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Within RF measurement systems, engineers commonly wish to know how much phase ripple will be present in a signal based on a given signal-to-noise ratio (SNR). In a past AMTA paper (Measurement Considerations for Antenna Pattern Accuracy, AMTA 1997), John Swanstrom presented an equation which demonstrated how the bound on the phase error could be calculated from the peak SNR value. However, it can be shown that the Swanstrom bound is broken when the signal has a peak SNR value of less than approximately 15 dB. This paper introduces a new equation that bounds the maximum phase error of a signal based on the signal’s peak SNR value. The derivation of this new bound is presented, and comparisons are made between the old Swanstrom bound and the new bound. In addition, the inverse relationship (i.e., calculating the SNR value of a signal from phase-only measurements) is investigated. In the past, analytical equations for this relationship have been presented by authors such as Robert Dybdal (Coherent RF Error Statistics in IEEE Trans. on Microwave Theory and Techniques) and Jim P.Y. Lee (I/Q Demodulation of Radar Signals with Calibration and Filtering in a Defense Research Establishment Ottawa publication). The analytical equations for calculating the SNR value using phase-only measurements are reviewed and discussed, and a brand new numerical relationship based on a polynomial curve fitting technique is proposed.
Electrically small antennas present tremendous design challenges. Plagued with a small radiation resistance and high quality factor (thus narrow bandwidth), these types of antennas are difficult to accurately measure. For use in HF communication applications, the problems associated with the entire development cycle become even more pronounced. This paper focuses on the development of two such electrically small HF antennas for a vehicular platform, specifically the Amphibious Assault Vehicle (AAV). The primary design objective is to develop antennas that operate over the entire near-vertical incidence (NVIS) band (2 – 10 MHz) with a minimum of 3kHz bandwidth. Additional design objectives are low profile, broadside directive pattern, and high power handling capability. The inverted L antenna and the half loop antenna were selected as probable candidates for this application. At 2 MHz, the antenna – vehicle system fits within the envelope ka < 0.2, where k is the free space wave number and a is the radius of a sphere completely enclosing the radiator. The full scale antenna design and performance were evaluated using method of moments and finite element method codes FEKO and HFSS respectfully. It is observed that the presence of the real ground plane poses a serious challenge for well established modeling techniques and considerable care must be exercised to obtain credible design data. For measurement validation and characterization of the antenna/vehicle interaction, a set of scaled antenna and vehicle prototypes were developed. Rapid prototyping and 3D printing were employed to build a scaled model (1:50 scale) of the complete antenna – vehicle system. The step-by-step process from the computational model to the measurement validation is discussed along with the description of the adopted fabrication techniques. In the concluding section of the paper, the measured results from the scaled model are presented alongside the simulated results. The good agreement between these results paves the way towards the successful use of such scaled model testing for more complicated antenna designs in the future.
One design of a smart plasma antenna is to surround a plasma or metal antenna by a plasma blanket in which the plasma density can be varied. In regions where the plasma frequency is much less than the antenna frequency, the antenna radiation passes through as if a window exists in the plasma blanket. In regions where the plasma frequency is high the plasma behaves like a perfect reflector with a reactive skin depth. Hence by opening and closing a sequence of these plasma windows this design can be computerized to electronically steer or direct the antenna beam into any and all directions. The plasma windowing design is one approach to the smart plasma antenna design. The beamwidth can vary from an omnidirectional radiation pattern with all the plasma windows open or a very directional radiation pattern when only one plasma window is open. The advantages of the plasma blanket windowing design are: 1. Beam steering of one omnidirection antenna with the plasma physics of plasma windowing. 2. A reconfiguable directivity. 3. The beamwidth can vary from an omnidirectional radiation pattern with all the plasma windows open to a directional radiation pattern with less than all the plasma windows open.
Abstract – This paper introduces a method for calibrating the gain and the frequency dependent phase center locations of Log Periodic Dipole Arrays (LPDAs). The method builds upon the three antenna method, but is conducted over a PEC ground plane in an Open Area Test Site (OATS). Similar to the traditional three antenna method, three pairings of transmission measurements are taken. In each measurement, one antenna is set at a fixed height above the ground plane, while the other antenna is scanned in height over 1 to 4 m heights. Magnitude and phase responses between the two antennas are taken at multiple heights. Measured results are fit to a theoretical model using a complex fit algorithm. From this process, the gain and frequency dependent phase center locations of each antenna can be solved. Measurement data show that it is effective in reducing systematic uncertainties associated with assuming fixed phase center locations. In addition, unlike other calibration methods over a conducting ground plane, no assumptions are made about the antenna patterns. This method provides an accurate, versatile and fast method for calibrating LPDAs from as low as 100 MHz.
Abstract—In this paper, a novel feeding method of microstrip line array is presented, with which every line array can be fed from the side part instead of from the center part .At the same time a novel compact slot patch antenna loaded with a pair of spirals is proposed, which is 66% smaller than the conventional half-wave patch antenna. The simulated and measured radiation patterns at center frequency are both presented. The -18dB side-lobe level for the sum pattern and -37dB null depth for the difference pattern have achieved in the experiment.
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: 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— Measurements and strategies for the calculation of radar cross-sections in the shorter millimeter wave region, especially of objects that include rough surfaces, are discussed. Because of decreasing wavelength, roughness becomes more significant in this spectral region, but also more difficult to characterize. A tabletop radar cross-section measurement system was set up to measure scattering from canonical objects and rough objects with regular or random patterns using a swept frequency continuous wave system. Random, rough objects of different surface roughnesses were measured and fit to statistical distributions governed by optical speckle theory. In this paper we consider the inclusion of optical speckle theory in the electromagnetic codes to address both issues associated with the characterization of target surfaces and the time required for numerical calculations.
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.
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.
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.
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.
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.
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.
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.
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.
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 [11]. 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.
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.
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.