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The sampling of the field first-order spatial derivative, in addition to the field itself, enables an increase of the sampling step to twice that of the standard sampling criterion – and thus facilitates a reduction of the measurement time. Here, we investigate so-called derivative probes and their usage for spherical near-field antenna measurements.
KRISS has introduced a 6-axis industrial robot into an antenna measurement system. This allows for various measurement applications and the continuous development of additional ones. Among these measurement applications, representative functions such as antenna gain measurement, material characteristics measurement, 3D field scanning, and RCS measurement are continuously being improved. The validity of the technology is discussed by comparing its results with measurements taken in a fully anechoic chamber.
To verify the proper working of a Reconfigurable Intelligent Surface (RIS), similar to antenna radiation patterns, the RIS reflection pattern has been established as key performance indicator. To overcome the necessity of a bistatic RIS qualification setup, where two antennas at different positions are used, this paper presents a novel measurement approach to obtain the RIS reflection pattern based on a monostatic indirect Far-Field (FF) Compact Antenna Test Range (CATR) setup. Due to the monostatic principle, only one antenna, which is used for transmission and reception, is required. Subsequently, the mono- static reflection patterns are transformed into bistatic reflection patterns by applying different Monostatic to Bistatic Equivalence Theorems (MBETs) known from radar-cross-section theory. With that, the required setup can be simplified in terms of mechanical complexity, setup footprint and the number of measurement scenarios, since incident and reflection angle correspond in the monostatic case. This paper analyzes three different MBETs, namely Kell, Crispin/Siegel and Falconer, with respect to their suitability for RIS reflection pattern measurements. Moreover, a monostatic CATR test environment is presented and two metal plate based RIS calibration approaches are introduced. This novel monostatic RIS measurement approach is validated with simulation and measurement data of two mmWave fixed beam RISs. Both of them are reflecting an impinging signal from broadside (θ = 0°) direction into 47° at a center frequency of 27GHz. The results prove the suitability of this approach.
This paper presents research validating the conductive resonant sphere creeping wave phase dilation discovered in high-resolution imaging presented at the 2023 Antenna Measurement and Techniques Association (AMTA), which focused on using a small resonant sphere as a test probe for assessing Radar Cross Section measurement accuracy [1]. The associated analysis uncovered a discrepancy in the creeping wave Standard Model physical pathlength around the sphere having less phase than required for resonance. This paper presents a new creeping wave phase dilation model resolving the phase difference and validating results with computational electromagnetic field predictions.
This paper investigates measurement uncertainty in a Reverberation Chamber (RC) within the lower FR2 bands (24.25-29.5 GHz). The study focuses on the impact of several factors contributing to RC measurement uncertainty, including finite sample size, polarization imbalance, and spatial non- uniformity. A series of 24 measurements were conducted using a horn antenna, known for its directivity in mmWave frequencies, varying antenna parameters such as height, orientation, position on the turntable, and polarization within a predefined chamber volume. The measurement uncertainty was evaluated by a method based on the standardized 3GPP and CTIA approaches, incorporating uncorrelated measurements and analyzing Pearson correlation coefficients between measurement pairs. An analysis of variance (ANOVA) was performed on the frequency-averaged power transfer function to identify the significance and impact of each variable on measurement variability. Additionally, the K-factor was estimated for each measurement set as part of the RC characterization, using an alternative approach to account for the turntable stirring effect. The findings highlight which variables most significantly influence measurement uncertainty, where the antenna orientation emerges as the most significant factor for the mmWave directive antenna setup.
Larger low-observable targets are being mounted onto RCS pylons. In many cases not only Azimuth rotation of the target, but a degree of movement in elevation is desired. This requires in many cases a large number of positioning cables to run from the base of the pylon to the tip where the rotator is placed. At the same time the low-observable qualities of the target call for pylon ogives with higher ratios to minimize the background RCS of the pylon that supports the target. The higher ratios call for very thin structures that cannot handle the weight of the rotator or have not enough space for the control and power cable to be fed to the rotator. A way of solving this problem is to have a variable ratio pylon, where the ogive at the tip is different from the ogive on the main body of the pylon. To analyze these pylons a higher-order basis-function method of moments (HOBFMoM) approach has been used in the past [1]. To conform the quadrilateral flat patches to the round geometry of the pylon, patches smaller than 0.3λ were used. While this was still an advantage over the typical 0.1to 0.05λ patches it placed limits on the highest frequencies that could be analyzed give the available computational resources. In this paper the authors present an approach to the meshing of the structure that allows for computing the monostatic RCS at frequencies in the x-band for a 2.4 m tall pylon. In addition, the effects of the non- physical absorber terminations are further analyzed.
Tapered anechoic ranges were introduced in the late 1960s. Since their introduction tapered anechoic chambers have become popular tools for the measurement of antenna patterns at frequencies under 1 GHz. Dating back to their first installations, several papers mention the fact that these chambers did not have a spherical wave propagation and thus, the Friis transmission equation to measure gain cannot be applied [1,2]. The array factor theory of taper chambers presented in [3] states that from the point of view of the antenna in the QZ the tapered chamber appears to be a free space environment. The phase behavior across the QZ, reported in [4] appears to agree with the theory since the phase distribution follows the far field equation. In this paper simulations for a dipole and a biconical antenna are performed that suggest that the array factor theory for the tapered ranges while not perfect provides an approximated explanation for their operation. The simulations confirm the measurements done in [2] and additionally show that at some discrete frequencies the propagation in the tapered range does follow closely the free space attenuation.
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.
The experimental characterization of vehicular wireless power transfer (WPT) systems, requires the measurement of all three components of the near magnetic field. The in-situ characterization of dynamic WPT systems requires the near-simultaneous measurement of these quantities. A WPT system can produce an intense near electric field and hence substantial electric field rejection is required of the magnetic field probes. A conventional shielded loop can provide this rejection, but co-locating three such loops with orthogonal axes presents several challenges. Here such a three-axis shielded loop is presented along with a detailed analysis of the isolation between the component loops and the electric field rejection. Discussion of the use of the probe in dynamic WPT characterization is provided.
In this paper we introduce a novel technique for the efficient production test and measurement of 5G, Massive MIMO array antennas for the purpose of verification, diagnostics, and fault detection that drastically reduces the number of measurements required and the associated acquisition time needed. The technique utilises compressive sensing and sparse sampling combined with a total variation measurement approach that enforces the requisite sparsity on the problem. In this paper, we compare this new spherical near-field total-variation based acquisition approach with the authors existing, analogous, planar technique. Extensive performance comparisons are presented which aggregate results across many test cases which is a necessity, and a consequence of the statistical nature of the compressive sensing technique that is imposed by virtue of the requirements of the Restricted Isometry Property (RIP). Crucially, this paper identifies and addresses a fundamental flaw within the application of many total-variation based methods and especially when used with the difference field between a reference antenna and a production test antenna. This extends the use of a novel analysis process that incorporates an l0 based minimisation strategy to overcome this problem thereby restoring the CS process to very nearly the levels of performance attained in our prior work.
An adaptable patch-like antenna element has been designed, tested, and implemented across several airborne flight applications. The element design improves upon the limited bandwidth of a typical patch antenna on a simple ground plane or within a cavity. The element position within the cavity, in conjunction with the distance from the opposing wall, can be used as degrees of freedom in steering gain along the direction of primary polarization. In addition, the Mono-Patch has been used in RF antenna test couplers for validation of section level and full vehicle RF system testing. When enclosed in shielded enclosures used for near-field coupling, the Mono-Patch antenna element has proven less sensitive to electrical loading than other candidate antennas. Antenna elements of this type have been designed to support both linear and circular polarization. These elements can be used in both single and multi-element array configurations for applications in L, S, and C frequency bands.
Planar near-field (PNF) acquisition always samples a limited or truncated subset of the infinite plane in front of an antenna under test (AUT). That truncation of the sampled field has two primary impacts: Power radiating to or from angles beyond the probing boundary is not fully captured and thus not included and erroneous ripple is injected throughout the pattern when the transformation algorithm sees by default a sudden drop to zero power beyond that boundary. The topic of truncation mitigation in the PNF geometry has been addressed with a variety of algorithms. This paper introduces a new algorithm that is similar to, yet distinct from, some that have come before. The new algorithm makes use of the recently introduced holographic PNF filter [1][2][3], treating the truncation effects like stray signals. Where the most common technique [2][4] uses the known planar-AUT bounds (2D) and a computed “valid region” of the plane-wave spectrum as truth through iterative transformations, this algorithm treats as truth the known AUT volume (3D) and the measured PNF data. The new algorithm is evaluated herein by retruncating a large set of measured PNF data.
The impact of receiver internal leakage on planar near-field measurement uncertainty is significantly influenced by the selection of near-field parameters. Understanding how specific scan parameters affect the far-field leakage level is essential for effective mitigation. This paper establishes quantitative relationships between near-field parameters and the far-field peak amplitudes of both leakage and the antenna under test (AUT), as well as the mean noise level in the far-field pattern, based on empirical results. Systematic scans were performed by altering only one or two specified near-field setup parameters per measurement, and graphical comparisons are provided. Practical approaches for mitigating receiver leakage are demonstrated through a case study involving receiver leakage on a planar scanner with a maximum scan area of 3.6 m x 3.6 m (12 ft x 12 ft). Additionally, a method for estimating the far-field receiver leakage level relative to the beam peak is discussed.
We report a new class of wearable loop sensors for monitoring human kinematics (particularly, joint flexion angles) while overcoming limitations in the state-of-the-art. Previous studies have demonstrated the feasibility of these loop sensors using tethered connections to a network analyzer. In this work, we take a major step forward to demonstrate untethered operation for the sensor. To this end, transmitter and receiver boards are designed and integrated into the loops. The transmitter board sends a Radio-Frequency (RF) power of 5.68 dBm at 34 MHz upon a 50 Ω load, while the receiver board detects the power level and transmits the data to a nearby personal computer (PC) via Bluetooth. Flexion tests are conducted upon a tissue-emulating phantom to validate the setup. To quantify performance, we calculate the root mean square error (RMSE) between the estimated angle from our sensor and the gold-standard angle from a marker-based motion capture camera system, as well as Pearson’s correlation coefficient (ρ). The proposed sensor shows outstanding performance with an average RMSE of 0.670° and an average ρ of 0.99966. Overall, our sensor outperforms state-of-the-art wearable kinematic technologies by being highly accurate, seamless, lightweight, unobtrusive to natural motion, and reliable over time.
The need for fast and accurate measurement techniques for electromagnetic exposure from modern communication devices has increased since few years. The exposure metric for frequencies up to 10 GHz is the Specific Absorption Rate (SAR). The Link approach has been studied and validated since few years to evaluate the SAR for passive antennas and some active devices which can be controlled in terms of output power and have no automatic power adjustment mechanism. In this paper, we go a step further and apply the Link approach to measure the SAR for a commercial smart phone, where we have no a priori knowledge or control, over the power control mechanism, and the antenna position inside the phone. The measurements are done with a 10MHz bandwidth LTE signal communication, between a commercial smart phone, and the Radio Communication Tester (RCT) emulating a mobile Base Station. The E-field distribution and SAR values, computed from the Link approach, are compared to results from the same DUT measured with a legacy SAR (single probe with a robot and phantom) measurement system. The results show SAR values, within 2.8% (0.1dB) for 10g SAR, and -7.1% (-0.3dB) for 1g SAR (at 5mm separation between phone and phantom), between the Link and Legacy approach. The SAR values at 0mm separation distance are calculated using extrapolation, and the difference is 7.0% (0.3dB) for 10g SAR and -6.2% (0.28dB) for 1g SAR. Based on these results, it is shown that the Link approach is a faster alternative SAR measurement approach, applicable for pre-compliance, during early stage of development, and for post-production scenarios.
This paper extends the authors prior studies to develop a more flexible definition for the shape of a blended rolled edge compact antenna test range (CATR). This is accomplished by utilising a more sophisticated definition for the junction contour. This definition ensures the reflector surface is smooth and provides additional parameters that can be used to optimise the performance of the CATR enabling wall illumination and quiet-zone performance to be managed and balanced. As with the authors prior work, a novel, parallel, physical optics based, genetic optimisation is performed that, over subsequent generations, breeds optimal designs for each test case selecting the preferred design from many thousands of potential mutated candidates. Results are presented and discussed for several CATR designs that illustrate the concept and achievable performance highlighting the utility of a hybrid serrated blended rolled edge CATR reflector.
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.
In modern integrated radar systems conventional antenna measurements are often impractical due to the lack of access to the antenna feed points. For frequency modulated continuous wave radars, the two-way radiation pattern can be characterized with a reflector while utilizing the integrated transmit and receive module. However, some post-processing steps are required for this measurement method to obtain the frequency-resolved radiation characteristic. This paper takes a closer look at the fast Fourier transform (FFT) and inverse FFT with the associated window functions and the necessary range gating including zero-padding based on simulations. A sufficiently wide range gating is necessary to reconstruct the frequency resolution of the antennas correctly. Yet a trade-off between the required wide range and the filtering of mutual coupling and reflections from the environment has to be made in the case of real measurements. Moreover, depending on whether a frequency in the center or at the edge of the chirp is to be reconstructed, different window functions provide the most accurate result.
The application of a series of interconnected single-axis motion controllers distributed throughout an antenna measurement range has some important advantages when compared to multi-axis controllers that must reside in a central control room. The technologies used for distributed real-time control based on the Ethernet for Control Automation Technology (EtherCAT) standard are discussed, as are advantages and tradeoffs to be considered. The greatly reduced requirement for signaling between the control room and the remote axes reduces cost in system design and manufacturing. In practice, the shorter electrical signal runs can enhance electromagnetic interference (EMI) performance, noise immunity and safety.
This paper presents a study on the performance of GNSS antennas at various vehicle positions. Simulations and measurements were conducted in the L1-Band with and without an additional ground plane. The results were evaluated in terms of Right-Hand Circularly Polarized (RHCP) gain, axial ratio, and accuracy at different frequencies and positions. Real-world measurements using a ublox receiver were performed to validate the simulation results. The findings provide insights into the optimal placement of GNSS antennas in vehicles to enhance signal reception and reliability.