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We tackle the problem of recovering 2-D complex fields starting from the spectral amplitude data, the support of the source, and a few additional information. In particular, we further elaborate on our ‘crosswords-solution like’ approach where the solution is found by solving 1D problems and congruence arguments. Its argued that intersecating lines and circles (rather than just lines) is more effective, and we show how the resulting approach, initially developed for the case of continuos (aperture) sources, is also effective in determining the excitations of discrete (array) sources.
Spherical wave function expansions involving a TM- R and TE-R field decomposition are widely used. Here we examine a spherical wavefunction expansion based on a TM- z and TE-z field decomposition. The impetus is the straightforward relationship between the TM-z and TE-z spherical wavefunctions and the cartesian multipoles which, in turn, have contemporary application in wireless power transfer. However, there are potentially other useful features of such a TM-z and TE- z spherical wavefunction expansion. For example, the TE/TM-z decomposition results in the ????-polarized far electric field being associated exclusively with the TM-z wavefunctions while the ????-polarized far electric field is associated exclusively with the TE-z spherical wavefunctions. Unfortunately, from the analysis given here, it appears that it is not possible to represent a generalized finite source in TE/TM-z spherical wavefunctions exclusively. One succinct way to show this is by attempting to expand the far field of an x or y directed electric or magnetic dipole in TE/TM- z spherical wavefunctions. The dipole can be represented by a single TE/TM-R spherical wavefunction, but the expansion in TE/TM-z wavefunctions is problematic.
Owing to the increasing interest in high frequencies, as the millimeter wave range, wherein accurate phase measurements are increasingly difficult and expensive, phaseless near-field techniques are prime candidates for antenna characterization. In this paper, an experimental validation of a phaseless near-fieldfar- field (NF-FF) transformation with plane-polar scanning for antenna characterization is presented. A proper representation of problem unknowns and data, using the available information on the antenna under test (AUT) and on the scanning geometry, is adopted in order to improve the reliability and the accuracy of the proposed characterization algorithm. By exploiting the nonredundant sampling representations of electromagnetic fields and by using an oblate spheroid to model the AUT, a remarkable reduction (about 90%) of the required NF samples is achieved. Experimental results on data acquired at the University of Salerno Antenna Characterization Lab are reported to validate experimentally the effectiveness of the proposed characterization technique.
There has been much discussion in the last few decades regarding redundancy in conventional near-field sampling, and that redundancy is most pronounced in the planar geometry. There has also been much discussion regarding modal filtering of near-field data to attenuate the effects of stray signals. Both discussions revolve around the limited local spatial bandwidth that can be produced at each probe location when the antenna under test’s (AUT’s) radiating sources are all contained within a known geometric boundary. This paper discusses a novel filtering technique that exploits the inherent sampling redundancy in conventional planar near-field acquisitions. The filtering is based solely on the known location and shape in the scanner’s coordinate system of a closed 3D boundary around the radiators of interest. The paper describes the algorithm and presents results from both measured and synthesized input. The new filter is also compared to other available filters in terms of speed, attenuation of stray signals, and preservation of AUT signals.
Cellular LTE MIMO downlink performance, for 4x4, 4x2, and 2x2 LTE MIMO architectures, in terms of average data throughput and availability, were investigated in an urban canyon environment of Frankfurt, Germany at 2110 MHz on a Sport Utility Vehicle (SUV) with metal and glass roofs for a virtual route. This study utilized the following measured antenna radiation patterns for total polarization on the SUV at 2110 MHz for the mobile station: 1) roof-mounted antenna on metal roof; 2) roof-mounted antenna on glass roof; 3) interior-mounted planarinverted F antenna; and 4) interior-mounted planar-inverted F antenna rotated 90 degrees. This research was carried out using a three-dimensional simulation software suite that enabled users to simulate electromagnetic wave propagation and wireless network planning. The following observations were obtained from this research. First, the MIMO architectures for the SUV with metal roof exhibited approximately 5% higher average data throughput levels compared to the same MIMO architectures on the SUV with glass roof. Second, the throughput availability for the 4x4 and 4x2 MIMO systems were comparable. Lastly, the average throughput for the 4x4 MIMO system was higher than the 4x2 and 2x2 MIMO systems for the SUV regardless of roof material.
Performing End-to-End testing of satellite payloads on planar near-field test ranges can greatly reduce the cost and real estate required compared to conventional far-field systems. Previous work has shown that this is theoretically possible, with limited test data showing viability. This paper provides additional validation of the technique’s ability to characterize various system-level parameters, including the equivalent isotropically radiated power , group delay, saturating flux density, system noise temperature and the gain vs. frequency response. Details of a new software satellite payload test suite is presented, along with the accompanying simulated payload that was developed for system verification and facility-to-facility comparison.
In this paper, we show how Prolate Spheroidal Wave Functions (PSWFs) can be reliably and accurately numerically computed to represent the field radiated by an oblong antenna. We show the convenience of the PSWFs representation by comparing its performance against a spherical harmonics expansion. We also point out how the PSWFs representation can be fruitfully exploited to face a Near-Field/Far-Field (NFFF) problem in a cylindrical geometry for the mentioned class of antennas.
Resistive materials are often employed in antenna or absorber design for radio frequency (RF) applications. Causal material models are needed when modeling wideband RF systems using time-domain numerical models (e.g. FDTD). To this end, the frequency-dependence, from 10’s of MHz to 10’s of GHz, of spatially patterned and un-patterned resistive-cards (R-cards) were measured using free space and specialty materials measurements fixtures. Specifically, the complex sheet-impedance of two R-card specimens were measured at VHF frequencies using either an 8.5-inch slotted rectangular-coax (R-coax) or a recently developed resistive material mapping probe (RMMP). At GHz frequencies measurements were conducted using a standard 2’ focused beam lens system. The multi-band complex-impedance data were fit using a set of causal sheet material models. Typically, the fit errors are in the 1-3% range for causal models of measured data over two-plus decades of bandwidth.
Prior literature in the subject area of far-field antenna measurements has demonstrated an extrapolation technique to isolate and correct the errors associated with nearzone proximity effects, specifically multiple reflections between the probe and the antenna under test (AUT), thus allowing measurements to be acquired at separation distances much shorter than the conventionally defined far-field criteria. A recent paper on this topic described a modern, indoor, far-field antenna measurement range specifically designed to support the traditional extrapolation technique while also incorporating high-speed RF instrumentation and advanced software control of a mobile probe tower. The automation of the traditional technique was emphasized, and the application focused primarily on X-band performance. Herein presented is an updated and more broadband approach which utilizes both amplitude and phase data to extend the implementation to frequencies in the UHF-, L-, and S-band. Optimized correction factors are generated for additional extraneous signals, most notably the effects of multi-path interference. Using the generalized three antenna measurement approach as highlighted in the original technique, measurement examples are provided for broadband antenna range horns, and the resultant far-field gain calculations are again compared to similar data extracted using traditional near-field scanning techniques.
Reconfigurable antennas are very widely useful antennas, but they require extended measurement periods to characterize the range of specified beams. Time-saving measures typically come at the cost of measurement quality. The goal of this effort was twofold: 1) to investigate ways to improve all antenna measurements, including analyzing antenna positions within range spaces, absorber configurations, and mounting structures and 2) to investigate the procedure by which reconfigurable antennas are optimized and determine efficient measurement quality and time-cost tradeoffs.
Modern antenna range design is often a careful balance of several competing objectives. Some of these design parameters are defined by the antenna under test (AUT), i.e. millimeter wave (Ka-band) test frequencies, frequencyconverting and non-converting AUTs, high-power radiation requirements, pulsed RF requirements, and interleaved transmit and receive (T/R) requirements. Other parameters are driven by the AUT’s application, like requirements for providing accurate pattern, gain, EIRP, and G/T predictions based on the measurement data. Yet other parameters are driven by cost and risk considerations, like the need for all-at-once acquisitions incorporating multi-frequency, multi-port, dual-pol, and multistate measurements. Also included in the “cost and risk” category is the need to collect all these measurements in the least amount of time. A planar near-field antenna range designed with all these parameters in mind has been realized and is currently operational. This 1 m x 1 m planar near-field range incorporates several novel electrical and mechanical features, and we illustrate these features in terms of their driving requirements and their limitations. Included in our discussion: modular T/R range “front ends,” reconfigurable probe networks, absorber cooling strategies, near-field probes for high-power measurements, interleaved single-port transmit and multi-port receive measurements, and distributed pulse mode range architectures.
A set of Dual-Polarized Antennas with a 3:1 operating bandwidth has been developed for use in near-field ranges as the probe or range antenna and for use as a Compact Antenna Test Range (CATR) feed [1]. Key development parameters of the antenna are: a wideband impedance match to the coaxial feed line, E and H-plane 1 dB beam widths in excess of 30 degrees, -30 dB on axis cross-polarization, minimum polarization tilt and a phase center that varies over a small region near the aperture. To accomplish these design parameters, a family of range antennas has been developed and previously introduced. Two versions of the antenna have been manufactured and tested for performance. A 2-6 GHz version has been developed using traditional machining techniques and a 6-18 GHz version has been produced using additive manufacturing (3D printing) techniques [4]. These antennas provide proper illumination of the quiet zone for compact ranges used for antenna measurements as well as radar cross section (RCS) measurements. For RCS measurements, an additional requirement for time-based energy storage performance is considered. Energy storage in the feed can result in a pulse spreading or additional copies of the pulse in time, resulting in poor performances of the target characterization. This effect is called ‘ringdown’. In this paper, we focus on the RCS ringdown performance of the 6-18 GHz antenna produced using additive manufacturing. The measured performance of the antenna will be presented and discussed. Finally, the applicability of the antenna as a CATR feed for RCS measurements will be discussed.
Mm-wave 5G base-stations are capable of emitting unprecedented EIRPs, necessary to achieve its high data rates. This capability introduces the opportunity to also use this wireless resource to wirelessly power IoT devices. However, the passive recipients of such power densities would need large enough apertures to harvest appropriate power levels to operate, which would naturally limit their angular coverage. In this work, we present an unconventional solution to this problem through the implementation of a passive beamforming network—the Rotman lens—in the receiving mode, as an intermediate element between antenna arrays and rectifiers to enable the surprising combination of high gain and wide angular coverage. The fullyprinted, flexible Rotman lens, operating in the mm-wave regime, is equipped with eight antenna ports and six beam ports, selected based on a scalability study. Tested in both planar and bent configurations, the Rotman lens demonstrates a robust, ultrabroadband behavior, with minimum variations in its gain and angular coverage over more than 20 GHz of bandwidth. These structures promise to power the next generation of passive IoT devices at distances exceeding 100 m using 5G base-stations, with the transmission of the full 75 dBm EIRP allowable by the FCC in the 5G/mm-wave bands, thereby enabling the emergence of ultra-low-cost mmIDs for ubiquitous sensing for smart-city and smart-infrastructure applications.
Reconfigurable antennas are very widely useful antennas, but they require extended measurement periods to characterize the range of specified beams. Time-saving measures typically come at the cost of measurement quality. The goal of this effort was twofold: 1) to investigate ways to improve all antenna measurements, including analyzing antenna positions within range spaces, absorber configurations, and mounting structures and 2) to investigate the procedure by which reconfigurable antennas are optimized and determine efficient measurement quality and time-cost tradeoffs.
A set of Dual-Polarized Antennas with a 3:1 operating bandwidth has been developed for use in near-field ranges as the probe or range antenna and for use as a Compact Antenna Test Range (CATR) feed [1]. Key development parameters of the antenna are: a wideband impedance match to the coaxial feed line, E and H-plane 1 dB beam widths in excess of 30 degrees, -30 dB on axis cross-polarization, minimum polarization tilt and a phase center that varies over a small region near the aperture. To accomplish these design parameters, a family of range antennas has been developed and previously introduced. Two versions of the antenna have been manufactured and tested for performance. A 2-6 GHz version has been developed using traditional machining techniques and a 6-18 GHz version has been produced using additive manufacturing (3D printing) techniques [4]. These antennas provide proper illumination of the quiet zone for compact ranges used for antenna measurements as well as radar cross section (RCS) measurements. For RCS measurements, an additional requirement for time-based energy storage performance is considered. Energy storage in the feed can result in a pulse spreading or additional copies of the pulse in time, resulting in poor performances of the target characterization. This effect is called ‘ringdown’. In this paper, we focus on the RCS ringdown performance of the 6-18 GHz antenna produced using additive manufacturing. The measured performance of the antenna will be presented and discussed. Finally, the applicability of the antenna as a CATR feed for RCS measurements will be discussed.
Mm-wave 5G base-stations are capable of emitting unprecedented EIRPs, necessary to achieve its high data rates. This capability introduces the opportunity to also use this wireless resource to wirelessly power IoT devices. However, the passive recipients of such power densities would need large enough apertures to harvest appropriate power levels to operate, which would naturally limit their angular coverage. In this work, we present an unconventional solution to this problem through the implementation of a passive beamforming network—the Rotman lens—in the receiving mode, as an intermediate element between antenna arrays and rectifiers to enable the surprising combination of high gain and wide angular coverage. The fullyprinted, flexible Rotman lens, operating in the mm-wave regime, is equipped with eight antenna ports and six beam ports, selected based on a scalability study. Tested in both planar and bent configurations, the Rotman lens demonstrates a robust, ultrabroadband behavior, with minimum variations in its gain and angular coverage over more than 20 GHz of bandwidth. These structures promise to power the next generation of passive IoT devices at distances exceeding 100 m using 5G base-stations, with the transmission of the full 75 dBm EIRP allowable by the FCC in the 5G/mm-wave bands, thereby enabling the emergence of ultra-low-cost mmIDs for ubiquitous sensing for smart-city and smart-infrastructure applications.
The conventional method for comparing the performance of antenna-receiver systems is the classical G/T metric. The G/T metric is the ratio of antenna-circuitgainrelative to the thermal noise temperature evaluated at the input of the low noise amplifier; the thermal noise at the input to the LNA consists of the received sky noise, the LNA's effective input noise temperature, and post LNA noise referenced to the LNA's input. While this has been a standard for many years, it will be shown that G/T does an incomplete job of describing the performance under all conditions. The noise figure metric was developed as a characteristic describing signal-to-noise degradation to be applied to circuit based input/output topologies, and cannot easily be applied to hybrid systems such as an antenna-receiver system in which the input power is described by spatial field density levels, and the output power is stated in terms of a circuit-based voltage-current environment. This paper presents a noise figure metric which has been expanded to include systems that are a hybrid of wave and circuit characteristics such as the marriage of an antenna and receiver. It will also be shown that whereas a system's noise figure is dependent upon a chosen noise reference temperature, the intrinsic Effective Input Noise Temperature of the system is an invariant that does not change when a different reference temperature is selected. It will also be shown that, in contrast to G/T, the effective input noise temperature of an antenna/receiver system will accurately predict the system's output SNR for all values of system input SNR. It will be shown in detail, how to measure the antenna/receiver system's Effective Input Noise Temperature (TE), resulting in the following equation: TE = (TD1 - Y£ TD2 )/(Y - 1) Where: TD1 , and TD2 are measured noise power densities at the face of the antenna, TE is the Effective Input Noise Temperature of the system, and "Y" is the classical "Y factor" metric.
In this paper, a loadbox was developed to perform theconductive and radiative Electromagnetic Compatibility (EMC) emission and immunity testing of the Global Navigation Satellite System (GNSS) and Satellite Digital Audio Radio Service (SDARS). To perform these tests, the supplier must purchase and build bias-tee, lowpass filter, choke, Diplexer and coupling circuitry to develop a loadbox. This means that same product made by different suppliers have different test set-up in place and therefore variability in the testing which create uncertainties in the test results and product approval or rejection. This is not reliable and can cause large amount of money wasted or bad product pass through. In this work, we propose an integrated loadbox design that can be built in-house with low cost and provide unique solution across the board. A loadbox consisting distributed Printed Circuit Board (PCB) made diplexer was developed that is easy to fabricate with low cost high durability and reliability during EMC testing and keep all the EMC testing consistent across the board which is enabling factor for proper decision making. A dual band diplexer was realized to separate the combined signal coming from the LNA's output port to two separate GNSS and SDARS ports. At the GNSS and SDARS frequencies due to the short wavelength of the RF signals, inductors and capacitors can be implemented using different transmission lines widths and lengths in short, open, parallel and straight-line formation. Distributed diplexer was designed using ADS RF Momentum simulator tool from Keysight and fabricated on a 2-layers PCB, FR2 of thickness 0.787 mm and a copper thickness of 35 um with overall size of 5.8x3.1 cm. Simulated and measured s-parameter for all of diplexer ports are in good agreement with measured insertion loss of better than 1.9 dB, return loss of 11.4 dB and GNSS-SDARS isolation of 16.8 dB at the GNSS frequency band and measured insertion loss of better than 2.1 dB, return loss of 14.1 dB and SDARS-GNSS isolation of 10.9 dB at the SDARS frequency band.
Three-antenna methods [1] are fundamental to modernantenna metrology. They enable the simultaneous determination of the on-axis polarizations and gains of three unknown antennas. For example, on-axis characterization of a probe antenna is necessary for the accurate far-field measurement of test antenna transmitting and receiving functions. Recently after renovation of antenna ranges, NIST has beeninvolved in an internal program to re-certify its polarizationcharacterization services. While reviewing the theory [2], werealized that a small modification to the standard algorithmcould improve the accuracy of the polarization determinationin many cases. Three-antenna techniques measure the antennas in pairswith one antenna of each pair rotating about its axis (Figure1). The ideal form of the measured signal is very simple (6). Previous methods [3][8], take an economical approach in which a minimal number of measurements are used to extractthe polarization parameters from the model. Some allow forthe averaging of multiple determinations to improve results. We propose, on the other hand, to use the discrete Fourier transform (DFT) to isolate the exp (¤i?) behavior in the data[9], [10]. The pair-polarization ratios (8) are easily computedfrom this transform. References [9] and [10] only came tolight after our analysis was completed. Rather the drop theproject, we have decided to offer this note as a tutorial andto call attention to what appears to be an under-appreciatedapproach to polarization measurement. All of the above methods work well when the error signalis small. Otherwise, the global nature of Fourier interpolationis expected to yield advantages over any local analysis. This hypothesis is supported by the simulations discussed below. Data were simulated for a number of combinations of axialratio, tilt angle, and sense of polarization. Noise was added atvarious levels. NOTE: The abstract refers to a figure, equations, and references not included in the abstract for brevity but which are available upon request
The future of cooperative automated and connected driving lies in the fusion of multiple mobile wireless sensor and data transmission nodes, covering 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 wireless channel models aim at including bi-static reflectivities of road users, depending on different illumination and observation angles, in the nearfield as well as in the far-field. The limitations of the measurement distances within anechoic chambers unavoidably induce nearfield effects, especially for electrically large radar objects like realistic road users, and conventional bi-static RCS calibration techniques would eventually fail. In order to model the transition from the nearfield to the far-field reflectivity of road users, this paper uses the object scaling approach, with combined measurements and electromagnetic simulations. Bi-static reflectivity measurements of selected vulnerable road users are described, from the chamber setup all the way up to data post-processing. The approach of electromagnetic object scaling is applied to such bi-static reflectivity measurements, and the results are evaluated and discussed in comparison with numerical simulations. Initial proof-of-concept measurements of differently sized metal spheres confirmed the applicability of the scaling approach under far-field conditions very convincingly. Based on this, scaled models of radar objects, namely a bicycle and a pedestrian, were 3D printed and then metallized with copper paint. Compared to corresponding electromagnetic simulations of the original bi-static reflectivity of the radar objects, the results measured for the scaled models show very promising agreement with the numerical expectation. This study contributes to the further development of future wireless channel models considering bi-static multipath components of different road users, being an indispensable prerequisite to enhance the safety in future road traffic.