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Most measurement instruments being terminated by unbalanced ports, the measurement of a balanced antenna’s radiation characteristics is generally done using balanced to unbalanced transformers (baluns). These circuits are lossy, cumbersome and generally narrowband thus introducing added measurement imprecision. In this paper, we present a novel method for measuring differential antennas’ radiation characteristics by using traditional RF instrumentation, without the use of baluns. By regarding the differential antenna as a two port device, we can obtain the radiation characteristics of the differential mode from the measurement of the radiation characteristics and the scattering parameters of the single access fed two-port antenna. A theoretical study, based on the superposition principle, establishes equations that allow the passage from the single access feed mode to the differential mode. This method is validated by comparing the measurement results with the simulation results of a canonical differential antenna, a half-wave dipole antenna printed on a dielectric substrate.
Reflections in anechoic chambers can limit the performance and can often dominate all other error sources. NSI’s MARS technique (Mathematical Absorber Reflection Suppression) has been demonstrated to be a useful tool in the fight against unwanted reflections. MARS is a post-processing technique that involves analysis of the measured data and a special mode filtering process to suppress the undesirable scattered signals. The technique is a general technique that can be applied to any spherical near field or far-field range. It has also been applied to extend the useful frequency range of microwave absorber down to lower frequencies. This paper will show typical improvements in pattern performance, and will show results of the MARS technique using data measured on numerous antennas.
Electromagnetic compatibility is a critical concern in the automotive industry, as customer safety depends on the reliability of vehicle electronics systems. The proximity of high current switching loads to sensitive vehicle electronics within the typical automobile results in serious EMC problems. Currently, passive EMI filters are used extensively as a means to reduce the conducted (and resulting radiated) emissions from interference-causing automotive devices. However, existing high current EMI filters incorporate expensive passive components. This paper investigates the application of active EMI filtering to high current switched loads typical of automobile applications. Several active EMI filtering topologies are discussed, and an active capacitance filter design is introduced. The measured noise reduction performance of two active EMI filter implementations presented, along with notes on measurement techniques, active filter viability, and motor drive design.
This paper discusses design aspects related to a tiltable lightweight near-field scanning system for use at sub-millimeter frequencies. It addresses design issues as they relate to accuracy and scanner distortions from multiple causes. Calibration methods to measure and correct for anticipated and unanticipated errors are briefly addressed. Actual test results are presented. The tiltable scanner being discussed was designed for the Atacama Large Millimeter/submillimeter Array (ALMA) [1] and is being used by the National Radio Astronomy Observatory (NRAO) [2]. It has many other applications by virtue of its light weight (approx. 120 lbs) and ability to be oriented at different angles. These include flight-line testing and other in-situ antenna test applications.
An important aspect of antenna measurements and numerical modeling, both for research activities and for industrial use, is the possibility to exchange and compare data from different measurements systems or modeling tools. The primary approach is the exchange of data in files. The need for a common way to describe physical objects and quantities involved in measurements and electromagnetic modeling of antennas has been discussed by many in the recent years [1]. This paper reports on the development of the Electromagnetic Data eXchange language (EDX). This joint Antenna Center of Excellence (ACE) and European Space Agency (ESA) activity on a common language for data exchange has yielded data dictionaries covering most essential types of data that are communicated among electromagnetic software tools. Although the joint activity is focusing on numerical modeling tools the field dictionary is a subset of this activity and of particular interest also to the antenna measurements community. The concept of Data Domain modeling and Data Dictionaries are first discussed. Then, the language developed to describe and record data is introduced, followed by a short illustration of the Electromagnetic Data Interface library and of the Translator, a utility that automatically translates Data Dictionaries definitions into program code to access the data. Finally the application of EDX as common data format in an international facility comparison campaign is discussed.
Focused-beam measurement systems are commonly employed in material characterization measurements due to their inherent broadband capability. Calibration of this system is typically performed using a simple response calibration in conjunction with gating techniques to eliminate unwanted reflections. An undesirable artifact of this calibration technique is the extracted permittivity and permeability measurements can be highly dependent on the width and shape of the gate. This paper explores a three-short full two-port calibration technique which eliminates the need for gating. The two-port calibration consists of three independent short measurements in both the forward and reverse directions (i.e., S11 and S22), two isolation measurements (S21 and S12) and four empty measurements (S11, S21, S12, S22). Material parameter extraction measurements based upon this calibration technique were performed using both a low-frequency (0.5 - 2 GHz) and high-frequency (4 - 18 GHz) focused-beam system. Initial results show the technique’s viability and the dependency on accurate positioning of the shorts used in the calibration process and possible interaction between the sample and the sample holder.
In this paper we show how a modification in the choice of mode normalization changes the pair-wise transmitting-receiving conversion to a one-to-one equality for a reciprocal antenna: This change affords us greater simplicity and the opportunity to avoid confusion when manipulating the scattering coefficients. For this relation to hold, there is a useful convention defining two fiducial coordinate systems for the antenna – one a transmitting and the other a receiving coordinate system.
ABSTRACT
This paper describes the miniaturization of a spiral antenna using inductive loading. The inductive loading of the spiral is implemented using a two dimensional approach (meandering) and a volumetric or three dimensional approach. It is shown that the volumetric approach can achieve greater miniaturization than the two dimensional approach. In addition, the simulation results for the volumetric approach are validated by the fabrication and measurement of one of the volumetric designs.
While using squat cylinders for calibrations, we study the MoM-simulated data in terms of surface waves. We have found that the fine structures in both the amplitude and the phase are related to the target geometry. Key Words: RCS calibration, simulation, polarization
This paper describes a new approach to improving the low frequency reflectivity performance of geometric transition radar absorbent materials through the use of impedance loading in the form of one or more included FSS layers. The discussion includes theoretical predictions and measured data on modified commercially available RAM which confirm the validity of the concept.
In this paper we present a direct optimization procedure which utilizes phase-less electric field data over arbitrary surfaces for the reconstruction of an equivalent magnetic current density that represents the radiating structure or an antenna under test. Once the equivalent magnetic current density is determined, the electric field at any point can be calculated. Numerical results using experimental data are presented to illustrate the applicability of this approach for non-planar near field to far field transformation as well as in antenna diagnostics.
The Air Force Research Laboratory (AFRL), RF Technology Branch at the Rome Research Site, Rome NY provides a capability of far field antenna testing on full scale aircraft. A computer program, APATS – Antenna Pattern Analytical Tool Set, was developed in conjunction with the Information Systems Research Branch to provide a better way to visualize and understand the antenna pattern data taken during testing. The program is written in Java and relies on JView, developed by the Information Systems Research Branch, to process and display the 3D, three-dimensional, elements of the program.
Techniques for measuring the radar cross section (RCS) of a target in a controlled environment are well known and established and many commercial systems are available for making these measurements. However, when RCS measurements need to be taken in a variable environment – such as over the ocean – several important issues are introduced that need to be carefully considered before a meaningful measurement can be made. This paper shall discuss some of these issues and present a measurement approach that appears to reduce the uncertainty that these factors introduce.
This paper discusses the Blue Airborne Target Signatures (BATS) database. BATS is the United States Air Force central repository for US and allied signature data. It resides at and is maintained by the Signatures Element, 453rd Electronic Warfare Squadron, Air Force Information Warfare Center, Lackland AFB TX. BATS contains radar cross section (RCS), infrared (IR), and antenna pattern (AP) data, both measured and simulated. The history and background of BATS is also presented, as well as current activities.
This paper describes the motivation and major issues related to the design of an RCS radar instrumentation system for use in a compact range. The high degree of sophistication implemented in commercially-available radar systems renders them subject to significant MTTR (mean time to repair) with corresponding losses in range productivity. The objective of the design effort was to develop a system of minimal complexity, maximally suited to troubleshooting and repair by laboratory personnel, while retaining the operational efficiency normally provided by the commercial systems.
The planar near-field antenna measurement system at KRISS has been upgraded to V-band (50 GHz – 75 GHz). This paper describes the upgraded planar near-field antenna measurement system that consists of a planar near-field scanner, a microwave subsystem and an extrapolation range, and shows the uncertainties in gain for a rectangular near-field probe and a Cassegrain antenna at 65 GHz.
A wide range of wireless services are being installed in modern vehicles. Applications including radio reception (FM), navigation systems (GPS), satellite radio, keyless entry, future data services (IEEE 802.11) and mobile telephone are increasingly installed in modern vehicles. Integration of these technologies in cars and trucks has generated a need to accurately determine the performances of the antenna devices when mounted on the vehicle.
Spherical near field measurement techniques combined with probe array technology offer a fast and accurate way to measure antenna performances. The use of increasingly higher frequencies and reduced testing time in all modern antenna applications has increased the need for probe array based measurement systems at higher frequencies.
OTA performance testing of active wireless devices has become an important part of evaluation and certification criteria. Existing test methodologies are extensions of traditional antenna pattern measurement techniques. A critical assumption of these methods is that the device under test utilizes a single active antenna. Advances in wireless technology continue to incorporate more complex antenna systems, starting with simple switching diversity and progressing to more advanced concepts such as adaptive arrays (smart antennas) and multiple-input multiple-output (MIMO) technologies. These technologies combine multiple antennas with various software algorithms that can dynamically change the behavior of the antennas during the test, negating the assumption that each position and polarization of an antenna pattern measurement represents a single component of the same complex field vector. In addition, MIMO technologies rely on the multipath interaction and spatial relationship between multiple sets of antennas. An anechoic chamber with a single measurement antenna cannot simulate the environment necessary to evaluate the performance of a MIMO system. New measurement methods and system technologies are needed to properly evaluate these technologies. This presentation will discuss the issues and evaluate possible solutions.