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Abstract— A non-destructive method for the characterization of sheet material in the VHF/UHF range using a 3 inch square device is presented. The device is a linearly polarized open resonating probe that measures sheet admittance. The probe can be tuned to a given resonant frequency and the sensitivity can be adjusted for measuring ranges of sheet admittance.
Abstract—this paper will cover the key design attributes of a high-speed frequency switching synthesizer. It will highlight the importance of a stable reference and then go on to examine the different types of commercial high speed synthesis approaches, including advantages and disadvantages in terms of speed, frequency range, phase noise and part count. We will then explore a new hybrid approach to synthesis utilizing a lower part count commercial approach.
Abstract— The measurement community has a substantial and increasing interest in utilizing computational electromagnetic (CEM) tools to minimize the financial resources and real estate required to design and construct a custom anechoic chamber without sacrificing performance. Although a full-wave numerical technique provides the most accurate solution, the computational resources can quickly become a hindrance as the electrical size increases with frequency. Fortunately, the assumptions underlying numerical solvers using asymptotic approximations become more valid and therefore more accurate as frequency increases. Simulations using these numerical solvers, available in commercial software such as FEKO [1], extend previous research [2] with a comparison between the power received by an antenna under test (AUT) and a reference antenna in an anechoic chamber across the UHF frequency band. The ability to simulate a measurement technique helps unite the measurement and computational communities by accounting for a variety of potential error sources. The respective antenna gain is then extracted with post-processing and ultimately provides further insight into the performance of anechoic chambers. Without loss of generality, a complete chamber measurement of half-wave dipole antennas at several frequencies has been simulated.
Abstract: A novel Inset fed microstrip patch antenna is designed on defected ground structure (DGS) to reduce the higher order harmonics and cross polarized radiations. Square rings, and square shaped slots are placed on the ground plane of the microstrip patch antenna to get the desired operation. These annular ring and arc DGS appears to be highly efficient in terms of suppressing the cross polarization. Relative suppression of radiated field is observed by placing and without placing the defected ground structures. The stop band property exhibited by the DGS is used to filter out the harmonics. The current model successfully reduced the DGS size and by comparing with the well known design, size reduction of 20% is achieved. Instead of normal square patch, a slotted aperture patch model is considered in the current design to reduce the overall size of the antenna.
Abstract—The measurement geometry and data processing techniques employed in spherical near-field (SNF) antenna measurements naturally quantify the directivity of an antenna under test. Computing antenna gain from these measurements requires additional information and processing. Equations that can be used to calculate the magnitude of antenna gain from spherical near-field measurements are provided in seminal SNF references, but equations that describe how to calculate the complex gain voltage of an antenna with spherical near-field methods have been largely absent in the literature. This paper presents equations that may be used to calculate the complex gain voltage of an antenna using the gain substitution method in a spherical near-field test range. The equations are presented in a more generalized format than previously seen, and will show how to use a combination of data collected in the near-field with data transformed to the far-field to calculate the gain voltage. Practical examples are provided for determining gain voltage using a single measurement set-up or multiple measurement set-ups, including a method to calculate gain voltage of each port of a multi-port antenna requiring only a single full sphere measurement of the standard gain antenna.
Abstract—The optimal allocation of coaxial-slot antennas for hyperthermia treatment has been determined by using the p-center location problem, which is an operations research problem. Some examples of various p-center solutions in a square are demonstrated. As a result, we clarified that the optimal coordinates and minimum number of antennas can be determined once the area of the tumor and the medical treatment radius of the coaxial-slot antenna are determined. Moreover, the specific absorption rate distribution inside the biological tissue-equivalent phantom has been calculated using the finite-difference time-domain method.
Abstract—A new technique is presented to measure the permittivity and permeability of conductor-backed magnetic absorbing materials using a triaxial probe. The probe consists of two coaxial transmission lines that share an aperture in a conducting flange, which is placed against the sample creating a two-port network. By measuring the reflection coefficients at each port and the transmission between the ports, the material parameters may be determined. This paper describes the technique and provides a theoretical method for computing the S-parameters of the triaxial system. Experimental implementation of the system is still under study.
The need to maintain very low observability, along with the need to manipulate the model through a large range of motion, result in a challenging set of problems. These have been effectively addressed over decades of RCS equipment design. In recent years however, RCS applications have become much more demanding. Models are ever larger and heavier, with length exceeding 150 feet, and with weight up to 50,000 lbs. Required accuracy with some applications has increased to ±0.01°, an increase of 67% as compared to legacy values. MI Technologies has developed products that significantly expand the structural and operational envelopes of rotator/pylon systems to meet the demand for higher performance. This paper presents the various challenges encountered in RCS Rotator and Pylon design, and the innovative solutions that have arisen from recent engineering efforts.
Modern antenna measurement systems require high dynamic range to accommodate a wide variety of high gain and low gain antenna testing. Network analyzers utilized as the baseline instrument in these systems (e.g., Agilent PNA series), typically offer more than adequate dynamic range. Of course, this is reduced to some extent by cable losses and other components in the transmission and reception paths. However, the capability for achieving the required dynamic range still is adequate in most RF configurations given the proper choice of mixers, amplifiers, etc. in the layout. However, often the achievable dynamic range is limited relative to the calculated values; this is quite often a result of leakage signals within the RF paths. The primary culprits of the leakage are typically rotary joint leakage in positioners and direct leakage into cable connectors. Various tests are required to isolate the leakage signals and to quantify them. This paper will identify the techniques used to isolate these signals and offer solutions to minimize the leakage and thus optimize dynamic range. Recent testing has shown that leakage signals may be as much as 10-20 dB or more above the achievable noise floor when commercially available rotary joints and multiple cables are utilized. These issues will be addressed in the paper.
Phase variation = +/-10 deg. 18 to 40 GHz Phase variation = +/-20 deg. 40 to 110 GHz Cross Polarization = -30 dB III. MAXIMUM AVAILABLE SPACE Consistency of performance across a waveguide band levies demands on compact range feeds. Because of the constraint of the room size, the design starts with determining the maximum space available for the This paper addresses a recent compact range development by MI reflector. The next step will be to determine the combination of Technologies that achieves desired extended low frequency and reflector body and edge treatment size within that space to millimeter wave performance (1 to 110GHz) while maintaining a deliver the desired performance. To determine the space cost effective reflector size and a small range footprint. The paper available for the reflector a chamber layout analysis is will explore the conventional rule-of-thumb relationships performed. Appropriate absorber is selected and, allowing for between feed, reflector, edge treatments and range geometries an air gap of at least 2 wavelengths at the lowest desired while contrasting them to the resultant design. The paper will frequency between the absorber and the reflector, and allowing highlight an impressive new family of compact range feeds and advancements in cost effectively achieving a superior reflector height for the compact range feed positioner yields the surface. allowable reflector dimensions to be 194 inches high and 222 inches wide as shown in Table 2. The combination of reflector
Abstract— Plasma antennas have more degrees of freedom then metal antennas making their applications have enormous possibilities. Plasma antennas use partially or fully ionized gas as the conducting medium instead of metal to create an antenna. The advantages of plasma antennas are that they are highly reconfigurable and can be turned on and off. Haleakala Research and Development, Inc. has done theoretical work, experiments, and built prototypes on plasma antennas, plasma waveguides, and plasma frequency selective surfaces. This research and development focused on reducing the power (to date this is less than 5 watts per tube and going down) required to ionize a plasma tube with higher plasma densities and frequencies, plasma antenna nesting, co-site interference reduction, thermal noise reduction, and the development of the smart plasma antenna. Haleakala Research and Development, Inc. has built and tested plasma antennas from 30 MHz to 50 GHz. At the higher frequencies, plasma antennas have lower thermal noise than metal antennas and the thermal noise of plasma antennas decreases with the operating frequency of the plasma antenna making them ideal for satellite antennas. Plasma satellite antennas can be made conformal with a surface and give the performance of a parabolic dish antenna. This is true because beam steering and focusing can be done by varying the plasma density from one tube of plasma compared to the next. With this design, plasma satellite antennas can be operated in the reflective or refractive mode. High powered plasma antennas have been built as a possible directed energy applications. Alexeff and Anderson and [1]-[2] Anderson and Alexeff [3] have done theory, experiments, and have built prototype plasma antennas. Anderson [4] wrote a comprehensive book on plasma antennas.
Abstract—Nowadays, radar retro-reflector has been widely applied as a decoy, to seduce an incoming assault away from the target, or towards a less vulnerable part of it to communication systems and remote identification as their characteristics of low-profile, low-cost and Radar Cross Section(RCS) enhancement. A passive retro-reflector is a device which can be used to be reflected most of the energy incident upon it in the direction of the in-going wave. The Luneberg lens and a sphere are widely used as their self characteristics. In this paper one of the retro-reflector, is paid more attention as time goes by, is introduced. The retroreflector is consist of patch antenna arrays and feeding system and can be defined as Retro-directive arrays (RDA). It has a very simple structure and can focus outgoing waves back at the direction of incident waves. The character of the re-radiation pattern affected by the size and type of patch and width and length of feeding network related are optimized by the HFSS. The final results are validated experimentally.
Abstract—When antennas are measured in echoic environments, there is usually a need to process the measured data in order to remove multipath contributions. Traditional measurement set-ups involving a single probe antenna provide limited information for the purpose of this separation. A multi-probe measurement technique whereby the AUT is measured with two sets of probe antennas is presented. One set of probe antennas are oriented such that they radiate mainly toward the AUT and the other set radiate away from it. This measurement technique allows for the separation of the direct AUT contribution from the multipath contributions. The acquired data is processed using a well-suited near-.eld far-.eld transformation algorithm with the echo sources considered as they were independent sources. The performance of the measurement technique is also evaluated for traditional spherical mode near-.eld far-.eld transformation whereby both incoming and outgoing spherical waves are considered. The results show a substantial improvement in the obtained far-.eld patterns when compared with non-compensated far-.eld results.
Abstract—This contribution introduces a technique that offers the possibility to reconstruct all scattering parameters of a given sample based on re.ection measurements only. Therefore, it is possible to obtain the transmission properties of a given device under test in a measurement setup which does not allow to perform transmission measurements. Thus, the new method combines the advantage of a two port measurement, which yields all four scattering parameters, with the more compact setup of a one port measurement. Free space material measurements are performed to validate the new approach.
Abstract— Compact ranges are ideal settings for collecting low-RCS measurement data at high pulse rates. However, until recently, two operating constraints have limited the efficiency of instrumentation radar systems in this setting: (1) system delays limiting Pulse Repetition Frequency (PRF) and (2) fixed integration across frequency resulting in more time spent on certain frequencies than required. In this paper, we demonstrate the capability to significantly increase data throughput by using a Burst-Mode to increase the usable PRF and a frequency table editing mode to vary integration levels across the frequency bandwidth. A major factor in the choice of PRF for a specific application is system hardware delays. We describe the use of a Burst-Mode of operation in the MkVe Radar to reduce delays caused by physical layout of the instrumentation hardware. Burst-Mode essentially removes setup time in the system, reducing the time between pulses to the roundtrip time of flight from the antenna to the target. Most pulsed-IF instrumentation radar users fix the coherent integration level for the entire measurement waveform, even though the set level of integration may not be required at all frequencies to achieve the desired sensitivity. We describe the use of a frequency table Parameter Editor Mode in the MkVe that allows the integration level to vary for each step in the waveform. We demonstrate the use of both methods to reduce data collection time by a factor of seven using a MkVe Radar installed in a compact range.
Abstract: In order to characterize the Boeing 9-77 compact range, the empty chamber background was measured as a function of frequency, polarization, and the azimuth angle of the upper turn-table (UTT). The results exhibited a near-field diffraction pattern with enlarged hot-spots on a 4-fold symmetry [1]. A 2-D FFT on the diffraction pattern yielded a mapping on the relative arrangement of the absorbers on the UTT [2]. In this paper, we take a closer look at the scattering geometry of the UTT as illuminated by the residual field above and beyond the quiet zone (QZ). The different responses in VV and HH are discussed. The enhanced diffraction due to a “blazed grating” condition is identified and analyzed.
Abstract—In order to optimize accuracy of near field measurements, it is required not only to acquire data for two orthogonal polarizations, but the relative amplitude and phase balance between the two channels must also be accurately matched. This can be difficult at millimeter wave frequencies because of the transmission lines and other components involved. ORBIT/FR has explored multiple methods of achieving optimum vertical and horizontal polarization matching and found a very simple solution to achieve acceptable results. Some of the methods investigated included the use of dual-polarized feeds, dual single-polarized feeds mounted adjacently, waveguide rotary joints with a mechanically rotated feed, and a mechanically-rotated feed using a 1.0 mm coaxial-based cable. Interestingly, the mechanically-rotated feed with coaxial cable provided acceptable results on par with or better than the other methods, which moreover results in a very simple implementation in the measurement system. Measured results are presented for the chosen implementation demonstrating the near field data quality is adequate for a variety of antennas.