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A comparison of antenna gain and radiation pattern for R-band (1.7 – 2.6 GHz) antennas has been performed between Korea Research Institute of Standards and Science (KRISS) and eight domestic participants including private companies and public institutes. Its purpose was to check equivalences between KRISS and participants in gain and radiation pattern measurements for antennas, particularly at R-band, to support antenna manufacturers and end users in Korea as a proficiency test program of the ‘Antenna Measurement Club’ of KRISS. This comparison uses three traveling standards (a general purpose antenna (pyramidal standard gain horn antenna), a fan-beam antenna (a sector antenna for mobile base stations), and a small antenna (a sleeve dipole antenna) and measurement parameters are the power gain and radiation pattern of the traveling standards. Gain comparison method, extrapolation method, and cylindrical near-field measurement method are used in this comparison.
ABSTRACT This work deals with the experimental validation of a direct near-field – far-field transformation with cylindrical scanning for electrically long antennas, which requires a minimum number of measurements. Such a transformation is based on a nonredundant sampling representation making use of a flexible source model-ling suitable to deal with electrically long antennas and allows the evaluation of the antenna far field directly from the acquired near-field data without interpolating them. The good agreement between the so recovered far-field patterns and those obtained via the classical cylindrical near-field – far-field transformation assesses the effectiveness of the approach.
Quiet zone sampling is a powerful tool to evaluate the performance of a compact antenna test range. Such procedure consists of carrying out typically planar field acquisitions of the quiet zone. Acquired data yields valuable information about the measurement capabilities of the range under consideration. However, the required amount of samples increases quadratically with frequency for full 2D acquisitions. In practice, millimeter wavelength assessment of CATR facilities implies extremely time-consuming acquisition campaigns in addition to intrinsic mm-waves challenges, such as strict mechanical tolerances in construction and alignment, and high sensitivity to environmental factors. In this communication, we will focus on the CATR facility at ESTEC. A time-efficient acquisition technique has been developed and used to carry out millimeter wavelength quiet zone measurements between 46 – 50 GHz. First tests of the technique show a high level of agreement between the results obtained with the proposed method and those corresponding to a classical Nyquist acquisition approach, while a time savings factor of about 8 is achieved.
Mathematical Absorber Reflection Suppression (MARS) has been used successfully to identify and extract range multi-path effects in a great many spherical [1, 2], cylindrical [3, 4], and planar [5, 6] near-field antenna measurement systems. This paper details a recent advance that enables the MARS measurement and post-processing technique to be used to correct antenna pattern data from far-field or compact antenna test ranges (CATRs) where only a single great circle pattern cut is taken. This paper provides an overview of the measurement and novel data transformation and post-processing chain that is utilised to efficiently correct far-field, frequency domain antenna pattern data. Preliminary results of range measurements that illustrate the success of the technique are presented and discussed.
In this paper, a coaxially fed broadband U-slot stacked rectangular microstrip patch antenna in corporating a high and low dielectric material combination is presented. The antenna essentially consists of two commercially available microwave substrates (Rogers TMM3 and Rohacell HF71 foam). Dielectric constants of materials are 3.27 and 1.07 respectively. Foam material doesn’t include copper surface thus a third dielectric substrate with thickness of 0.254 mm and dielectric constant of 2.2 is added over the foam material to ease of fabrication. The antenna return loss bandwidth is about 52.94%, centered about 3.4 GHz. The effect of the parameters, such as u slot length and width, on the antenna performance are determined, experimentally verified and discussed.
A method is presented to accurately characterize the backscatter and attenuation properties of vegetation using high resolution measurements with the vegetation placed on a turntable. By this method we obtain a controlled scenario of realistic vegetation. To obtain high cross range resolution, 2D-ISAR technique was used. The full obtainable resolution is then defined by the registered bandwidth (2 GHz) and aspect angle width. 2D-ISAR images were produced from which areas of interest were gated out where the vegetation backscatter coefficient was calculated. This, along with antenna tapering compensation and distance compensation allowed us to accurately normalize the vegetation backscatter coefficient. The received signal power was made independent of range and system parameters by calibration. Hence the received power signal can be written to be only dependent on the backscattering radar cross sections. The resulting values of the volume backscattering and extinction parameters are presented for reeds and birch vegetation at HH and VV polarization.
Azimuthal mode (µ mode) truncation of a high-order probe pattern in probe-corrected spherical near-field antenna measurements is studied in this paper. The results of this paper provide rules for appropriate and sufficient µ-mode truncation for non-ideal first-order probes and odd-order probes with approximately 10dBi directivity. The presented azimuthal mode truncation rules allow minimizing the measurement burden of the probe pattern calibration and reducing the computational burden of the probe pattern correction.
In the first part of the contribution the simulation setup of compensated compact ranges is described. The Multilevel Fast Multipole Method (MLFMM) can be efficiently employed for frequencies up to C-band. In the second part of the paper the field distribution is investigated for horizontal and vertical feed antenna excitation. Diffraction effects of edge serrations and their influence on the plane wave quality are outlined. Apart from the theoretical point of view it is discussed how to deal with low frequency effects under practical considerations, e.g. moving the DUT positioner toward the main reflector might be limited. Thus the measurement performance has to be evaluated w.r.t. typical test range conditions.
In this work we study the near-field antenna measurement using cubical surface scanning and related near-field to far-field (NF-FF) transformations. The cubical surface scanning is a fascinating idea because it can be realized using widely used planar scanning on six surfaces of a cube, and it provides the possibility to determine the complete 3-D pattern instead of the pattern in a limited angular region as in traditional planar scanning. The NF-FF transformation presented in this paper is based on spherical vector wave expansion (SWE). The most important issue of this paper is to introduce the azimuthal mode decomposition technique to be applied as a part of the NF-FF transformation allowing a reduction in the computational burden of the transformation.
Multi-layer dielectric rod (MLROD) antenna has been shown to provide wideband, dual-polarization, symmetric patterns, and stationary phase center. The key challenge in designing a MLROD antenna is to choose proper thickness and dielectric constant of each layer, and shape of radiation tip to meet desired VSWR, pattern, and phase center requirements. This becomes even more difficult as the number of layers increases for achieving greater bandwidth. This paper discusses a design optimization procedure of a UWB 3-layer MLROD using Genetic algorithm with novel fitness functions for simultaneously controlling reflection coefficient, phase center, and pattern three key characteristics. The final design exhibited excellent desired performance throughout the desired frequency range.
Recently the problem of exhaustive testing of the high number of multi beam antennas embarked on future satellite systems has received considerable attention. Based on conventional measurement techniques this testing would lead to unacceptable cost and duration. The use of fast probe array technology to replace the spatial dimension of the measurements is a proven solution to drastically reduce the measurement time compared to conventional single probe test systems. Another solution to reduce the overall measurement time consists in measuring several beams simultaneously instead of sequentially. This paper presents an innovative hardware solution to virtually reduce the number of antenna ports to be measured by characterizing several beams of a multi-beam antenna at the same time. The solution is applicable to both the receive and the transmit modes. This technique has been demonstrated by the manufacturing, installation and test of a full size demonstrator at Thales Alenia Space in Cannes and at Intespace in Toulouse.
Antenna pattern measurement in the presence of obstacles requires an accurate characterization of the antenna-scatterer interaction in order to retrieve the multipath effects that distort the antenna pattern. In this contribution, a new approach based on the Sources Reconstruction Method is proposed. The idea is to characterize the Antenna-Under-Test (AUT) and the scatterers through a set of equivalent currents that radiate the same fields as the original problem. Thus, it is expected that the equivalent currents retrieved on the surface enclosing just the AUT will provide the AUT radiation pattern. A comparison with modal expansion of the fields on the reconstruction domains is also performed.
Anechoic chamber characterization typically requires measuring the level of extraneous signals within an arbitrarily defined quiet zone volume. From this data, measurement uncertainty due to the presence of extraneous signals can be quantified for various test scenarios. For the anechoic chamber designer, however, it is equally important to determine the magnitude and source of the extraneous signals so that they can be minimized or controlled. This paper discusses improvements in Spherical Near-Field Chamber Imaging as applied to anechoic chamber design and characterization. Measurement system improvements to improve image resolution are described. Data sampling requirements to eliminate processing artifacts is discussed. Critical sampling probe characteristics limiting UHF measurement capabilities are outlined. Test data on an outdoor range and on a large anechoic chamber are presented and discussed.
Mobile communication devices have many different requirements; namely they often have stringent size constraints, and must efficiently radiate over several frequencies in a myriad of different environments. Furthermore, the antenna is often electrically small or unintentionally loaded by environmental effects which cause unpredictable changes in antenna impedance. Therefore an agile matching network that is self-tuned to increase matching efficiency is desired. Most existing tuning approaches minimize reflections looking into the matching network. It will be demonstrated that this approach does not guarantee optimal performance due to circuit losses. A better approach is to also maximize power transmitted through the matching network. This paper presents a real-time frequency and impedance-agile tuning design that automatically matches a very wide load impedance range (0.5. < Re{ZL} < 1K. and -1K. < Im{ZL} < 1K.) from 200 to 400 MHz by the use of varactor diodes with impedance tuning stubs.
When making antenna measurements, great care must be taken in order to obtain high quality data. This is especially true for near-field antenna measurements as a significant amount of mathematical post-processing is required in order that useful far-field data can be determined. However, it is often found that the integrity of these measurements can be compromised in a large part through range reflections, i.e. multipath [1]. For some time a technique named Mathematical Absorber Reflection Suppression (MARS) has been used to reduce range multi-path effects within spherical [2, 3], cylindrical [4, 5] and most recently planar [6, 7] near-field antenna measurement systems. This paper presents the results of a recent test campaign which yields further verification of the effectiveness of the technique together with a reformulation of the post-processing algorithm which, for the first time, utilises a rigorous spherical wave expansion based orthogonalisation and filtering technique.
The desire to acquire Radar Cross Section (RCS) data on full scale models poses a number of challenges to the users of pylon / rotator systems. Typically, these full scale models have significant mass but have a relatively small foot print on which it is acceptable to mount the model to the rotational flange. The challenges to be addressed in this paper include designing a rotator that will have sufficient strength to support the weight of the model and the stress generated by the overturning moment. This rotator must have a sufficiently low profile and small volume so that it will conveniently fit within the model volume but still achieve a sufficient elevation travel to meet test objectives. This rotator must still properly close out the pylon at all elevation angles to prevent unwanted reflections. Additional design considerations include the test conditions and the test environment. A rigorous test requirement can demand special engineering features to mitigate the demands of relatively high scan speeds and extended run times. Environmental concerns including wind loads, temperature, humidity, and contaminants, must be factored into the design of modern RCS rotators. This paper presents the system design approach to address the requirements of a full scale model rotator. The paper examines consequences of selected potential design solutions and demonstrates the importance of performing trade studies.
The commercial aviation industry faces several issues in regard to servicing and maintaining the radomes that abound in the aircraft fleet flying today. The first issue is the historically high cost of radome test systems. As a result of this, there are limited numbers of test systems in operation today and some geographic regions have insufficient radome test capacity. Advances in weather radar and increased reliance on them for turbulence avoidance and more efficient route planning around storm systems will increase the importance of ensuring that weather radar systems are performing well and consequently that weather radar radomes are in good condition and have been adequately tested. Because of the potential consequence of flying with a bad radome and the demands of new radar systems, its more important than ever to ensure test systems in use adhere to requirements and to spread awareness of these challenges within the aviation community. Recently, a design effort was conducted specifically geared towards developing a system concept for radome testing that would both provide a robust test capability that fully meets the RTCA-DO-213 after repair test requirements and one that is much lower in cost than traditional systems that are fielded today. This paper describes the issues cited above and provides a description of the low cost -compliant solution
Ultra wideband (UWB) systems use short pulses in order to achieve high data rate wireless communications and/or radar resolution. Thus, UWB antennas should be designed carefully, both in time and frequency domains, with the system performance in mind. Time domain characterization of an antenna can be performed first by measuring the frequency domain transfer function of a direct link consisting of two identical antennas. Then, the time domain response is obtained by post processing the frequency domain data using the Inverse Fast Fourier Transform (IFFT). This paper discusses frequency and time domain performance of four-arm equiangular and Archimedean spiral antennas operating in mode 2. The frequency domain transfer function is synthesized using complex far field information measured in a spherical near-field chamber from 2GHz to 12GHz. The synthesized approach is validated using simulation and direct link measurements. The quality of radiated pulses is evaluated in terms of fidelity factor over a full field of view, a task not trivial for the direct link measurements.
Planar low-profile antennas over high-impedance surfaces show improved performance compared to that over metal ground planes. Unfortunately, these high-impedance surfaces often operate over narrow bandwidths. This paper describes an approach to high-impedance surfaces which permits improved performance over a broader bandwidth. Current approaches to the design of high-impedance substrates typically employ identical unit cells with the same resonant frequency to produce high-impedance behavior over a relatively narrow frequency range. The wide bandwidth performance described in this paper derives from cells having a size and subsequent resonant frequencies that vary with position on the PMC substrate. This approach is explored through simulations using CST Microwave Studio which show the improved performance of these wideband structures.
New developments in ortho-mode junctions (OMJ) and probe technologies has enabled near field probes with up to 1:4 bandwidth, while maintaining the high performance standards of traditional narrow band probes [1–3]. The new probe technologies are based on inverted ridge structures providing four symmetrical feeding points for external balanced feeding. The inverted ridge structure stabilizes the frequency dependence of the OMJ while the external balanced feeding is a crucial feature to achieve the desired high performances. This paper briefly review the theory of balanced feeding and derive performance guide lines on the external beam forming network for achieving high port-to-port isolation and matching on a wide bandwidth with the inverted ridge probe technology. The relationship between excitation errors in the balanced feeding scheme and the spherical mode index µ.1 content of the probe is also investigated and upper bounds on acceptable excitation errors are derived.