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Spectrum is presently one of the most valuable goods worldwide as the demand is permanently increasing and it can be traded only locally. The United States FCC has opened the spectrum from 3.1 GHz to 10.6 GHz, i.e. a bandwidth of 7.5 GHz, for unlicensed use with up to -41.25 dBm/MHz EIRP. Numerous applications in communications and sensor areas are showing up now. Like all wireless devices these devices have an antenna as integral part of the air interface. The antennas are modeled as linear time invariant (LTI) systems with a transfer function. The measurement of the antenna’s frequency dependent directional transfer function is described. Furthermore the measured transfer function is transformed into time domain, where it is used to characterize pulseshaping properties of the antennas. Additionally, measurements in time domain, which were performed with a pico-second pulse generator and a 50 GHz sampling oscilloscope, are presented and compared to the transformed frequency domain measurements. These measurements enable the realistic characterization of ultra wideband antennas for UWB link level simulations.
The use of multimode antennas to aid problems of direction finding (DF) has been examined and shown to provide benefit over standard interferometric techniques [8, 9]. In this work, we consider the issue of performing the DF in an adaptive processing environment. This work examines the use of the ADaptive Estimation / detection for sPecific Tasks (ADEPT) algorithm [3, 4]. The ADEPT algorithm performs weight optimization by maximizing the Fisher Information Matrix (FIM) as a Figure of Merit. Previous work by the authors has sought to characterize and optimize spiral antenna configurations based on the FIM [1, 2]. Measured spiral antenna data is utilized to examine the relative capability of the algorithm with a 4-arm spiral multimode antenna.
In measurements performed on remote, outdoor antenna ranges operating in the HF (2-30 MHz) band, it is desirable to have a method by which the effective heights of the reference loop antennas used on the range can be easily double checked on-site. A technique is presented that is based on one used in the VLF/LF (10-300 kHz) band. In this method, the effective height of an unknown loop antenna may be simply and accurately measured without the need for specialized or cumbersome test equipment. Results and limitations of the technique are presented along with its application at the NUWC Fishers Island Antenna Range.
This paper presents advances in the instrumentation techniques that can be used for the measurement and characterization of antennas that are to be tested in a pulsed mode of operation. A digital filtering process is described which allows accurate measurements under a wide range of pulse conditions using a single receiver. A novel approach to achieving point-on-pulse measurements using receiver time-gating at the IF frequency is described. Measurements made using an Agilent E8360 PNA series Microwave Network Analyzer are presented as a demonstration of a practical implementation of these techniques.
The direction of arrival of multiple coherent electromagnetic signals can be determined by measuring the pattern of an antenna probe when it is rotated off its phase center and then exciting a synthetic array with the same geometry as the probe measurement points using the signals received in the measurement. The offset and angle of sweep, which defines the aperture size required for separating the waves, depends upon the resolution required. The sampling resolution must also fall within the Nyquist sampling criteria.
At a Department of Defense antenna measurement laboratory, an important measurement is the accurate measurement of gain for circularly polarized antennas. An additional requirement is that a wide population of engineers and technicians that do not spend a significant amount of time using the facility make the measurements as they test the antennas for their projects. The objective was to create a highly automated, accurate test structure that was easily used by visiting engineers to make high quality measurements. Consistency of results across the user population was a paramount requirement. This paper describes the instrumentation and software used to meet this objective. The paper describes basic measurement techniques, the exploitation of instrumentation capabilities to make the measurements, the software processing of the data and the graphical user interface that was developed to make the test process essentially a “one button” operation. Significant components in the test scenario were the ability to accurately collect data on a linearly polarized Standard Gain Horn in orthogonal polarizations without inducing errors caused by various axes of motion and to provide channel imbalance correction for the orthogonal channels of the instrumentation and range.
A continuous discussion exists in comparing the theoretical and measured performance differences of serrated versus rolled edge treatment for compact ranges. Since rolled edge reflectors are significantly more expensive, the price / performance trade off needs to be well justified. Such an evaluation is very application dependent. A large amount of measurement data has been published for serrated edges, and comparisons between serrated edge theoretical data and measurement data shows good agreement. However, only a very small amount of measuerement data has been published for rolled edge compact ranges. For evaluation purposes, ORBIT/FR built a rolled edge and a serrated edge compact range. Both were designed for 2 ft quiet zones and have equal focal length and offset angle. Measurement data was acquired for both configurations, and is presented here.
Instead of moving the antenna under test (AUT), it is possible to change the direction of arrival of the plane wave. This is done moving the feed horn in the reflector focal area. Scanning the feed antenna allows measurement of the AUT without moving it. This is useful in cases, when moving the AUT is difficult or even impossible. In the Compact Payload Test Range (CPTR) at ESA-ESTEC, the linearity of the scanning has been measured before [1] and scanning has been proven to be nearly linear (1%). What was not known, is that how do the quiet zone properties (amplitude and phase ripple) change during the scanning. It will be shown the basic properties of the quiet zone remained almost the same, but some other properties of the range were found.
Highly accurate antenna and payload measurements in antenna test facilities require highly accurate alignment and boresight determination. The Angle of Arrival (AoA) of the plane wave field in the quiet zone of the CCR Compensated Compact Range CCR 75/60 of EADS Astrium GmbH, installed at Alcatel Space in Cannes . France, has been measured using three different methods (optical geometrical determination using theodolites, Radar Cross Section (RCS) maximization, planar scanner phase plane alignment). The proposed paper describes the three methods and the performed measurement campaign and provides the correlation between the resulting angles via a comparison of the results. The achieved absolute worst case values of lower than 0.005° demonstrates the high level of accuracy reached during the campaigns.
A compact radar cross section (RCS) test range for scale model measurements is being developed. The test range is based on a phase hologram that converts the feed horn radiation to a plane wave needed for RCS determination. The measurements are performed at 310 GHz using continuous wave operation. A monostatic configuration is realized using a dielectric slab as a directional coupler. The main advantage of a scale model RCS range is that the dimensions of radar targets are scaled down in proportion to the wavelength. Therefore, RCS data of originally large objects can be measured indoors in a controlled environment. So far simple test objects such as metal spheres have been measured. The feasibility of the phase hologram RCS range has been verified. The basic operation and first measurement results of the monostatic measurement range are reported here.
This paper describes and discusses relevant performance issues concerning the quiet zone illumination of a baseline interferometer antenna using a compact range system. Typical baseline interferometer antennas are utilized for precision direction finding applications, and are designed on the principle of detecting the incoming phase wave front as a means to determine the direction of arrival of the detected signal. Quiet zone illumination of the antenna using a compact range deviates from the ideal illumination by introducing some levels of amplitude and phase taper and ripple. Unwanted relative differences in the illumination of the individual elements of the interferometer antenna will introduce errors in the subsequent analysis of the direction finding accuracy and precision of the array. Sources of these errors are examined in this paper, and relevant compact range performance trade-offs are discussed to optimize the range. Considerations are given to both utility of the range, as many interferometer antennas are broadband EW type arrays, and thus require single feed, single test broadband measurements, as well as to the accuracy in characterizing the performance of the interferometer over its full operating bandwidth. In addition, this paper discusses the analysis of high precision compact range field probe data, and the subsequent application of relevant statistical parameters to characterize the data. The analysis techniques utilized highlight the important performance features required of the compact range to effectively test baseline interferometers. The implementation of an automated utility is described that applies the relevant corrections, and applies the statistical algorithms, to the data to effectively reduce the data and summarize it in a fashion that provides immediate utility to the field probe test operator.
Shielded anechoic chambers have been extensively used to measure antennas for various applications. Recent proliferation of mobile telecommunications presented high demands for measurements of antennas that are used in mobile wireless handsets. Since antennas in mobile handsets are low-directive for better mobile links to base stations, they are capable of transmitting or receiving nearly all unwanted reflected signals from imperfections through various reflection and scattering paths in the anechoic chamber in addition to desired signal from the direct path during the measurements. The Quiet Zone (QZ) characterization method has to be re-examined. This paper presents measurements and analyses comparing the difference in chamber designs and verifications of anechoic chamber QZ’s. Through this development, design guidelines are provided to improve the anechoic chamber QZ signal-to-noise ratio for measuring low-directive antennas. Techniques derived from this requirement can also benefit for measurements of high sensitivity Radar-Cross-Section.
MTI Technology and Engineering Ltd. in Israel has installed an antenna test facility for the development and production testing of communication link antennas. Link antennas are typically high gain, medium size (< 2 ft) and medium to high frequency (10 to 50 GHz), with strict requirements on sidelobes, back-radiation and cross-polarization. Production testing is typically done on the main cuts. The facility is also used for PTMP and WLL antennas down to 2 GHz. This is an ideal requirement for a small size compact range. The ORBIT/FR single reflector compact range with a cylindrical quiet zone of a size 4 x 4 ft (diameter x length) was selected. The performance is compliant to international regulations (e.g. FCC, ETSI, DTI-MPT), and has a cross polarization as low as –40 dB for 0.4-m antennas. The total chamber size is 31 x 18 x 15 ft (L x W x H). The positioner system is roll over model tower over azimuth over lower slide. The instrumentation is Agilent 8530 based. The system was installed and qualified in late 2002. Qualification was performed from 2 to 50 GHz for quiet zone field probing and antenna sidelobe level accuracy testing. A system description, as well as an excerpt of the qualification data are presented in the paper.
This paper describes a family of new measurement systems, termed “test cells”, designed to satisfy the certification requirements of the Cellular Telephone & Internet Association’s (CTIA) “Method of Measurement for Radiated RF Power and Receiver Performance” test plan for wireless subscriber stations. These test cells employ simultaneous dual-axis mechanical scanning and operate in both far-field and near-field modes over the 750MHz to 6 GHz frequency range. Operation can be extended to higher frequencies through the use of suitable sampling antennas. Test cell facility configuration is detailed. Scanner layout and RF sampling antenna designs are discussed. Anechoic chamber characterization data is presented along with typical measured pattern and efficiency data for both broadbeam and directive AUT’s. Measurement test times for various test scenarios are discussed.
Specific Absorption Rate (SAR) constitutes a key issue for mobile phones. Indeed, SAR which represents the power per unit mass delivered in biological tissues must comply with existing standards. The averaged SAR required by standards can be deduced from the measurement of E-field distribution in a volume of biological phantoms, filled with a tissue equivalent liquid. Such a standard procedure is time consuming and rather incompatible with the rapidity required for developing new mobile phone models. This paper describes a new rapid SAR measurement approach based on near-field techniques. The use of a plane wave decomposition of the measured field in a plane allows the reconstruction of the electric field in the phantom from which the averaged SAR can be deduced. The combination of this approach a with probe array technology should bring real-time SAR measurements possibilities.
The performance of Bluetooth wireless technology can be enhanced by using antenna diversity. The Bluetooth diversity system using a two-branch switching method is presented in this paper. The measurement system was implemented and the performance was analyzed in terms of bit error rate and packet error rate. According to the results, the advantage of space diversity is found significant when two antennas are spaced by 1/3 wavelengths. The antenna increased throughput 3-5% compared with the single antenna case. Temporarily, the improvement was as high as 150% due to fading.
The Cellular Telecommunication and Internet Association has developed a ripple test measurement for qualifying the quiet zone of wireless pattern measurement systems for their Mobile Station Over the Air Test Plan. The data produced by this ripple test provides a very thorough characterization of the worst possible contributions to an antenna pattern measurement performed on the qualified system. However, the characterization represented by the maximum ripple significantly overestimates the ripple seen on typical pattern measurements produced by the qualified system, and greatly overestimates the actual uncertainty involved in the determination of integral quantities such as Total Radiated Power (TRP). In order to better account for the results of this test, a statistical analysis method referred to as the Surface Standard Deviation (SSD) has been developed to determine an expected uncertainty for surface integral quantities. This paper will present the background and formulation of the SSD method and show some typical results.
A novel structure for accurate measurements of antennas mounted on an infinite ground plane has been designed and built. The structure is eight feet in diameter and can be used to measure antennas as big as fourteen inches at the base at frequencies as low as 1 GHz. The structure is defined by blending a planar surface with an elliptical surface such that near the antenna under test the surface resembles a planar surface and then it slowly rolls back to minimize any diffractions due to discontinuities in the surface. Patterns of a few antennas mounted on the structure are presented and compared with the expected patterns of the antennas mounted on an infinite ground plane.
Preliminary investigations for cohering multiple apertures into a single distributed aperture were performed at the Georgia Tech Research Institute. Data were collected on complex targets in near realtime with two individual HP8510 Network Analyzer systems controlled by a single data acquisition computer as an interferometeric measurement. The data were analyzed and presented for high-accuracy angular resolution by examining the amplitude and phase difference between the two network analyzers. In addition, further upcoming tests on the Georgia Tech Research Institute far-field range will be outlined, showing how both measured angular resolution improvement and power-aperture gain product will be collected over a wideband frequency range.
Over the last decade there has been great interest in ultrawideband (UWB) communication systems. Ultrawideband antennas that are able to transmit or receive short pulses with no distortion are called Impulse Radiating Antennas (IRA). One of the most commonly used IRA.s consists of a parabolic reflector fed by conical transmission lines that propagate a spherical TEM wave. The reflector IRA was constructed, analyzed and measured at UCLA. A method of moments based software, Hybrid EFIE and MFIE Iterative (HEMI), is employed to simulate the antenna. The software has to be run many times for a wide frequency range. The simulation results for the current distribution on the conical coplanar feeds show that one of the arms can be used as an UWB balun and the unbalanced line can be connected to the antenna. The aperture field is studied by calculating the surface current on the reflector. These current distributions show that the aperture field is tapered from edge to center and the center part is less illuminated in comparison with the edges. This increases the side lobe level for reflector IRA. To measure the time domain characteristics of an IRA, we have to use either short pulses and a time-domain setup or many frequencies in a wide frequency band and use an inverse Fourier transformation to calculate the time-domain results. In this work, we used frequency domain measurement setup to measure the antenna characteristics. The recently constructed spherical near-field measurement chamber at UCLA is used to measure the radiation characteristics of the antenna. The far-field calculated from the near-field measured data is compared with the HEMI results. Calculated and measured results show good agreement.