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Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS) are the two metrics most commonly used to characterize the over the air (OTA) performance of a wireless device. Measurement of these quantities requires a reference measurement of the loss from the origin of the spherical coordinate system to the power measurement device. Calibrated dipoles are typically used as gain standards for the reference measurement. These narrow bandwidth dipoles can provide low uncertainty reference measurements, but numerous dipoles are required to cover all of the wireless frequency bands. Since typical wireless measurement systems must be calibrated from 700MHz to 6GHz, calibration of the measurement system with narrow bandwidth dipoles becomes a tedious and time-consuming exercise. Broadband gain standards can be used, but due to the uncertainty in their absolute gain and their interaction with the measurement system, these add uncertainty to the reference measurement. This paper reports on a broadband gain standard and a measurement procedure that allow an extremely fast reference measurement while at the same time does not appreciably increase the uncertainty of the reference measurement.
Modern vehicle telematics subsystems often employ wireless interfaces. The design and evaluation of these subsystems involves measurement of antenna characteristics or Over-The-Air (OTA) performance of the subsystem as installed in a vehicle. Several subsystems servicing multiple user applications may be installed in a single vehicle, with antenna structures located anywhere on or within the vehicle. In general, the radiation characteristics of each subsystem must be measured over a partial spherical surface surrounding the vehicle and of sufficient radius to be outside the reactive near-field of the Device Under Test (DUT). This paper describes a distributed axis spherical scanning system designed for vehicle applications. The elevation axis which supports the probe antenna has a measurement radius of 25 ft (7.62m). The elevation positioner is supported on a hydraulic vertical lift axis to permit the adjustment of the measurement coordinate origin to be in the same horizontal plane as the DUT phase center. The measurement instrumentation system supports VNA based antenna pattern measurements or active OTA testing of telematics subsystems. The system is suitable for outdoor or indoor measurement facilities. An outdoor installation is described.
The Georgia Tech Research Institute (GTRI) performed modeling and measurements for the problem of using multiple antennas on a platform with crew locations. GTRI personnel analyzed the electromagnetic compatibility/interference between multiple antenna systems on the platform by modeling the electromagnetic (EM) fields with Method-of-Moments (MOM) and Physical Optics/Uniform Theory of Diffraction (PO/UTD) modeling methodologies. Power densities were generated with the model at various crew locations on the platform and compared with the appropriate radiation hazard standard. Following the modeling effort, power density measurements were performed on the multiple antennas at various crew locations. The measured results were compared with the modeled results and the radiation hazard standard, and samples of both results are presented. In cases where measured and modeled data results do not agree to within the measured data error budget, the model and modeled data results were re-analyzed for errors. Updated modeled data results were generated and compared with measured data results, with the updated results presented.
We present an innovative Near-Field test range, named Compact Near-Field (CNF) test range, using photonic probes and advanced Near-Field Far-Field transformations (NFFF). The photonic probe allows distances of one wavelength or less between AUT and probe, drastically reducing test range and scanner dimensions, improving the Signal to Clutter Ratio and the Signal to Noise Ratio, and reducing the scanning area and time. The NFFF, properly formulated as a linear inverse problem, further improves the rejection to clutter, noise and truncation error. The advantages of CNF test ranges are numerically foreseen and experimental results are presented under both, planar and cylindrical scanning geometries.
In this paper, we consider the dynamic RCS signature measurement challenges for target signals in clutter. A clutter rejection technique is presented that relies on target motion to isolate target returns from clutter. While some clutter rejection techniques rely on generating a background map, this technique does not require measurement of background clutter. Therefore, it is particularly useful for scenarios where background data are not available or background clutter cannot be measured independent of the target. This clutter mitigation technique utilizes Range-Doppler processing over a coherent processing interval incorporating a one-pole or two-pole filter to minimize processing delays. Data from a “Moving Target Simulator” demonstrates that without clutter rejection, targets are completely buried in clutter and accurate RCS measurements are impossible. Implementing the clutter rejection filter allows target trajectories to be clearly identified, further enabling target range gating and accurate RCS measurements.
Bipolar planar antenna measurements have been used as an alternative to other planar scanning techniques such as plane-rectangular or plane-polar scanning. Bipolar scanning features important advantages such as the elimination of linear motion in measurement, increased stability, compact footprint, and a variety of data acquisition modes. The most rapid data acquisition mode for planar measurements overall, depending on range implementation, is the linear spiral sampling mode. This technique involves simultaneous incrementation of both the radial and azimuthal positioners to create a data grid in a spiral configuration. Data sampling and interpolation for linear spiral sampling has been obtained previously through rigorous development and modification of bipolar sampling requirements and interpolation techniques [1]. Implementation of the continuous linear spiral technique is not a trivial task. Positional program requirements require non-uniform acceleration and velocity for each axis. Data acquisition requires precise synchronization of both positional and RF equipment. Finally, post-processing is complicated by the inherent nature of a linear spiral data grid. This paper will describe, in detail, the implementation of the linear spiral technique with our portable millimeter-wave bipolar planar measurement system with emphasis on the issues mention here. In addition, measurements of a 31GHz rectangular patch array using both the conventional bipolar and linear spiral techniques are compared for both measurement time requirements and pattern accuracy. The continuous linear spiral technique has shown a significant measurement time reduction and has shown excellent agreement with results obtained in comparison to previously implemented stepped spiral measurements.
As antennas become more complex, their test requirements are also becoming more complex, requiring more data to fully evaluate the performance of today’s modern antennas. At the same time, competition and time-to-market concerns are driving the need to reduce the cost of test. This places stringent demands on our test facilities, personnel, and resources. To be competitive, new and creative ways are needed to meet these new demands. Fortunately, technology is changing, and these advances in technology if properly applied, can provide a way to reduce total test times and increase the productivity of test ranges. This paper will look at this new technology and examine how it can be applied to antenna measurements to significantly reduce measurement times. This paper will describe new technology features applicable to antenna/RCS measurements, configuration diagrams, typical antenna/RCS measurement scenarios, and measurement time comparisons for the different measurement scenarios. This will allow antenna test professionals to determine the measurement time reductions and productivity gains that can be achieved for their specific measurement ranges and test scenarios.
The Phaseless techniques have gained considerable attention during the past two decades in the antenna measurements community. The removal of the phase measurements has some immediate advantages over the common vectorial measurements. They are cost effective, well-adapted for higher frequencies and insensitive to phase instabilities. Recent advances in the near-field phaseless antenna measurement techniques have provided cost-effectiveness and robustness. A potential drawback of these techniques is the necessity of two-plane amplitude measurements in comparison to the standard one-plane near-field amplitude and phase measurements. This additional second-plane phaseless measurement typically requires longer overall measurement time. Consequently it is desirable to speed up the phaseless measurements by some means. The linear spiral measurement technique is utilized with the planar phaseless measurements to characterize a high directive circularly polarized reflector antenna. This spiral measurement scheme provides noticeable reduction of the measurements time while retaining all of the advantageous of the phaseless technique. A circularly polarized offset reflector antenna is measured in the UCLA bi-polar facility in the linear spiral mode to assess the applicability of the proposed scheme.
As antennas become more complex, their test requirements are also becoming more complex, requiring more data to fully evaluate the performance of today’s modern antennas. At the same time, competition and time-to-market concerns are driving the need to reduce the cost of test. This places stringent demands on our test facilities, personnel, and resources. To be competitive, new and creative ways are needed to meet these new demands. Fortunately, technology is changing, and these advances in technology if properly applied, can provide a way to reduce total test times and increase the productivity of test ranges. This paper will look at this new technology and examine how it can be applied to antenna measurements to significantly reduce measurement times. This paper will describe new technology features applicable to antenna/RCS measurements, configuration diagrams, typical antenna/RCS measurement scenarios, and measurement time comparisons for the different measurement scenarios. This will allow antenna test professionals to determine the measurement time reductions and productivity gains that can be achieved for their specific measurement ranges and test scenarios.
This note highlights the connection of antenna gain to the measurement of insertion loss based on established SNF formulations, relating directly among antenna transmission coefficients, antenna gain, acquired SNF raw scan data and the parameters acquired during a range insertion loss measurement. It shows how the measured insertion loss parameters are applied in normalizing raw SNF scan data in determining antenna gain.
This paper presents the methodology to generate a pseudo time domain holography from frequency swept measurements. This is an approximation to the time domain holography (TDH) invented by the authors [1,2], which opens a new possibility for antenna diagnostics using conventional instrumentation and in the absence of time domain measurements. Practical examples using two spaceborne antennas are provided and discussed.
RCS measurements of two larger squat cylinders (with dia. 18” and 15”) have been studied. Numerical extrapolation from the best available MoM-simulation is used to generate the finer oscillations (< 0.1 dB) in RCS-PO at higher frequencies. Though the uncertainties at 0.4 dB would obscure the opportunity for a comparison at this time, a smoothly silver-painted surface did yield error bars at 0.2 dB for the Ku-band.
A compact antenna test range has been analysed for stray signals. The analysis is based on GTD ray trac-ing, i.e. obeying the reflection law in the chamber walls and assuming straight edges of reflectors and walls. Comparisons to an RCS as well as a time-domain measurement of the quiet-zone performance show good agreements with respect to identification of the ray paths of the stray signals. Rough estimates of the power loss at reflections and diffractions show acceptable agreements with the measured levels.
The electromagnetic field within a test volume can be determined by use of spherical scanning techniques. Characterization of the field within the sphere requires compensation for probe-pattern effects. We provide a simple analysis to estimate uncertainties associated with this deconvolution.
One means to measure the G/T of a large antenna compares its response with a smaller antenna that can be carefully calibrated. Both antennas are illuminated by a common signal source. The G/T response of this technique is derived and contrasted with the commonly used radio source technique. Two alternative approaches to performing the comparative measurements are described and an error budget methodology to determine measurement uncertainty is discussed.
In the last ten years, coordination and networking of Antenna Research in Europe have been greatly influenced by the scientific strategy and policies of the European Union and in particular by the recent "Framework Programmes" FP6 and FP7, launched by the European Commission. Doubtless, there are still relevant R&D programmes at the national level and, obviously, the key European industries and companies continue to perform internally funded (and frequently confidential) research and development on antennas. But there is a clear trend now to put together the expertises of the different actors from all the European countries (industry and academia) and perform mid-term or long-term research within large international groups. The Networks of Excellence (NoE) and the European Cooperation in the field of Scientific and Technical Research (COST) are two of these European Research funding instruments and the European Antenna Community has managed to be present in both.
This paper describes some of the activities developed in the Working Group 4: “Measurements and Characterization, Technological Issues” of the European COST Action IC603 ASSIST (‘Antenna Systems and Sensors for Information Society Technologies’) in the frame of European research cooperation during its first year of working. During this time COST IC0603 – WG4 has been the unique framework for European research cooperation in the field of Antenna Measurement from the ending of EU Network of Excellence ACE (Antenna Centre of Excellence) until the beginning of the professional organization EurAAP (European Association of Antennas and Propagation). The paper outlines the activities of such WG4, mainly those presented in the COST IC0603 Workshops held up to now.
Prior to modern computer-aided measurement techniques all measurements were made with analog procedures that required the personal attention of measurement professionals. Modern techniques rely on careful set-up involving standards, and the test equipment applies error correction based on these standards. How-ever, there is an over-reliance on computer-based measurement equipment to do all of the thinking, leading to inappropriate use of these techniques, in turn leading to large, unsuspected measurement errors. This paper analyzes a situation wherein a network analyzer was used to isolate radome insertion loss from a combination measurement. The procedure used led to gross errors indicating gain in a passive device. The source of these errors is identified as an incorrect referencing procedure used to isolate radome characteristics from the combined antenna-radome characteristics. This error is common and applies to an entire class of measurement problems.
The extension of the frequency range for commercial applications of mm-waves to 80 GHz and beyond often requires extended antenna characterization capabilities both at manufacturer and end-user facilities. Presently, most measurements are based on direct measurements using vector network analyzers (VNAs). VNAs that cover a continuous frequency range up to 67 GHz are commercially available. Above 50 GHz, extensions based on external mixers in waveguide technology are typically utilized. They require a tunable local oscillator (LO) that is usually provided by the two additional ports of a 4-port VNA. However, these extensions not only are restricted in bandwidth but also require a significant financial investment especially considering the fact that the expensive 4-port instrumentation is needed. As most laboratories already have conventional 2-port VNAs usable up to 10 GHz or higher and most antenna characterizations are based on transmission measurements, we present a simple extension scheme based on external mixers and a fixed frequency LO that allows for transmission factor measurements. We demonstrate the feasibility of such an extension scheme for transmissions between a pair of horn antennas ranging up to 60 GHz. The measurements include variation of antenna spacing and steering angle and are verified with a computational analysis based on the finite differences time-domain (FDTD) method.
The Noise Radar (actually an ultra-wide band (UWB) spread spectrum radar) is a radar that generates a very wide band pseudo-random waveform and (optionally) up-converts the waveform to a desired microwave frequency spectrum. The bandwidth may be more than 5 GHz. The digital system generates a pair of GHz bandwidth pseudo-random waveforms. The two waveforms may either be identical or the pair of waveforms can be specially designed to be matched to the radar target and its environment. The first waveform is transmitted without a carrier, or it may be up-converted to a high microwave frequency. On receive; the second waveform is cross correlated with the received signals. Specific design of the two waveforms is possible so that the cross correlation coefficient forms an optimized peak for a particular target or class of targets, or to maximize the difference in the response between clutter and targets of interest. A design where a multi-GHz waveform is generated using a FIFO chip and a serializer chip will be developed. Construction of this radar and sample data will be shown. Detection range versus Doppler images will be presented.