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Anechoic Chamber

BIANCHA: A spherical indoor facility for bistatic electromagnetic tests
Patricia López-Rodríguez, Olga Hernán-Vega, David Poyatos-Martínez, David Escot-Bocanegra, November 2016

BIANCHA (BIstatic ANechoic CHAmber) is a singular facility located at the premises of the National Institute for Aerospace Technology (INTA), Spain, and was devised to perform a wide variety of electromagnetic tests and to research into innovative measurement techniques that may need high positioning accuracy. With this facility, both monostatic and bistatic tests can be performed, providing capability for a variety of electromagnetic measurements, such as the electromagnetic characterization of a material, the extraction of the bistatic radar cross section (RCS) of a target, near-field antenna measurements or material absorption measurements by replicating the NRL arch system. BIANCHA consists of two elevated scanning arms holding two antenna probes. While one scanning arm sweeps from one horizon to the other, the second scanning arm is mounted on the azimuth turntable. As a result, BIANCHA provides capability to perform measurements at any combination of angles, establishing a bistatic, spherical field scanner. In this regard, it is worth noting that in the last years, a renewed interest has arisen in bistatic radar. Some of the main reasons behind this renaissance are the recent advances in passive radar systems added to the advantages that bistatic radar can offer to detect stealth platforms. On the other hand, with the aim of developing new aeronautic materials with desired specifications, research on the electromagnetic properties of materials have also attracted much attention, demanding engineers and scientists to assess how these materials may affect the radar response of a target. Consequently, this paper introduces BIANCHA and demonstrates its applicability for these purposes by presenting results of different tests for different applications: a bistatic scattering analysis of scaled aircraft targets and the extraction of the electromagnetic properties of composite materials utilized in an actual aeronautical platform.

Limitations of the Free Space VSWR Measurements for Chamber Validations
Zhong Chen, Zubiao Xiong, Amin Enayati, November 2016

Free Space VSWR measurement has been the de facto standard method for anechoic chamber performance evaluation for more than 50 years.  In this method, a probe antenna is kept at a fixed angle while traveling along a linear path to record the standing wave pattern.  The probe antenna is then rotated to a different angle to repeat the measurement.  Reflectivity, which is used as the chamber performance metric, is calculated for each probe rotation angle.   In this paper, we show that the reflectivity is affected by the antenna patterns of the probe antenna.  When the probe antenna is aimed at the specular reflection point of a chamber surface, measurement dynamic range is improved, and the method provides a measure of the reflectivity primarily from that surface.  When the probe is not directed at a specular point, other reflections in the chamber can contribute to the VSWR, and the chamber reflectivity becomes more dependent on the probe antenna pattern.

Advances in MIMO Over-the-Air Testing Techniques for Massive MIMO and other 5G Requirements
Michael Foegelle, November 2016

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.

Advances in Over-the-Air Performance Testing Methods for mmWave Devices and 5G Communications
Michael Foegelle, November 2016

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.

Characterization Of Dual-Band Circularly Polarized Active Electronically Scanned Arrays (AESA) Using Electro-Optic Field Probes
Kazem Sabet, Richard Darragh, Ali Sabet, Sean Hatch, November 2016

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.

Instantaneous TRP Measurements
James Huff, November 2016

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 Phase Centers and Its Application to Gain Measurement of Spacecraft-borne Antennas in an Anechoic Chamber
Yuzo Tamaki, Takehiko Kobayashi, Atsushi Tomiki, November 2016

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.

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 Reduced Uncertainty Method for Gain over Temperature Measurements in an Anechoic Chamber
Vince Rodriguez,Charles Osborne, November 2015

Gain over Temperature (G/T) is an antenna parameter of importance in both satellite communications and radio-astronomy. Methods to measure G/T are discussed in the literature [1-3]. These methodologies usually call for measurements outdoors where the antenna under test (AUT) is pointed to the “empty” sky to get a “cold” noise temperature measurement; as required by the Y-factor measurement approach [4]. In reference [5], Kolesnikoff et al. present a method for measuring G/T in an anechoic chamber. In this approach the chamber has to be maintained at 290 kelvin to achieve the “cold” reference temperature. In this paper, a new method is presented intended for the characterization of lower gain antennas, such as active elements of arrays. The new method does not require a cold temperature reference thus alleviating the need for testing outside or maintaining a cold reference temperature in a chamber. The new method uses two separate “hot” sources. The two hot sources are created by using two separate noise diode sources of known excess noise ratios (ENR) or by one source and a known attenuation. The key is that the sources differ by a known amount. In a conventional Y-factor measurement [4], when the noise source is turned off, the noise power is simply the output attenuator acting as a 50 ohm termination for the rest of the receive system.  But by using two known noise sources, the lower noise temperature source takes the place of T-cold in the Y-factor equations. The added noise becomes the difference in ENR values. An advantage of this approach is that it allows all the ambient absorber thermal noise temperature change effects to be small factors thus reducing one of the sources of uncertainty in the measurement. This paper provides simulation data to get an approximation of the signal loss from the probe to the antenna under test (AUT). Another critical part of the method is to correctly define the reference plane for the measurement. Preliminary measurements are presented to validate the approach for a known amplifier attached to an open ended waveguide (OEWG) probe which is used as the AUT. [1] Kraus J.  Antennas 2nd ed.1988 McGraw-Hill: Boston, Massachusetts. [2] Kraus J.  Radio Astronomy Cygnus-Quasar Books 1986. [3] Dybdal R. B. “G/T Comparative Measurements” 30th Annual Antenna Measurement Techniques Association Annual Symposium (AMTA 2008), Boston, Massachusetts, November 2008. [4] “Noise Figure Measurement Accuracy – The Y-Factor Method”, Agilent Technologies, Application Note AN57-2. [5]  Kolesnikoff, P. Pauley, R. and Albers, L “G/T Measurements in an Anechoic Chamber” 34th Annual Antenna Measurement Techniques Association Annual Symposium (AMTA 2012), Bellevue, Washington Oct 2012. Keywords: Gain over Temperature (G/T), Satellite Communication, Radio Astronomy, Noise Figure Measurement

Spherical Geometry Selection Used for Error Evaluation
Greg Hindman,Patrick Pelland, Greg Masters, November 2015

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)

Phase Center Stabilization of Wideband Millimeter-Wave Horn Antenna for Implementation with a Luneburg Lens
Brian Simakauskas,Maxim Ignatenko, Dejan Filipovic, November 2015

Unlike most antenna performance parameters (directivity, beamwidth, and efficiency, e.g.), phase center is not strictly defined and warrants further clarification when used.  Put simply, the phase center is the point at which antenna radiation seems to emanate and is determined as the center of a spherical surface of constant phase in the far field.  For practical antennas, however, such a point is fictional and can only be established by minimizing the phase variation on a portion of the spherical surface over a smaller angle of interest, generally where the radiation intensity is greatest (e.g. the 3dB beamwidth).  Most commonly, the phase center is defined for a two dimensional planar cut parallel to the direction of propagation, for example the E or H plane of a horn. Knowledge of the phase center is particularly critical in the feeds of reflectors or lenses, where it is required to be located at the focal point of the reflecting or refracting structure to maximize aperture efficiency.  Due to its electro-mechanical properties the horn antenna has often been used as the feed for the above mentioned configurations.  For wideband applications, the stabilization of the phase center over the entire frequency band poses a significant challenge since this point generally tends from the mouth to the throat of a horn as frequency is increased.  The design discussed in this paper involves a feed horn operated in conjunction with a Lunenburg Lens for increased directivity and gain over 18-45 GHz bandwidth.  A design overview is discussed with the primary focus on phase stabilization considerations.  Methods for determining the phase center of the design are also discussed and compared.  These include analytical solutions using the aperture current approximation, simulations using method of moments and finite element method from FEKO and HFSS, respectively, as well as measurements taken in the anechoic chamber at the University of Colorado Boulder.

Investigation of Higher Order Probe Corrected Near-Field Far-Field Transformation Algorithms for Precise Measurement Results in Small Anechoic Chambers with Restricted Measurement Distance
Yvonne Weitsch,Thomas. F. Eibert, Raimund Mauermayer, Leopold G. T. van de Coevering, November 2015

For today's sophisticated antenna applications, the accurate knowledge of 3D radiation patterns is increasingly important. To measure the antennas under far-field conditions over a broad frequency band is hereby hardly impossible. By near-field to far-field transformation, one can overcome the difficulties of limited measurement distances. In common spherical near-field antenna measurement software, the transformation based on spherical mode expansion is typically implemented. These software tools only provide to correct the influence of first order azimuthal probe modes. The influence of the probe’s higher order modes though increases with shorter measurement distances. To measure a broad frequency range in one measurement set-up and to save time, dual ridged horns are popular candidates since they operate over a wide frequency range. The drawback is that they are probes of higher order. In this contribution, we will present an investigation on near-field measurements which are transformed into the far-field deploying the transformation technique based on spherical modes which is extended by a higher order probe correction capability. The resulting diagrams comparing first and higher order probe correction show that a correction is important in particular for the cross polarization In addition, the near-field data is transformed with an algorithm which employs a representation by equivalent currents. In this method, a higher order probe correction based just on the probe’s far-field pattern is integrated. The equivalent currents supported by an arbitrary Huygens surface allows to reconstruct the current densities close to the actual shape of the AUT which is mandatory for precise antenna diagnostics. Another issue needs to be accounted for regarding limited measurement distances and spherical modal expansion. While representing the AUT and the probe in spherical modes the radii of the spheres grow the more modes are included which depends on the sizes of the TX and the RX antennas. It has to be ensured that both spheres do not interfere.  All measurements were carried out in the anechoic chamber of our laboratory in which measurements starting at 1 GHz are practicable according to the dimension of the chamber and of the absorbers. Due to our restricted measurement distance of 0.57 m, all the above mentioned rules need to be considered. In conclusion, small anechoic chambers are also capable of delivering precise antenna measurements over a broad frequency range due to algorithms capable of higher order probe correction.

A Study on the Effects of Influence Factors for Antenna Radiation Efficiency Measurements in Anechoic Chamber
Qi Wanquan ,Tian Hong Loh, November 2015

?Radiation efficiency is an important attribute of an antenna that can be calculated from its gain and directivity. This paper focuses on investigating the effects of influence factors for antenna radiation efficiency measurement in an anechoic chamber (AC). The gain transfer method (GTM) is used widely during the gain measurement, but the results can be influenced by many factors. A comparison of gain measurement performed by GTM and the three-antenna method (TAM) is presented. All measurements were carried out between 1 GHz and 8 GHz in an anechoic chamber with a double-ridged waveguide horn antenna as the antenna under test (AUT), which has a relatively broad half-power beamwidth. The results show that the maximum difference between the two methods is about 1.5 dB and the GTM may bring greater measurement uncertainty. To evaluate the influence of directivity and its repeatability, two sets of directivity measurements were performed using four different antenna mounting brackets, namely: Rohacell foam, Tufnol, metal, and metal covered by radio frequency absorber. Amongst the antenna mounting brackets, the Tufnol bracket gives the best repeatability performance. The antenna axial symmetrical properties were also assessed for each antenna mounting bracket except for Rohacell foam. The results shows that the gain measurement has more influence over characterization of antenna radiation efficiency as compared with the directivity measurement. To improve accuracy for radiation efficiency measurement, one suggests to use TAM for the antenna gain measurement.

Methods of Shaping Directional Characteristics of Microstrip Antenna Arrays
Leszek Nowosielski,Marian Wnuk, November 2015

In the contemporary world there is high demand for mutual communications and data transmissions. More and more new radio communication systems are developed that require to prepare new types of antennas. Such requirements are satisfied by microstrip antennas. These antennas are characterised by many interesting features, both positive and negative, these attributes have to be taken into account in the design process. These antennas allow to miniaturise antenna system, and by this its highest density. It causes appearance of mutual couplings changing fields distributions on aperture antennas as well currents distributions in linear antennas. A methodology of shaping directional characteristics of microstrip antenna arrays will be presented in the article using phase shifters. Basing on the CST Microwave Studio software, two models of microstrip antenna arrays were designed and done using a method of radiation patterns shaping as well as real models that were put on measurements. Shapes of radiations patterns optimised according to the effects of signal amplitude and phase of particular antenna array radiators were presented in the article. The results were also presented in the tables taking into account values of phase shifts and amplitudes of power supplying system. The results achieved were compared with the results of measurements done on a special measuring position at the anechoic chamber.

Simulation of Antenna Measurements using Advanced Computational Techniques
C.J. Reddy,Derek Campbell, November 2015

Recent advances in Computational electromagnetic (CEM) simulations made them possible to be a cost-effective solution for designing and characterizing antenna measurement facilities. Using both full wave and asymptotic techniques, it is possible to characterize the performance of large measurement facilities such as anechoic chambers and compact antenna test ranges (CATR) with large parabolic reflectors. In this paper, we present the use of full wave techniques such as Finite Element Method (FEM) and Multi level Fast Multipole Method (MLFMM) as well as asymptotic techniques such as Physical Optics (PO) and Ray-Launching Geometrical Optics (RL-GO) for quiet zone characterizations as well as emulation of antenna measurements in both anechoic chambers as well as CATRs. Computational resources required for different techniques have been compared.

A Portable Antenna Measurement System for Large-Scale and Multi-Contour Near-Fields
Alexander Geise,Torsten Fritzel, Hans-Jürgen Steiner, Carsten Schmidt, November 2014

Antenna measurement facilities face their physical limits with the growing size of today’s large and narrow packed antenna farms of telecom satellites but also of large unfurlable reflector antennas for low frequency telecom applications. The special operational constraints that come along when measuring such large future antennas demand for new measurement approaches, especially if the availability or realization of present measurement systems with large anechoic chambers is not an option. This paper presents a new system called PAMS (Portable Antenna Measurement System). The most characteristic part of PAMS is that the RF instrumentation is installed inside a gondola that is positioned by an overhead crane. The gondola is equipped with one or several probes to scan the near-fields of the antenna under test. With a modified crane control the gondola can be placed anywhere within the working space of the crane, which is considered as being giant in comparison to measurement volumes of existing large antenna test facilities. The whole system supports but is not limited to common classical near-field scanning techniques. Thanks to new near-field to far-field transformations the system can deal with arbitrary free form scanning surfaces and probe orientations allowing measurements that have been constrained by the classical near-field theory so far. The paper will explain the PAMS concept on system level and briefly on sub-system level. As proof of concept, study results of critical technologies are discussed. The paper will conclude with the status about on-going development activities.

Full-wave Modelling of Pyramidal Absorbers
Amin Enayati,Arya Fallahi, November 2014

There are different applications where the radiation level of the electromagnetic waves are needed to be controlled or reduced. One way to achieve a functional passive control of the radiation level is by the use of electromagnetic-wave absorbers. The absorption efficiency is not only gained by the electromagnetic characteristics of the base material but also by the geometrical shape of the absorber specifically for wideband absorbers. One of the main applications of wideband absorbers is in anechoic chambers. In anechoic chambers, the walls of the chamber are lined with different absorbing panels each of which have different geometrical shapes. Two major groups of wideband absorbers are the wedge and pyramidal absorbers. When an infinite wall is lined completely with one type of these absorbers, the resulting electromagnetic problem will be a 1-dimensional (for the case of wedge absorber) or a 2-dimensional (in the case of pyramidal absorber) periodic-boundary-condition problem. A semi-analytical method based on a multi-conductor-transmission-line model has been previously introduced to solve the 1-dimesional problem (wedge absorbers) [1]. A modified method has been developed and will be introduced for the 2-dimensional problem (pyramidal absorbers). Some examples comparing the simulation results with the measurements ones will show the efficiency of the proposed method for the pyramidal absorbers. [1] A. Enayati, and A. Fallahi,“ Full-wave modeling of wedge absorbers”, ATMS 2014, Chennai, India.

Accurate Planar Near-Field Antenna Measurements Without Full Anechoic Chamber
Greg Hindman,Stuart Gregson, Allen Newell, November 2014

In recent times, planar near-field antenna measurements have largely been performed within fully absorber lined anechoic chambers.  However this is a comparatively recent development as, due to the nature of the electromagnetic radiation when measuring medium to high gain antennas, one can often obtain excellent results when testing within only a partially absorber lined chamber [1], or in some cases even when using absorber placed principally behind the acquisition plane. As absorber can be bulky and costly, optimizing its usage often becomes a significant factor when planning a new facility.  This situation becomes more pressing when the designated test environment is not exclusively devoted to antenna pattern testing with non-ideal absorber coverage being, in some cases, mandated, c.f. EMC testing.  Planar test systems lend themselves to deployment within multipurpose installations as they are routinely constructed so as to be portable [2] thereby allowing partial or perhaps complete removal of the test system between measurement campaigns. This paper will present measured data taken using a number of different planar antenna test systems with and without anechoic chambers to summarize what is achievable and to provide design guidelines for testing within non-ideal anechoic environments.  NSI’s Planar Mathematical Absorber Reflection Suppression (MARS) technique [3, 4] will be utilized to show additional improvements in performance that can be achieved through the use of modern sophisticated post processing. Keywords: Planar Near-Field, Reflection Suppression, Scattering, MARS. REFERENCES S.F. Gregson, A.C. Newell, G.E. Hindman, M.J. Carey, “Extension of The Mathematical Absorber Reflection Suppression Technique To The Planar Near-Field Geometry”, AMTA, Atlanta, October 2010. G.E. Hindman, “Applications of Portable Near-Field Antenna Measurement Systems”, AMTA, October, 1991. S.F. Gregson, A.C. Newell, G.E. Hindman, “Advances In Planar Mathematical Absorber Reflection Suppression”, AMTA, Denver, Colorado, October 2011. S.F. Gregson, A.C. Newell, G.E. Hindman, P. Pelland, “Range Multipath Reduction In Plane-Polar Near-Field Antenna Measurements”, AMTA, Seattle, October 2012.

Near-Field to Far-Field Transformation for ICs Using Dipole-Moment Models on EMI Measurement
Guochang Shi,Yuan Zhang, Yi Liao, November 2014

The electromagnetic compatibility (EMC) problems are becoming more challenging and noticeable due to the increasing complexity of integrated circuits (IC). Currently, most electromagnetic interference (EMI) standards specify that the measurements must be performed in the far field which is time consuming and expensive for the use of semi-anechoic chambers or open area test site. While near-field measurement is usually fast and much more flexible, especially for the complex structures, the near-field results could be obtained more efficiently for built-in ICs. The transformation between near-field and far-field data is of great significance as long as the near-field data is measured. Many methods including near-field scanning method and Huygens’ equivalence method are used to complete the transformation from near-field data to far-field radiation. However, the near-field scanning method is inherent complex and requires strict mathematical derivation, which is difficult to handle for some practical cases. Huygens’ equivalence method is restricted by the location of observation point and the results are hardly obtained under scanning plane. In contrast, near-field to far-field transformation based on inverse method appears to be more desirable by reconstructing a dipole-moment model instead of an IC. The dipole-moment model can be used to predict the far-field data, but also can be incorporated into a numerical full-wave tool as an equivalent source for complex systems. In this paper, the inverse method is firstly introduced. A noise source model from an IC is proposed based on an array of dipoles. These dipole moments can be extracted from the near-field measurement in a scanning plane above the IC. Each dipole is modeled as an equivalent combined source consists of wire antennas and loop antennas. Then the radiation of IC in far-field region can be easily obtained. Finally, an example of physical IC is given to validate the approach.

Uncertainty Analysis of Spherical Near Field Antenna Measurement System at VHF
Gwenn Le Fur,Francisco Cano-Facila, Daniel Belot, Lise Feat, Luc Duchesne, Anthony Bellion, November 2014

Recent enhancements in military telecommunication systems for monitoring and tracking in low VHF range (30-80MHz) imply the use of specific antenna measurement facilities to characterize either the antenna alone or the antenna mounted on a supporting structure which can be heavy and bulky. The indoor Near-Field approach shows benefits in terms of compactness. However this approach involves issues due to high levels of reflectivity of the anechoic chamber, the antenna under test positioner and the measurement probe structure at these larges wavelengths. Studies and simulations of each contribution have been performed in a previous paper. The proposed paper focuses on the improvement of measurement results using post-processing techniques and associated uncertainty analysis of the mono-probe near-field system at the CNES. First the new 50-400 MHz dual polarized probe and the measurement system are briefly presented. Then the estimation of each error term is detailed providing a global error budget in order to appreciate the benefit of post-processing technique. All the considered errors terms are all of those included in the well-known 18 NIST terms. Each of them is evaluated using the most appropriated approaches (specific measurement, simulation).







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