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This paper describes how Radio Frequency Identification (RFID) utilizes typically backscattering communication between reader unit and transponder. In passive UHF RFID system the transmitted electromagnetic wave must propagate two times thru the medium. The level of moisture changes electromagnetic properties of medium and the electromagnetic properties of medium have effects on quality of backscattered signal [1]. The well-known fact is that the demand for item level RFID tag will face challenge of different packing materials. However, environment where some parameter such as humidity and temperature changes a lot, will be a great operational challenge for future RFID systems as well. In this paper we have used one application and present measured result how different moisture levels effects for passive UHF RFID operational main parameters such as threshold power level and level of backscattered signal.
We examined the electromagnetic emissions, and performance of commercial High-Frequency (HF) proximity Radio Frequency Identification (RFID) systems including their susceptibility to jamming and eavesdropping. These proximity RFID systems are used in an increasing number of financial, identification, and access control applications. We performed investigations of whether transactions can be detected and read at a distance. The measurements were performed to determine the power radiated by commercial systems and how they performance in adverse electromagnetic (EM) environments.
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.
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.
A plane wave generator [1] is of interest in many applications such as the testing on complex and large structures, f.i. the testing of the aircraft-integrated electronic components, or in the characterization of large antennas by means of Compact Antenna Test Ranges (CATR). In these applications it is required to generate a plane wave field in a prescribed volume V in the near zone of the source, disregarding the field behaviour outside V. Concerning the first application, new ideas have been recently introduced in [1] by considering a (highly integrated) Plane Wave Synthesizer (PWS), wherein arrays of radiators are used as electromagnetic sources and are optimized to generate the required plane wave field in a prescribed region. On the other side, standard CATRs, usually made by means of large and expensive reflectors or lens, can be substituted by suitably designed PWS to avoid their main drawbacks caused by diffraction, blocking effects and mechanical tolerances.
Methods for measuring the gain of an antenna at low frequencies (i.e. below 30 MHz) operating at or near the surface of the ocean on an open-air antenna range have been considered and reported previously. These methods employ a groundwave correction approach and a virtual reference antenna consisting of an idealized quarter wave monopole. However, this approach is not appropriate for application at the shorter wavelengths that occur in the VHF band owing to a variety of factors. In this paper, we shall discuss some of the issues associated with the use of the more conventional substitution method for measuring the gain of an unknown antenna that is operating near the air-sea interface. Issues and challenges related to instrumentation, antenna siting, range assessment, multipath effects, and reference measurements shall be considered.
Currently there is a lack of facilities capable of measuring the full upper hemisphere radiation patterns of antennas mounted on an infinite ground plane. Measurements performed with a finite ground plane suffer diffraction interference from the truncated edges. To circumvent this problem, a new measurement setup was developed at the Ohio State University ElectroScience Laboratory (ESL) for fully characterizing upper hemisphere radiation gain patterns and polarization for antennas up to 4” in diameter from 1-18 GHz. A probe antenna is positioned 46” away from the antenna under test (AUT). The ground plane end diffractions are removed using time-domain gating. The key design consideration is to position the probe antenna in the far-field region and yet shorter than the radius of the ground plane. This paper will present the calibration procedure necessary for the measurement system and it’s limitations due to ground plane probe antenna coupling at low elevation angles. In addition, the complete radiation pattern of a 4” monopole measured from 1-5.5GHz to demonstrate the systems capability for the lower third of the systems operating frequency range.
Vector Network Analyzers (VNA’s) are finding increasing utilization in antenna measurement ranges. At the same time, complex measurement scenarios involving many data channels in the antenna under test along with integration to beam steering computers for phased array antennas require management of the data collection beyond the VNA. Traditional methods have added control cards in the measurement control computer, increasing software complexity and reducing measurement throughput. The MI-788 Networked Acquisition Controller is designed to manage the hardware handshakes between position controllers, external sources and VNA’s, control up to 16 channels of multiplexed data from the antenna under test and/or interface with a beam steering computer. The MI-788 tremendously increases system throughput, particularly in these more complex measurement scenarios by removing real time data collection responsibilities from the measurement control computer. In addition, this unit makes all instrument communication Ethernet based, eliminating the spacing and operational limitations of GPIB based measurement systems. This paper will describe the operation of the MI-788 and demonstrate the increased measurement capabilities while using VNA’s in antenna measurements.
This paper gives a detailed account of free space Voltage Standing Wave Ratio (VSWR) method. We first review the formulations and terms commonly used in this method. We then discuss errors involved in its direction determination of extraneous signals, contrasting them among plane wave, spherical wave and specular reflection. We highlight issues relating to its application in anechoic chamber electromagnetic performance. Also discussed is the practice of data processing through analyzing a measured VSWR pattern.
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.
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.
A device and algorithm of measuring of microwave airborne radar antenna impedance and input power level are presented. A compact five-port microwave reflectometer, p-i-n diodes switch, single microwave detector are used. The output detector signal is processed. All of that results in decreasing of the cost of equipment, elimination of instrument components non-ideality and reaching of high equipment accuracy.