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Wireless communication is occupying new application areas all the time. Data intensive applications require high quality of services level. This emphasizes the need for better solution in every part of wireless communication. In spite of increasing requirements these components should be low priced and robust especially in industrial environments. All this set up an interesting and challenging framework for antenna design. The aim of this paper is to present parameters that have to be considered when new antennas are designed to harsh environments with strong multipath propagation. These parameters are demonstrated by measurements of phase error and attenuation in underground tunnel environment with a few different antenna designs including a new photonic bandgap design.
The automobile antenna industry is facing a rapidly growing trend leading to the incorporation of effective, low cost, conformal antenna designs. There are many situations where an omnidirectional azimuth pattern is desired for a conformal antenna on a vehicle. Conformal antennas, however, are typically restricted to mounting locations on the side of vehicles where the vehicle itself obstructs the signal. It is very difficult to obtain omnidirectional performance in these cases. A technique to substantially improve omnidirectionality of automotive conformal antennas is described. This technique is based on the use of dual symmetric antennas connected to a common junction point using equal length cables. Experimental results of implementing this technique using a dual sideUte film antenna on a commercial vehicle in the FM frequency band are presented. It is shown that the dual sidelite conformal antenna is an effective, low cost solution for achieving omnidirectional performance in FM automotive applications.
In this paper, we present an interferometric in verse synthetic aperture radar (IF-ISAR) image processing technique for three-dimensional (3-D) radar cross section (RCS) imaging of complex radar targets. A general bistatic 3-D imaging geomet ry and the corresponding 3-D image pro cessing algorithm which relates the interferomet ric phase to the target altitude are developed. The impact of multiple scattering centers on al tit ude image formation is discussed. 3-D RCS image formation examples from both indoor and outdoor test range data are demonstrated for complex radar targets.
This paper describes the alignment procedure for using a spherical near-field measurement facility to determine incident fields throughout a spherical volume. This information can be used, for example, to characterize an anechoic chamber or the quiet zone of a compact range. A probe is mounted on a standard roll-over-azimuth positioner and aligned looking out of the sphere so its aperture maps out the surface of a sphere. The probe measures the amplitude and phase of the fields incident on the sphere. This method differs from the standard spherical near-field measurement where the source antenna serves as the probe and is looking into a sphere containing the test antenna.
In this paper we discuss the experimental issues encountered in the measurement of the local electromagnetic fields in the reactive region of a scattering or radiating body using the NRL Near-Field Facility. Our investigations require high-resolution measurements, reaching spatial resolutions of small fractions of wavelength, high polarization sensitivity, and broad bandwidth. We present techniques currently successfully being used in these investigations. The complexity of the reactive zone fields imposes difficult requirements on probe designs. Currently, the NRL probes include coaxial and coplanar configurations. We will discuss their properties and characterization. Design trade-offs to reach spatial resolutions of one-tenth of a wavelength, bandwidths of several giga-hertz and limitations on polarization sensitivity will be addressed. We will correlate these observations with the results of the back-propagation algorithms being developed at the Naval Postgraduate School.
The accuracy of near field measurements have in the past largely been judged by inspection however the authors have developed an objective measure of the accuracy and repeatability of such measurements. This paper illustrates the measurement process and the techniques associated with statistical image classification used to confirm its accuracy and repeatability. The technique will be illustrated via the correlation of data sets acquired over a variety of different frequencies and scan plane areas. The examination of these measurements will demonstrate the applicability and sensitivity of the technique when the accurate assessment of highly correlated patterns is required.
A reconstruction method that calculates bi-dimensional equivalent magnetic currents from the tangential electric field components over a hemispherical region is presented. The method is applied for diagnosis as well as for near field to far Field (NF-FF) transformation. The method is well suited for antenna radiation pattern measurement using a near-field spherical acquisition system in anechoic chamber.
The angular coverage of planar near-field measurements is limited by the size of the scan plane, and the "region of validity" is defined by the angle between the edge of the AUT and the edge of the scan plane. In some applications, results are required over a larger angular region than is possible with the available scanner. The angular coverage can be increased by rotating the antenna and repeating the measurement. The results of the two measurements are then combined. Successful combination depends on using both the coordinate system and vector components that are appropriate for the antenna rotation. In general for a single antenna orientation, any coordinate system can be used with any vector components, but when combining or comparing patterns for two antenna rotations, the axis of rotation must be the polar axis and the vector components must correspond to that coordinate system. Measurements results will be used to demonstrate the proper choice of coordinates and components and to illustrate potential problems that may arise.
Microwave Instrumentation Technologies (MI Technologies) in cooperation with Hollandse Signaalapparaten B.V. (Signaal) and the Royal Netherlands Navy has designed and produced a compact antenna test range to specifically address the unique testing requirements imposed in the testing of active phased array antennas. The compact range was built specifically to test Signaal's new Active Phased Array Radar (APAR) prior to introduction into various naval fleets throughout the world. This reversible Compact Antenna Test Range (CATR) allows antenna testing in both transmit and receive modes. The measurement hardware is capable of testing both CW and pulsed waveforms with high dynamic range. In addition to conventional antenna pattern measurements the system is capable of measuring EIRP, Gff and G/NF, as well as providing analysis software to provide aperture reconstruction. A special Antenna Interface Unit (AIU) was designed and built to communicate with the Beam Steering Computer which controls the thousands of T/R modules which make up the APAR antenna system. A special high power absorber fence and other safeguards were installed to handle the transmit energy capable of being delivered from the APAR antenna system.
In order to reduce the cost of building compact range reflectors, a combination of a circular rim reflector and R-card fence can be used. Circular rim reflectors are commercially available at reasonable prices. The R-card sheets are also inexpensive. Since the R-card works as a fence to block/reduce the reflector edge diffraction from degrading the plane wave in the test zone, the manufacturing cost is very low. However, the design is much more difficult since the convex nature of the circular reflector rim diffracts more stray signal into the test zone. Thus, the R-card fence should be carefully designed all around the reflector rim. The optimum continuous resistance distribution is replaced by a discretized one to result in lower cost. The R-card design, that reduces the variations in the test zone for a reflector with a circular rim, will be presented in this paper. Calculated and measured results will be shown for the proposed design.
This paper is focused on a recent installation of a probe array for direct far-field. measurement. Such an array has been installed in a well-established compact antenna test range at CNES called BCMA in Toulouse, France. It describes the interests of using such multi-sensor approach for characterizing directive antennas within far-field conditions without any mechanical movements. The paper shows how this facility has been dimensioned for operating over frequencies ranging from 7 GHz up to 15 GHz. Performances and general descriptions of both the probe array and its associated instrumentation will be given. A specific calibration procedure that has been studied and implemented is discussed and finally preliminary results are shown.
Modern Satellite Antennas and Payloads are characterized by a lot of physical parameters like e.g. Radiation Pattern, Gain, EIRP, Flux Density, Gff and PIM, whereas the available time frame for measurements is getting shorter and shorter. The DSS Compensated Compact Range (CCR) allows a time efficient measurement of all payload parameters with high accuracy under controlled environmental conditions. The CCR consists of two doubly curved reflectors, which prevent inherent cross-polarization and create a very high constant amplitude and phase distribution in the quiet zone with a very good scanning performance. Most of the payload parameters can be measured directly or have to be calculated from a set of measurement values. For the G/T measurement of active antennas a new method for the noise power measurement was established. This paper describes the principle test set-ups with the corresponding measurement techniques to improve the measurement accuracy. Error budgets will be presented for pattern and gain measurement.
A compact range based measurement system for automotive radars is presented. The design driver for the system was production testing. Key characteristics of the system are: compact size, short test times, no need for an anechoic chamber, ease of operation, mobility and ruggedness. The measurement system is based on electronic equipment from Dornier GmbH, the company who developed the automotive radar for the new Mercedes S-Class. It uses a small rolled edge millimeter wave compact range from ORBIT/FR Europe GmbH. Some general characteristics of automotive radars are presented, followed by a more detailed description of the key subsystems of the measurement system: Simulator, Compact Range and Processing Control Unit. Finally some measurement results are presented and discussed.
An efficient algorithm for the RCS evaluation of the Monostatic Radar Cross Section (RCS) from a reduced set of bistatic near-field data is proposed. The algorithm allows to evaluate the monostatic RCS from near field data collected in an angular region centered on the direction of interest, whose amplitude depends on the size of the scatter and the distance of the measurement zone. Numerical examples on two dimensional elliptical cylinders show the effectiveness of the proposed technique.
A network model derived from a moment method solution can be used to form a physically meaningful basis set for an adaptive decomposition of measured scattering data. In recent years, EI has presented techniques for using the network model decompositions for several applications [1,2] including data interpolation, and multipath removal. However, for some applications such as target editing (analogous to image editing) and defect localization, the minimum norm solution, typically used with the network model, does not adequately localize scattering sources to be effective. The reweighted minimum norm (RMN) method [3] is a nonparametric approach by which the localization of the minimum norm solution can be improved by iteratively constraining the solution space in which the minimum norm is computed. In this paper, we will describe how the RMN method can be used in conjunction with the network model decomposition and demonstrate the improved localization properties.
Theory and experiments for a ground wave UWB radar system for human and vehicle detection will be shown. We will consider the case where the radar uses a low gain VP antenna located 20 to 40 cm above the ground and the radar target is a moving vehicle or moving humans out to 200 meters. The nominal frequency for these tests was from 1.0 to 3.8 GHz in a step frequency scan. We will show SIN predictions using the free space radar range equation, then add ground wave attenuation effects. We will then compare these predictions with experimental measurement data for various vehicles and humans. An application using a noise radar as a UWB spread spectrum radar system in this application is our final goal.
RATSCAT has been heavily involved, as part of the DoD Range Certification Demonstration Program, in examining and documenting the underlying principles of all aspects of the outdoor measurement process. Our goal is to replace historical or "anecdotal" measurement approaches with processes founded on validated and documented procedures. This paper reports on the results of two areas of study. These are the effects on measurements caused by wind and calculation of target rotation rates. When RCS targets are measured outdoors on pylons or columns, some uncertainty will be introduced due to the effect of wind on the target and target support structure. This paper will present the results of an investigation into the errors introduced by wind motion on targets mounted on pylons or columns. When rotation rates are determined for target collection, the usual procedure is to employ a rule of thumb like "collecting three points per lobe" or "meeting the Nyquist criterion." This paper examines these common methods to determining rotation rates, and their impact on the measurement of the peak values of RCS magnitude and phase. Finally, the significance of these two measurement errors will be examined in light of their impact on outdoor range operations as well as on decisions based upon the collected RCS data.
Uncertainty analysis for fundamental standards is mature, but the cost overhead has, until recently, prevented much of this work being taken up by the UK RCS measurement community. The requirement to verify the radar signature of new equipment has made it necessary to examine in detail the RCS measurement process and to create a methodology for error budgeting. The paper reviews some basic concepts in estimating uncertainties, and describes work on 'squat' cylinder calibration standards that have been manufactured following designs proposed at previous AMTA conferences. The moment method code CLASP has provided the basic theoretical solutions which have been verified on a compact range through reference to a precise 100mm spherical standard. The concept of multiple standard calibrations is discussed, and recommendations are made for overall error budgeting and the intercomparison of range types.
An interlaboratory comparison is made between radar cross section (RCS) measurements at the test ranges at FOA Defence Research Establishment and SAAB Dynamics, Sweden. The comparison is made in order to increase the measurement and calibration quality at the ranges. An analysis of the deviations in the measured RCS data from the ranges provides a better understanding of the sources of errors. The RCS of two generic targets are measured at the X-band. The targets are simple airplane models, length and width are approximately 1.0 m, with no cavities. A brief comparison between some theoretical results and experimental RCS data are also presented.
The U.S. Navy has considerable experience in the radar cross section (RCS) measurement of dynamic targets. An understanding of the possible error sources and their relative magnitudes is critical to obtaining accurate and repeatable results. In addition to the usual potential sources of error in RCS measurements of stationary items, considerations with dynamic targets include target range and angle tracking, calibration, and various environmental effects. The primary considerations are identified and discussed, and an error budget is developed for a particular test scenario.