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An error simulator based on virtual cylindrical near-field acquisitions has been implemented in order to evaluate how mechanical or electrical inaccuracies may affect the antenna parameters. In outdoor ranges, where the uncertainty could be rather important due to the weather conditions, an uncertainty analysis a priori based on simulations is an effective way to characterize measurement accuracy. The tool implemented includes the modelling of the Antenna Under Test (AUT) and the probe and the cylindrical near-to-far-field transformation. Thus, by comparing the results achieved considering an infinite far-field and the ones obtained while adding mechanical and electrical errors, the deviations produced can be estimated. As a result, through virtual simulations, it is possible to determine if the measurement accuracy requirements can be satisfied or not and the effect of the errors on the measurement outcomes can be checked. Several types of results were evaluated for different antenna sizes, which allowed determining the effect of the errors and uncertainties in the measurement for the antennas under study.
An estimator of the RicianK-factor for reverberation chamber is derived in this paper using maximum likelihood estimation approach. This is done by reviewing the existing statistical model of the fields in the reverberation chamber. The functionality of the derived K-factor estimator is tested with the measurement data for the well stirred and unstirred (only platform stirring) chamber. Moreover, the impact of polarization of the antenna on the Rician Kfactor is also investigated. The Rician K-factor is found to be almost zero for a well stirred reverberation chamber whereas it is higher for unstirred (only platform stirring) chamber. It is also observed that the orientation of half wavelength dipole influence significantly the K-factor values.
The near-field aperture distribution excited on the guiding surface of various planar leaky-wave antenna designs is examined. The investigated antennas (for millimeter wave applications) are realized by circular, straight and elliptical metallic strip gratings on a high permittivity dielectric substrate. With such straight and curvilinear grating configurations, analytical determination of the near-field, and hence the leaky-wave phase and attenuation constants along the guiding surface, can be mathematically intensive. To assist in such complex characterizations, the near-field/far-field extrapolation techniques can provide insight and thus illustrate such 2- D aperture field distributions. Specifically, by taking the inverse Fourier transform of measured 2D far-field beam patterns, the near-field distribution along the aperture can be estimated.
There is a desire for antenna technologies that will support surveillance needs in a complex Radio Frequency (RF) environment. There are many current technologies that support these needs, including individual components such as broadband phased array antennas, broadband RF components, and miniaturized digital receivers. A testbed has been established to develop systems combining these elements, resulting in wideband phased arrays encompassing multiple receiver channels and capable of forming multiple independent beams through digital beamforming. This effort revolves around phased array calibration and testing, RF component characterization, system integration, system testing, and digital beamforming. The Transformational Element Level Arrays (TELA) Testbed allows for the integration of these technologies so that they can be tested and verified as a system. What will be described here is recent and current work taking place in this testbed. Some of this work includes system integration and testing and subsequent digital beamforming of a four-channel recieve system. Also included is the calibration process of an 8:1 bandwidth, 256-element phased array, and integration and testing of the 16-channel recieve system corresponding to this array.
The purpose of the nose radome has changed over the past twenty or so years. As the antennas and electronics become more sophisticated the radome becomes more important to the overall system performance. Electrical testing of the radome has become a necessary part of the radome repair process. In addition to Transmission Efficiency, radome test facilities must also test Boresight Error, Reflections, Sidelobes and Polarization. Radome repair is also becoming very sophisticated. As the performance expectations of the radome increase, the difficulty in making an electrically transparent repair increases significantly. This paper is a general overview of the radome testing process, range requirements that make radome test ranges unique from antenna test facilities. This paper also shows some examples of good and bad repair techniques and their effect on electrical testing.
Measurement of the antenna pattern of the Haystack Auxiliary Radar (HAX), an experimental Ku band radar system developed by the Massachusetts Institute of Technology Lincoln Laboratory for deep space experimentation, was recently carried out utilizing a ground based, mobile recording system. The HAX radar system uses a 12.19 m parabolic antenna placed inside of a radome which is located on Millstone Hill in Westford, Massachusetts. The recording system, which includes a Ku-band analog front end and a high-speed digitizer with 500 MHz instantaneous bandwidth and long duration recording capability, was located at the summit of Mt. Wachusett, 36.1 km southwest of HAX. Several azimuth and elevation antenna pattern cuts were acquired by transmitting towards a wide-band ground based recording system placed down range while rotating the HAX antenna. Throughout these pattern measurements the radar was operated in a reduced power pulsed CW mode. Continuous wide-band recordings from the slowly scanned pattern measurements were taken and the data was processed to detect individual pulses, retaining only the portions of the recordings containing detected pulses. Post-processing of the pulsed CW data allowed for measurement of the antenna pattern with a significant dynamic range, characterizing both the mainbeam of this antenna and the far-out sidelobes.
Electromagnetic Anechoic Chamber has recently been built by Alenia Aeronautica at Caselle South Plant: The Anechoic Chamber is a full anechoic chamber, and it has been designed to carry out electromagnetic vulnerability tests mainly on fighter and unmanned aircraft. In addition measurement can be carried out on many different vehicles that can be brought into the chamber through the main access door. A system to extract exhaust gas was installed in order to carry out tests on a wide variety of vehicles. The Anechoic Chamber has been designed to carry out both HIRF/EMC test and High Sensitivity RF measurement: in particular HIRF/EMC tests in the frequency range 30MHz ÷ 18GHz with the capability of radiating a very high intensity electromagnetic field and High Sensitivity RF measurement, including antenna pattern measurements on antennas installed on aircraft in the frequency range 500MHz ÷ 18GHz. During the design phase a 1/12th scale model of the chamber had been fabricated to assess the desired electromagnetic performance. In this phase of design the model was tested at the scale frequencies for Filed Uniformity, Site Attenuation and Free Space VSWR results. This study was published at the AMTA 2004 meeting. In addition to the physical model, during the construction phase, various computer simulations were performed to further define the detailed internal absorber layout and to define test acceptance methods for procedures not covered by the standards. The computer model analysis was conducted to identify areas of scattering that could be treated with higher performance absorbers to improve the chambers quiet zone performance. The identified “Fresnel Zones." have been treated with high performance absorbers optimized to provide improved performance at microwave frequencies. The absorber optimization was reported at the AMTA 2006 meeting. This optimization has allowed validation of the chamber according to the requirements of CIRSP 16-1-4 2007-02 in the range of frequency 30 MHz - 18GHz. The size (shield to shield) of chamber is 30m wide, 30m long and 20m high, and the 18m wide by 8.5m high main door allows the SUT access. The shielded structure is a welded structure of 3mm-thick steel panels which guarantees shielding effectiveness of more than 100 dB in the frequency range 100 kHz to 20GHz. The chamber includes a 10 meter diameter turntable to rotate a 30 ton SUT with an angular accuracy of ± 0.02° and a pathway to allow SUT access. Both the pathway and the turntable are permanently covered by ferrite tiles. A hoist system permits lifting of the SUT (max 25 tons) up to 10 meters from the turntable centre enabling EMC testing on aircraft with the landing gear retracted.
Wireless network adapters are now standard in most notebook computers. These network adapters are typically compliant with at least IEEE 802.11a/b/g and often include IEEE 802.11n. This requires that the antenna subsystem of the notebook computer operate at both 2.4 GHz and 5.25 GHz. The antennas used in the wireless system of a notebook computer are themselves small, but they are incorporated into a much larger device. It is unclear exactly what range length is required in order to make accurate pattern and radiated power measurements. This paper reports on a series of measurements made at different range lengths with the goal of determining the minimum range length required for acceptable measurements of radiation patterns and total radiated power (TRP).
Advantages of Far-Field (FF) anechoic chambers utilized for antenna measurements, as compared to conventional outdoor ranges, such as security, interference-free radiation, and immunity to weather conditions allowing broadband antenna measurements on a 24/7 basis, are well known. The dimensions of an anechoic chamber are primarily determined by the lowest operating frequency and are, therefore, significantly increased if operation is required down to VHF and UHF frequency bands. As a result, the advantages of indoor chambers are often disputed when considering low frequency applications. The main counter-argument is the real estate required for chamber construction. In addition, such chambers require the use of high performance absorbing materials, and consequently, chamber certification is always a challenging task. Therefore, rigorous and accurate 3D EM analysis of the chamber is an important procedure to increase confidence, reduce the risk associated with achieving the required test zone performance, and to make the design more efficient. Thus, an accurate simulation of the chamber is even more important these days due to a dramatically growing number of antenna manufacturers supplying products at VHF and UHF bands. Such analysis is a standard procedure at ORBIT/FR, and is described below for the example of a chamber with dimensions of 6m (W) x 6m (H) x 10m (L), operating down to 150 MHz.
NSI’s MARS technique (Mathematical Absorber Reflection Suppression) has been used to improve performance in anechoic chambers and has been demonstrated over a wide range of frequencies on numerous antenna types. MARS is a post-processing technique that involves analysis of the measured data and a special filtering process to suppress the undesirable scattered signals. The technique is a general technique that can be applied to any spherical or far-field range or Compact Antenna Test Range (CATR). It has also been applied to extend the useful frequency range of microwave absorber to both lower and higher frequencies than its normal operating band. This paper will demonstrate the use of the MARS capability in evaluating the performance of anechoic chambers used for spherical near-field measurements, as well as in improving chamber performance.
Previous AMTA papers have discussed pulsed antenna measurements and the importance of parameters such as pulse width, pulse repetition frequency (PRF) and receiver dynamic range in determining the appropriate technique for performing pulsed measurements. Typically, the pulse width and PRF determine the IF bandwidth required of the instrumentation receiver to achieve a specific level of receiver performance. Less emphasis has been given to the receiver timing and synchronization required to achieve optimum performance for a full pulsed antenna measurement scenario. This paper will discuss receiver timing considerations and show examples of scan time performance during high-speed pulsed measurements. Inter-pulse and intra-pulse measurements will be compared with respect to their impact on measurement time. Pulse profile measurements will be examined to show the importance of a fast synchronous receiver for sub-microsecond pulse characterization. Pulsed antenna pattern results will also be presented and compared with CW measurements.
The development and implementation of the radome measurement Range 12 at the Raytheon Advanced Product Center, (APC) indoor range complex at McKinney, Texas will be covered. A cooperative relationship between Raytheon and the vendor allowed the realization of a very demanding set of requirements to be built, installed, and verified. Very precise simultaneous multi-axis motion was achieved. Range performance after installation was verified with planar probe techniques pioneered by another vendor. Repeatability studies with antenna removal, radome placement, and RF drift have been performed to verify long-term stability. All of this brought up a number of lessons learned resulting in better reliability and improved knowledge for the next implementation.
This paper describes the development of a test procedure for OMNI directional antenna pattern measurements in Compact Antenna Test Facility (CATF). This study is also of importance as it was presumed that OMNI directional antennas can not be tested in ISAC-CATF due to reflections coming from high-rise metallic structure of DUT positioner. As in ISAC-CATF, DUT positioner is not at all covered with the RF absorbers. Further, effect of Spacecraft body on radiation pattern is also studied. In addition to that effect of high-rise metallic structure of DUT positioner is also presented. It was observed that due to spacecraft body ripples were generated in the radiation pattern of OMNI directional antenna. It was also observed that effect of high-rise metallic structure of DUT positioner was not as significant as of Spacecraft body. At the end of this study, to exactly simulate the integrated spacecraft level condition a 33 dB coupler was connected at antenna output port and measurements were performed with the help of coupled port. Those results are also presented in this paper.
A probe-compensated near-field-to-far-field transform algorithm has been developed that can generate far-field patterns from near-field measurements made on an arbitrary surface. We present the concept, the algorithm, and computer simulated and measured test results for measurements on a conical surface. The prototype conical near-field measurements were made in a planar near-field range on a horn antenna under test (AUT) mounted on an azimuth-over-elevation positioner to produce a conical measurement surface. This system is especially applicable for producing full-hemisphere far-field patterns for antennas mounted on vehicles where other standard measurement systems may not adapt to the profile well, may not provide full-hemisphere coverage, or may require large, mechanically complex systems.
This paper presented a theoretical and numerical investigation of the performance comparison of Compact Antenna Test Range (CATR) equipped with Hybrid and Super Hybrid modulated serrations. The performance of the quiet zone will be degraded for a traditional CATR without both an edge treatment of the reflector antenna and a high quality anechoic chamber. Usually, the ripples in both the phase and magnitude of the field intensity inside the quiet zone are caused by stray signals, which come from edge diffraction. In order to solve the edge diffraction problems, edge treatments such as a different shaped serrated edge are often applied along the edge of the reflector antenna. The quiet zone field analysis of such reflectors has traditionally taken the form of ray tracing using numerical integration of the reflector surface currents called physical optics (PO). PO technique is used to obtain Fresnel Zone field of a plane square aperture embedded with a hybrid and super hybrid serrated CATRs. It is observed that super hybrid serrated CATR gives lesser ripples and enhanced quiet zone width than hybrid serrated CATR.
The measurement of the dielectric constant of a sample of unknown material is the sort of measurement that occurs frequently in the laboratory environment. At low frequencies, simple methods are well established, such as the parallel plate method. However at microwave frequencies, the methods for measuring the dielectric constant can be cumbersome and often require accurate knowledge of the dimensions of the sample being tested and the fixture used, as in the case of the well-known perturbation method. This paper shall present some observations on a simpler method based on a modest sample of the unknown dielectric material. The method employs a rectangular waveguide fixture in which the portion of the waveguide containing the sample to be measured is deliberately narrowed to half the guide width in order to increase its cutoff frequency. It turns out that this approach yields a measurement method that is insensitive to the length of the sample and that allows accurate determination of the real portion of the dielectric constant.
This paper presents the methodology for performing the measurement of the effective area of a passive RFID tag antenna. Measurements were completed in the Giga-Hertz Transverse Electromagnetic (GTEM) cell using RFID reader and tags operating in Ultra High Frequency band. The measured results are reasonable with respect to the effective area of a half-wave dipole.
This paper presents a novel method to evaluate very small stray signals in compact range. The ripples of signals probed by an omni-directional antenna along the orthogonal direction of the bore sight could be treated as signals in time domain. Transforming the probed data with fast Fourier transform (FFT), the direction and amplitude (relative to the test signal) of each stray signal could be obtained. To improve the accuracy, time domain software gating should also be used in calibrating the measurement error of amplitude and phase. The presented method has the ability to measure very small stray signals with good angle resolution. The method has been tested by both simulation using MATLAB and experiment in the compensated compact range CCR120/100 in CAST using a monopole antenna centered on a circular ground plane as a probe. Good results were obtained.
Traditional passive antenna measurements result in well-known quantities like Directivity, Efficiency, and Gain. However, when testing over-the-air (OTA) performance of active devices, there are additional effects that cannot be lumped together as part of the antenna performance. Terms like gain and efficiency are defined based on transmit or receive signal levels at the antenna port relative to the radiation pattern of the device. Thus, OTA performance is often assumed to be equivalent to the conducted performance of the device combined with the passive radiation pattern. However, when that antenna port is attached to an active radio in a typical wireless device, interactions between the circuitry and the antenna can produce results that do not match that predicted by the conducted performance and the passive radiation pattern. The difference between the predicted and actual performance of a device can be quantified in terms of "interaction factors", which represent the often non-linear behavior of the active circuitry when operating in an OTA environment. These factors include such effects as variation in amplifier gain due to heating caused by antenna mismatch, and receiver desensitization due to platform noise that couples through the antenna of the device. This paper will discuss the concept of interaction factors and define a number of sub-components of these factors that may be useful in predicting the level of some interaction factors.
This paper presents the results of an intensive investigation for trading off size vs. frequency for a large bandwidth antenna. Theoretical limits were established to determine minimum size as a function of gain and frequency. Bandwidth for the antenna developed was 50 MHz to 2000 MHz; stimulation was done with 50 ohm input impedance. The antenna broadband elements were located in a unique cavity, 6 inches in depth and 15 inches in diameter. The unique ground plane was composed of a combination of a Ferrite Region and Perfect Electric Conductor region which was implemented using Silver particles embedded in MEK. The cavity was fabricated using Carbon Composites to reduce weight. FireFly Opus antenna is in the testing phases.