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Design, Fabrication, and Testing of a Low Profile Wideband Reflector Antenna
Abstract— A special X-band PEC-backed dipole with integrated split coaxial balun was designed, fabricated, and tested for feeding a low-profile parabolic reflector. The aperture size and height of the reflector is 7.876” and 2.0315”, respectively. The reflector is covered with a 1/16” Teflon sheet radome for weather protection. The antenna has a measured peak gain of 23.72dB and first side lobe level of less than –25dB at 10.2GHz in both E and H planes. The worst case 3dB beamwidth is 11.09o in the H-plane. The -10 dB reflection coefficient bandwidth of this design is from 9.5 to 11 GHz. The E and H plane patterns were designed to have similar tapering and minimum coupling between TX and RX reflector antennas in an array configuration. Within an array configuration the measured coupling level is less than -66dB from 9.5 to 11 GHz.
Cylindrical near-field antenna measurement system using photonic mm-wave generation with UTC-PD
Abstract— In order to achieve precise antenna pattern measurement in mm-wave frequency region, we propose a cylindrical near-field antenna measurement system using photomixing technique with UTC-PD. Due to this system, we can use an optical fiber as the transmission line of mm-wave signal and downsize the mm-wave signal source. Accordingly, we can achieve flexible cable movement and suppress the disturbance from the waveguide components. In this paper, we will show the measured near-field distribution on cylindrical coordinate by the proposed system and calculated far-field antenna pattern of standard gain horn antenna in W-band.
New Method to Design a Multiband Flexible Textile Antenna
Abstract— This paper presents an original way for the design simulation, implementation, and measurement of a multiband flexible textile antenna. The aim is to realize an antenna with a dipolar radiation at several resonance frequencies. The radiating element is a monopole antenna. This antenna naturally exhibits a dipole and a quadripole radiation pattern for the first and second resonance frequency respectively. This behavior is due to the current distribution on the antenna. To constrain the second mode to change into a dipolar radiation pattern, two decorrelated and non-radiating parasitic elements are added to the antenna. At this second resonance frequency, the current distribution is different from the one of the quadripolar mode by the parasitic elements. The dimensions of these parasitic elements are defined by electromagnetic simulations and measurements. To validate this method, the monopole antenna is studied. The radiating element of the antenna is sewn on the textile flexible substrate. This substrate was previously characterized in terms of relative permittivity and losses. The near-field magnetic field and the far-field radiation pattern are studied in simulations and measurements.
Four-Arm Wideband Log-Periodic Antenna and its High Power Measurements
Abstract—Four arm Log-Periodic (LP) antennas are frequency independent antennas that are capable of producing dual circular polarizations from the same aperture and over the same bandwidth making them more versatile than commonly used spiral antennas. In this paper we present a four arm LP that is capable of being a high power radiator. Each pair of arms of the LP is fed with a microstrip line that functions as both an impedance transformer and a 180° balun, thereby greatly simplifying the required beamformer. The antenna is tested successfully up to 500W of input CW power. Post high power characterizations of the antenna (far-field gain, radiation patterns, and VSWR) for linear polarization are presented and the stable high power performance of the antenna is demonstrated. With an appropriate beamformer, good quality circular polarization can be expected. Presented results should pave the way for use of the LP in relevant wideband high power applications.
Detailed diagnostics of the BIOMASS Feed Array Prototype
Abstract—The 3D reconstruction algorithm of DIATOOL is applied to the prototype feed array of the BIOMASS synthetic aperture radar, recently measured at the DTU-ESA Spherical Near-Field Antenna Test Facility in Denmark. Careful analysis of the measured feed array data had shown that the test support frame of the array had a significant influence on the measured feed pattern. The 3D reconstruction and further post-processing is therefore applied both to the feed array measured data, and a set of simulated data generated by the GRASP software which replicate the series of measurements. The results of the diagnostics and the corresponding improvement of the feed array field obtained by removal of the undesired effect of the frame are presented and discussed.
Numerical Analysis of EM scattered field for semicircular array elements using Artificial Neural Network
Abstract—This paper describes the approach of solving the electromagnetic scattered field of semicircular array using numerical method (MoM). Considering the variable number of elements, uniform radius of element, element spacing, azimuth plane as inputs of the numerical model and distributed complex current coefficients, scattered E-field are extracted as the outputs. The desired input and output to the artificial neural network are pattern values and number of elements respectively. The purpose of applying neural network is to change from lengthy analysis and design cycles required to develop high performance systems to very short product development times. The work allows the designer to achieve any desired values of pattern without requiring the usage of more elements. The generated data is divided in to training and test sets, for observing the error behavior with the progress of training. It is proved that the network gives a high success rate.
The Use of Statistical Image Classification In Assessing Antenna Pattern Measurements
Abstract— Attempts to produce robust, objective, and quantitative measures of similarity between antenna pattern data sets using statistical methods have been widely reported in the open literature [1, 2]. Hitherto, such techniques have primarily been restricted to the purposes of comparing two or more images as a means in itself. However, no measurement can be considered to be completely free from error, and as such each data set inevitably contains an associated uncertainty. Therefore, in contrast to previous work, this paper discusses and extends some commonly used comparison techniques to take account of the finite, non-zero, measurement uncertainties that complicate the comparison process. Results are presented that illustrate the effectiveness of the comparison method and conclusions drawn.
High Gain Antenna Back Lobes from Near-Field Measurements
Abstract -We propose a method of utilizing near-field spherical measurements so as to obtain the back lobes of high gain antennas without sacrificing the accuracy of the far-field, high-gain main lobe prediction. While a spherical scan is perfectly adequate to gauge the relatively broad back lobes, it is in general inadequate to capture the required details of a sharp forward peak. We overcome this difficulty through recourse to our Field Mapping Algorithm (FMA), which latter allows us to assemble planar near-field data based upon the spherical measurements actually acquired. In particular, planar data of this sort on the forward, main-lobe side offers the standard route to predicting the desired, high-gain, far-field pattern. Our spherical-to-planar FMA near-field data manufacture showed excellent agreement with direct planar near-field measurements for a slot array antenna, each one of them, naturally, underlying a common, far-field, high-gain pattern.
Metal-backed Antenna Miniaturization Based on Reactive Impedance Surface
Abstract— This paper presents a two-layer mushroom-like reactive impedance surface (RIS) and patch antenna miniaturization with potential application in matel-backed antennas. RIS, known as meta-substrate, has shown the ability to miniaturize printed antennas with omni-directional radiation pattern, when served as the substrate for the antenna . However, the area of conventional RIS substrate usually has to much larger than that of miniaturized antenna, since the cell’s dimension is comparable with the antenna, even using a high dielectric constant. Here an RIS with very small unit cell dimensions (cell area reduction by 95% compared to traditional RIS) is proposed and utilized to design a miniaturized antenna over the RIS substrate with the same size as the antenna itself. A microstrip transmission line over the RIS substrate model is studied and shown to have a high propagation constant near the resonant frequencies of the RIS. This model is used to predict the much reduced resonant frequency of patch antennas over the RIS. Applying the two-layer RIS substrate and an optimized miniaturized patch antenna topology, several UHF band patch antennas working around 400MHz have been designed and fabricated. Using this approach a miniaturized antenna with dimensions .0/11.4× .0/11.4 × .0/74, including the RIS substrate is developed.
Advanced Waveform Generator For Integrated Phased Array Testing
This paper will discuss a highly customizable and integrated waveform generator (WFG) subsystem used to coordinate the phased array test process. The WFG subsystem is an automated digital pattern generator that orchestrates the command and triggering interface between the NSI measurement system and a phased array beam steering computer. The WFG subsystem is controlled directly by the NSI 2000 software and allows the test designer to select and generate a sequence of up to sixteen unique synchronized timing waveforms. Test scenarios, results and data for the WFG subsystem will be presented along with plots showing the key timing characteristics of the system.
Positioner Effects in Measurements of Low-Medium Gain Antennas
Abstract—In this paper, a bespoke, fully automated anechoic chamber is discussed and the positioner effects on measurements of antennas are investigated. Antenna measurements performed in this robust anechoic chamber are undertaken in two parts namely; acquisition and analysis, with the aid of low cost positioner hardware and low level software language. In order to get a measure of validation of our measuring system only the important parts of the chamber have been modelled and measurements carried out using a balanced sleeved dipole and a microstrip patch antenna, which have well-known characteristics. It was noticed from the results that the positioner, exaggerates the performance of some antennas particularly small antennas without a ground plane at certain distances and frequencies. The positioner has a tendency to reflect energy, and distort radiation patterns; hence, it was important to ensure that such antennas are placed at an appropriate distance away from the positioner. The comparison between the simulated and measured efficiency of a balanced sleeved dipole is good. The predicted and measured peak efficiency at 2.49 GHz was 95% and 94% respectively. It was also observed that the variability in efficiency measurements was less than 3% for measurements with different angular resolutions on different days.
Cold test Measurements of a Circular Waveguide Bragg reflector for Cerenkov devices
A Gaussian electromagnetic radiation is always attractive for many scientific research and some practical applications. The importance of the Gaussian microwave beam, especially for high power microwave region of operation, is that its maximum energy density is concentrated on its axis. A two-spiral corrugated Bragg reflector, at the inner surface of a circular waveguide, is a novel way to provide such a radiation. The Bragg reflector has been designed and optimized using the fully electromagnetic HFSS tool. Such a reflector converts the operating TM01-mode of the Cerenkov devices to the forward TE11-mode with a Gaussian microwave beam at the output. The use of the Bragg reflector is not only to reflect the injected TM01-mode but also to convert it to a clean TE11-mode pattern. A cold test structure is fabricated to test the theoretical predictions of the microwave transmission versus frequency and the dispersion characteristics. The dispersion relation is found from the discrete measured resonant frequencies and wave numbers of a cavity containing eight periods of the slow-wave structure. Generally, a slow wave structure has N periods will exhibit N+1 resonant frequencies when shorted at planes of mirror symmetry. The main purpose of this study is to experimentally determine the dispersion relation of the structure. Test results using a vector network analyzer showed a good agreement with the simulations for the excitation of the TM01-mode at 10 GHz.
Slotted Waveguide Array Beamformer Characterization Using Integrated Calibration Channel
In military applications, where low sidelobes and high precision in beam pointing are vital, a phased array antenna beamformer requires to be calibrated regarding the cabling that connects the beamformer to the antenna and mutual coupling between antenna elements. To avoid problems associated with mismatched phase transmission lines between the beamformer and the antenna and include the coupling effects, beamforming network characterization must be done with the antenna integrated to the beamformer. In this paper, a method to characterize the beamformer of a slotted waveguide array antenna in the antenna measurement range is introduced. The antenna is a travelling wave slotted waveguide array scanning in the elevation plane. The elevation pattern of the antenna is a shaped beam realized by a phase-only beamformer. The calibration channel includes serial cross-guide couplers fed by a single waveguide line. The channel is integrated to the waveguide lines of the antenna. In the first phase of the characterization, the far field pattern of each antenna element is obtained from the near field measurements at the “zero” states of the phase shifters. In the second stage, all states of the phase shifters are measured automatically using the calibration channel described above. The results of calibration channel measurements are used to determine the changes in phase and magnitude for different states of phase shifters. The phase and magnitude of the peak point of the far field pattern is referenced to the zero state measurement of the calibration channel. Phase only pattern synthesis is carried out using the results of both zero-state near field and calibration channel measurements and the required phase shifter states are determined accordingly. Measured patterns show good agreement with the theoretical patterns obtained in the synthesis phase.
Advances in Instrumentation and Positioners for Millimeter-Wave Antenna Measurements
Applications using millimeter-wave antennas have taken off in recent years. Examples include wireless HDTV, automotive radar, imaging and space communications. NSI has delivered dozens of antenna measurement systems operating at mm-wave frequencies. These systems are capable of measuring a wide variety of antenna types, including antennas with waveguide inputs, coaxial inputs and wafer antennas that require a probing station. The NSI systems are all based on standard mm-wave modules from vendors such as OML, Rohde & Schwarz and Virginia Diodes. This paper will present considerations for implementation of these systems, including providing the correct RF and LO power levels, the impact of harmonics, and interoperability with coaxial solutions. It will also investigate mechanical aspects such as application of waveguide rotary joints, size and weight reduction, and scanner geometries for spherical near-field and far-field measurements. The paper will also compare the performance of the various mm-wave solutions. Radiation patterns acquired using some of these near-field test systems will be shared, along with some of the challenges encountered when performing mm-wave measurements in the near-field.
Source Reconstruction for Radome Diagnostics
Radome enclose antennas to protect them from environmental influences. Radomes are ideally electrically transparent, but in reality, radomes introduce transmission loss, pattern distortion, beam deflection, etc. Radome diagnostics are acquired in the design process, the delivery control, and in performance verification of repaired and newly developed radome. A measured near or far-field may indicate deviations, e.g., increased side-lobe levels or boresight errors, but the origin of the flaws are not revealed. In this presentation, source reconstruction from measured data is used for radome diagnostics. Source reconstruction is a useful tool in applications such as non-destructive diagnostics of antennas and radomes. The radome diagnostics is performed by visualizing the equivalent currents on the surface of the radome. Defects caused by metallic and dielectric patches are imaged from far-field data. The measured far-field is related to the equivalent surface current on the radome surface by using a surface integral representation together with the extinction theorem. The problem is solved by a body of revolution method of moment (MoM) code utilizing a singular value decomposition (SVD) for regularization. Phase shifts, an effective insertion phase delay (IPD), caused by patches of dielectric tape attached to the radome surface, are localized. Imaging results from three different far-field measurement series at 10 GHz are presented. Specifically, patches of various edge sizes (0.5?2.0 wavelengths), and with the smallest thickness corresponding to a phase shift of a couple of degrees are imaged. The IPD of one layer dielectric tape, 0.15 mm, is detected. The dielectric patches model deviations in the electrical thickness of the radome wall. The results from the measurements can be utilized to produce a trimming mask, which is a map of the surface with instructions how the surface should be altered to obtain the desired properties for the radome. Diagnosis of the IPD on the radome surface is also significant in the delivery control to guarantee manufacturing tolerances of radomes.
On-Orbit Characterization of SDRs on ISS Utilizing Antenna Off-Pointing Capabilities on the SCaN Testbed
The Space Communications and Navigation (SCaN) Testbed was developed to investigate the applicability of software defined radios (SDR) to NASA space missions, study the operation of SDRs and their waveform applications in an operational space environment, and reduce cost and risk for future space missions using SDRs. The SCaN Testbed, developed at NASA’s Glenn Research Center, is currently installed on the International Space Station and has line-of-sight connection to NASA’s Space Network and compatible ground stations. To characterize the operation of the SDRs and their waveforms, a new and unique capability was developed at GRC, which uses purposeful antenna off-pointing to provide a wide range of power levels to the input of the SDR. With this capability, a radio can be more fully tested and characterized on-orbit. This paper describes the new antenna off-pointing capability and methodology, and how it was applied to characterize the on-orbit performance of an S-Band radio in the SCaN Testbed. It provides details of the antenna pointing system control algorithm, gimbal articulation limitations, medium gain antenna pattern profile, and phase limitations associated with the medium gain antenna. Finally, the paper presents test results and lessons learned.
Simulation Experiments with Ultra-Wideband Antennas and Arrays in the Time Domain
The performance of a typical narrowband antenna array is reduced by mutual coupling between radiating elements. The degree to which this inter-element coupling occurs may be correlated with the resonant characteristics and tendency for late time ringing of an individual element. The parabolic reflector impulse radiating antenna (IRA) is an ultra-wideband (UWB) antenna which by virtue of its design and aim to radiate a very short time-domain signal demonstrates significantly decreased late time ringing. Given this quality, the suitability and performance of the reflector IRA in an array configuration is examined. Modeling and simulation of the reflector IRA is accomplished using commercially available software and single antenna results are compared to measured data. Full-wave simulation of arrayed reflector IRAs in varying physical configurations and excitation modes is performed The relative levels of coupling and degradation of radiation pattern and signal quality are discussed.
Antenna Alignment and Positional Validation of a mmWave Antenna System Using 6D Coordinate Metrology
Antenna alignment for near-field scanning was typically done at NIST with multiple instruments (theodolites, electronic levels, motor encoders) to align multiple stacked motion stages (linear, rotation). Many labs and systems are now using laser trackers to measure ranges and perform periodic compensation across the scan geometry. We are now seeing the use of laser trackers with 3D coordinate metrology to align ranges and take positional data. We present the alignment techniques and positional accuracy and uncertainty results of a mmWave antenna scanning system at 183 GHz. We are using six degree-of-freedom (6DOF) AUT and Probe measurements (x, y, z, yaw, pitch, roll) to align the AUT and then to align the scan geometry to the AUT. We are using a combination of 3DOF laser tracker measurements with a combined 6DOF laser tracker/photogrammetry sensor. We combine these measurements using coordinated spatial metrology to assess the quality of each motion stage in the system, tie the measurements of each individual alignment together, and to assess scan geometry errors for position and pointing. Finally we take in-situ 6DOF position measurements to assess the positional accuracy to allow for positional error correction in the final pattern analysis. The knowledge of the position and errors allow for the correction of position and alignment of the probe at every point in the scan geometry to within the repeatability of the motion components (~30 µm). The in-situ position knowledge will eventually allow us to correct to the uncertainty of the measurement (~15 µm). Our final results show positioning errors on the spherical scan surface have an average error of ~30 µm with peak excursions of ~100 µm. This robust positioning allows for accurate analysis of the RF system stability. Our results show that at 183 GHz, our RF repeatability with movement over 180° orientation change with a 600 mm offset to be less than ±0.05 dB and ±5°.
Measurement of Operational Orientations Using Coordinate Transforms and Polarization Rotations
Antenna and Radar Cross Section (RCS) measurements are often required for orientation sets (cuts) that are difficult or impossible to produce with the positioning instrumentation available in a given lab. This paper describes a general coordinate transform, combined with a general polarization rotation to correct for these orientation differences. The technique is general, and three specific examples from actual test programs are provided. The first is for an RCS measurement of a component mounted in a flat-top test fixture. The component is designed to be mounted in a platform at an orientation not feasible for the flat-top fixture, and the test matrix calls for conic angle cuts of the platform. The transforms result in a coordinated, simultaneous two-axis motion profile and corresponding polarization rotations yielding the same information as if the component had been mounted in the actual platform. The second example is for a pattern measurement of an antenna suite mounted on a cylindrical platform (such as a projectile). In this case, the test matrix calls for a roll-cut, but the range positioning system does not include a roll positioner. The transforms again result in a coordinated, simultaneous two-axis motion profile and corresponding polarization rotations to provide the same information as the required roll-cut but without the use of a roll positioner. Finally, the third example is for an antenna pattern measurement consisting of an extremely large number of cuts consisting of conic yaw cuts, roll cuts and pitch cuts. The chosen method involves the use of the Boeing string suspension system to produce great-circle cuts at various pitch angles combined with the use of the coordinate and polarization transforms to emulate, off-line, any arbitrary cut over any axis or even multiple axes. Keywords: Algorithm, Positioning, Polarization, Coordinates, RCS
Experimental Tests on an Effective Near-Field to Far-Field Transformation with Spherical Scan From Irregularly Spaced Data
The near-field – far-field (NF–FF) transformation with spherical scanning is particularly interesting, since it allows the reconstruction of the complete radiation pattern of the antenna under test (AUT) . In this context, the application of the nonredundant sampling representations of the electromagnetic (EM) fields  has allowed the development of efficient spherical NF–FF transformations [3, 4], which usually require a number of NF data remarkably lower than the classical one . In fact, the NF data needed by this last are accurately recovered by interpolating a minimum set of measurements via optimal sampling interpolation (OSI) expansions. A remarkable measurement time saving is so obtained. However, due to an imprecise control of the positioning systems and their finite resolution, it may be impossible to exactly locate the probe at the points fixed by the sampling representation, even though their position can be accurately read by optical devices. As a consequence, it is very important to develop an effective algorithm for an accurate and stable reconstruction of the NF data needed by the NF–FF transformation from the acquired irregularly spaced ones. A viable and convenient strategy  is to retrieve the uniform samples from the nonuniform ones and then reconstruct the required NF data via an accurate and stable OSI expansion. In this framework, two different approaches have been proposed. The former is based on an iterative technique, which converges only if there is a biunique correspondence associating at each uniform sampling point the nearest nonuniform one, and has been applied in  to the uniform samples reconstruction in the case of cylindrical and spherical surfaces. The latter relies on the singular value decomposition method, does not exhibit the above limitation, but can be conveniently applied only if the uniform samples recovery can be reduced to the solution of two independent one-dimensional problems . Both the approaches have been applied and numerically compared with reference to the positioning errors compensation in the spherical NF–FF transformation for long antennas  using a prolate ellipsoidal AUT modelling. The goal of this work is just to validate experimentally the application of these approaches to the NF–FF transformation with spherical scanning for elongated antennas , using a cylinder ended in two half-spheres for modelling them. The experimental tests have been performed in the Antenna Characterization Lab of the University of Salerno, provided with a roll over azimuth spherical NF facility supplied by MI Technologies, and have fully assessed the effectiveness of both the approaches.  J.E. Hansen, ed., Spherical Near-Field Antenna Measurements , IEE Electromagnetic Waves Series, London, UK, Peter Peregrinus, 1998.  O.M. Bucci, C. Gennarelli, C. Savarese, “Representation of electromagnetic fields over arbitrary surfaces by a finite and nonredundant number of samples,” IEEE Trans. Antennas Prop. , vol. 46, pp. 351-359, 1998.  O.M. Bucci, F. D’Agostino, C. Gennarelli, G. Riccio, C. Savarese, “Data reduction in the NF–FF transformation technique with spherical scanning,” Jour. Electr. Waves Appl ., vol. 15, pp. 755-775, June 2001.  F. D’Agostino, F. Ferrara, C. Gennarelli, R. Guerriero, M. Migliozzi, “Effective antenna modellings for NFFF transformations with spherical scanning using the minimum number of data,” Int. Jour. Antennas Prop ., vol. 2011, Article ID 936781, 11 pages, 2011  O.M. Bucci, C. Gennarelli, G. Riccio, C. Savarese, “Electromagnetic fields interpolation from nonuniform samples over spherical and cylindrical surfaces,” IEE Proc. Microw. Antennas Prop ., vol. 141, pp. 77-84, April 1994.  F. Ferrara, C. Gennarelli, G. Riccio, C. Savarese, “Far field reconstruction from nonuniform plane-polar data: a SVD based approach,” Electromagnetics, vol. 23, pp. 417-429, July 2003  F. D’Agostino, F. Ferrara, C. Gennarelli, R. Guerriero, M. Migliozzi, “Two techniques for compensating the probe positioning errors in the spherical NF–FF transformation for elongated antennas,” The Open Electr. Electron. Eng. Jour. , vol. 5, pp. 29-36, 2011.
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