are commonly used in near-field antenna measurements because their frequency behaviour is widely well-known and modeled. Nevertheless, in the last years, the substrate integrated waveguide technology has been developed as a harder competitor. These new circuits are a compromise between the advantages of classical rectangular waveguides, such as high quality factor and low losses, and the advantages of planar circuits, such as low cost and easy compact integration. Also, SIWs present lower weight and dimensions than their equivalent circuits based on metallic waveguides. In this paper we study, under the same measurement conditions, the behaviour of a commercial open-ended rectangular waveguide probe and its equivalent probe in SIW technology. We will compare the near-field measurements obtained with both probes and will show that SIW probes present higher spatial resolution than their equivalent commercial probes. So, SIW probes can detect possible abrupt electric field circuit changes with more accuracy than commercial rectangular waveguides, under the same measurement conditions. The ability of the presented probes has been investigated measuring the simulated amplitude and phase of the electric field of a pyramidal horn placed a few centimetres of the probes. And the study has been validated with the measurements of a microstrip antenna in X-band that presents non-uniform electric field.
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.
A single reflector CATR exhibits certain depolarizing properties, as any other offset reflector antenna, when illuminated by a linearly polarized feed in its focal point. One way to improve the polarization purity in the Quite Zone (QZ) is to use a feed antenna which aperture fields provide a conjugate match to the electric-field distribution in the reflector’s focal plane when illuminated with a linearly polarized plane wave. MVG developed and built a proof-of-concept demonstrator in the form of a 3x1 array of linearly polarized elements, exited to match the focal plane distribution as predicted by a full-wave simulation of the specific range. This demonstrator has been installed in the CATR at RWTH Aachen University, which is a corner-fed serrated edge reflector system with a 1.2 m diameter QZ and a specified maximum cross polarization level of -30 dB (edge of QZ) due to the offset geometry. In this paper we will show measurement results for planar co- and cross-polar probing of the QZ in X-band, using the demonstrator and compare it to the respective results using the range’s conventional, low cross polarization, corrugated feed horn. The measured data will also be cross-checked against the full-wave simulation results for the fields in the QZ. Furthermore, we will compare 0°, 90°, ±45° pattern cuts of a demanding Antenna Under Test, a 40 cm x 40 cm offset reflector antenna with a wide band dual ridge horn as a feed, again using the demonstrator and the conventional feed. This is to show the potential improvement in measurement quality by using a matched feed in a single reflector CATR.