Welcome to the AMTA paper archive. Select a category, publication date or search by author.
(Note: Papers will always be listed by categories. To see ALL of the papers meeting your search criteria select the "AMTA Paper Archive" category after performing your search.)
surfaces overagroundplane hasbeenusedfor anumber ofultra--wideband(UWB) applications.Thispaperdiscussespracticalchallenges associatedwithaccuratecharacterization andverificationofmultilayer UWBantennasdesignedfor highpowerapplications.Akeydesignconstraintforhighpowerantennasisanextremelylowimpedancemismatch atthefeedterminalsneededtoefficientlycoupleenergyintothe antenna.Carefuldesign and optimization oftheantennalayersandradiatingsurfacecantheoreticallyachievetherequiredefficiencies.However,verificationofthedesignischallengingduetopracticallimitations ofboththeantennafabricationprocessand measurementmethodologies.Analysisoftheantennaarchitecturefromatestandevaluationperspective isusedtoidentify potentialmeasurementriskareasandguidethedevelopmentofanincremental testmethodologydesignedtomitigateorbetter understand therisks.Laboratory testcouponswere fabricatedandmeasuredtodetermineconstitutivelayerandcompositestack--up performance.Throughtheincrementaltestingmethodology,developerswereabletodeterminethat prototypeperformancewas limitedduetothevariabilityofetchedresistor valuesonthe drivenlayer.Thepaperconcludes withashortdiscussionoffrequencyscalabilityandsummaryofplansforfuturetests.
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—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.
Abstract—Identification and separation of electromagnetic mixed sources within a narrow bandwidth are required in various applications. The Independent component analysis (ICA) is here applied in the separation of three independents electromagnetic sources. An efficient algorithm and a measurement setup are proposed for capturing and separating mixed signals. Three uncorrelated microwave signal generators are used to provide multiple independent wireless sources (transmitters). The receivers are high gain broadband antenna placed in the azimuthal plane and randomly positioned. Here the signals are CW waves with a very small frequency difference (.F = 0.1%). In the present analysis the environment noise is also taken into account as an additional source. The estimated signals by ICA and original measured ones have good agreement. Considering the complexity of the measurement setup and the proximity between the frequencies of signal sources the proposed algorithm is suitable for applications in Jamming treatment and Direction of Arrival.
Compensated compact ranges offer accurate testing techniques for large devices under test. The quiet zone field performance is affected by diffracted field components from the sub and main reflector edges even though they are equipped with serrations in order to reduce this effect. The size, shape, and alignment of the serrations have a strong influence on the range performance and are important design parameters. For performance estimation and optimization, detailed EM simulation models are required. Integral equation methods like the Method of Moments (MoM) with Multilevel Fast Multipole (MLFMM) acceleration promise accurate simulation results. However, the memory requirements limit simulations nowadays to lower frequencies due to the electrical size of the compact range reflectors. For example, the main reflector of Astrium's Compensated Compact Range CCR 120/100 including serrations is 1860 ? by 1600 ? in size at 40 GHz. Asymptotic methods are suitable for objects of this size, however, the accuracy has to be investigated and is related to the degree of detail in the model. A detailed simulation model based on the Physical Optics (PO) / Physical Theory of Diffraction (PTD) method is developed in GRASP. Each serration is realized as an individual scatterer and can thus be modeled with arbitrary shape and orientation. Different modeling techniques have been applied in order to realize an accurate simulation model with acceptable runtime. In this paper, the simulation model will be described in detail and a comparison of the quiet zone fields will be drawn with the MoM / MLFMM tool Feko as well as with quiet zone probing measurements.
A new material validation and verification standard is designed to imitate the behavior of a lossy dielectric absorber. This standard is constructed from well-characterized, low-loss materials in a manner that ensures manufacturing repeatability. The performance of this standard is verified with S-parameter and permittivity measurements in a free space focused beam system and with finite difference time domain simulations. A sensitivity analysis, based on a series of simulations, is presented to quantify the uncertainty in the measured S-parameters due to dimensional and alignment variations from the ideal design values.
There are many ways to acquire the current location, global positioning system (GPS), triangulation, radar, and dead reckoning. Today GPS is the most reliable and accurate navigation technique when there is a clear, unobstructed view of the satellite constellation. However, when GPS is not available, another means of reliable navigation must be accomplished. The Air Force Institute of Technology (AFIT) random noise radar (RNR) is a possible solution to the indoor navigation problem. However, the current implementation of the RNR requires a large amount of data to be transfered between radar pulses. This research determined if using a template replay strategy has the same RNR performance as using an analog noise source. Using the template replay approach, each RNR node has a priori knowledge about the transmitted waveforms of other nodes and does not require the large data transfer between radar pulses. The analysis here revealed that modifications do not significantly alter RNR functionality. The analysis revealed that even at signalto- noise plus interference ratio (SNIR) equal to 0 dB, there are no parameters that can be reliably extracted other than transmitted signal bandwidth and transmitted template length; the transmitted message length was able to be extracted because the message was repeated over and over. If the message was not replayed the analysis showed that there would be no ability to extract parameters. Finally, by using the RNR to transmit digitally generated templates, digital communication is possible and the symbol error rate (SER) is traceable to simulated SER.
Advances in computational resources facilitate anechoic chamber modeling and analysis at VHF frequencies using full-wave solvers available in commercial software such as FEKO. The measurement community has a substantial and increasing interest in utilizing computational electromagnetic (CEM) tools to minimize the financial and real estate resources required to design and construct a custom anechoic chamber without sacrificing performance. A full-wave simulation analysis provides a more accurate solution than the approximations inherent to asymptotic ray-tracing techniques, which have traditionally been exploited to overcome computational resource limitations. An anechoic chamber is simulated with a rectangular down-range cross-section to utilize the software’s capability to assess polarization performance. The absorber layout within the anechoic chamber can be optimized using FEKO for minimal reflections and an acceptable axial ratio in the quiet zone. Numerical results of quiet zone disturbances and axial ratios are included for both low- and medium-gain source antennas over a broad frequency range.
Streaming SDR (software defined radio) communication receivers are now high performance, common place and cost effective. Yet these receivers are not easily used for antenna measurements for a variety of reasons including their inability to accept phase reference and measurement trigger information. A new technique called Time Space Coherence Interferometry (TSCI) solves this problem in a simple and elegant manner. TSCI combines the concepts of temporal phase coherence with spatial division multiple access (SDMA) to directly encode phase and spatial information into a single continuous receiver data stream. The stream can be recorded for later analysis or efficiently decoded in real time producing conventional spatially sampled S21 amplitude and phase measurements. Additional data including antenna pulse timing, dynamics and signal quality metrics can be extracted from the TSCI data stream. Several representative TSCI systems are described.
Radar Cross Section (RCS) and Antenna measurement ranges share many common features and are often used for both purposes. Calibration of these dual-purpose ranges is typically done using the substitution method for both RCS and antenna testing, but with separate RCS and antenna standards. RCS standards are typically based on a geometric shape having a well known theoretical value – and corresponding small uncertainty. By contrast, antenna standards typically must be “calibrated” in a separate antenna calibration system to be used as a gain standard, often yielding higher uncertainties. This paper presents an efficient method for transferring an RCS measurement calibration to an antenna measurement range configuration, allowing a range to be used for both purposes with a single calibration. Insight into the best ways to re-configure the instrumentation between RCS and antenna testing is included. Validation measurements from a compact range are included along with an uncertainty analysis of the method.
The numerical analysis used for efficient processing of spherical near-field data requires that the far-field pattern of the probe can be expressed using only azimuthal modes with indices of µ = ±1. (1) If the probe satisfies this symmetry requirement, near-field data is only required for the two angles of probe rotation about its axis of . = 0 and 90 degrees and numerical integration in . is not required. This reduces both measurement and computation time and so it is desirable to use probes that will satisfy the µ = ±1 criteria. Circularly symmetric probes can be constructed that reduce the higher order modes to very low levels and for probes like open ended rectangular waveguides (OEWG) the effect of the higher order modes can be reduced by using a measurement radius that reduces the subtended angle of the AUT. Some analysis and simulation have been done to estimate the effect of using a probe with the higher order modes (2) – (6) and the following study is another effort to develop guidelines for the properties of the probe and the measurement radius that will reduce the effect of higher order modes to minimal levels. This study is based on the observation that since the higher order probe azimuthal modes are directly related to the probe properties for rotation about its axis, the near-field data that should be most sensitive to these modes is a near-field polarization measurement. This measurement is taken with the probe at a fixed (x,y,z) or (.,f,r) position and the probe is rotated about its axis by the angle .. The amplitude and phase received by the probe is measured as a function of the . rotation angle. A direct measurement using different probes would be desirable, but since the effect of the higher order modes is very small, other measurement errors would likely obscure the desired information. This study uses the plane-wave transmission equation (7) to calculate the received signal for an AUT/probe combination where the probe is at any specified position and orientation in the near-field. The plane wave spectrum for both the AUT and the probe are derived from measured planar or spherical near-field data. The plane wave spectrum for the AUT is the same for all calculations and the receiving spectrum for the probe at each . orientation is determined from the far-field pattern of the probe after it has been rotated by the angle .. The far-field pattern of the probe as derived from spherical near-field measurements can be filtered to include or exclude the higher order spherical modes, and the near-field polarization data can therefore be calculated to show the sensitivity to these higher order modes. This approach focuses on the effect of the higher order spherical modes and completely excludes the effect of measurement errors. The results of these calculations for different AUT/probe/measurement radius combinations will be shown.
In this paper application of quasi-planar near-field measurements to characterize the radiation from a test object with the purpose of electromagnetic compatibility (EMC) will be described. First a brief description of an EMC radiated emission Open Area Test Site (OATS) and the setup of a typical EMC quasi-planar table top near-field scanner will be presented. Then the challenges of adapting the near-field scanning technology used for antennas to near-field scanning of EMC test objects will be discussed. Specifically the challenges of 1) Obtaining phase from active equipment under test (EUT) with a radiation caused by quasi stationary random processes. 2) Challenges in probe design and construction that yields satisfactory sensitivity, cross polarization rejection and field disturbance. 3) Measurement in the reactive near-field region and analysis of the probe impact on the measured data. 4) The problems of characterization of non-planar EUT geometry that violates the equivalent surface theorem due to cables leaving the box enclosed by the surface. 5) Near-field measurements on non-directionally radiating test objects 6) Post processing of EMC near-field data: combining of several measurement data sets and taking multiple reflections into account when inserting measured near-field in a CAD model of the full apparatus. 7) Current status in predicting the absolute radiation level in dBuV/m, as measured in OATS, from a near-field measurement
Far-field uncertainty due to probe errors in planar near-field measurements is analyzed for the fast irregular antenna field transformation algorithm. Results are compared with the classical technique employing two dimensional Fast Fourier Transform (2D FFT). Errors involving probe's relative pattern, alignment, transverse and longitudinal position, interaction with AUT etc. have been considered for planar measurements. The multiple reflections error originating from the interaction of the probe and the AUT tends to deteriorate the radiation pattern to a greater extent. Therefore, a novel technique which utilizes near-field measurements on two partial planes is presented to reduce the multiple reflections between the probe and the AUT.
Spiral antennas have been well established as good radiators of circularly polarized radiation that are capable of achieving very large bandwidths. Though traditionally used for receiving applications, this paper will show that printed spiral antennas are also capable of performing as high-power radiators. Several printed 4-armed spiral antennas are presented, along with measured data that attest to their ability to handle hundreds of watts of continuous wave (CW) power at microwave frequencies. This high-power data includes temperature, electric field, and return loss readings recorded during the tests. Such high power performance is achieved through the use of a high-power capable substrate, lossless cavity, multi-arming, and applying a dual-layering technique which serves to reduce the current density and improve the spiral antenna’s match to 50O. Radiation and impedance measurements are taken to fully verify wideband performance. Analysis of the current densities from simulations is also presented. Data from the high-power tests indicate that the chief factors limiting the spirals’ power handling are their beamformers and resistive terminations.
For future NASA Manned Space Exploration of the Moon and Mars, a blunt body capsule, called the Orion Crew Exploration Vehicle (CEV), composed of a Crew Module (CM) and a Service Module (SM), with a parachute decent assembly is planned for reentry back to Earth. A Capsule Parachute Assembly System (CPAS) is being developed for preliminary parachute drop tests at the Yuma Proving Ground (YPG) to simulate high-speed reentry to Earth from beyond Low-Earth-Orbit (LEO) and to provide measurements of landing parameters and parachute loads. The avionics systems on CPAS also provide mission critical firing events to deploy, reef, and release the parachutes in three stages (extraction, drogues, mains) using mortars and pressure cartridge assemblies. In addition, a Mid-Air Delivery System (MDS) is used to separate the capsule from the sled that is used to eject the capsule from the back of the drop plane. Also, high-speed and high-definition cameras in a Video Camera System (VCS) are used to film the drop plane extraction and parachute landing events. To verify Electromagnetic Compatibility (EMC) of the CPAS system from unintentional radiation, Electromagnetic Interference (EMI) measurements are being made inside a semi-anechoic chamber at NASA/JSC at 1m from the electronic components of the CPAS system. In addition, EMI measurements of the integrated CPAS system are being made inside a hanger at YPG. These near-field B-Dot probe measurements on the surface of a parachute simulator (DART) are being extrapolated outward to the 1m standard distance for comparison to the MIL-STD radiated emissions limit.
This paper describes the behavior of the antenna radiation pattern for different planar near-field measurement errors superimposed on the near-field data. The disturbed radiating near field is processed using multilevel plane wave based near-field far-field transformation to determine the far-field. Errors like scan area truncation, transverse and longitudinal position inaccuracy of measurement points, and irregular sample spacing are analyzed for an electrically large parabolic reflector at 40 GHz. The error behavior is then compared with the standard transformation technique employing 2D Fast Fourier Transform (FFT) using the same near-field data. In order to exclude the effect of any other measurement or environmental error, electric dipoles with appropriate magnitude profile and geometrical arrangement are used to model the test antenna.
A low cost transportable short range Synthetic Aperture Radar (SAR) measurement system is constructed by placing a linear positioner on the bed of a truck. The radar system is based on a network analyzer and a pair of standard horn antennas. The SAR system gives a resolution of 0.3 m at X-band frequencies and 100 m measurement distance. By using the terrain the objects can be measured at depression angles up to at least 10. . The near field SAR images are processed using back projection algorithms. The system can be used to estimate camouflage efficacy in realistic environments. Flexible software based entirely on open source components is developed for the data processing, presentation and analysis of the SAR images. Results from the evaluation of two generic camouflage nets using reference targets in different backgrounds and SAR images of vehicles are presented.
The installation of power-generating wind turbines near outdoor radar cross-section measurement ranges for low-observable targets presents a number of problems for accurate measurements on those ranges. The turbines, with towers up to 100 meters tall and blades 45 meters long, are enormous scatterers that raise clutter levels well above returns from LO targets. The movement of the rotors, rotating about both a horizontal and vertical axis, generates a dynamic and unpredictable Doppler smear that cannot be mitigated with phase coding techniques or Doppler filtering. Lastly, the large wind farms over which the turbines are installed lowers the unambiguous-return PRF to extremely low levels, raising test times and dropping rotation speeds below acceptable levels. A method of varying pulse spacing into a burst mode is presented that maintains data throughput in RCS collection while avoiding the clutter returns of downrange wind turbines. This burst mode has the radar transmit and receive a string of closely-spaced pulses, and then idle while that string of pulses propagates through the wind farm. By careful selection of timing parameters, clean-range clutter levels can be maintained with little to no degradation in test time.
This paper validates the sub-reflectarray technique for main reflector antenna distortion compensation through simulations and measurements. First, axial defocusing of the feed creates spherical aberration distortion and it is corrected using sub-reflectarray by conjugate field matching method. Then, a ring-type distortion is created on the main reflector and it is also compensated using a similar approach. A hybrid HFSS/PO simulation approach was used for the design and analysis. Bipolar planar near-field measurements are performed to validate the compensation technique and back projection holography is used to locate the position of distortions and to study the effects of the distortion on the antenna performance.