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In-situ Diagnosis of Direction Finding Antenna using Optically-fed Transmitting Miniature Probes
Serge Bories, Lama Ghattas, Dominique Picard, November 2016
Direction Finding (DF) Antennas are usually designed and tested in controlled environments. However, antenna far field response may change significantly in its operational environment. In such perturbing or not -controlled close context, the antennas calibration validity becomes a major issue which can lead to DF performance degradation and to a costly re-calibration process. Even if in-situ re-calibration is still complicated; the DF antenna response can be monitored, during the mission, in order to ensure the DOA accuracy. This paper presents an innovative design and the performance of a low-disturbing solution to detect the near field antenna response deviations from a nominal case. The proposed system is based on an array of transmitting miniature dipoles deployed all around the DF antennas. These probes are optically fed through a non-biased photodiode that carries the direct conversion into a RF signal at the desired frequency. The detection re-used the DF receiving RF chains to analyze any deviation (complex values) of the antennas array manifold. Compared to the Optically Modulated Scatterer (OMS) technique, the benefits of the proposed approach are demonstrated experimentally over a frequency decade (UHF band). First a better sensitivity is shown (higher than 80 dB on the monitored link), and secondly the phase detection is made really simple compared to the OMS technique. Finally, a relation between this in-situ diagnosis mode and the DF angular direction accuracy is established. Thus the capacity to detect, on the near field response, the presence of various types of closed obstacles (open trap on the carrier, additional antenna…) which perturb significantly the far field antenna response, is evaluated.
Measurement Uncertainties in Millimeter Wave “On-Chip” Antenna Measurements
Edward Szpindor, Wenji Zhang, Per Iversen, November 2016
As a result of recent technical and regulatory developments, the millimeter wave frequency band (30GHz – 300 GHz) is being adopted for wide range of applications.  Based on array signal processing technologies used for 4G and MIMO, companies are developing small active array antennas operating throughout the millimeter-wave bands.  These arrays may include radiating elements and feed structures that are fraction of a millimeter in size and cannot be fed via a coaxial cable.  Connection to the antenna is instead performed through a micro-probe more commonly used in the chip industry.  MVG-Orbit/FR has developed a compact antenna measurement system which integrates hardware and software necessary to provide antenna gain and radiation patterns of antennas fed with such a micro-probe. To evaluate uncertainties in the measurements of the Antenna Under Test (AUT) gain, directivity, efficiency, pattern, or VSWR, reference antennas are an invaluable tool.  The authors have recently driven the development of a micro-probed chip reference antenna.  This reference antenna was designed to be mechanically and electrically stable and with reduced sensitive to its mounting fixture and feeding method.  Close agreement between measured and simulated characteristics has been achieved.  With low losses, the antenna provides good dynamic range and confidence in the measured antenna efficiency and gain. Without chip antenna gain standards, a micro-probed antenna test system requires the use of the insertion loss method for gain calibration.  This method requires correction for additional losses such as cables, attenuators, or adaptors that are included in the calibration but not in the subsequent measurement of the AUT.  In addition, the micro-probe (which is in the measurement but not in the calibration) should be calibrated and de-embedded from the measurement.   Each of these measurements and associated connections and related processing, increases uncertainty and chance of mistakes by the user.  It is therefore essential to validate the calibration using a well characterized reference antenna. This paper will outline design requirements and present test results of 60 GHz Chip Reference antennas.  Several dozen antennas have been tested.  The related uncertainties in the micro-probed antenna measurements will be evaluated with particular emphasis on the gain calibration uncertainty.  The paper will also describe the next steps towards developing a chip antenna gain standard, that should reduce gain uncertainties while also significantly simplifying the calibration process.
Dual-calibration Processing Based on Minimum Weighted Mean Squared Error (MWMSE) in RCS Measurement
Xiaojian Xu,Yongze Liu, November 2015
Dual-calibration was first proposed by Chizever et al. in 1996 [AMTA'1996] and had get wide applications in evaluation of the uncertainty in radar cross section (RCS) measurement and calibration. In 2013, LaHaie proposed a new technique based on jointly minimizing the mean squared error (MMSE) [AMTA'2013] among the calibrated RCS of multiple calibration artifacts, which estimates both the calibration function and the calibration uncertainty for each artifact. MMSE greatly improves the estimation accuracy for the radar calibration function as well as results in lower residual and RCS calibration errors. This paper presents a modified version of LaHaie's MMSE by minimizing the weighted mean squared error (MWMSE) for RCS calibration processing from  multiple calibrator measurements, which is related to the following functions and parameters: the calibration function; the theoretical and measured RCS; the number of calibration artifacts the number of frequency samples and the weight for ith calibration artifacts which may be defined in terms of the theoretical RCS of all the calibration artifacts. For example, if the weight is defined as the inverse of the total theoretical RCS of the ith calibration artifacts for all frequency samples, the error then represents the total relative calibration error instead of an absolute error as in MMSE. MWMSE then means that an optimal calibration function is found in terms of minimum total relative calibration error, which is expected for most applications. Numerical simulation results are presented to demonstrate the usefulness of the proposed technique.
Insertion Phase Calibration of Space-Fed Arrays
Jacob Houck,Brian Holman, November 2015
Calibrating a passive, space-fed, phased array antenna is more difficult and time consuming then calibrating corporate-fed arrays because individual elements cannot be activated or deactivated. We will present our method of determining element state-phase curves and insertion phase bias between elements. We will also explain this method’s theoretical basis and validate it by comparing data measured in an anechoic chamber with data measured in a planar near field range. The anechoic chamber data will be compared with the typical, proven, but more time-consuming planar near field calibration method.
A New Method for VHF/UHF Characterization of Anisotropic Dielectric Materials
John Schultz,James Maloney, November 2015
Recent interest in anisotropic metamaterials and devices made from these materials has increased the need for advanced RF material characterization. Moreover, the quest for measurement of inhomogeneous and anisotropic materials at VHF and UHF frequencies has long been one of the primary stretch goals of the RF materials measurement community. To date, the only viable method for these types of materials has been either fully filled or partially filled VHF waveguides, which are large, expensive, and slow. This paper introduces a new fixture design that greatly simplifies the process of obtaining intrinsic properties for inhomogeneous and anisotropic dielectric materials. The fixture combines low frequency capacitance and high frequency coaxial airline concepts to measure cube shaped specimens, and is termed an “RF Capacitor”. Furthermore, a significant limitation of past measurement methods is their reliance on approximate analytical models to invert material properties. These analytical models restrict the available geometries and frequency ranges that a measurement fixture can have. The present method avoids this limitation by implementing a new inversion technique based on a full-wave, finite difference time domain (FDTD) solver to exactly model the measurement geometry. In addition, this FDTD solver is applied in a novel way to enable inversion of frequency-dependent dielectric properties within seconds. This paper presents the fixture design and calibration for this new measurement method, along with example measurements of isotropic and anisotropic dielectric materials. In particular, 3” cube specimens are measured and the bulk dielectric properties in the three principal planes are determined by measuring the same specimen in three different orientations within the measurement fixture. Finally, calculations are presented to show the relative accuracy of this method against a number of probable uncertainty sources, for some characteristic materials.
Characterization of Reflectivity Losses in Space Reflector Antennas at Temperatures above 350°C
Luis Rolo,Eric van der Houwen, Elena Saenz, November 2015
In the recent years, the microwave and mm wave communities have been experiencing a strong interest in the characterisation of the RF proprieties of materials used in the manufacture of antennas and structures that, in one way or another, interact with propagating electromagnetic fields. Of particular interest are materials used for for space applications, where antennas face a harsh environment at all times making it challenging to keep antenna performances in all orbital conditions, whether in eclipse or under full sunlight exposure. A particular example is the coming Solar Orbiter mission, where the antenna reflector will be exposed to a high intensity of solar energy. This paper describes a measurement system with a custom-built setup that enables the measurement of reflectivity losses of space antenna materials and coatings at very high temperatures - up to 500 degrees Celsius. The design of the high temperature fixture will be presented in detail, together with the development of the necessary measurement and calibration techniques. The paper will conclude with a critical assessment of the obtained results and system performance and achieved accuracies.
A Calibration Method Using Interpolation to Reduce Measurement Errors in Electromagnetic Compatibility Measurements
Vince Rodriguez,Dennis Lewis, November 2015
MIL STD 461 is the Department of Defense standard that states the requirements for the control of electromagnetic interference (EMI) in subsystems and equipment used by the armed forces. The standard requires users to measure the unintentional radiated emissions from equipment by placing a measuring antenna at one meter distance from the equipment under test (EUT). The performance of the antenna at 1m distance must be known for the antenna to measure objects located at this close proximity. MIL STD 461 requires the antennas to be calibrated at 1 m distance using the Society of Automotive Engineers (SAE) Aerospace Recommended Practice (ARP) 958. This SAE ARP 958 document describes a standard calibration method where two identical antennas are used at 1m distance to obtain the gain at 1m for each antenna. In this paper the authors show using simulations that the SAE ARP 958 approach introduces errors as high at 2 dB to the measured gain and AF. To eliminate this problem the authors introduce a new method for calibrating EMC antennas for MIL STD 461. The Method is based on the well-known extrapolation range technique. The process is to obtain the polynomial curve that is used to get the far field gain in the extrapolation gain procedure, and to perform an interpolation to get the gain at 1 m. The results show that some data in the far field must be collected during the extrapolation scan. When the polynomial is calculated the antenna performance values at shorter distances will be free of near field coupling. Measured results for a typical antenna required for emissions testing per the MIL STD 461 match well with the numerical results for the computed gain at 1 m distance. Future work is required to study the use of this technique for other short test distances used in other electromagnetic compatibility standards, such as the 3 m test distance used by the CISPR 16 standard. Keywords: Antenna Calibrations, EMC Measurements, Extrapolation Range Techniques
Comparison of Payload Applications in Near Field and Compact Range Facilities
Carsten Schmidt,Josef Migl, Alexander Geise, Hans-Juergen Steiner, November 2015
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.
Development of a FMCW Radar Sensor For Soil Humidity Estimation
Maria C. Gonzalez,Christian Hurd, Jose Enrique Almanza Medina, Xiaoguang Liu, November 2015
To determine the proper moisture content in the soil is critical to get maximum grow in plants and crops and its estimation it is used to regulate the amount of irrigation that it is needed. For this reason, many sensors that measure water content have been developed to give the grower some feedback of the water content.   Some methods such as the ones based in gravimetric properties are accurate but labor consuming, other such as the tension meters require periodic service, the neutron probe is also accurate but expensive. The more popular sensor is based in electrical resistance measurement that gives acceptable accuracy and it is not expensive. However, this sensor has the disadvantage that needs to be buried in the soil. Here, we are exploring the characteristics of electromagnetic propagation and its scattering properties as a tool to identify the physical soil composition. The presence of water changes drastically the dielectric properties of the soil affecting the reflected signal. In this research, we are assessing the viability of a sensor based in FMCW radar technology for water detection with the advantage of being portable and low cost. The research involves the fabrication of a directive antenna operating in a broadband regimen, transmitter/ receiver circuit and the signal processing of the return signal adjusted to the detection of moisture in soil. We present the calibration methods and graphic results of the intensity of the reflected signal of dry bare soil, wet soil, and soil covered by plants.
Monostatic RCS Calibration of Radar Target Using Extrapolation Method in Millimeter-wave Frequency Band
Michitaka Ameya,Satoru Kurokawa, Masanobu Hirose, November 2015
In this paper, we propose a calibration method for monostatic radar cross section (RCS) of simple radar targets (e.g. trihedral corner reflectors and square flat-plate reflectors) using extrapolation method. By the proposed method, we can calibrate the monostatic RCS of radar targets from 1-port S-parameter measurements. In our system, the applicable size of radar targets are 75 mm to 125 mm for corner reflectors and 40 mm to 75 mm for square flat-plate reflectors, respectively. The nominal RCS of reflector targets calculated by physical optics ranges from +3 dBsm to +15 dBsm in W-band.  The measured results are agree well with simulation results calculated by method of moment (MoM).
Experimental In-Situ Antenna Array Calibration with Signals of Opportunity
Andrew L. Kintz,Inder J. Gupta, November 2015
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.
Research on Unwanted Reflections in an OATS for Precise Omni Antenna Measurement
Donglin Meng,Xiao Liu, Dabo Li, November 2015
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.
A Comparison of Antenna Range Polarization Correction Techniques
Justin Dobbins,Jason Jerauld, November 2015
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.
Slotted Waveguide Array Beamformer Characterization Using Integrated Calibration Channel
Akin Dalkilic,Caner Bayram, Can Baris Top, Erdinc Ercil, November 2014
In military applications, where low sidelobes and high precision in beam pointing are vital, a phased array antenna beamformer requires to be calibrated regarding the cabling that connects the beamformer to the antenna and mutual coupling between antenna elements. To avoid problems associated with mismatched phase transmission lines between the beamformer and the antenna and include the coupling effects, beamforming network characterization must be done with the antenna integrated to the beamformer. In this paper, a method to characterize the beamformer of a slotted waveguide array antenna in the antenna measurement range is introduced. The antenna is a travelling wave slotted waveguide array scanning in the elevation plane. The elevation pattern of the antenna is a shaped beam realized by a phase-only beamformer. The calibration channel includes serial cross-guide couplers fed by a single waveguide line. The channel is integrated to the waveguide lines of the antenna.  In the first phase of the characterization, the far field pattern of each antenna element is obtained from the near field measurements at the “zero” states of the phase shifters. In the second stage, all states of the phase shifters are measured automatically using the calibration channel described above. The results of calibration channel measurements are used to determine the changes in phase and magnitude for different states of phase shifters. The phase and magnitude of the peak point of the far field pattern is referenced to the zero state measurement of the calibration channel. Phase only pattern synthesis is carried out using the results of both zero-state near field and calibration channel measurements and the required phase shifter states are determined accordingly. Measured patterns show good agreement with the theoretical patterns obtained in the synthesis phase.
Computational Electromagnetic Modeling of Near-Field Antenna Test Systems Using Plane Wave Spectrum Scattering Matrix Approach
Allen Newell,Stuart Gregson, November 2014
In recent years a number of analyses and simulations have been published that estimate the effect of using a probe with higher order azimuthal modes with standard probe corrected spherical transformation software.  In the event the probe has higher order modes, errors will be present within the calculated antenna under test (AUT) spherical mode coefficients and the resulting asymptotic far-field parameters [1, 2, 3, 4] where the simulations were harnessed to examine these errors in detail.  Within those studies, a computational electromagnetic simulation (CEM) was developed to calculate the output response for an arbitrary AUT/probe combination where the probe is placed at arbitrary locations on the measurement sphere ultimately allowing complete near-field acquisitions to be simulated.  The planar transmission equation was used to calculate the probe response using the plane wave spectra for actual AUTs and probes derived from either planar or spherical measurements.  The planar transmission formula was utilized as, unlike the spherical analogue, there is no limitation on the characteristics of the AUT or probe thereby enabling a powerful, entirely general, model to be constructed.  This paper further extends this model to enable other measurement configurations and errors to be considered including probe positioning errors which can result in ideal first order probes exhibiting higher order azimuthal mode structures.  The model will also be used to determine the accuracy of the Chu and Semplak near-zone gain correction [5] that is used in the calibration of pyramidal horns.  The results of these additional simulations are presented and discussed. Keywords: near-field, antenna measurements, near-field probe, spherical alignment, spherical mode analysis. REFERENCES A.C. Newell, S.F. Gregson, “Estimating the Effect of Higher Order Modes in Spherical Near-Field Probe Correction”, Antenna Measurement Techniques Association (AMTA) 34th Annual Meeting & Symposium, Bellevue, Washington October 21-26, 2012. A.C. Newell, S.F. Gregson, “Higher Order Mode Probes in Spherical Near-Field Measurements”, 7th European Conference on Antennas and Propagation (EuCAP 2013) 8-12 April 2013. A.C. Newell, S.F. Gregson, “Estimating the Effect of Higher Order Modes in Spherical Near-Field Probe Correction”, Antenna Measurement Techniques Association (AMTA) 35th Annual Meeting & Symposium, Columbus, Ohio, October 6-11, 2013. A.C. Newell, S.F. Gregson, “Estimating the Effect of Higher Order Azimuthal Modes in Spherical Near-Field Probe Correction”, The 8th European Conference on Antennas and Propagation (EuCAP 2014) 6-11 April 2014. T.S. Chu, R.A. Semplak, “Gain of Electromagnetic Horns,’’ Bell Syst. Tech. Journal, pp. 527-537, March 1965
Investigations on Gain Measurement Accuracies at Limited Far-Field Conditions
Engin Gülten,Andreas Drexler, Josef Migl, Jürgen Habersack, November 2014
Driven by the mobile data communications needs of market broadband antennas at the upper frequency bands are already state-of-the-art, e.g. at the Ka-Band. For the characterization of an antenna the antenna gain is one of the major test parameters. This measurement task is already challenging for standard applications at the Ka-Band. However, for the calibration of remote station antennas utilized in high precision test facilities, e.g. the compact range, even higher measurement accuracies are typically required in order to fulfil the overall system performance within the later test facility. Therefore the requirement for this investigation is to improve the measurement set-up and also the steps to get a failure budget which is better than ± 0.15 dB. Every antenna gain measurement technique is affected by required changes in the measurement setup, e.g. the Device under Test (DUT) or the remote station, respectively. This results for example in a variation of mismatch with resulting measurement errors. To determine and compensate the occurred mismatches, the scattering parameters of the involved components have to be measured and be evaluated with a corresponding correction formula. To quantify the effect for the gain measurement accuracy the remaining uncertainty of the mismatch correction values is examined. Another distortion is caused by multiple reflections between the antenna apertures. To reduce this error source, four additional measurements each with a decreased free space distance should be performed. In addition to the common methods, this paper explains in detail an advanced error correction method by using the singular value decomposition (SVD) and compares this to the standard mean value approach. Finally the restricted distance between both antennas within the applied anechoic far-field test chamber has to be analysed very critically and optionally corrected for the far-field gain at an infinite distance in case the measurement distance is fulfilling the minimum distance requirement, only. The paper will discuss all major error contributions addressed above, show correction approaches and verify these algorithms with exemplary gain measurements in comparison to the expected figures.
Advantages and Disadvantages of Various Hemispherical Scanning Techniques
Eric Kim,Anil Tellakula, November 2014
When performing far field or near field antenna measurements on large antennas, it is often necessary to have various types of mechanical positioning systems to achieve the required hemispheric scans.  Measurement systems employing a single-arm gantry, a dual-arm gantry, a fixed arch moving probe, or a fixed arch multi-probe have been paired with either an azimuth positioner or a vehicle turntable to provide hemispheric scanning of the object being tested. This paper will highlight the key characteristics of various scanning methods making comparisons between the different techniques.  Positioning and system accuracy, speed, stowing ability, calibration, frequency range, upgradability, relative cost and other key aspects of the various techniques will be discussed in detail to help the end user during the system design and selection process.  In addition, the paper will highlight novel hemispheric and truncated spherical scanning approaches. In many applications, the success of the entire project often centers on the judicious selection of the positioning subsystem.  This paper will provide guidance toward making the proper selection of the scanning concept as well as of the positioning system.
Equiangular Phase Shifting Holography for THz Near-field/Far-field Prediction
Gary Junkin,Josep Parrón Granados, Pedro de Paco Sánchez, Yi Lu, November 2014
A three-step equiangular (120º) phase shifting holography (EPSH) technique is proposed for THz antenna near-field/far-field prediction. The method is attractive from the viewpoint of receiver sensitivity, phase accuracy over the entire complex plane, simplified detector array architecture, as well as reducing planarity requirements of the near-field scanner. Numerical modeling is presented for the holographic receiver performance, using expected phase shift calibrations errors and phase shift noise. The receiver model incorporates responsivity and thermal noise specifications of a commercial Schottky diode detector. Additionally, simulated near-field patterns at 372GHz demonstrate the convenience of the method for accurate and high dynamic range THz near-field/far-field predictions, using a phase-shifter calibrated to ±0.1°.
Testing of Panels And Radomes Using De-embedding To Reduce Probe Interaction Errors
Henry Burger, November 2014
Legacy methods for testing the performance of radome panels and finished radomes have always been in isolation from the system antenna, for many reasons. The legacy method of testing employed horn antennas at relatively close distances, a fixed-frequency signal source, and primitive receivers. More modern systems used much better receivers capable of measuring both phase and amplitude, and these gave way to automatic network analyzers. The network analyzer system also replaces the fixed-frequency source, because it has its own step-frequency source. The rest of the setup remains the same. A network analyzer can itself be calibrated, but that calibration cannot include the probe antennas, nor can it account for interactions, particularly at normal incidence. With increasing demands on performance, it is essential that the interaction effects of the probe antennas with the radome be removed.    The micorwave integrated circuit industry has the identical problem. The circuit probes that are used to reach into the circuit assemblies have very small tips, and the internal elements to accomplish this size reduction make probe mataching difficult. Thus the probe parameters become embedded into the overall measured response. The circuit testing community has developed a process to de-embed these probes, yielding the S-parameters of the circuit under test in isolation from surroundings.    This paper investigates a method for applying this closed-system technique to open-system testing, such as panel-measuremsnt tables, by using a secondary calibration technique that is adapted to open systems. This effectively extends the calibration of the analyzer system to encompass the probes, thus improving accuracy.
Combining Pattern, Polarization and Channel Balance Correction Routines to Improve the Performance of Broad Band, Dual Polarized Probes
Patrick Pelland,Allen Newell, November 2014
Broad band, dual polarized probes are becoming increasingly popular options for use in near-field antenna measurements. These probes allow one to reduce cost and setup time by replacing several narrowband probes like open-ended waveguides (OEWG) with a single device covering multiple waveguide bands. These probes are also ideal for production environments, where chamber throughput should be maximized. Unfortunately, these broadband probes have some disadvantages that must be quantified and corrected for in order to make them viable for high accuracy near-field measurements. Most of these broadband probes do not have low cross polarization levels across their full operating bandwidths and may also have undesirable artifacts in the main component of their patterns at some frequencies. Both of these factors will result in measurement errors when used as probes. Furthermore, the use of a dual port RF switch adds an additional level of uncertainty in the form of port-to-port channel balance errors that must be accounted for. This paper will describe procedures to calibrate the pattern and polarization properties of broad band, dual polarized probes with an emphasis on a newly developed polarization correction algorithm. A simple procedure to measure and correct for amplitude and phase imbalance entering the two ports of the near-field probe will also be presented. Measured results of the three calibration procedures (pattern, polarization, channel balance) will be presented for a dual-polarized, broad band quad-ridged horn antenna. Once calibrated, this probe was used to measure a standard gain horn (SGH) and will be compared to baseline measurements acquired using a good polarization standard open-ended waveguide (OEWG). Results with and without the various calibration algorithms will illustrate the advantage to using all three routines to yield high accuracy far-field pattern data.

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