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Consolidated methodologies have long been established to assess measurement uncertainties in near-field antenna measurements. More recently, similar detailed approaches have been developed for compact ranges and adopted as standard practice. However, currently there is no analogous methodology for outdoor far field measurement facilities. This paper presents a framework for assessing the measurement uncertainties on an outdoor far-field elevated range. Various sources of uncertainty in an outdoor far-field range are identified, using the industry standard 18 term analysis for nearfield range assessment as a baseline. An example analysis based on an actual outdoor far-field range is presented. The uncertainty terms are quantified by analysis, observation, or measurement, and finally combined by the root sum squared method to arrive at the gain uncertainty and the -30 dB sidelobe level uncertainty.
This paper presents the design of an ultrawideband (UWB) open-boundary dual-polarized quad-ridged horn antenna (QRHA) having an impressive 3-decades bandwidth from 1 to 32 GHz, making it an ideal choice for a wide range of applications in radars and communication systems. Its unprecedented bandwidth performance in a single and compact antenna geometry covers various frequency bands including L, S, C, X, Ku, and K. The ridge tapering profile of the proposed QRHA ensures excellent impedance matching, while the aperture matching prevents any phase distortion. The back-cavity design as well as cavity flaring is carefully optimized to achieve wideband performance along with no presence of pattern degradation specifically at the higher end of the frequency band. The antenna design exhibits a favorable impedance matching below -10 dB, well-matched copolar antenna patterns in the principal planes, and good crosspolarization (exceeding -20 dB) over a 3-decades bandwidth.
This paper discusses the novel development of a lightweight RF front-end system aimed at enhancing airborne antenna measurements in the far-field. The proposed system leverages advancements in software-defined radio (SDR) technology and high-performance RF front-end systems. While there are instances of SDR applications in UAS measurements, these systems are predominantly designed for anti-UAS and communication purposes, lacking focus on antenna and radar characterization. In contrast, the proposed system is purposefully tailored for RF applications, completely self-contained and airborne, possessing both RX and TX capabilities, and minimizing reliance on ground-based components. The system facilitates transmission and reception in both H- and V-polarization, employing two independent channels. Consequently, it allows for the simultaneous measurement of antenna or radar properties in both copolar (Cp) and cross-polar (Xp) orientations. The comparison between antenna measurements conducted within an anechoic chamber and those carried out utilizing the proposed UAS system demonstrates a substantial level of agreement.
This paper discusses the novel development of a lightweight RF front-end system aimed at enhancing airborne antenna measurements in the far-field. The proposed system leverages advancements in software-defined radio (SDR) technology and high-performance RF front-end systems. While there are instances of SDR applications in UAS measurements, these systems are predominantly designed for anti-UAS and communication purposes, lacking focus on antenna and radar characterization. In contrast, the proposed system is purposefully tailored for RF applications, completely self-contained and airborne, possessing both RX and TX capabilities, and minimizing reliance on ground-based components. The system facilitates transmission and reception in both H- and V-polarization, employing two independent channels. Consequently, it allows for the simultaneous measurement of antenna or radar properties in both copolar (Cp) and cross-polar (Xp) orientations. The comparison between antenna measurements conducted within an anechoic chamber and those carried out utilizing the proposed UAS system demonstrates a substantial level of agreement.
Compact Ranges are widely used for antenna measurements across wide frequency ranges spanning frequencies as low as 350MHz to as high as 60GHz and above. Advances in electromagnetic (EM) simulations have significantly improved the design process for compact ranges, resulting in reduced costs. Characterizing compact range including the anechoic chamber is computationally very challenging in terms of computer memory and time. In this paper, we will present the full wave method, MLFMM for characterizing compact range without the chamber and application of asymptotic method, RL-GO to characterize the compact range inside the anechoic chamber.
This paper addresses the circularly-polarized (CP) gain uncertainty when using linearly-polarized feeds to obtain circular polarization in Compact Antenna Test Ranges. In particular, our emphasis is placed on quantifying the inaccuracy caused by deviations in amplitude and in phase of the two orthogonal linear measurements. This is of paramount importance especially for highly directive CP antennas operating at high frequencies in that the CP gain will be adversely impacted even by a small deviation from an ideal 90- degree rotation, as well as by a situation when the rotation may cause a slight boresight misalignment. To characterize the gain uncertainty, we look at ratio differences between the peak amplitude of the linear measurements, as well as cases when the phase shift of the two orthogonal linear measurements is no longer 90 degrees. The former is done through mechanical and electrical boresighting technique in the initial setting. The latter, which is the focus of this paper, is carried out through several case studies in practice mimicking some non-ideal 90- degree rotation settings.
Spherical Near Field (SNF) measurement systems are
primarily limited in usable bandwidth by the probe frequency
coverage. This limitation mainly arises from the presence of
higher-order azimuthal modes in the probe pattern [1]. In case of
electrically large or offset AUTs, such a limitation may be
overcome by a full probe correction algorithm for the NF/FF
transformation [2]. However, probes approximating first order
performance over the full bandwidth are generally preferred.
Traditionally, first-order probes based on geometrically
symmetric Ortho-Mode Junctions (OMJ) with externally
balanced feeding have been widely accepted. These probe designs
rely on couplers that provide equal amplitude and opposite phase
distribution at their output ports [3]. In this paper, the design
and validation of a novel 3dB/180° coupler is presented. The
concept is based on the natural anti-symmetric properties of the
electric field within the component, providing a quasi-perfect
amplitude and opposite phase distribution. To achieve these
properties, an architecture based on slot coupling is selected. The
design has been implemented in several frequency bands, from
UHF to Ku-band, as stand-alone cased components.
Experimental data at L/S-band is presented in this paper,
showing excellent performance in terms of matching, balance,
and isolation between output ports, well in-line with full-wave
electromagnetic predictions. In addition, the impact of the
coupler accuracy is also assessed on a relevant SNF test case.
Unmanned aerial systems (UASs) enable the in situ diagnostic of antennas operated in outdoor environments. Additionally, their flexibility introduces the possibility of performing several diagnostic methods. In this overview work, the challenges of performing outdoor measurements with UASs are discussed and some of the possibilities they introduce are outlined. The main diagnostics tool when performing outdoor far-field measurements with UASs is the so-called raster scan. This is the two-dimensional scanning of a limited portion of the measurement sphere about the main lobe. From the information raster scans provide, it is possible to retrieve antenna parameters critical for the deployment of large antennas, such as the Side Lobe Level (SLL) in all directions, as well as the First Null Level. Additionally, assuming a fine scan, i.e., sufficient resolution, the interpolation of any 1D cut for diagnostics is possible. Once a problematic cut is interpolated and assessed, it can be measured using the UASs and increasing the measured angular range for further assessment. Assuming the measured large antennas are reflector antennas, the finding of a higher-than-expected SLL may point to a problem with the positioning of the feed. Measuring with UASs allows for an iterative measurement-and-adjustment process directly in situ, which guarantees that the antenna’s performance is within the boundaries required by either the application or regulations. Additionally, the flexibility of UASs provide further advantages, such as the assessment of the impact of environmental reflections in the radiation characteristics by flying along the radial component of the measurement sphere and assessing the measured ripple, using a method similar to the Voltage Standing Wave Ratio (VSWR) method used for the characterization of anechoic chambers. With this technique, the impact of the environment of candidates for an antenna deployment site can be assessed before the antennas are installed, thus supporting the choice process, and reducing the risk of malfunction. The discussion of the introduced techniques is supported by measurements, and future possibilities and advantages are studied.
An antenna’s practical far-field distance can be estimated from the upper bound on the ratio of its gain to quality factor. This upper bound is an infinite series that can be truncated based on the desired accuracy. We investigate the convergence properties of this bounding series. We find that the number of terms required for convergence depends on the antenna’s electrical radius in a way similar to the Wiscombe criterion used in Mie scattering theory. For typical experimental accuracy requirements, such convergence can significantly reduce the effective far-field distance.
Phased array antennas are often built from sub-arrays with identical or symmetrical layout. At an early project stage, performance verification measurements of the sub-array are valuable to proof the single module design. However, the characteristics of the final antenna are questionable without further processing. This work presents a concept that is based on far-field measurements of a sub-array in a Compact Antenna Test Range (CATR) in conjunction with planar near-field (PNF) processing to synthesize the entire phased array antenna characteristics. The procedure is explained with an example of a dual linear polarized L-band planar phased array antenna for an airborne synthetic aperture radar application. It is shown that the measured sub-array can be complemented by the synthesized twin to evaluate the characteristics of a final antenna that is not yet available in this form. The resulting performance of the synthesized entire phased array is presented and compared with simulations. The presented post-processing method would be beneficial to characterizing radiation patterns of large phased arrays by measuring only sub-arrays in a limited test-zone with any measurement principle.
Unmanned Aerial Systems (UAS), colloquially known as drones, offer unparalleled flexibility and portability for outdoor and in situ antenna measurements, which is especially convenient to assess the performance of systems in their realworld conditions of application. As with any new or emerging measurement technology, it is crucial that the various sources of error must be identified and then estimated. This is especially true here where the sources of error differ from those that are generally encountered with classical antenna measurement systems. This is due to the larger number of mechanical degrees of freedom, and to the potentially less repeatable and controllable environmental conditions. In this paper, the impact of some of these various error terms is estimated as part of an ongoing measurement validation campaign. A mechanically and electrically time invariant reference antenna was characterized at ESAESTEC’s measurement facilities which served here as an independent reference laboratory. The reference results were compared and contrasted with measurements performed outdoors at Quad- SAT’s premises using QuadSAT’s UAS for Antenna Performance Evaluation (UAS-APE). While a direct comparison between the measurement results from ESA-ESTEC and QuadSAT delivers information about the various uncertainties within a UAS-APE system in comparison to classical measurement facilities’ and the validity of such a system for antenna testing, other tests aim at providing an estimation of the impact of each error source on the overall uncertainty budget, thus paving the way towards a standardized uncertainty budget for outdoor UAS-based sites.
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.
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.
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.
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.
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.
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.
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.