Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
Linear motion components are widely used in antenna metrology positioning systems, but long motion ranges can reduce positioning accuracy due to the difficulty of eliminating rail component non-linearity. Further, offset device-under-test (DUT) mounting can magnify rotation errors arising from slight variations of rail parallelism not captured by a strictly linear motion model. We present methods to reduce position and rotation inaccuracy through kinematic calibration using a Legendre polynomial model. The motion range of the rail system is conditioned for use over an appropriate evaluation range. The calculation of calibrated coefficients is detailed for an individual rail calibration and is further integrated in a pose error minimization calibration framework for general robotic implementation. This approach is validated using experimental 6 degree-of-freedom (DoF) measurements collected using the Large Antenna Positioning System robotic antenna range. Compared to a strictly linear rail model, the Legendre polynomial model reduced the RMS position error by 67.7 % to 27.90 μm and RMS rotation error by 29.9 % to 84.92 μrad.
Near-Field (NF) antenna measurement ranges have evolved as an alternative to Far-Field (FF) ranges to be the prominent method for pattern estimation from measurement. This is because NF ranges are more convenient to use and require much less space in laboratories [1]. The Microwave Vision Group (MVG) StarGate series, such as the legacy Satimo StarGate 64 (SG64), employs an array of multiplexed probes to perform measurements, sampling across a synthetic aperture created by moving the test antenna with respect to the probe array. This example of a commercial system does not use a Vector Network Analyzer (VNA), and was not designed to be updated. This means that it cannot benefit from improvements made in RF measurement equipment, requiring instead that a new system be purchased, which is unrealistic for many users. This work describes the initial process of updating a legacy SG64 to use a VNA. It includes characterization of the control signals, the transmit and receive paths, as well as the potential improvements to performance and lifetime that upgrading the legacy system to a VNA-based configuration offers.
An international comparison of antenna calibration results was conducted between two internationally recognized laboratories—NICT (Japan) and RRA (Korea)—in the 18–40 GHz frequency band. Due to the high cable loss in the band, antenna calibrations were performed inside SACs using two different configurations. In the first configuration, absorbers were lined on the floor, and the antenna height was set to 1.5 m. In the second configuration, no floor absorber was used, and the antenna height was set to 2.0 m. Results obtained using the extrapolation method were used as a reference to assess the accuracy of each method. The results indicate that the antenna gains of horn antennas and double-ridged horn antennas obtained using the configuration with floor absorbers showed good agreement with the extrapolation method, with differences within 0.5 dB for both NICT and RRA. These findings are expected to contribute to the ongoing development of CISPR standards, particularly by supporting the establishment of harmonized calibration procedures for high-frequency EMC measurements.
An automated scan plane alignment technique for robot-based planar near-field antenna measurements enables precise and efficient calibration of unknown and arbitrarily oriented antennas under test (AUTs). By integrating a high- resolution laser line profile sensor with a robotic arm, the system dynamically determines the AUT’s position, orientation, and outline without requiring detailed prior knowledge. A real- time feedback loop guides the robot to adaptively align the scan plane based on measured surface profiles, taking into account tilts or non-ideal AUT placements. Edge detection and reference mark identification further enhance accuracy, allowing to precisely align the scan center with the AUT’s geometric center. The method is validated using a reference metal plate and is particularly suited for spatially flat antennas or radomes. Beyond alignment, the same setup enables high-resolution optical inspection, capable of detecting fine surface details such as cracks, dents, or even the thickness of ink from printing. The approach significantly reduces setup time by eliminating manual alignment steps, and broadens the functionality of robot-based measurement systems by combining self-alignment and optical inspection into a single automated process.
With the increasing number of channels in integrated radar MMICs, radar modules and networks, beamformer calibration techniques must adapt to the physical dimensions of these sensors. Typical far-field calibration requires measurements at the Fraunhofer distance. This ensures a maximum phase error of 22.5° over the aperture. However, literature shows that phase errors below 5° are required for acceptable side-lobe suppression. Compact Antenna Test Ranges (CATR) create virtual far-field conditions in limited space but unfortunately they introduce magnitude and phase errors in their measurement. A method for calibrating MIMO radars in CATR settings is presented using spatial averaging to reduce these errors systematically. Simulations with a 16-channel FMCW radar show maximum errors of below 0.25dB for magnitude and less than 2◦ for the phase with a single-digit number of spatial averages. Calibration with a 77-GHz MIMO radar sensor in the CATR confirms the technique’s ability to mitigate test zone non-idealities, improving radar imaging quality.
Modern wireless standards such as LTE, HSPA, WiMAX, and 5G have introduced the need for more sophisticated testing of devices that use multi-antenna systems. Traditional Over-the-Air (OTA) test methods, initially developed for single-input single-output (SISO) devices, fall short when evaluating complex systems like Multiple-Input Multiple-Output (MIMO) devices. This paper discusses the convergence of traditional testing methodologies based on conducted RF testing and OTA antenna system test methodologies toward testing of the full antenna equipped device. This convergence embraces two important testing needs and scenarios: replay of preconfigured scenario, based on spatial fading emulation (SFE) / channel modelling and dynamic hardware-in-the-loop testing, where changes in the hardware state in reflected in the status of the testing scenario. By the integration of channel emulation and multiprobe anechoic configurations, scalable and flexible test strategies can be achieved accommodating testing needs in personal and automotive communication systems but also defense applications.
In support of the National Science Foundation Next Generation Radar Designs Mid-Scale-Research-Infrastructure-1 (MSRI-1) project, Raytheon, an RTX company, has finished preliminary design of a high power phased array transmitter for integration onto the 100-meter Green Bank Telescope (GBT). GBT is the largest steerable radio astronomy antenna in the world located in Green Bank, WV. This system combines a fixed transmit-only phased array with a steerable reflector system. Due to the unique size and architecture of the Green Bank Telescope assembly, along with the power output of a fully collimated transmitter, a safe terrestrial calibration reflector is not a readily convincible option. As such, a novel calibration approach for the high-power transmitter feed is necessary, combining radio astronomy techniques for receive-only calibration in combination with a purposeful rigidity of variables for a valid transmit-only calibration. Additionally, due to the number of individual transmitter elements involved, a wideband calibration waveform is proposed for separable over-the-air calibration of all the individual transmitter elements on a drastically reduced timescale. This paper walks through the patent-pending Raytheon proposed calibration process and the details of this novel approach.
Historically, the Thru-Reflect-Line (TRL) method for complex permittivity and permeability extraction has been sufficient in producing accurate and cost-effective measurements of material characteristics. However, this method requires rigorous setup for accuracy and more time to collect all necessary data samples. The Position-Insensitive and Calibration-Independent (PiCi) method for complex permittivity extraction offers an alternative method that is quicker and simpler, requiring less time and only two measurements – sample and line – instead of the TRL method’s four – thru, line, reflect, and sample. This method is currently limited to coaxial line and rectangular waveguides only. This paper extends the PiCi method to stripline using unique functions in the Newton-Raphson root search algorithm different from the functions used to characterize the waveguide and coaxial line parameters. The results show the stripline provides an accurate estimation of the material’s permittivity and permeability without adjusting for detector mismatch within the network analyzer. Further, detector mismatch correction provides improved stability at all frequencies of observation and increased precision at a sufficiently high frequency. Thus, this research validates another comparable method to the PiCi method for material characteristic extraction for the waveguide and coaxial line, further reducing measurement time and improving cost effectiveness.
Group delay (GD) is a critical parameter in satellite payloads and radar systems, directly impacting overall system performance. Although several antenna group delay measurement methods exist, most overlook the challenges posed by frequency conversion chains commonly used in these applications. This paper introduces a method to accurately address this issue by implementing an additional calibration step of the vector network analyzer (VNA) using a harmonic phase reference (HPR). The method is validated through far-field measurements on a device equipped with a mixer.
This work presents an integrated 3D-printed ultra-wideband (UWB) graded-index (GRIN) lens antenna that offers a simple, efficient, and cost-effective solution to the inherent wide beamwidth and asymmetric radiation problems of the commercial wideband antenna probes. The integration of the proposed antenna enables the effective use of these wideband probes on UAV/UAS platforms, which was previously not feasible due to the aforementioned problems. The proposed integrated antenna system covers a wide range of frequencies from 3 to 32 GHz, enabling the use of a single probe antenna for in-situ UAV-based calibration of maritime, weather, surveillance, and airborne radars. The proposed GRIN lens provides symmetric radiation patterns and reduced half-power beamwidth performance, especially in the lower part of the frequency band between 3 to 7 GHz, where the commercial UWB ridged-horn probes have significantly wider beamwidth values. Measured results show that the integration of the GRIN lens achieves a relatively constant beamwidth as well as an average beamwidth reduction of around 68% in both E- and H-planes, meeting the probe antenna performance requirements for radar characterization using UAVs/UAS.
Plane Wave Generators (PWGs) utilize arrays of radiating elements to approximate plane wavefronts, thereby creating localized far-field-like conditions within a Quiet Zone (QZ). Their compact form factor makes them especially advantageous at low frequencies, such as in the VHF and UHF bands, where traditional Compact Antenna Test Ranges (CATRs) become impractically large. This paper presents results from a comprehensive validation campaign of a 19-element PWG demonstrator, conducted as part of a broader development program aimed at realizing a full-scale system for VHF/UHF testing. The campaign, executed at Pulsaart by AGC, involved both element-level and array-level assessments using a spherical near-field multi-probe system. Key objectives included validating QZ synthesis, calibrating array excitations via digital twin modeling and field expansion methods, and quantifying realized excitation errors. The findings confirm the robustness of the PWG design, the effectiveness of the calibration process, and the minimal impact of mutual coupling and active impedance variations on performance.
The use of electro-optical (EO) Probes to acquire planar near-field measurements offers advantages over conventional radio frequency (RF) measurement techniques for some applications. Placing the measurement probes in the reactive near-field region also allows the antenna test ranges and enclosures to be much smaller. Due to their small size, installation of these probes directly inside the antenna’s radome for calibration/diagnostics is even possible. The EO probe evaluated in this paper utilizes Pockels effect to measure the time-varying electric fields of the antenna under test (AUT). After post-processing, the resulting far-field patterns compare very closely to those generated from conventional near-field measurements [1]. The use of a non-invasive, broadband EO probe facilitates measurement of the tangential electric field components very close to the AUT aperture in the reactive near-field region. This close proximity between the EO probe and AUT is not possible with conventional metallic probes due to mutual coupling effects. Another major difference between the reactive near-field and radiating near-field measurements is the number of data samples required to accurately generate the far-field pattern, and that is the primary focus of this paper.
Metamaterial-based blackbodies are playing an increasingly important role in spaceborne remote sensing due to their tailored terahertz emissivity profiles. Accurate characterization of their angular-dependent reflectivity is essential for establishing reliable radiometric baselines, particularly given their structured surfaces. In this work, we present a focused-beam, angular-resolved measurement method using a monostatic configuration that integrates a polymethylpentene (TPX) lens with a standard gain horn antenna. The setup, implemented on the Configurable Robotic Millimeter-wave Antenna (CROMMA) system at NIST, enables micron-level spatial precision through a robotic arm and hexapod stage. For calibration, a reflecting mirror is employed to extract system parameters, thereby eliminating the need for near-field lens antenna characterization. A forward model based on plane- wave scattering matrix decomposition is developed to extract the target’s angular reflectivity, with time-gating and spectral filtering applied to isolate temporal reflections and mitigate modal interference. Using this calibrated system and signal processing workflow, we measure the angular reflectivity of a metamaterial-based blackbody designed for the G-band (140–220 GHz). The results reveal elevation-angle-dependent reflectivity about the boresight normal, demonstrating the method’s ability to resolve angular variations with high accuracy. This approach offers a practical and precise framework for characterizing structured terahertz absorbers and supports the advancement of calibration standards for microwave and terahertz applications.
The MIMO radar technique enables high angular resolution by virtually synthesizing a larger number of receiving antennas [1]. This paper leverages this technique to generate reliable point cloud data of an outdoor space, by applying a series of radar processing techniques and a point cloud denoising function. This work provides a comprehensive explanation of our methodology, from calibration and measurements to data processing and plotting. Our strategy is validated through real-world measurements conducted using the cascaded TI AWR2243 radar, highlighting the potential of mmWave MIMO radars in static 3D mapping scenarios and offering insight into practical implementation challenges.
Time-varying metasurfaces, also known as reconfigurable intelligent surfaces (RISs) or smart surfaces, offer new opportunities and applications, where fast-time modulation of the biasing conditions of individual elements enables beam- steering, frequency shifting, information encoding, and more. The unexplored potential offered by these modulated surfaces is matched by a number of challenges in the characterization of their performance. This work highlights ongoing efforts at GTRI to develop standard techniques for the characterization of these surfaces, with an emphasis on those designed for frequency conversion. First, the complex reflection response must be obtained for the entire range of static DC biasing conditions in order to compute the phase-voltage relationship required to design modulation waveforms. We present a three-standard offset short calibration method to perform static characterization of surface phase versus DC bias conditions in the free-space focused beam system, avoiding phase errors that are introduced by over- constrained time gating of resonant structures with two-standard calibrations. Second, the metasurface must be characterized over frequency under various modulation conditions.
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.
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.
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.
The standard Near-Field antenna characterization allows to reconstruct the Far-Field pattern over the whole visible domain, even if, in many cases, the partial characterization of the Far-Field pattern just along some cuts can be sufficient, and becomes preferred if realized in shorter measurement time with respect to the standard case. A method for Partial Characterization has been proposed. The approach provides a general framework and defines the optimal distribution of the near-field samples required to reconstruct the Far-Field pattern along the cut of interest. The main features of the method are presented, and the performance is verified, experimentally, for two test cases.