AMTA Paper Archive
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Unifying G/T and Noise Figure Metrics for Receiver Systems
The conventional method for comparing the performance of antenna-receiver systems is the classical G/T metric. The G/T metric is the ratio of antenna-circuitgainrelative to the thermal noise temperature evaluated at the input of the low noise amplifier; the thermal noise at the input to the LNA consists of the received sky noise, the LNA's effective input noise temperature, and post LNA noise referenced to the LNA's input. While this has been a standard for many years, it will be shown that G/T does an incomplete job of describing the performance under all conditions. The noise figure metric was developed as a characteristic describing signal-to-noise degradation to be applied to circuit based input/output topologies, and cannot easily be applied to hybrid systems such as an antenna-receiver system in which the input power is described by spatial field density levels, and the output power is stated in terms of a circuit-based voltage-current environment. This paper presents a noise figure metric which has been expanded to include systems that are a hybrid of wave and circuit characteristics such as the marriage of an antenna and receiver. It will also be shown that whereas a system's noise figure is dependent upon a chosen noise reference temperature, the intrinsic Effective Input Noise Temperature of the system is an invariant that does not change when a different reference temperature is selected. It will also be shown that, in contrast to G/T, the effective input noise temperature of an antenna/receiver system will accurately predict the system's output SNR for all values of system input SNR. It will be shown in detail, how to measure the antenna/receiver system's Effective Input Noise Temperature (TE), resulting in the following equation: TE = (TD1 - Y£ TD2 )/(Y - 1) Where: TD1 , and TD2 are measured noise power densities at the face of the antenna, TE is the Effective Input Noise Temperature of the system, and "Y" is the classical "Y factor" metric.
Loadbox Design for EMC Testing in Automotive GNSS/SDARS Application
In this paper, a loadbox was developed to perform theconductive and radiative Electromagnetic Compatibility (EMC) emission and immunity testing of the Global Navigation Satellite System (GNSS) and Satellite Digital Audio Radio Service (SDARS). To perform these tests, the supplier must purchase and build bias-tee, lowpass filter, choke, Diplexer and coupling circuitry to develop a loadbox. This means that same product made by different suppliers have different test set-up in place and therefore variability in the testing which create uncertainties in the test results and product approval or rejection. This is not reliable and can cause large amount of money wasted or bad product pass through. In this work, we propose an integrated loadbox design that can be built in-house with low cost and provide unique solution across the board. A loadbox consisting distributed Printed Circuit Board (PCB) made diplexer was developed that is easy to fabricate with low cost high durability and reliability during EMC testing and keep all the EMC testing consistent across the board which is enabling factor for proper decision making. A dual band diplexer was realized to separate the combined signal coming from the LNA's output port to two separate GNSS and SDARS ports. At the GNSS and SDARS frequencies due to the short wavelength of the RF signals, inductors and capacitors can be implemented using different transmission lines widths and lengths in short, open, parallel and straight-line formation. Distributed diplexer was designed using ADS RF Momentum simulator tool from Keysight and fabricated on a 2-layers PCB, FR2 of thickness 0.787 mm and a copper thickness of 35 um with overall size of 5.8x3.1 cm. Simulated and measured s-parameter for all of diplexer ports are in good agreement with measured insertion loss of better than 1.9 dB, return loss of 11.4 dB and GNSS-SDARS isolation of 16.8 dB at the GNSS frequency band and measured insertion loss of better than 2.1 dB, return loss of 14.1 dB and SDARS-GNSS isolation of 10.9 dB at the SDARS frequency band.
Correction of the Measured Phase of the Radiation Pattern of Millimeter-Wave Antennas
To characterize the radiation characteristics of an antenna, determining the power pattern of the antenna is often sufficient. In some cases, however, both the amplitude and phase response are important. For instance, for accurate channel modeling, the antenna has to be de-embedded, requiring knowledge of the complex radiation pattern of the antenna. A vector network analyzer typically measures complex S-parameters, hence, determining the complex radiation pattern seems like a straightforward task. When measuring at higher frequencies, as the wavelength becomes shorter, antenna phase measurements are very sensitive to positioning and alignment errors. Using sophisticated measurement tools, the position and orientation of the antennas can be determined, and this information can be used to correct the measurement data. The stringent requirements on positioning and alignment at millimeter-wave frequencies, however, makes correcting the data based on physical insight, in some cases, a more practical solution. The results of a radiation pattern measurement of a WR-28 rectangular open-ended waveguide will be shown in the full paper. The magnitude of the radiation pattern is symmetric in its two principal planes, which is to be expected, but the phase of the radiation pattern is not symmetric. To explain this lack of symmetry, a two-parameter misalignment model will be presented. It will be shown that the measured phase is much more sensitive to the misalignment than the measured magnitude, explaining why the symmetry is only lacking in the measured phase. Based on the 1,708 available planar cuts, the two parameters in the misalignment model are determined with great confidence. Subsequently, the parameters are used to correct the phase of the measured radiation pattern, restoring the expected symmetry in the phase measurement.
Nearfield Antenna Measurements over Seawater - Challenges and Prospects
The question of how to perform a nearfield antenna measurement in the presence of the air-sea interface is one that has been raised previously by the author. When discussing spherical near field measurements various approaches have been proposed for addressing this problem, that are also applicable to measurements taken over a conducting ground plane. In this paper we shall discuss some of the practical challenges involved in data collection and measurement methods when performing this type of measurement. Examples shall be taken from both spherical nearfield measurements of simple sources along with single-point at-horizon measurements to examine the challenges associated with these approaches. A notional approach for measuring realized power gain at the horizon will also be discussed.
Balun Design for CISPR 16-1-5 Calibration and Reference Test Site Verification
The CISPR 16-1-5 standard requires site attenuation (SA) measurements for the validation of Calibration Test Sites (CALTS) and Reference Test Sites (REFTS). CALTS validation requires horizontally-polarized SA measurements, while REFTS validation requires both horizontally- and vertically-polarized measurements. These measurements are made with tuned linear dipole antennas driven from coaxial transmission lines via balancing networks (baluns). According to the CISPR standard, the effects of the baluns are removed with a substitution measurement. Specifically, the baluns are connected back-to-back (balanced to balanced) with the elements removed and the port-to-port insertion loss then measured. This insertion loss is then subtracted from the port-to-port insertion loss with the antennas assembled and in place on the OATS. Thus, the measurement is a true RF substitution measurement. The baluns must be perfectly symmetric for this measurement to be sound. It is then accurate only if the baluns are very well matched simultaneously to both to the coaxial transmission lines and the dipole antennas. Essentially, the dipole-to-dipole transmission, the 2-port network which is substituted, would have to behave as a matched attenuator. In the CISPR standard SA measurements are made a a minimum of 24 specific frequencies between 30 and 1000 MHz. The height of the transmitting antenna above the ground plane in all cases is 2 m, but the height of the receive antenna varies in order to avoid a transmission null. For each one of these measurements it is possible to obtain a perfect match for each dipole antenna. However, the matching network would be different for each frequency and also for the different heights involved. Thus, there is impetus to use broadband baluns and resistive matching pads. If this approach is selected, neither dipole can be perfectly matched. Moreover, if the balun is required to operate over a broad bandwidth, it is difficult for itsperformance to be made so good that it could be considered ideal. By employing a full 4-port model for antenna-to-antenna transmission on an OATS between linear dipoles with imperfect baluns and thus unbalanced antennas, we assess measurement error for topologies of balun/attenuator combinations for the CISPR 16-1-5 SA measurements.
Increasing 4-D Imaging Radar Calibration Accuracy Using Compact Antenna Test Range
Advanced driver assistance systems (ADAS), such as blind spot warning and braking assistants, have been in use for years to improve road security. ADAS are currently further promoted through the autonomous driving trend. Due to their cost / performance trade-off, the automotive industry perceives 4-D high-resolution radar sensors, as one of the backbones of autonomous driving. With human safety being at stake, the topic of calibration of these sensors is obviously of the utmost importance. Performing an accurate calibration requires a test condition where the target is in the far-field of the radar under test (RUT). Due to the requirements for angular resolutions, 77 / 79 GHz radars with 15 cm radiation aperture or more are quite common. Applying Fraunhofer formula then results into a necessary measurement range length of 11.5m. Because of the high cost of ownership of an adequate anechoic range, radar manufacturers usually limit their measurements to the strict minimum and try to simplify the calibration process. A typical approach is to go for a diagonal calibration where the target is always at boresight for each beam-formed pattern of the RUT. This technique however delivers a sub-optimal compensation of the RUT biases. In particular, it creates high peak-to-side-lobe ratios (PSLR), where energetic echoes are observable in directions of side lobes of each beam. This paper introduces a new system for radar measurements, made of a short-size focal length offset-fed compact antenna test range (CATR), interfaced with an analog echo generator. With a chamber size of only 0.9 m x 2 m x 1.6 m, the setup has been designed to test apertures up to 30 cm size. The quality of the quiet zone achieved is discussed in the paper, as well as various uncertainty contributions relating to radar measurements. Tests are presented which involve a latest generation 4-D imaging radar on chip (RoC). Results obtained in the CATR are compared to a reference 7 m far-field range. Diagonal and full angular calibrations of the RoC are carried out and analyzed, demonstrating an improvement of 10 dB PSLR when the target is swept over the complete azimuth region.
Nearfield Measurements on Integrated Antennas with a Frequency Convertor and Embedded Local Oscillator
Near-field measurements on antennas require magnitude and phase information dependent on the antenna position to support the near-field to far-field transformations. Modern active antennas are often integrated into frequency converters with embedded local oscillators (LO). For example, devices ranging from small 5G transceivers to large satellite payloads often need to be tested with the antenna integrated into the overall solution. There is no access to the embedded LO signal in these systems. The unknown phase of the embedded LO masks or corrupts the near-field phase measurement of the integrated antenna under test. A novel solution to this challenge is presented based on a new Vector Network Analyzer (VNA) platform. The system utilizes two stimulus signals (a measurement signal and a pilot signal) to characterize the antenna under test which is integrated into the frequency convertor. The pilot signal captures the phase information of the embedded LO, allowing the measurement signal to capture the antenna's magnitude and phase pattern as the antenna under test is moved within the near-field region.
Adding Phase to the Rotating-Source Antenna Polarization Measurement Method
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.
Measurement Traceability in the CISPR 16-1-6 pattern measurements for CISPR 16-1-4 Site Validations
The publication of CISPR 16-1-6  in 2107 marked a significant change in the CISPR documents, for the first time the consideration of how to perform antenna pattern measurements in and determine the associated estimate of the uncertainty of those measurement. This is a look at that technique and presentation of how that helps and relates to measurement traceability.
Comparison and contrast of the antenna calibration methods of ANSI and CISPR
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.
Measurements of Non-Metallic Targets for the Austin RCS Benchmark Suite
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.
GSS (Gated-Short-Short) Calibration for Free-space Material Measurements in millimeter-Wave Frequency Band
Electrical properties of materials are requisite to design electromagnetic (EM) devices and systems. Free-space material measurement method, where the measurands are the free-space scattering parameters of MUT (Material Under Test) located at the middle of transmit (Tx)/receive (Rx) antennas, is suitable for non-destructively testing MUT without prior machining and physical contact in high frequencies. In this paper, GSS (Gated-Short-Short) calibration method using a planar offset short is proposed for calibrating a free-space material measurement system and the measurement result is shown in W-band (75-110 GHz).
Personal Near-field System
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.
Indoor 3D Spherical Near Field RCS Measurement Facility: A new high resolution method for 3D RCS Imaging
Indoor RCS measurement facilities are usually dedicated to the characterization of only one azimuth cut and one elevation cut of the full spherical RCS target pattern. In order to perform more complete characterizations, a spherical experimental layout has been developed at CEA for indoor Near Field monostatic RCS assessment . This experimental layout is composed of a 4 meters radius motorized rotating arch (horizontal axis) holding the measurement antennas while the target is located on a polystyrene mast mounted on a rotating positioning system (vertical axis). The combination of the two rotation capabilities allows full 3D near field monostatic RCS characterization. 3D imaging is a suitable tool to accurately locate and characterize in 3D the main contributors to the RCS. However, this is a non-invertible Fourier synthesis problem because the number of unknowns is larger than the number of data. Conventional methods such as the Polar Format Algorithm (PFA), which consists of data reformatting including zero-padding followed by an inverse fast Fourier transform, provide results of limited quality. We propose a new high resolution method, named SPRITE (for SParse Radar Imaging TEchnique), which considerably increases the quality of the estimated RCS maps. This specific 3D radar imaging method was developed and applied to the fast 3D spherical near field scans. In this paper, this algorithm is tested on measured data from a metallic target, called Mx-14. It is a fully metallic shape of a 2m long missile-like target. This object, composed of several elements is completely versatile, allowing any change in its size, the presence or not of the front and / or rear fins, and the presence or not of mechanical defects, … Results are analyzed and compared in order to study the 3D radar imaging technique performances.
A Compact Reconfigurable Millimeter-Wave Antenna Measurement System Based Upon an Industrial Robot
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  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  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).
A Review of the CW-Ambient Technique for Measuring G/T in a Planar Near-Field Antenna Range
Techniques for measuring G/T have been previously presented at AMTA; however, there are very few papers that discuss how to measure G/T in a near-field antenna range. One recent paper discussed such a method and gave a brief description within the larger context of satellite payload testing . The paper's treatment of G/T was necessarily brief and gives rise to several questions in relation to the proposed method. Other papers that treated this topic required the antenna aperture to be separable from the back-end electronics, which may not be possible in all cases [2-3]. In this paper, we discuss in great detail a slightly modified version of the G/T measurement method presented in . A signal and noise power diagram is presented that can be useful for understanding how system signal-to-noise ratio (SNR) relates to G/T, and a few common misconceptions concerning the topic of G/T are addressed. The CW-Ambient technique for computing G/T of a Unit Under Test (UUT) from measurements in a planar near-field system is described in detail, and a list of assumptions inherent to the CW-Ambient technique is presented. Finally, the validity of the CW-Ambient technique is assessed by analyzing measured data collected from a separable UUT.
Experimental Verification of 3D Metal Printed Dual Circular-Polarized Horn Antenna at V-Band
In this paper, a 3D metal printed dual circular-polarized horn antenna operating in the V-band is proposed, built and tested. This antenna consists of a horn and a circular waveguide, a single groove polarizer and is side-fed by orthogonally placed rectangular waveguide ports. The groove is placed at 45° with respect to the input ports and provides a phase delay of 90° to generate right-or left-hand circular polarization (RHCP or LHCP). The proposed antenna provides symmetric patterns for all planes and exhibits polarization isolation of more than 30 dB at broadside. This antenna is analyzed to realize wide impedance matching bandwidth and wide 3dB axial ratio (AR) bandwidth. A prototype of the horn antenna has been fabricated using 3D metal printing technology. Metal material with finite surface roughness is considered when modeling this antenna.
A Methodology for Instantaneous Polarization Measurements Using a Calibrated Dual-Polarized Probe
Accurately measuring the polarization of an antenna is a topic that has garnered much interest over many years. Methods abound including phase-referenced measurements using two orthogonal polarizations, phase-less measurements using two or three pairs of orthogonal polarizations, spinning linear probe measurements, and the rigorous three-antenna polarization method. In spite of the many publications on the topic, polarization measurements are very challenging and can easily lead to confusion, particularly in accurately determining the sense of polarization. In this paper, we describe a method of accurately and rapidly measuring the polarization of an antenna with the aid of a multi-channel measurement receiver and a dual-polarized probe. The method acquires phase-referenced measurements of two orthogonal polarizations. To enable such measurements, we describe a methodology for calibrating the probe. We also describe a tool for automating the polarization measurement and display of the polarization state. By automating the process, it is hoped that the common challenges and confusions associated with polarization measurements may be largely obviated.
Near-Field Techniques for Millimeter-Wave Antenna Array Calibration
A reliable technique for antenna array characterization and calibration is demonstrated for two state-of-the-art antenna measurement systems, a near-field system and a compact antenna test range system. Both systems are known to reduce the measurement distance between device under test and the probe antenna in comparison to classical far-field systems, which need to provide at least the Fraunhofer distance as minimum range length. Equivalent magnetic surface currents are derived from measurements, which represent the electric field on the applied Huygens surface. The calculated equivalent magnetic currents are utilized for characterizing two completely different antenna arrays in the millimeter-wave region. Magnitude and phase calibration opportunities of antenna arrays are discussed, as well as the accuracy provided by the proposed calibration technique.
Testing mmWave Phased Arrays for the 5G New Radio
As the wireless industry continues the move to 5G, the development and subsequent testing of mmWave radios for both base stations and user equipment still face numerous hurdles. The need to test most conformance and performance metrics through the antenna array at these frequencies poses significant challenges and has resulted in excessively large measurement uncertainty estimates to the point where the resulting metrics themselves may be useless. A large contribution to this measurement uncertainty is the impact of the over-the-air (OTA) test range used, driving the industry towards expensive compact range reflector systems in order to overcome the path loss considerations associated with direct far-field measurements. However, this approach necessitates the use of a combined axis measurement system, which implies the need for considerable support structure to hold the device under test and manipulate it in two orthogonal axes. This paper explores some of the limitations and considerations involved in the use of traditional "RF transparent" support materials for mmWave device testing.
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