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The characterization of the radiation performances is a necessary step in the conception of any wireless system. These systems require always more demanding radiation performances that calls for time consuming characterizations. This duration can be reduced by the decrease of the number of field samples. By enclosing the antenna in a Huygens’ surface, we can build a radiation matrix that maps equivalent surface currents to the radiated field. A singular value decomposition of this matrix enables to build a compressed representation of the antenna measurement and more specifically a reduced basis of the radiated fields. By harnessing the outer dimensions of the antenna, the number of field samples can be reduced as compared to spherical wave expansion techniques. This number is shown to be connected to the area of the convex equivalent surface enclosing the AUT, as hinted by previous analytical works for canonical enclosing surfaces. The whole antenna characterization procedure is validated by simulations and experiments.
While the size of the parabolic reflector in general determines the usable area of the quiet zone of a compact antenna test range (CATR) inside which a pseudo plane-wave condition is produced, the reflector edge treatment also plays a significant role in terms of overall quality and electromagnetic field distribution & uniformity, and especially so at mm-wave frequencies. Using modern powerful digital computational simulation technology in combination with genetic optimization, the edge treatment can be evolved for a specific CATR application as part of the design process. This is crucial as it attempts to maximize the performance of a given solution while ensuring efficient use of the available space which correspondingly provides an economical implementation. This is particularly important in 5G production test applications where, in many instances, multiple systems are required to be collocated within a given host building and in which case, the savings become multiplicative. In this paper the novel design methodology is introduced for the genetic optimization (GO) of blended rolled edge single offset reflector CATRs. Several edge blends and treatments are considered with the genetically optimized design parameter. For each variation the quiet-zone performances are compared and contrasted.
One benefit of cooperative automated and connected driving lies in the fusion of multiple mobile wireless sensor and data transmission nodes, covering complementary technologies like radar, cellular and ad-hoc communications, and alike. Current developments indicate enormous potential to increase the environmental awareness through joint communication and radar sensing. In this respect, future channel models require knowledge of bi-static reflectivities of road users over a range of illumination and observation angles, both in the nearfield and in the far-field. To establish reference data and model such angle-dependent RCS variations, this paper deals with realistic pedal and wheel rotations of a bicycle based on electromagnetic simulations. In the simulation setup, idealized far-field conditions with plane-wave illumination and observation were assumed, while the angles covered the entire azimuth with 201 variations of the pedal and wheel positions. The fluctuation of the RCS is analyzed and discussed in terms of its probability density and cumulative distribution functions. Depending on the angular constellation, the range of the fluctuation varied between 1 dB and 14 dB, while the specular reflection and forward-scattering showed almost no fluctuation.
Using beam-steering technologies, 5G massive MIMO base stations are capable to radiate typical equivalent isotropic radiated powers as high as 80 dBm (100 kW). Such levels create challenges in Over-The-Air (OTA) testing, both for the RF test system hardware, and the anechoic chamber / absorber layout designs. In this paper, a calculation tool is introduced which allows evaluations of the Poynting vector at ”mid range” distances, from given base station models. This code is used to deduce conservative power density distribution estimates and identify possible critical exposure areas in the test facility. General design criteria for the chamber, absorber layout and choice of material are derived. The specific case of a plane-wave synthesis OTA test site is investigated, where an experimental setup is used to demonstrate the power tolerance of the solution and its compatibility with base station testing requirements.
This paper presents a reliable design and measurement methodology of using various feeding networks for mmWave/Sub-THz SoP/SoC/SoD antennas in 5G and 6G communication. In order to achieve reliable and precison testing results, the electrical, mechanical, and thermal consideration have been precendently investigated and discussed through various examples of feeding network based on lots of the advanced materials and fabrication process. First, for a realization of the minimized discrepancy between simulation and measurement without any calibration kit and resistive films for 50-Ω termination load, two examples have been presented. In other words, a symmetrical power divider with back-to-back transition structures and a leaky wave antenna design topology featuring high attenuation constant have been demonstrated. Finally, despite challenging fabrication condition resulting in performance degradation, a low-loss transition structure in mmWave SoD antenna and its design methodology is also presented and discussed.
Radio Base Stations (RBS) must comply with applicable radio frequency electromagnetic field exposure regulations. Although compliance evaluation is typically carried out using field strength acquisitions or computations, Specific Absorption Rate (SAR) measurement is the reference method for low-power RBS, such as those used for indoor coverage. As classical robotbased probing is extremely time-consuming, especially when the whole-body SAR in a large phantom is to be assessed, faster alternative techniques are of high interest. Such solutions are becoming even more crucial, as the number of test modes is multiplying with modern communication technologies. This paper introduces an alternative, based on the convergence of Over- The-Air (OTA) measurements, equivalent current reconstruction and full-wave electromagnetic simulation. A first set of results demonstrates the relevance of this combination, by comparing actual dosimetric measurements to OTA-based reconstructed SAR values in a flat body mannequin, for a commercial lowpower RBS. A test system is realized which enables OTA electric field phase evaluations for a self-powered device under test, using digitally modulated signals. This proof of concept establishes the applicability of the technique to actual regulatory testing conditions.
Evaluation and calibration of individual elements of a phased array is a time-consuming process that involves not only the radiation pattern and RF circuitry of each element, but the interaction of each element with all of the other elements within the array. Iterating through each element in order to test them one at a time is extremely time consuming, and in some cases, depending on the design of the array, this approach may not work reliably at all. In cases where the impedance of the “off” elements differs from their impedance when actively transmitting or receiving, they can distort the resulting single element pattern due to mutual coupling. Even in the case where the elements themselves are well behaved, the driving circuitry can exhibit non-linearities due to the differences in signal levels or device heating present when all elements are active vs. only a single element. Thus, it would be ideal to be able to extract individual element performance from the combined pattern of the array with all elements active. This paper will investigate the use of orthogonal coding applied to each element of the array through the onboard gain/phase control circuitry using different modulation coding schemes in order to extract the average performance of each element from the measured total result.
A custom radar kit that integrates with a portable computer (laptop) for assembly and operation by students and researchers has been developed at MIT Lincoln Laboratory. The assembled radar kit uses two low-cost cylindrical metal cans that serve as the antennas, one for transmitting and one for receiving radar signals. The antennas operate as linearly polarized openended circular waveguides (10.5 cm diameter) fed with a thinwire monopole probe. Over the 2.4 to 2.5 GHz band, the measured reflection coefficient is less than −10 dB, the peak realized gain is greater than 7 dBi, and the half-power beamwidth is approximately 70 degrees in both the E- and Hplanes. FEKO method of moments simulations of the antenna are compared with the measured data and good agreement is demonstrated.
5G base stations are gradually evolving into Active Antenna Systems, improving the link budget with beamsteering capabilities. As such antenna arrays are typically eight wavelength large or more, the question of reducing the footprint of far-field testing facilities has experienced a growing interest. Recent research results have established that it is possible to conduct accurate Over-The-Air measurements around the peak radiation, at an effective far-field distance which can be as low as 20% of the Fraunhofer distance, depending on the electrical size of the antenna aperture. This paper complements the published validations of this finding, with an application to commercial massive MIMO base stations. The previously identified midrange far-field distance is even shown to be conservative for such devices. A mathematical analysis based on plane-wave expansion is proposed and allows for a general interpretation of this result.
The most common antennas used for antenna pattern or gain measurements are Standard Gain Horn Antennas, Circular Horn Antennas, Dual Ridge Horn Antennas or Quad Ridge Horn Antennas. In addition, the far-field criteria for the antennas is currently revised as per the latest draft of IEEE 149 standard, based on the largest dimension, D, of the antenna and wavelength, of interest. Conventionally, the largest aperture dimension of the antenna is considered as the dimension, D. One could question, if considering the same aperture dimension to compute the far-field distances over entire frequency range is accurate. It could lead to longer test range distances at higher frequencies for broadband horn antennas, which in turn will lead to much larger chamber sizes. Thus, it is imperative to investigate the electrical dimension, D, as a function of frequency for the broadband horn antennas to accurately yield the far-field distances needed to characterize the different antenna parameters like half-power beam width, first null level, side lobe level, etc. This paper explores the utilization of the spherical modes and underlying Minimum Radial Extend (MRE) from Nearfield to Far-field transformation theory to extract the electrical dimension, D, so as to accurately characterize the HPBW across the frequency range. Firstly, the near fields are transformed to far-fields by incorporating spherical modes. The transformed farfields are compared to the ideal far-field pattern for standard gain horns, with respect to the equivalent noise level parameter over the HPBW solid angle, to compute the acceptance criteria. Based on the acceptance criteria of the equivalent noise level for standard gain horns, the same exercise is repeated for a broadband quad-ridge horn over the HPBW solid angle across the frequency range. The MRE is computed from the number of spherical modes across the frequency range and the electrical dimension, D, is calculated to be twice of the MRE value. The far-field distance is calculated based on the computed electrical dimension and compared to the far-field distance calculated per the physical dimension of the antenna structure.
In a previous presentation[1], the author has reported that nearfield antenna measurements taken in the presence of a lossy half space such as the ocean can be accomplished by the use of Complex Image Theory. The approach allows the user to collect data over the upper hemisphere of space and employ Complex Image Theory to “fill in” the field information in the lower hemisphere. The approach has been limited, though, in application due to the limited applicability of the Complex Image approach. In this paper, a fresh look is taken at Complex Image Theory and a new field expansion proposed that allows the fields due to a source operating above a lossy half space to be expressed in terms of the fields due to an infinite sequence of equivalent Huygens sources located in complex space. The new expansion has advantages over previous work in that it properly predicts the formation of a surface wave along the interface between the two half-spaces in addition to properly accounting for the space wave field.
Countless degrees of freedom in the design of antenna test ranges are enabled if the measurement errors caused by the environment can be precisely compensated. Measurements in highly reflective measurement chambers and with broadband feeds or probes are possible since the quality of the test zone is not essential anymore. To create a reflective environment, a metal plate is installed in an anechoic chamber and a base transceiver station antenna is characterized with and without the additional scattering source at a frequency of 2:11GHz. To compensate for the undesired signals, the field of the test zone is measured on a spherical surface using a scanning arm. Via a wave expansion of the field and the antenna under test into spherical mode coefficients, the undesired signals are compensated. It is shown that the error of the compensated pattern compared with the undistorted measurements is mainly below 30dB and that the directivity is retrieved with a difference of only 0:011dB>
This communication provides the experimental validation of an effective probe-compensated near-field to far-field (NFFF) transformation with a nonconventional plane-rectangular scan suitable for flat antennas under test (AUTs). It is based on the nonredundant sampling representations of the electromagnetic fields, on the use of optimal sampling interpolation expansions, and assumes a flat AUT as enclosed in a dish having diameter equal to its maximum dimension. This source modeling results to be very effective from the NF data reduction viewpoint, since, by fitting very well the geometry of such a kind of AUT, it is able to reduce as much as possible the residual volumetric redundancy related to the use of the other modelings suitable for quasi-planar AUTs (an oblate spheroid or a double bowl). Experimental results, assessing the practical feasibility of the proposed NF-FF transformation technique, are shown.
Closed form expressions, based on curve fitting have been derived for the gain characteristics of Standard Gain Horns from three brands (Scientific Atlanta/MI Technologies, Narda and Custom Microwave). These polynomials are not more accurate than the original data but since the maximum deviation is 0.01 dB (in most cases a rounding off error), they also do not add inaccuracy. They just replace the Look-Up data sheets, provided as tables or graphs. These polynomials can easily be implemented in a tool (nowadays called “app”) that provides the gain value based on model number and frequency of interest. Curve fitting coefficients have been derived for 12 Scientific Atlanta horns (0.4 – 26.5 GHz), 10 Narda Horns (1.12-40 GHz) and 12 Custom Microwave Horns (18-325 GHz).
Along with the growth of communication and satellite industry, the importance of satellite antenna evaluation is increasing. Particularly Communication On The Move (COTM) terminal antenna, including the communication between new types of constellations on LEO and MEO, requires tracking accuracy test for the communication on moving vehicles. The conventional test facilities are locally fixed and lack flexibility. To make the antenna measurement more accessible, we are developing a methodology for in-situ measurement by introducing multiple Unmanned-Aerial-Vehicles (UAVs) system with RF payload. Thanks to the dynamic flexibility of UAVs, this system can flexibly change the test configuration on site and make new test scenarios available, such as emulating the orbit of non-GEO satellites during the measurement. However, one of the challenges of the proposed system is the additional uncertainties during the measurement due to the mobility of UAVs. To overcome this challenge, we design recursive stochastic filtering and fusion approaches, and evaluate their estimation performance via numerical simulations. By introducing stochastic filter and fusion algorithms, the effect of error is mitigated, and better accuracy can be achieved compared to an existing method. This project is performed in collaboration with Cranfield University in the UK and QuadSAT in Denmark.
Tapered chambers use the reflections from the surfaces adjacent to the range antenna to illuminate the quiet zone (QZ). Polyurethane substrate is the preferred and most widely used radio frequency (RF) absorber in these chambers, due to its ability to be cut into complex shapes to conform to the tapered sections. Unfortunately, this type of absorber always presents slight differences in permittivity related to the manufacturing process. To analyze the effects of the permittivity of the lossy foam on the QZ illumination in a tapered chamber, a series of numerical experiments using a full wave analysis technique are executed. The results are mainly obtained for frequencies under 1 GHz. The upper frequency of the simulation is limited by the electrical size of the problem and by the available information on the material permittivity. However, frequencies below 1 GHz is where the tapered chambers are superior to other methods for indoor antenna measurements. Magnitude and phase are recorded over a 1.82m diameter spherical QZ to show the effects of the different absorber on the illumination. Results show that a variation on the absorber around the range antenna will deviate the illumination and skew the amplitude taper across the QZ. The amplitude distribution peak can be shifted by as much as 3.5 degrees from boresight. The effect on the phase taper is smaller with a negligible change in phase.
We present the synthesis, prototyping and measurement of a transmitarray antenna for the generation of circularly-polarized (CP) orbital angular momentum (OAM) beams. A novel ”S-ring” transmitarray element is designed to sustain CP operation with only three metal patterned layers. The unit cell provides arbitrary CP phase compensation by merely changing the rotation angle of the element, while the transmission magnitude remains greater than 0.9. In previous work, transmitarrays that support circular polarization were designed based on the assumption of normal plane wave incidence; thus, the feed source of the transmitarray must be placed far from the transmitarray. In this work, an aperture phase synthesis methodology that accounts for the spherical phase of the feed is presented such that the feed can be placed near the aperture at about F=D = 1. A proof-of-concept prototype transmitarray antenna with a thickness of 0.3 cm operating at 19 GHz is constructed and measured for far-field performance. The measurements agree well with predictions obtained by full-wave simulations and demonstrate that the proposed transmitarray antenna can be a unique apparatus that generates OAM CP cone-shaped patterns.
A probe-compensated near-field-far-field (NF-FF) transformation with planar spiral scan, particularly suitable for flat antennas under test (AUTs), is proposed in this communication. It relies on the nonredundant sampling representations of electromagnetic fields and has been achieved by properly applying the unified theory of spiral scannings for nonvolumetric antennas, when such a kind of AUT is considered as enclosed in a dish with diameter equal to its maximum dimension, thus better shaping its geometry. An efficient two-dimensional optimal sampling interpolation (OSI) algorithm is then developed to recover the NF data required by the standard NF-FF transformation with plane-rectangular scan from those collected along the spiral. Since the number of NF data and spiral turns is related to the area of the modeling surface, the here proposed NF-FF transformation technique allows one to further reduce the measurement time with respect to those based on the modelings for quasi-planar AUTs, which instead involve, in such a case, a residual volumetric redundancy. Some numerical simulations, assessing the accuracy of the OSI algorithm and of the so developed NF-FF transformation, are shown.
We present a fast source reconstruction method suitable for antenna diagnostic applications of radiating structures on electrically large platforms. The method is based on a novel implementation of a recent reformulation of the inverse electromagnetic scattering problem, and is solved using a Higher Order Method of Moments (MoM) discretization. The novel implementation achieves asymptotically better scaling the previously possible, and in particular the memory use is substantially lower than was previously possible. Results from two example cases are presented where the new method is compared to the current commercial state-of-the-art solver in DIATOOL 1.1, and significant improvements are observed in terms of computation times and memory requirements.
The main goal of this work is to present a real-time system to evaluate the impact of multi-sines in Multiple Signal Classification (MUSIC) algorithm. The MUSIC algorithm is applied in several localization applications, where the accuracy of this algorithm is required. For this reason, a specific real-time system was developed to characterize the impact of multi-sine parameters in the MUSIC algorithm in order to improve system efficiency. From several experiments, the impact multi-signal number of tones and space between tones is analyzed.