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There are some antennas where rapid validation is required, maintaining a reduced measurement space and sufficient accuracy in the calculation of some antenna parameters as gain. In particular, for cellular base station antennas in production phase the measurement time is a limitation, and a rapid check of the radiation performance becomes very useful. Also, active phased arrays require a high measurement time for characterizing all the possible measurement conditions, and special antenna measurement systems are required for their characterization. This paper presents a single or dual cut near field antenna test procedure for the measurement of the gain of antennas, especially for separable array antennas. The test set-up is based on an azimuth positioner and a near to far field transformation software based on the expansion of the measurements in cylindrical modes. The paper shows results for gain measurements: first near to far field transformation is performed using the cylindrical modes expansion assuming a zero-height cylinder. This allows the use of a FFT in the calculation of the far field pattern including probe correction. In the case of gain, a near to far field transformation factor is calculated for theta = 0 degrees, using the properties of separable arrays. This factor is used in the gain calculation by comparison technique. Depending on the antenna shape one or two main cuts are required for the calculation of the antenna gain: for linear arrays it is enough to use the vertical cut (larger dimension of the antenna), for planar array antenna 2 cuts are necessary, unless the array was squared assuming equal performance in both planes. Also, this method can be extrapolated to other kind of antennas: the paper will check the capabilities and limitations of the proposed method. The paper is structured in this way: section 1 presents the measurement system. Section 2 presents the algorithms for near to far field transformation and gain calculation. Section 3 presents the validation of the algorithm. Section 4 presents the results of the measurement of different antennas (horns, base station arrays, reflectors) to analyze the limitations of the algorithm. Section 5 includes the conclusions.
A number of European Space Agency's (ESA) initiatives planned for the current decade require metrology level accuracy antenna measurements at frequencies extending from L-band to as low as 400 MHz. The BIOMASS radar, the Galileo navigation and search and rescue services could be mentioned among others. To address the needs, the Technical University of Denmark (DTU), who operates ESA’s external reference laboratory “DTU-ESA Spherical Near-Field (SNF) Antenna Test Facility”, in years 2009-2011 developed a 0.4-1.2 GHz wide-band higher-order probe. Even though the probe was manufactured of light-weight materials -- aluminium and carbon-fibre-reinforced polymer (CFRP) -- it still weighs 22.5 kg and cannot be handled by a single person without proper lifting tools. Besides that, a higher-order probe correction technique necessary to process the measurement data obtained with such a probe is by far more demanding in terms of the computational complexity as well as in terms of calibration and post- processing time than the first-order probe correction. On the other hand, conventional first-order probes for SNF antenna measurements utilizing open-ended cylindrical waveguides or conical horns fed by cylindrical waveguides operating in the fundamental TE11-mode regime also become excessively bulky and heavy as frequency decreases, and already at 1 GHz an open-ended cylindrical waveguide probe is challengingly large. For example, the largest first-order probe at the DTU-ESA SNF Antenna Test Facility operates in the frequency band 1.4–1.65 GHz and weighs 12 kg. At 400 MHz, a classical first-order probe can easily exceed 1 cubic meter in size and reach 25-30 kg in weight. In this contribution, a compact P-band dual-polarized first-order probe is presented. The probe is based on a concept of a superdirective linear array of electrically small resonant magnetic dipole radiators. The height of the probe is just 365 mm over a 720-mm circular ground plane and it weighs less than 5 kg. The probe covers the bandwidth 421-444 MHz with more than 9 dBi directivity and |µ| ? 1 modes suppressed below -35 dB. The probe design, fabrication, and test results will be discussed.
The possibility to use Near Field (NF) representation of antenna measurements in terms of equivalent currents, implemented in the commercial tool INSIGHT, is recently available in most CEM solvers. This method allows to use measured data to enhance numerical simulations in complex and/or large scenarios where antennas are installed. In the past this approach has been investigated and validated by determining the antenna radiation pattern in different antenna placement conditions. The aim of this paper is to present how this method can be extended for simulation of antenna coupling. Indeed using this innovative approach, after antennas are measured, their measured models can be imported in CEM tools and coupling with other radiators in arbitrary configurations can be simulated. No information about mechanical and/or electrical design of the measured antenna model are needed by the CEM tool, since the measured NF model in terms of equivalent currents already fully represents the antenna. Investigations have been performed on a H/V polarized array of three identical elements. Only the radiation pattern of the central element of the array has been measured, then starting from the measured data, the coupling between the other elements has been simulated by numerical tools. Accuracy of the procedure has been checked comparing the simulated results with the measured data of the entire array antenna. The testing procedure combining measurements and simulations consists of the following stages: · Measurement of the single element of the array and creation of the measured NF source representation. · Importing NF source in the CEM tool and placement in the array configuration. · Numerical simulation of the antenna coupling between the measured model and the other two elements of the array. Each element has two feeding ports implementing the dual H/V polarization. Preliminary analysis of the coupling is simulated and comparison with the measured data of the entire array agreement is acceptable. This study is currently under development for improving the accuracy of the results and including new test cases of different complexity.
Probe correction in standard spherical near field measurements are typically limited to probes with |µ|=1 spherical wave spectrum when performing spherical wave expansion. The design of such probes is often a trade-off between achievable performance, modal purity and bandwidth. Compensation techniques for probes with higher or full order modal spectrum have recently been proposed. The advantages of such techniques are more freedom in the selection of the probe for a given measurement scenario and increased bandwidth. The technique reported in this paper is valid for probes with a known modal spectrum of arbitrary order. Probe compensation is performed directly on each spherical wave function before expanding the measured field. This leads to a computationally very effective algorithm. In this paper, the accuracy of the new algorithm is validated experimentally for different higher order probes in the measurement of a standard gain horn. For each scenario, the accuracy and computational requirement of the new algorithm is compared to standard transformations.
Compact Antenna Test Range (CATR) provide convenient testing, directly in far-field conditions of antenna systems placed in the Quiet Zone (QZ). Polarization performance is often the reason that a more expensive, complex, compensated dual reflector CATR is chosen rather than a single reflector CATR. For this reason, minimizing the QZ cross-polarization of a single reflector CATR has been a challenge for the industry for many years. A new, dual polarised feed, based on conjugate matching of the undesired cross polar field in the QZ on a full wave-guide band, has recently been developed, manufactured and tested. The CXR feed (cross polar reduction feed) has shown to significantly improve the QZ cross-polar discrimination of standard single reflector CATR systems. In previous papers, the CXR feed concept has been discussed and proved using a limited scope demonstrator and numerical analysis. In this paper, for the first time, the exhaustive testing of the dual polarised feed operating in the extended WR-75 waveguide band (10-16 GHz) is presented. Accuracy improvements, achieved in antenna cross-polar testing, using this feed is also illustrated by measured examples.
In order to achieve high accuracy in measuring sidelobes and/or nulls in antenna patterns, it is necessary to use a test system with very high dynamic range. This is particularly important when the antenna has extremely high gain such as those used for certain satellite communications or radio astronomy applications or when transmit power is limited relative to range loss as is often the case in millimeter wave applications. For several years, commercially available antenna measurement receivers have offered a dynamic range as high as 135dB for such applications. This dynamic range has been made possible, in part, by a simple correlator in the receiver’s DSP chain. In this paper, we model the various sources of error in a test signal due to imperfections and uncertainties of the test equipment and the physical environment and analyze these models as they propagate through the receive chain. The results of that analysis demonstrate the correlator’s ability to reduce carrier frequency offset (CFO) and local oscillator (LO) phase noise to offer the fidelity of test signal necessary to achieve extremely high dynamic ranges of up to 135dB.
Dual polarized probes are convenient for accurate and time efficient Planar Near Field (PNF) antenna testing. Traditional probe designs are often bandwidth limited and electrically large leading to high scattering in PNF measurements with short probe/AUT distances. In this paper, an octave band probe design with minimum scattering characteristics is presented. The scattering minimization is largely obtained by a very small axially symmetric aperture of 0.4? diameter at the lowest frequency. The aperture also provide a near constant directivity in the full bandwidth and very low cross polar. The probe is fed by a balanced ortho-mode junction (OMJ) based on inverted quad-ridge technology and external feeding circuitry to obtain high polarization purity.
Needs of antenna measurements at low VHF range require the development of specific facilities. Costs saving could be found by reusing existing chambers and extending the frequency band down to few tens of MHz, especially if the implementation of such a system is performed in undersized chambers with already existing absorbers. CNES began such an adaptation in the 2000’s by adding a VHF measurement probe (80-400 MHz) in their CATR chamber which allows performing spherical single probe Near Field measurement thanks to the existing positioner. In the past four years, intensives studies have been led to reduce uncertainties onto measurements results and to wide again the lower frequency down to 50 MHz. Major error terms were identified and both a new measurement probe and post processing tools have been designed and implemented. This paper focuses on the hardware and software upgrades. Details will be first provided on the mechanical upgrades of the probe positioner, aiming to improve the accuracy and the repeatability of the positioning, as well as the ergonomic usage for saving installation time. A dedicated reference antenna in gain and polarization has been developed and validated. Such reliable reference antennas at this frequency range are a key point to reduce uncertainties onto measurement results. Finally, optical tool for aligning the measurement probe and the AUT as well as the post processing tool will be presented.
For near-field antenna measurement it is sometimes desirable or necessary to measure only the magnitude of the near-field - to perform so-called phaseless (or amplitude-only or magnitude-only) near-field antenna measurements [1]. It is desirable when the phase measurements are unreliable due to probe positioning inaccuracy or measurement equipment inaccuracy, and it is necessary when the phase reference of the source is not available or the measurement equipment cannot provide phase. In particular, as the frequency increases near-field phase measurements become increasingly inaccurate or even impossible. However, for the near-field to far-field transformation it is necessary to obtain the missing phase information in some other way than through direct measurement; this process is generally referred to as the phase retrieval. The combined process of first measuring the magnitudes of the field and subsequently retrieving the phase is referred to as a phaseless near-field antenna measurement technique. Phaseless near-field antenna measurements have been the subject of significant research interest for many years and numerous reports are found in the literature. Today, there is still no single generally accepted and valid phaseless measurement technique, but several different techniques have been suggested and tested to different extents. These can be divided into three categories: Category 1 – Four magnitudes techniques, Category 2 – Indirect holography techniques, and Category 3 -Two scans techniques. This paper provides an overview of the different phaseless near-field antenna measurement techniques and their respective advantages and disadvantages for different near-field measurement setups. In particular, it will address new aspects such as probe correction and determination of cross-polarization in phaseless near-field antenna measurements. [1] OM. Bucci et al. “Far-field pattern determination by amplitude only near-field measurements”, Proceedings of the 11’th ESTEC Workshop on Antenna Measurements, Gothenburg, Sweden, June 1988.
Installing a large compact range reflector and electromagnetically qualifying the quiet zone is a major undertaking, especially for very large panelized reflectors. The approach taken to design the required rolled-edge reflector geometry for achieving a 5 meter quiet zone across a frequency range of 350 MHz to 40 GHz was previously presented [1]. The segmentation scheme, fabrication methodology, and intermediate qualification of panels using an NSI-MI developed microwave holography tool were also presented. This reflector has since been installed and the compact range qualified by direct measurement of the electromagnetic fields in the quiet zone using a large field probe. This paper presents the comparison and correlation between the holography predictions and the field probe measurements of the quiet zone. Installation and alignment techniques used for the multiple panel reflector are presented. Available metrology tools have inherent accuracy limitations leading to residual misalignment between the panels. NSI-MI has overcome this limitation by using its holography tool along with existing metrology techniques to predict the field quality in the quiet zone based on surface measurements of the panels. The tool was used to establish go/no-go criteria for panel alignment accuracy achieved on site. Correlation of the holography predictions with actual field probe measurements of the installed reflector validates the application of the holography tool for performance prediction of large, multiple-panel, rolled-edge reflectors. Keywords: Rolled-Edge Reflector, Compact Range, Field-Probing, Quiet Zone, Microwave Holography
Spherical near-field (SNF) antenna test systems offer unique advantages over other types of measurement configurations and have become increasingly popular over the years as a result. To yield high accuracy far-field radiation patterns, it is critical that the rotators of the SNF scanner are properly aligned. Many techniques using optical instruments, laser trackers, low cost devices or even electrical measurements [1 - 3] have been developed to align these systems. While these alignment procedures have been used in practice with great success, some residual alignment errors always remain. These errors can sometimes be quantified with high accuracy and low uncertainty (known error) or with large uncertainties (unknown error). In both cases, it is important to understand the impact that these SNF alignment errors will have on the far-field pattern calculated using near-field data acquired on an SNF scanner. The sensitivity to various alignment errors has been studied in the past [4 - 6]. These investigations concluded that altering the spherical acquisition sampling grid can drastically change the sensitivity to certain alignment errors. However, these investigations were limited in scope to a single type of measurement system. This paper will expand upon this work by analyzing the effects of spherical alignment errors for a variety of different measurement grids and for different SNF implementations (phi-over-theta, theta-over-phi) [7]. Results will be presented using a combination of physical alignment perturbations and errors induced via simulation in an attempt to better understand the sensitivity to SNF alignment errors for a variety of antenna types and orientations within the measurement sphere. Keywords: Spherical Near-Field, Alignment, Uncertainty, Errors. References [1] J. Demas, “Low cost and high accuracy alignment methods for cylindrical and spherical near-field measurement systems”, in the proceedings of the 27th annual Meeting and Symposium, Newport, RI, USA, 2005. [2] S. W. Zieg, “A precision optical range alignment tecnique”, in the proceedings of the 4th annual AMTA meeting and symposium, 1982. [3] A.C. Newell and G. Hindman, “The alignment of a spherical near-field rotator using electrical measurements”, in the proceedings of the 19th annual AMTA meeting and symposium, Boston, MA, USA, 1997. [4] A.C. Newell and G. Hindman, “Quantifying the effect of position errors in spherical near-field measurements”, in the proceedings of the 20th annual AMTA meeting and symposium, Montreal, Canada, 1998. [5] A.C. Newell, G. Hindman and C. Stubenrauch, “The effect of measurement geometry on alignment errors in spherical near-field measurements”, in the proceedings of the 21st annual AMTA meeting and symposium, Monterey, CA, USA, 1999. [6] G. Hindman, P. Pelland and G. Masters, “Spherical geometry selection used for error evaluation”, in the proceedings of the 37th annual AMTA meeting and symposium, Long Beach, CA, USA, 2015. [7] C. Parini, S. Gregson, J. McCormick and D. Janse van Rensburg, Theory and Practice of Modern Antenna Range Measurements. London, UK: The Institute of Engineering and Technology, 2015
The evaluation of RF Sensors often requires a test capability where various RF scenes are presented to the Unit Under Test (UUT). These scenes may need to be dynamic, represent multiple targets and/or decoys, emulate dynamic motion, and simulate real world RF environmental conditions. An RF Scene Generator can be employed to perform these functions and is the focus of this paper. The total test system is usually called Hardware in the Loop (HITL) involving the sensor mounted on a Flight Motion Simulator (FMS), the RF Scene Generator presenting the RF Scene, and a Simulation Computer that dynamically controls everything in real time. This paper describes the system concept for an RF Scene Generator that simultaneously represents 4 targets, in highly dynamic motion, with no occlusion, over a wide range of power, frequency, and Field of View (FOV). It presents the test results from a prototype that was built and tested over a limited FOV, while being scalable to the total FOV and full system capability. The RF Scene Generator employs a wall populated with an array of emitters that enables virtually unlimited velocity and acceleration of targets and employs beam steering to provide high angular resolution and accuracy of the presented target positions across the FOV. Key words: RF Target Simulator, RF Scene Generator, Multiple Targets, Beam Steering Wall of Emitters, Steering Array Calibration, Plane-Wave Generator, Radar Environment Simulator.
Although In the 1970’s and 1980’s the near-field technology was proven to work properly for antenna characterization. It was until the late 1990’s that antenna communities begun to trust this technology and depend heavily on it. This same scenario could happen to the phase-less near-field technologies. It is true that there is still much to be done in the sense of reliability of these techniques. Nevertheless there are still situations where these techniques must be applied. This paper will be dealing with the phase-less near-field antenna measurement technique. The well-known iterative Fourier transformation (IFT) technique is used. The amplitude of the field distribution on concentric spheres surrounding the antenna under test (AUT) is used to reconstruct the phase information necessary for the spherical near-field to far-field transformation (SNFFF). It will be shown that despite its geometrical and computational complexity this technique can be applied on the spherical case achieving very good accuracy. In addition this paper makes use of global optimization techniques especially genetic algorithm (GA) to establish an initial estimate of the phase distribution necessary for the algorithm which is later on fine-tuned using the local optimization i.e. IFT to retrieve a closer estimate of the solution. It will be shown that except for the null positions the far-field accuracy can be enhanced. The implementation of the GA will be shortly given and the concept of masks, which simplifies the implementation, will be discussed.
RCS and Antenna measurement accuracy critically depends on the quality of the incident field. Both compact and far field ranges can suffer from a variety of contaminating factors including phenomena such as atmospheric perturbation, clutter, multi-path, as well as Radio Frequency Interference (RFI). Each of these can play a role in distorting the incident field from the ideal plane wave necessary for an accurate measurement. Methods exist to mitigate or at least estimate the measurement uncertainty caused by these effects. However, many of these methods rely on knowledge of the incident field amplitude and phase over the test region. Traditionally the incident field quality is measured directly using an electromagnetic probe antenna which is scanned through the test region. Alternately, a scattering object such as a sphere or corner reflector is used and the scattered field measured as the object is moved through the field. In both cases the probe/scatterer must be mounted on a structure to move and report the position in the field. This support structure itself acts as a moving clutter source that perturbs the incident field being measured. Researchers at the Air Force Institute of Technology (AFIT) have recently investigated a concept that aims to eliminate this clutter source entirely. The idea is to leverage the advances in drone technology to create a free flying field probe that doesn’t require any support structure. We explore this concept in our paper, detailing the design, hardware, and software developments required to perform a concept demonstration measurement in AFIT’s RCS measurement facility. Measured data from several characterization tests will be presented to validate the method. The analysis will include an estimate of the applicability of the technique to a large outdoor RCS measurement facility.
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.
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.
This paper explores the accuracy capabilities of a two element phase interferometer measurement in a planar near-field scanner. Traditional phase interferometer applications utilize wide field of view antennas such as spirals making the utilization of planar near-field measurements less than ideal. In this application, high directivity antennas were utilized which allowed us to consider a planar near-field measurement solution. Leaving the AUT stationary and the stability of the planar near-field coordinate system were primary considerations in deciding to utilize a planar near-field measurement system. Typical interferometer performance metrics include comparing measured phase differences to ideal element phase differences at the same locations. Often the nominal drawing locations are used to generate the ideal element phase difference curves. The sensitivity of actual element vector displacement values versus ideal displacements can be reduced by deriving the best-fit displacement vector from the measured data and is utilized in the processing and reporting of results. This paper reviews the measurements, analysis techniques and results from this investigation and illustrates the capabilities of a planar near-field scanner to perform these types of measurements with a high degree of measurement fidelity.
ABSTRACT Spherical near-field error analysis is extremely useful in allowing engineers to attain high confidence in antenna measurement results. NSI has authored numerous papers on automated error analysis and spherical geometry choice related to near field measurement results. Prior work primarily relied on comparison of processed results from two different spherical geometries: Theta-Phi (0 =?= 180, -180 = f = 180) and Azimuth-Phi (-180 =?= 180, 0 = f = 180). Both datasets place the probe at appropriate points about the antenna to measure two different full spheres of data; however probe-to-antenna orientation differs in the two cases. In particular, geometry relative to chamber walls is different and can be used to provide insight into scattering and its reduction. When a single measurement is made which allows both axes to rotate by 360 degrees both spheres are acquired in the same measurement (redundant). They can then be extracted separately in post-processing. In actual fact, once a redundant measurement is made, there are not just two different full spheres that can be extracted, but a continuum of different (though overlapping) spherical datasets that can be derived from the single measurement. For example, if the spherical sample density in Phi is 5 degrees, one can select 72 different full sphere datasets by shifting the start of the dataset in increments of 5 degrees and extracting the corresponding single-sphere subset. These spherical subsets can then be processed and compared to help evaluate system errors by observing the variation in gain, sidelobe, cross pol, etc. with the different subset selections. This paper will show the usefulness of this technique along with a number of real world examples in spherical near field chambers. Inspection of the results can be instructive in some cases to allow selection of the appropriate spherical subset that gives the best antenna pattern accuracy while avoiding the corrupting influence of certain chamber artifacts like lights, doors, positioner supports, etc. Keywords: Spherical Near-Field, Reflection Suppression, Scattering, MARS. REFERENCES Newell, A.C., "The effect of measurement geometry on alignment errors in spherical near-field measurements", AMTA 21st Annual Meeting & Symposium, Monterey, California, Oct. 1999. G. Hindman, A. Newell, “Spherical Near-Field Self-Comparison Measurements”, Proc. Antenna Measurement Techniques Association (AMTA) Annual Symp., 2004. G. Hindman, A. Newell, “Simplified Spherical Near-Field Accuracy Assessment”, Proc. Antenna Measurement Techniques Association (AMTA) Annual Symp., 2006. G. Hindman & A. Newell, “Mathematical Absorber Reflection Suppression (MARS) for Anechoic Chamber Evaluation and Improvement”, Proc. Antenna Measurement Techniques Association (AMTA) Annual Symp., 2008. Pelland, Ethier, Janse van Rensburg, McNamara, Shafai, Mishra, “Towards Routine Automated Error Assessment in Antenna Spherical Near-Field Measurements”, The Fourth European Conference on Antennas and Propagation (EuCAP 2010) Pelland, Hindman, “Advances in Automated Error Assessment of Spherical Near-Field Antenna Measurements”, The 7th European Conference on Antennas and Propagation (EuCAP 2013)
The design of modern Compact Antenna Test Ranges (CATRs) is a challenging task, and to achieve strong performance, simulation using computational electromagnetics is a vital part of the design process. However, the large electrical size, geometrical complexity and high accuracy requirements often mean that the available computer resources are not sufficient for running the simulation. In the present paper, we highlight some recent developments that allow for much larger, faster and more accurate simulations than was possible just a few years ago, and apply them to realistic ranges. The conclusion is clear: Modern software tools allow designers of CATRs to achieve better performance in shorter time than was previously possible.
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.