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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.
The radiation and scattering pattern characteristics of open-ended rectangular waveguide with a chamfered tip are examined. Despite common and widespread use as a probe antenna for planar near-field antenna measurements, a methodical investigation of the chamfered-tip design and resultant performance has not been published. A computational electromagnetics (CEM) model for an open-ended rectangular waveguide probe with a parameterized chamfered tip has been constructed and results for both radiation and scattering patterns are presented. A comparison of results includes a probe without a chamfer and a probe typical of that available from commercial suppliers. It is shown that, for a series of standard waveguide size probes sharing a common thickness for the waveguide wall and chamfered tip, the radiation pattern is relatively insensitive to the chamfer tip designs studied until frequency increases into W-band (WR-10). The scattering pattern characteristics for the same series of standard waveguide size probes show a reduction in on-axis (boresight) monostatic radar cross section (RCS) for chamfered tip waveguides compared to blunt-ended waveguides and that this reduction increases for increasing frequency.
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.
Antennae in critical applications such as in-flight navigation, e.g. the instrument landing system (ILS), have to be calibrated on a regular basis. This allows for an error-free operation by verifying the absolute field strength as well as the spatial field distribution. Hence, it remains indispensable to calibrate the receiving antenna used by flight inspection services in absolute terms. The Calibration itself can only be achieved by measurements within a well known field distribution, ideally in situ, hence in the measurement environment of the targeted system. In this contribution a modular pyramidal horn antenna capable of providing reference field strengths within the frequency range of 75 MHz - 114 MHz is presented. The aperture’s field strength can be calculated analytically as well as measured with a high degree of accuracy. For the frequency range at hand, the size of the reference antenna ends up in a challenging scale of a truck. Construction details and manufacturing aspects of the light weight, modular and easy to assemble horn antenna are presented. Near field measurement results are shown, compared with simulations and discussed with respect to one another.
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>
The brick-based antenna design is a new concept to the literature. Metals and dielectrics are in brick-form to let the antenna designers connect and disconnect the cells easily. Designing and prototyping an antenna takes only a few minutes with this concept. Antenna engineers directly build their design in front of a network analyzer and iterate to reach their requirements. This hardware-based antenna design solution also creates a design cycle of measure-iterate instead of simulateiterate. This study starts with introducing this new method and continues with a dual-port 3.5 GHz patch antenna design and measurement. After the single antenna reaches the target frequencies, the 16 element 4x4 planar patch antenna array is built and measured.
In this paper, an investigation was conducted to find materials that are optically transparent and radio frequency (RF) shielding. Materials were first optically tested, followed by a shielding effectiveness test. The optical test evaluated metal mesh sizes 20, 22, 40 and 100, single layer RF film, double layer RF film, and combinations of film and mesh. Size 22 copper mesh and RF film demonstrated desirable optical properties and were then RF tested from 26 MHz to 40 GHz. The test was conducted using a shielded enclosure featuring an aperture in a wall panel to mount the material under test. Reference field strength measurements of the aperture were compared to measurements taken when material samples were placed within the aperture in order to characterize the shielding effectiveness of each shielding material. Test results for size 22 copper mesh, RF shielding film, and a combination of one layer of size 22 copper mesh with one layer of film demonstrate average shielding effectiveness results of 43 dB for the mesh, 46 dB for the film, and 69 dB for the mesh and film together. This information can be used when there is a requirement for a material to provide optically transparent RF shielding.
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).
A microwave water-cut meter for production fluids applications was designed and a basic test performed. The meter uses a vector network analyzer to measure the reflection (S11) and transmission (S21) spectra of the material under test (MUT), such as production fluids, oil spills, rock cores or soil. The initial design concept consisted of a pair of waveguides whose ends face each other and are placed on the inner surface of the pipe/core holder. The waveguides have a diameter similar to the main pipe and are filled with specific low loss materials with dielectric constant similar to that of the fluid in the pipe. Based on the initial design, a refined water-cut meter design was optimized, via numerical simulations, built and tested. To maximize bandwidth, the improved design adds ridges to the original cylindrical waveguide and optimizes the feed details to maintain an impedance match to the feed connectors. Results show that the ridges in the waveguide significantly improve transmission compared to just the waveguide alone. Initial experimental results show the measuring system is sensitive to the water content of production fluids.
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.
This paper investigates on the postprocessing of spherical near-field measurements in phaseless scenarios. Traditionally, iterative algorithms have been used to propagate between two measurement surfaces to retrieve the near-field phase. In the last years, advanced phase retrieval techniques have been developed formulating the phaseless problem in matrix form. Both approaches are introduced and investigated, comparing its performance with numerical and measurement data. Preliminary results indicate that iterative propagation techniques offer superior performance, yet with a more irregular and nonlinear behavior. The matrix approach, however, offers much more flexibility on its formulation leaving room for more potential improvements.