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This paper proposes a novel approach based on a Multi-Probe Near-Field Scanner system utilizing bipolar and phased array antenna technology to measure antenna arrays with highly reliable precision. The innovative system incorporates a phased array antenna with full amplitude and phase control, enabling complete manipulation of the polarization state. This advanced capability allows the system to accurately measure and characterize antenna arrays while addressing and correcting polarization distortions caused by polar motion. By using the multi-probe configuration, the system significantly enhances measurement efficiency by capturing near-field data simultaneously across multiple probes. The integration of bipolar technology [1] ensures robust signal processing, while the phased array design enables the electronic rotation of the polarization of the probe array antenna. This feature is critical for mitigating errors introduced by polarization mismatches or distortions, ensuring high-fidelity measurements even in complex scenarios. The proposed system demonstrates superiority over traditional single-probe scanners by reducing measurement time, providing comprehensive polarization control and size reduction of the controlled environment. The paper discusses the system’s design, implementation, and performance.
A new method is developed for accurate transmission measurements through a surface using a far-field Gaussian weighting approach for use in anechoic chambers. A trivial approach to measuring transmission characteristics would be to mount a sample-under-test between two antennas and simply measure the boresight transmission using a network analyzer. This approach is enhanced by instead measuring the transmitted fields over a hemispherical field-of-view and then weighting the measured far-fields to synthesize a Gaussian illumination of the sample. This approach can be utilized to effectively illuminate the sample-under-test with an arbitrary excitation with a high degree of customization in post-processing (e.g., beam polarization, direction, waist size, and location). The approach is validated by characterizing transmission through a copper clad substrate and a frequency selective surface (FSS) from 4 to 40 GHz. Additionally, a sample of Rogers 5870 is measured from 8 to 40 GHz. For each sample-under-test, S21 measurements are compared for the boresight and Gaussian weighted methods, showing greater agreement with theoretical or simulated values for the Gaussian case.
This study presents the design, fabrication, and testing of a 2P3T switch module for a 5G high-speed measurement system. The module is developed to switch the polarization signals received from multiple probes to a measurement program for 5G certification testing or to multiple receivers for modulated signal detection. Three signal paths are used to control the module. The module includes a low-noise amplifier (LNA) and uses a grounded coplanar waveguide (GCPW) structure to integrate the integrated circuit (IC) chip. The switch paths are controlled using a LabVIEW program. The performance of the switch module is evaluated as satisfactory.
This paper presents an extended uncertainty analysis of a multiprobe antenna measurement system developed for large platform testing across the 64 MHz to 6 GHz frequency range. Installed at the Pulsaart by AGC facility in Belgium, the system enables fast and accurate characterization of complex structures integrating multiple antennas. Building on previous studies, the analysis expands the uncertainty budget by including a broader set of antennas, such as monocones operating down to 50 MHz, and evaluating key figures of merit including radiation pattern, gain, efficiency, and cross-polarization. Particular emphasis is placed on reflectivity-related uncertainty, which is a dominant factor at lower frequencies due to chamber electrical size and absorber limitations. The methodology incorporates modal filtering and spatial displacement of antennas to isolate the environmental effects. The results offer detailed insights into antenna-dependent uncertainties and, for the first time, provide complete uncertainty estimations for the aforementioned metrics across the full operating frequency range.
This paper presents a compact lens-integrated metasurface antenna system for beamwidth reduction and polarization conversion in the sub-THz D-band. The proposed metasurface achieves a circular polarization (CP) bandwidth of 2.86GHz (2.12%) within the 133.41-136.27 GHz band and has an axial ratio < 3 dB. A 3D-printed graded-index (GRIN) dielectric lens is integrated with the metasurface to provide beamwidth reduction and gain enhancement in both E-and H-planes. Moreover the proposed GRIN lens helps in achieving pattern symmetry and improved side-lobe levels. The lens-integrated metasurface configuration has a compact overall structure and provides efficient linear-to-circular polarization (LP–CP) conversion and beamwidth reduction. The proposed design can be a strong candidate for the future sub-THz 6G wireless and satellite communication (SatCom) systems.
This paper presents an over-the-air (OTA) characterization approach for a dual-polarized on-chip antenna fabricated in BiCMOS technology for a THz focal plane array (FPA). The antenna integrates a mixer-based detector to enhance sensitivity, enabling the simultaneous wireless reception of radio frequency (RF) and local oscillator (LO) signals. A fully automated measurement system performs azimuth and elevation scans to acquire the radiation patterns. The measured results, presented using the Ludwig-3 co-polarization definition, demonstrate excellent agreement with simulations for both orthogonal components.
We present a bench top demonstration of dropped-channel polarimetric compressive sensing to recover range profiles of a simple scene. Four antennas (H and V transmit and H and V receive) are connected to an arbitrary waveform generator and digital oscilloscope with programmable attenuators and phase shifters inline to control crosstalk. Range profiles of the scene are generated for three measured channels; the fourth is reconstructed from information imbedded in crosstalk using basis pursuit denoising. Reconstructed range profiles are shown to agree with measurements of all channels obtained without crosstalk contamination. Thus, the bench top setup demonstrates the potential use of dropped-channel polarimetric compressive sensing to reduce data storage and transmission burden while preserving full pol information.
This paper presents an overview of the induced ripples observed in the far-field antenna patterns of the Antenna Under Test (AUT) when measured with an open-ended waveguide antenna probe in a near-field planar system. The author hypothesized that induced ripples in far-field patterns are primarily originated by diffracted fields on the ground plane that supports the collar absorber. This study systematically evaluates the effects of absorber size and quality. Numerical simulations and experimental measurements are employed to validate the author’s hypothesis, providing insights into the relationships between these parameters and their influence on the induced ripples in far-field patterns. Results indicate that collar absorbers with reflectivity better than -30 dB are optimal for achieving accurate element characterization of phased array antennas.
This paper presents the design, simulation, and experimental validation of a compact full-polarimetric antenna module for short-range radar sensors. Existing radar modules often use same-polarized antennas, potentially missing cross-polarized signals. While polarimetric radar systems offer superior polarization diversity, they are typically costly and complex. Research on radar polarimetry for short-range radar sensors is limited, and a compact antenna design is desirable for seamless integration and flexible placement in modern sensors. Additionally, collecting full-polarimetric data with a small sensor is crucial for developing realistic channel model tailored to short-range sensors. Developing a radar sensor with full-polarimetric operation is challenging due to size limitations and design complexity. This study introduces a 24-GHz full-polarimetric radar system utilizing a novel compact antenna module that captures both co- and cross-polarized signals. The well-designed antenna module, combined with generalized calibration techniques (GCT) demostrated outstanding performance in simulations and experimental validation. Both results closely aligned with ideal target scattering matrices. The proposed module's accuracy and reliability were confirmed through the successful characterization of various targets. These findings highlight the potential of the proposed antenna module for advanced radar sensors applications.
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
RFID technology can be classified as active, passive, or chipless based on tag design. While active and passive tags rely on electronics to modulate and return the irradiating signal, chipless tags rely on geometry to produce a distinct signal which is viewed in the time-, frequency-, or spatial-domain. Within the field of chipless RFID, frequency-domain tags are the most popular and different design approaches with different polarization schemes have emerged. Primarily, these tag design approaches can be categorized as linearly polarized (LP), orientation insensitive (OI), and cross-polarizing. This diversity in tag designs leads to a variety of requirements for reader antennas and also leads to current reader antennas being non-universal (i.e., reader antennas can only be used for specific types of tags rather than all tags). LP and cross-polarizing tags require that the reader antennas have their polarization be perfectly aligned with that of the tag, as a small tag rotation with respect to the reader can greatly affect the response. Cross-polarizing tags additionally require either a dual-polarized reader antenna or a bistatic measurement setup. While specialized chipless RFID reader antennas and bistatic reading schemes have been developed, there are still limitations with these approaches, such as requiring tag/reader polarization alignment, hardware complexity, mutual coupling, and other related issues in bistatic setups. Tag interrogation with circular polarization (CP), however, accommodates the polarization diversity of different tag designs, while also relaxing the tag/reader relative alignment requirements. This work proposes a novel chipless RFID tag reading methodology that utilizes a single existing dual CP X-band (8.2-12.4 GHz) septum polarizer antenna as a universal (i.e., all types of tags) frequency-domain reader antenna that can generate and receive both right-hand and left-hand CP, as well as LP (through mathematical manipulation). This antenna has been optimized for this application and its specifications are provided. Additionally, through post processing the rotation offset of LP tags can be determined, a capability which can then be used for rotation sensing. To demonstrate the tag reading methodology and the rotation determination capabilities of the method, simulation and measurement results are presented for LP and OI tags.
The rotating-source measurement method is usually described as an amplitude only measurement method and the axial ratio is the only characteristic that can be measured. The article illustrates how adding a phase measurement allows to get the sense of polarization and to calculate the circular partial gains over a full cut-plane of the antenna under test. Simulations and a measurement example are shown.
This is a brief comparison between the two recently released documents that detail the methods used for the calibration of antennas intended for use in measuring electromagnetic compatibility.
A near-field far-field transformation (NFFFT) technique with a plane-wave synthesis is presented for predicting two-dimensional (2D) radar cross sections (RCS) from multistatic near-field (NF) measurements. The NFFFT predicts the FF of the OUT illuminated by each single source, then the plane-wave synthesis predicts the FF of the OUT each illuminated by each plane-wave by synthesizing the FFs given in the NFFFT step. The both steps are performed in the similar computational procedure based on a single-cut NFFFT technique that has been proposed previously. The method is performed at low cost computation because the NF and source positions are required only on a single cut plane. The formulation and validation of the method is presented.
The significant measurement standards in the antenna measurement community all present suggested error analysis strategies and recommendations. However, many of the factors in these analyses are static in nature in that they do not vary with antenna pattern signal level or they deal with specific points in the pattern, such as realized gain, side lobe magnitude error or a derived metric such as on-axis cross polarization. In addition, many of the constituent factors of the error methods are the result of analyses or special purpose data collections that may not be available for periodic measurement. The objective of this paper is to use only a few significant factors to analyze the error bounds in both magnitude and phase for a given antenna pattern, for all levels of the pattern. Most of the standards metrics are errors of amplitude. However, interest is increasing in determining phase errors and, hence, this methodology includes phase error analysis for all factors.
The traditional characterization of the quiet zone for a CATR is to perform field probe scans perpendicular to the range axis at one or more depths of the quiet zone, usually front, middle and back. There is usually no attempt to compare the peak signals across the field probe scans. In recent years, users of CATRs have been using these devices at lower and lower frequencies, sometimes below the lowest frequency that provides the specified performance for the CATR. It is recognized that as a CATR is used at lower and lower frequencies compared to its optics, the quiet zone quality will degrade. The purpose of this study was to create a quiet zone depth variation model to characterize the variation, particularly for low frequencies. The model was to treat the CATR as an antenna aperture and apply a power density versus distance model. It is well known that the extreme near field of an aperture is oscillatory at distances up to approximately 10% of the far-field distance, at which point the power density begins to follow the Fraunhofer approximation. The optics of a CATR place the quiet zone well within the oscillatory zone, indicating that the field will vary through the depth of the quiet zone. This variation will decrease with increasing frequency as the far-field distance for the CATR increases with frequency. The model has been compared to a simulation in GRASP and experimental data collected on a CATR.
Pyramidal RF absorber, widely used in indoor antenna ranges, is designed to minimize reflectivity by creating an impedance transform from free space to the impedance of the absorber material. The pyramidal shape provides this transition quite well at normal incidence. It has been shown in [1] that pyramidal RF absorber performs very well up to angles of incidence of about 45 degrees off-normal, but at wider angles of incidence, the performance degrades significantly. Unfortunately, it is very difficult to perform RF absorber measurements at large oblique incidence angles. In such measurements, the reflected path and the direct path between the antennas are very close in length, making it difficult to use time-domain gating techniques to eliminate the direct coupling. In this paper, a novel approach for performing oblique RF absorber measurements is introduced based on spectral domain transformations. Preliminary measurements using this technique have been compared to RF simulations. Results appear to indicate that this approach is a valid way to perform RF absorber reflectivity measurements at highly oblique incidence angles.
A simulation-supported measurement campaign was conducted to collect monostatic radar cross section (RCS) data as part of a larger effort to establish the Austin RCS Benchmark Suite, a publicly available benchmark suite for quantifying the performance of RCS simulations. In order to demonstrate the impact of materials on RCS simulation and measurement, various mixed-material targets were built and measured. The results are reported for three targets: (i) Solid Resin Almond: an almond-shaped low-loss homogeneous target with the characteristic length of ~10-in. (ii) Open Tail-Coated Almond: the surface of the solid resin almond's tail portion was coated with a highly conductive silver, effectively forming a resin-filled open cavity with metallic walls. (iii) Closed Tail-Coated Almond: the resin almond was manufactured in two pieces, the tail piece was coated completely with silver coating (creating a closed metallic surface), and the two pieces were joined. The measured material properties of the resin are reported; the RCS measurement setup, data collection, and post processing are detailed; and the uncertainty in measured data is quantified with the help of simulations.
Echodyne has recently completed and qualified a new millimeter-wave antenna measurement system for characterization of beam-steering antennas such as our Metamaterial Electronic Steering Arrays (MESAs). Unlike most far-field systems that employ a standard Phi/Theta or Az/El positioner, we use a six-axis industrial robot that can define an arbitrary AUT coordinate system and center of rotation. In different operational modes, the robot is used as an angular AUT positioner (e.g., Az/El) or configured for linear scan areas. This flexible positioning system allows us to characterize the range illumination and quiet zone reflections without modification to the measurement system. With minor modifications, the system could also be used in a planar-near field configuration. Range alignment can be easily performed by redefining the coordinate system of the AUT movement in software. The approximate 5.2-meter range length is within the radiating near-field of many arrays of interest, so we employ spherical near-field (SNF) correction when necessary, using internally-developed code. Specialty tilted absorber was installed in the chamber to improve quiet zone performance, over standard absorber treatment for similar aspect ratio ranges. Narrower ranges often have specular reflections that exceed 60° and benefit from the specialty tilted absorber designed to reduce the angle of incidence. We present an overview of the measurement system and some initial measurement data, along with lessons learned during design and integration. I. MEASUREMENT SYSTEM OVERIVEW A 7.3m x 3.7m x 3.7m footprint was allocated for the new R&D millimeter-wave antenna measurement chamber. After accounting for structural considerations, the final chamber interior dimensions are 7.1m(L) x 3.45m(W) x 3.35m(H) and the final range length (separation between range antenna and quiet zone center) is about 5.2 m. Table 1 lists the high-level goals of the measurement system are listed in. Table 1. Echodyne R&D chamber goals. Parameter Goal Frequency range 12-40 GHz, with provisions up to 80 GHz Polarization Dual-linear switched or simultaneous AUT positioner Azimuth-over-Elevation and linear scanning Quiet zone size 0.4m(L) x 0.4m(W) x 0.4m(H) Side lobe uncertainty +/-1 dB for-20 dB sidelobe Figure 1 shows the dimensions of the rectangular chamber, which is lined with the special absorber design described in Section II. Figure 2 shows an overview of the measurement system. The RF subsystem consists of a 4-port vector network analyzer (VNA), a Gigatronics GT-1050A power amplifier, a directional coupler (placed after the amplifier) to provide the VNA reference signal and a MVG QR18000 dual-polarized closed boundary quad-ridged horn [1] as the range antenna. This setup provides continuous frequency coverage from 12 to 40 GHz. External frequency converter modules can be used to extend the range further into millimeter wave. Horizontal and vertical polarization are acquired simultaneously by measuring three receiver channels (B, C & R1) and calculating the ratios B/R1 and C/R1 which remove the effects of amplifier drift (such as temperature coefficient). The range antenna is mounted to a rotary stage to allow direct measurement of Ludwig-III polarization if desired (versus polarization synthesis in post-processing). The AUT positioner described in Section III is a six-axis industrial robot that provides both angular azimuth-over-elevation and linear scanning with high-accuracy. Linear scanning allows planar near-field measurements in addition to the quiet zone evaluation shown in Section IV. The 5.2 m range length is within the radiating near-field of many arrays of interest, especially at higher frequencies. For example, even a relatively small (140 mm) AUT would have a 22.5° phase taper across at 40 GHz. We use the spherical near-field measurement correction [2] described in Section V to obtain true far-field patterns in the Az/El coordinates described by the robot motion. Figure 1. Rectangular chamber dimensions (in inches).
In 1987 the author built the world's first Personal Near-field antenna measurement System (PNS). This led to the formation of Nearfield Systems Inc. (NSI) a company that became a major manufacturer of commercial near-field antenna measurement systems. After leaving NSI in 2015 several new personal antenna measurement tools were built including a modern updated PNS. The new PNS consists of a portable XY scanner, a hand held microwave analyzer and a laptop computer running custom software. The PNS was then further generalized into a modular electromagnetic field imaging tool called "Radio Camera". The Radio Camera measures electromagnetic fields as a n-dimensional function of swept independent parameters. The multidimensional data sets are processed with geometric and spectral transformations and then visualized. This paper provides an overview of the new PNS and Radio Camera, discusses operational considerations, and compares it with the technology of the original 1987 PNS. Today it is practical for companies, schools and individuals to build low-cost personal antenna measurement systems that are fully capable of meeting modern industry measurement standards. These systems can be further enhanced to explore and visualize electromagnetic fields in new and interesting ways.