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Indoor antenna ranges must have the walls, floor and ceiling treated with RF absorber. The normal incidence performance of the absorber is usually provided by the manufacturers of the materials, however, the bi-static or off angle performance must also be known. Some manufacturers provide factors at discrete electrical thickness for a discrete range of incident angles. This approximation is based on the curves presented in [1]. In reference [2], a polynomial approximation was introduced. In this paper, a more accurate approximation is introduced. Pyramidal RF absorber is modeled using CST’s frequency domain solver. The numerical results are compared to results from other numerical methods. The highest reflectivity of the two principal polarizations for a given angle of incidence and thickness of material is calculated. Different physical thickness pyramids are modeled. Once the worst case reflectivity is calculated, a polynomial curve fit is done to get a set of equations that provide the bi-static performance for absorber as a function of angle of incidence and thickness of material. The equations can be used to predict the necessary RF absorber to treat the walls of an indoor range.
In this case study, an existing spherical near-field test facility that was used productively and effectively for many years had become a bottleneck. Recent needs for more extensive antenna characterization had driven test times to an extreme, approaching 300 hours of data acquisition for a single antenna and 160 hours for additional processing. The size of collected data files had also become extremely large, exceeding the 2 GB capacity of the commercial database used to store acquisition files. A system measurement timing assessment was conducted for this test facility to determine the most effective means of reducing the data acquisition time. A timing model was created to optimize the current system resulting in an immediate reduction of data acquisition time by 45%. A sensitivity study was conducted to show the tradeoffs between additional test time improvements that could be achieved. Results showed that by using a combination of several of these improvements along with a modest investment in new equipment, total acquisition time could be further reduced to 16 hours, achieving a 95% reduction in acquisition time as compared to the baseline. In addition to acquisition time, post-acquisition processing time was also improved. Some of the additional processing time was caused by the data file size limitation, which had been addressed by creating multiple files during the acquisition and combining the result afterward. By implementing an alternate file structure to support data acquisitions greater than 2GB, approximately 25% of the additional processing time was eliminated. This study illustrates that periodic evaluation and optimization of system test processes and measurement timing can sometimes pay large immediate dividends in range throughput and productivity. In addition, by creating an accurate system measurement timing model, sensitivity studies can easily be conducted to provide guidance in selecting the most effective alternative test plans or incremental investments in new equipment.
This paper presents a study on the low-frequency coaxial reflectometer measurement procedure. A time domain gating algorithm is developed by ETS-Lindgren and the results are validated after comparing to the Keysight 8753-time domain algorithm. The in-house time gating algorithm is then applied to the simulated reflectivity results of absorbers in reflectometer to the simulation results of the same absorbers with plane wave excitation using finite element method numerical computation. Based on the simulation results, the operable upper frequency limit and the minimum length of the straight coaxial section for the reflectometer are suggested. The errors introduced during measurement due to higher order modes are studied and the permissible limit for the errors is analyzed. The different higher order modes and their effects on field distribution are studied. The impact of the non-uniform field distribution on the absorber reflectivity measurement is also discussed.
We have developed a 60 GHz chip antenna designed for use as a gain and pattern verification tool in the calibration process of a millimeter wave antenna test chamber. The antenna is designed to interface with ground-signal-ground (GSG) micro-probes that have a probe pitch of 150 um to 250 um. This low temperature cofired ceramic (LTCC) chip antenna is fabricated using DuPont’s 9K7 GreenTapeTM material system with gold conductors. Features include a wafer-probe transition, a shielded stripline corporate feed network, aperture coupled patch elements, and an integrated Sievenpiper electromagnetic bandgap (EBG) structure for surface wave mode suppression. The use of the EBG structure enables main beam gain enhancement and side lobe level suppression. This 2x2 antenna array is directive such that it offers a nominal gain of 12 dBi at broadside over 58-62 GHz with an antenna efficiency of at least 60%. The entire antenna package has a nominal size of only 10.9 mm x 12.2 mm x 0.71 mm. Since this antenna package material is hermetic, it has stable performance under varying humidity and temperature which is highly desirable as a reference antenna.
The higher the frequency is, the greater the influence of the precision and the realism of the CAD models on electromagnetic (EM) scattering characteristics are. In the terahertz (THz) regime, surfaces of most objects can’t be taken as smooth according to Rayleigh criterion. The interaction of EM waves and the surface presents a coherent part in the specular direction and a scattering part in the other directions. Unfortunately, the roughness of surface can’t be represented by the CAD geometry. Based on statistics theory, the rough surface height profile is fully determined by the height probability density function (pdf) and its autocorrelation functions. Without loss of generality, the height pdf of surface is assumed to be Gaussian. Under the assumption, the random Gaussian rough surface is correspondingly generated. The original CAD geometry and the random Gaussian rough surface are superposed as the input of EM computation. To demonstrate the roughness impact on RCS, EM scattering characteristics of simple canonical objects such as plate, dihedral and trihedral in the THz regime are investigated. Taking into account the statistical surface roughness, the ray-based high-frequency EM method, shooting and bouncing rays (SBR), is utilized to compute the RCS of the above objects in the THz regime. Furthermore, the inverse synthetic aperture radar (ISAR) images are also carried out via filtered back projection (FBP) method. The EM scattering characteristics of the above objects in the THz regime are analyzed. Great differences of the objects EM scattering characteristics between the smooth and rough ones are observed and discussed.
Near-field antenna test systems are typically designed to optimize measurement results for a specific type of antenna. The measurement system is selected and sized based on the antenna aperture dimensions, directivity, weight and operating frequency, among other parameters. These factors are used to select either a planar, cylindrical, or spherical near-field test system for the given antenna test requirements. Antennas with different characteristics may not be compatible with the selected range and often require costly upgrades to the existing range or a different range altogether. One solution to test a wide variety of antenna types is a combination planar-cylindrical-spherical (PCS) test system. These systems usually require some level of facility re-configuration and present drawbacks when switching between the various modes of operation. The adaptation of a six-axis robotic test system is an attractive solution in these situations, as the system’s flexibility allows for rapid reconfiguration that is inherent to the system. This allows the user to select the optimal test solution for the antenna under test with little effort. This paper presents the performance of a six-axis robotic near-field measurement system showing near-field modes of operation and the system’s performance in antenna measurements when compared to a traditional spherical near-field range
“RTCA DO-213 Minimal Operation Performance Standards For Nose-Mounted Radomes” is a document frequently referenced in nose-radome testing requirements for commercial aircraft. This document was produced and is maintained by the Radio Technical Commission for Aeronautics (RTCA). The specifications of weather-radar systems have recently changed within RTCA’s DO-220A, and as a result DO-213 was updated to DO-213A in March, 2016, to ensure that radome requirements are consistent with those of the weather radar. In addition to the new requirements for radome evaluation, several existing requirements were clarified. These clarifications addressed such things as suitability of near-field measurements, proper procedures and processing, and appropriate measurement geometries. RTCA coordinated the document revision, with the bulk of the technical inputs coming from a broad-based working group. This working group had representatives from radar, aircraft, and radome manufacturers, government agencies, and providers and users of radome-testing systems. When requirements were added or when common practice conflicted with existing requirements, there was considerable effort and analysis employed to ensure that each change or clarification was truly required. Nevertheless, DO-213A has some significant impacts to many existing radome-testing facilities. This paper discusses the significant changes in DO-213A and their implications for radome test facilities, concentrating on after-repair radome electrical testing.
At AMTA 2006, we introduced the world to a system and method for over-the-air (OTA) testing of MIMO wireless devices with the concept of the boundary array technique, whereby the far-field over the air RF propagation environment is emulated to produce the realistic near field multi-path propagation conditions necessary for MIMO communication. Last year, the CTIA released Version 1.0 of their "Test Plan for 2x2 Downlink MIMO and Transmit Diversity Over-the-Air Performance," which standardizes on the boundary array technique (commonly referred to as the Multi-Probe Anechoic Chamber technique to differentiate it from the use of a reverberation chamber) for MIMO OTA testing. As the wireless industry just now prepares to perform certification testing for MIMO OTA performance for existing 4G LTE devices, the rest of the community is looking forward to the development of 5G. The corresponding future releases of the 3GPP wireless standard are expected to standardize the use of Massive MIMO in existing cellular communication bands. Massive MIMO is similar to the concept of mulit-user MIMO in IEEE 802.11ac Wi-Fi radios, but is taken to the extreme, with potentially hundreds of antennas and radios per cellular base station. This high level of radio to antenna integration at the base station will for the first time drive the industry beyond just antenna pattern measurements of base stations and OTA performance testing of handsets to full OTA performance testing of these integrated systems. At the same time, handset design is evolving to use adaptive antenna systems that will pose additional testing challenges. Likewise, manufacturers are looking to evaluate real-world usage scenarios that aren't necessarily represented by the test cases used for mobile device certification testing. This paper will discuss a number of these advances and illustrate ways that the MIMO OTA test systems must evolve to address them.
At AMTA 2006, we introduced the world to a system and method for over-the-air (OTA) testing of MIMO wireless devices with the concept of the boundary array technique, whereby the far-field over the air RF propagation environment is emulated to produce the realistic near field multi-path propagation conditions necessary for MIMO communication. Last year, the CTIA released Version 1.0 of their "Test Plan for 2x2 Downlink MIMO and Transmit Diversity Over-the-Air Performance," which standardizes on the boundary array technique (commonly referred to as the Multi-Probe Anechoic Chamber technique to differentiate it from the use of a reverberation chamber) for MIMO OTA testing. As the wireless industry just now prepares to perform certification testing for MIMO OTA performance for existing 4G LTE devices, the rest of the community is looking forward to the development of 5G. In the search for ever more communication bandwidth, the wireless industry has set its sights on broad swaths of unused spectrum in the millimeter wave (mmWave) region above 20 GHz. The first steps into this area have already been standardized as 802.11ad by the members of the WiGig Alliance for short range communication applications in the unlicensed 60 GHz band, with four 2.16 GHz wide channels defined from 58.32-65.88 GHz. With the potential for phenomenal bandwidths like this, the entire telecommunications industry is looking at the potential of using portions of this spectrum for both cellular backhaul (mmWave links from tower to tower) as well as with the hopes of developing the necessary technology for mobile communication with handsets. The complexity of these new radio systems and differences in the OTA channel model at these frequencies, not to mention limitations in both the frequency capabilities and resolution requirements involved, imply the need for a considerably different environment simulation and testing scenarios to those used for current OTA testing below 6 GHz. The traditional antenna pattern measurement techniques used for existing cellular radios are already deemed insufficient for evaluating modern device performance, and will be even less suitable for the adaptive beamforming arrays envisioned for mmWave wireless devices. Likewise, the array resolution and path loss limitations required for a boundary array system to function at these frequencies make the idea of traditional OTA spatial channel emulation impractical. However, as we move to technologies that will have the radio so heavily integrated with the antenna system that the two cannot be tested separately, the importance of OTA testing cannot be understated. This paper will discuss the potential pitfalls we face and introduce some concepts to attempt to address some of the concerns noted here.
Antennas utilized as probes, sources, and for gain comparison are typically specified to have excellent cross polarization levels, often on the order of 50 dB below the primary polarization component. In many cases, these antennas are fed with a waveguide-to-coaxial adapter, which can be sourced from a multitude of vendors. Depending on the design and construction of the adapter, and the distance from the excitation probe to antenna aperture, the adapter itself can contribute significantly to the degradation of the polarization purity of the antenna. These adapters typically use one of several methods to achieve a good impedance match across their bandwidths, including tuning screws, posts and stubs. These tuning elements may be arranged asymmetrically and can cause the waveguide to be overmoded locally. Additionally, there is wide variance in the separation of the adapter excitation probe and waveguide electrical flanges, which may not be long enough to suppress the higher order modal content. In this paper, we study the effects of adapter to antenna aperture coupling, including the coupling of fields local to the current probe as well as those that are induced by design asymmetries. The results of the analysis lead to a number of rules of thumb which can be used to ensure that the antenna polarization purity is optimized.
We present a channel sounder that can operate without a tether and still maintain an absolute time reference between the source and receiver. Based on a sliding correlator, with synchronized rubidium clocks to generate phase references for the up- and down- converted RF carriers, and a synchronous trigger, the system generates locked signals in the short term – 10’s of hours. The system has an operational range of 10 MHz to 6 GHz with an instantaneous channel bandwidth of up to 200 MHz. We start with a discussion on processing measurements for oversampled band-limited signals. Spectral truncation is compared with transmit spectrum filtering; DC bias removal and referencing to remove systematic effects are discussed. We conclude with channel sounding results, power delay profile, RMS delay spread, and time of arrival versus position for an electromagnetically complex environment.
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.
In near-field antenna measurements, the pattern effect of the measuring probe represents a systematic error and thus probe pattern correction is a constitutive part of the existing processing algorithms. However, as it was shown in [1], in spherical near-field measurements, for typically used measurement distances, not exceeding two to four diameters of the measured antenna, the probe pattern effect is relatively small, and in many situations the probe pattern can be taken as that of a Hertzian dipole with the resulting effect on the measured antenna pattern being either very small or even negligible. On the other hand, for shorter measurement distances, the probe pattern effect becomes significant and omitting the probe pattern causes noticeable changes in the measured antenna pattern. It was shown in [2] by approximate simulations that in these cases applying the correction using the probe pattern not at the measured frequency, but at the center frequency of a standard waveguide band provides negligible error for even very small measurement distances, not exceeding one or two diameters of the measured antenna, depending on the probe type. Since an approximate model was used for the simulations, the obtained results show only preliminary picture and can only be used as tentative guidelines. In this paper, in order to prove the results of the simulations and the derived conclusions, experimental validation of the simplified probe pattern correction was carried out by processing measured results of several electrically large antennas including probe pattern correction at the measured frequency and at the center frequency of the waveguide band, and comparing the difference. The measured results of a center-fed parabolic reflector, an offset reflector, and a base-station antenna were used for the validation. The obtained results generally confirm the simulations and prove the conclusions that just a single probe pattern can be used for all frequencies over a standard waveguide band for majority of spherical near-field measurement scenarios. [1] S. Pivnenko, J.L. Besada, A. Ruiz, C. Rizzo: On the probe pattern correction in spherical near-field antenna measurements. Proc. 37th AMTA Symposium, Long Beach, CA, USA, October 2015 [2] S. Pivnenko, E. Venero, C. Rizzo: Application of single probe correction file for multi-frequency spherical near-field antenna measurements. Proc. 10th EuCAP, Davos, Switzerland, April 2016
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.
Electro-optic (EO) probes provide an ultra-wideband, high-resolution, non-invasive technique for polarimetric near-field scanning of antennas and phased arrays. Unlike conventional near field scanning systems which typically involve metallic components, the small footprint all-dielectric EO probes can get extremely close to an RF device under test (DUT) without perturbing its fields. In this paper, we discuss and present measurement results for EO field mapping of a dual-band circularly polarized active phased array that operates at two different S and C bands: 2.1GHz and 4.8GHz. The array uses probe-fed, cross-shaped, patch antenna elements at the S-band and dual-slot-fed rectangular patch elements at the C-band. At each frequency band, the array works both as transmitting and receiving antennas. The antenna elements have been configured as scalable array tiles that are arranged together to create larger apertures. Near-field scan maps and far-field radiation patterns of the dual-band active phased array will be presented at the bore sight and at different scan angles and the results will be validated with simulation data and measurement results from an anechoic chamber.
This paper describes an mm-wave extrapolation range installed at KRISS, which may be used for testing standard gain antennas by using the three-antenna extrapolation technique in the frequency range from 110 GHz to 325 GHz. It consists of a precision linear slide and an mm-wave S-parameters measurement system. The precision linear slide for changing the separation distance between transmitting and receiving antennas is realized with a linear motor with 1.6 meter long on a precision stone surface plate. The mm-wave measurement system for measuring S-parameters at extrapolation antenna measurements consists of a 67 GHz vector network analyzer used as a main frame and three frequency extenders which are operating at three frequency bands (D-band (110 -170 GHz), G-band (140-220 GHz) and J-band (220-325 GHz)). The S-parameters measurement system is calibrated with TRL/LRL method. The general procedure of the extrapolation technique is as follows; 1) The effect of multiple reflections between transmitting and receiving antennas is removed from data measured at a reduced distance. 2) A polynomial is determined for curve-fitting the data removed the effect of multiple reflections. 3) Finally, far-field antenna properties are calculated from the polynomial. In this paper, a method using measured S-parameters for reducing multiple reflections between transmitting and receiving antennas is used. Power gain of D-band standard gain horn antennas is measured with the mm-wave extrapolation range. Description of detailed measurement system and measurement result will be presented at the symposium.
One of the most useful metrics for a wireless device is Total Radiated Power, or TRP as it is commonly abbreviated. The total radiated power of a wireless device is determined by measuring the radiated power at a number of sample points (typically 264) over a spherical surface surrounding the device under test and integrating the results to get the total power radiated by the device. A measurement of a single channel typically takes between one and two minutes. This paper presents a method of measuring TRP with only a single data point measurement which can be made in less than one second. This method uses a conductive ellipsoid surface. The device under test is placed at one focal point and the measurement antenna is placed at the other. The surface of the ellipsoid performs the integration of the radiated power and only a single measurement is needed to determine the total radiated power. A proof of concept model was built and measurements made on both active and passive devices. These same devices were then measured in a classical anechoic over-the-air (OTA) chamber and the results compared. The comparison of the two measurement methods, although not perfect, is encouraging and supports a conclusion that this is a viable technique for quickly determining the total radiated power of a wireless device. The method can be expanded to measure the Total Isotropic Sensitivity (TIS) of a wireless device. Although not as fast as a TRP measurement, the sensitivity measurement is still many times faster than the same measurement in an anechoic chamber. The design of the proof of concept model is presented along with the data taken both in the ellipsoid and in the anechoic chamber.
Precise determination of antenna phase centers is crucial to reduce the uncertainty in gain when employing the three-antenna method, particularly operated over a short range-such as a 3-m radio anechoic chamber, where the distance between the phase centers and the open ends of an aperture antenna (the most commonly-used reference) is not negligible, compared with the propagation distance. An automatic system to determine the phase centers of aperture antennas in a radio anechoic chamber has been developed and the absolute gain of horn antennas have been thereby evaluated with the three-antenna method. The phase center of an X-band horn was found to migrate up to 55 mm from the open end. Uncertainties in the gain were evaluated in accordance with ISO/IEC Guide 93-3: 2008. The 95% confidence interval of the horn antenna gain was reduced from 0.39 to 0.25 dB, when using the phase center location instead of the open end. Then the gains, polarization, and radiation pattern of space-borne antennas were measured: low-, medium-, and high-gain X-band antennas for an ultra small deep space probe employing the polarization pattern method with use of the horn antenna. Comparison between the radiation properties with and without the effect of spacecraft bus was carried out for low-gain antennas. The 95% confidence interval in the antenna gain decreased from 0.60 to 0.39 dB.
The automotive industry is changing rapidly through the evolution of on board and embedded components and systems. Many of these systems rely on the over the air performance of a communication link and the evaluation of these links is a key requirement in understanding both the real world performance, and associated operating limits of a particular system. The operating frequency range of the installed communication systems now extends from the traditional AM bands from 540KHz to almost 6GHz for WiFi. There are several different antenna design options available to cover this range and in many cases, the performance of an antenna when installed on a vehicle differs from a measurement of the same antenna in isolation. There is also a growing use of high frequency RADAR systems operating at frequencies approaching 80GHz that also need to be included in the performance analysis. The behavior of the individual components using conducted methods for example, is an important step but the direct measurement of antenna pattern and data throughput under ideal steady state and also varying spatial and operating conditions is likely to be the most robust method of channel evaluation. There is a steady march toward vehicle autonomy that is pushing the development of increasingly complex and sophisticated sensors, receivers, transmitters and firmware, all installed on an already well populated platform. The interoperability and EMC performance of these embedded systems is an extension to the need for a fundamental understanding of performance. This paper will present some of the available measurement and evaluation options that could be used as part of an integrated test environment which takes advantages of a number of established techniques.
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.