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.)
Over the last decade there has been great interest in ultrawideband (UWB) communication systems. Ultrawideband antennas that are able to transmit or receive short pulses with no distortion are called Impulse Radiating Antennas (IRA). One of the most commonly used IRA.s consists of a parabolic reflector fed by conical transmission lines that propagate a spherical TEM wave. The reflector IRA was constructed, analyzed and measured at UCLA. A method of moments based software, Hybrid EFIE and MFIE Iterative (HEMI), is employed to simulate the antenna. The software has to be run many times for a wide frequency range. The simulation results for the current distribution on the conical coplanar feeds show that one of the arms can be used as an UWB balun and the unbalanced line can be connected to the antenna. The aperture field is studied by calculating the surface current on the reflector. These current distributions show that the aperture field is tapered from edge to center and the center part is less illuminated in comparison with the edges. This increases the side lobe level for reflector IRA. To measure the time domain characteristics of an IRA, we have to use either short pulses and a time-domain setup or many frequencies in a wide frequency band and use an inverse Fourier transformation to calculate the time-domain results. In this work, we used frequency domain measurement setup to measure the antenna characteristics. The recently constructed spherical near-field measurement chamber at UCLA is used to measure the radiation characteristics of the antenna. The far-field calculated from the near-field measured data is compared with the HEMI results. Calculated and measured results show good agreement.
Microwave Hyperthermia has been used successfully in non-invasive treatment of tumors on the surface or just below the surface of the human body. The precise focusing of beams in the near-field zone of the applicator is quite complex, and conformal antennas, owing to their flexible contour, can blend with the local body surface area. This paper details experimental studies on a K band waveguide array (18-26 Ghz), operating in different geometries: 1-dimensional linear arc array, 2- dimensional planar array or 3-dimensional spherical volumetric array. The array has N directing waveguides (2 = N = 8) and one focusing waveguide, and conformal shape can be achieved by movement of primarily the focusing element. This paper presents both linear z-axis near-field measurement, and planar x-y axis measurement. In this particular application, the primary motivation is to get a focused beam in the near-field, and to control the axial movement of the beam by the position of the focusing element of the array.
In a previous AMTA paper [1], we presented a firstprinciples algorithm called wavenumber migration (WM) for estimating a target’s far-field RCS and/or far-field images from extreme near-field linear (1-D) or planar (2-D) SAR measurements, such as those collected for flight-line diagnostics of aircraft signatures. However, the algorithm assumes the radar antenna has a uniform, isotropic pattern on both transmit and receive. In this paper, we describe a modification to the (1-D) linear SAR WM algorithm that compensates for nonuniform antenna pattern effects. We also introduce two variants to the algorithm that eliminate certain computational steps and lead to more efficient implementations. The effectiveness of the pattern compensation is demonstrated for all three versions of the algorithm in both the RCS and the image domains using simulated data from arrays of simple point scatterers.
In a previous AMTA paper [1], we presented a firstprinciples algorithm called wavenumber migration (WM) for estimating a target’s far-field RCS and/or far-field images from extreme near-field linear (1-D) or planar (2-D) SAR measurements, such as those collected for flight-line diagnostics of aircraft signatures. However, the algorithm assumes the radar antenna has a uniform, isotropic pattern on both transmit and receive. In this paper, we describe a modification to the (1-D) linear SAR WM algorithm that compensates for nonuniform antenna pattern effects. We also introduce two variants to the algorithm that eliminate certain computational steps and lead to more efficient implementations. The effectiveness of the pattern compensation is demonstrated for all three versions of the algorithm in both the RCS and the image domains using simulated data from arrays of simple point scatterers.
The task of performing reliable RCS measurements in complex environments under near-field conditions is gaining more and more interest, mainly for a rapid assessment of RADAR performance of constructive details. This paper describes a low-cost compact measurement system fully developed by IDS, that allows fast and effective acquisition of diagnostic images under nearfield conditions and far-field RCS estimation in a nonanechoic environment. The hardware of the system is composed of a planar scanner, two horn antennas, a Vector Network Analyzer and a computer. The two axes scanner allows 2D scanning of antennas in a vertical plane. For each point of a predefined grid along the scanned area, the Analyzer performs a frequency scan. The acquisition software synchronizes scanner movements with data acquisition, transfer and storage on the computer’s HDD. The software has post-processing capabilities as well. A number of focusing algorithms permit to produce 2D and 3D diagnostic images of the target as well as 2D backprojection. It is moreover possible to reconstruct the RCS starting from near-field images. Along with system features, a summary of performances and some simple targets images are presented.
Monostatic backscatter measurements made in the near-field have been used to generate high resolution images of complex targets; however, the appropriate use of this data for obtaining far-field RCS values needed further examination. In this paper we comment on some of the available methods, and discuss in some more detail the concept that Fourier Transform of monostatic backscatter data collected over a planar array indeed provides samples in Fourier Space directly.
A fully-functional Fresnel Zone (FZ) antenna was designed and measured using PO simulation programs and the bi-polar near-field facility. The results from these measurements and simulation are presented in this paper. First, a detailed description of an FZ antenna and its operation is given. Then, a discussion of the design and construction procedure for both the FZ antenna and supporting structure is included. The resulting far-field pattern, near-field plots, and holographic images are shown in this paper. The antenna was measured with different feed positions to observe how it affects the overall antenna performance.
This paper will discuss the capability of spherical near-field test ranges using probe arrays to measure electrically large directive antennas. More particularly, the operating range of the existing Stargate equipment in terms of antenna dimensions has been identified. The advantages of using such equipment to measure quasi isotropic antennas will be first reminded. Then a study that aims to give a limit of the dimensions of the antenna under test will be presented. The sources of error that contribute to the limits will be described. Finally it will shown how an extension of Stargate equipment can be implemented in order to increase its the capability to the measurement of directive antennas, i.e. largest in dimension. This paper will be illustrated with real measurements of directive antennas. A comparison with both probe array near-field scanner and a far-field test range will be commented.
The National Institute of Standards and Technology (NIST) characterized three phase retardation plates for the National Oceanic & Atmospheric Administration (NOAA). These plates are used to produce known polarized signals needed to calibrate polarimetric radiometers. The plates were tested at 10.7 and/or 18.7 GHz. The plates produce a phase shift between perpendicular field components of transmitted waves. The planar nearfield measurement technique was used to determine the phase shift. This paper will discuss the measurement procedure and results.
A new spherical near-field probe positioning device has been designed and constructed consisting of a large 5.0 meter fixed arc. This arc has been installed in a near-field test facility located at Alenia Marconi Systems on the Isle of Wight, UK. As part of the nearfield qualification, testing was performed on a ground based radar antenna. The resultant patterns were compared against measurements collected on the same antenna on a large outdoor cylindrical near-field test facility also located on the Isle of Wight [1]. These measurements included multiple frequency measurements and multiple pattern comparisons. This paper summarizes the results obtained as part of the measurement program and includes discussions on the error budgets for the two ranges along with a discussion on the mutual error budget between the two ranges.
A technique to identify failures in an antenna array using corporate feeding is presented. This technique combines near-field imaging close to the radiating elements and the printed transmission lines forming the feeding network. Planar near-field probing is done with a loop and a miniature dipole probe less than 0.1 free-space wavelength above the antenna under test. Two cases are considered, one where the feed lines would be separated from the radiating elements by a metal ground plane and another where the lines and the elements are on the same metal layer. In the first case, precise diagnostic based on extraction of vectorial forward and reverse wave complex coefficients on each line segment is possible. In the second case, it is not possible to extract these coefficients. However, defect localization is still possible by relying on symmetries present in the near-field maps of selected line segments.
We present the results of developing a MATLABbased Near-field Antenna measurements toolbox. The purpose of this package is two-fold. First, it functions as a training tool, to help the user understand the near-field measurement process. Second, it can also function as an analysis aid, providing insight into the effect of errors on the measurement process. Results obtained from using the beta version of the toolbox are presented and the toolbox will be available as a download from the website listed in the paper, to solicit feedback from the measurement community.
In order to diagnosis array antennas we implemented the back projection technique in our bi-polar near field laboratory. Using capabilities of microwave holography we investigated actual distribution of excitation coefficient values in a variety of antenna arrays operating at 5 GHz and around 10 GHz. We investigated phase and amplitude alignment of the linear MC-8 phased array with eight elements operated in the band centered at 5000 MHz. The reconstructed phase distribution images reveal phase distributions consistent with the design values. A major technical impairment is that the resolution at the element level can not be easily assured and it is related to the element spacing.
In order to diagnosis array antennas we implemented the back projection technique in our bi-polar near field laboratory. Using capabilities of microwave holography we investigated actual distribution of excitation coefficient values in a variety of antenna arrays operating at 5 GHz and around 10 GHz. We investigated phase and amplitude alignment of the linear MC-8 phased array with eight elements operated in the band centered at 5000 MHz. The reconstructed phase distribution images reveal phase distributions consistent with the design values. A major technical impairment is that the resolution at the element level can not be easily assured and it is related to the element spacing.
A Wideband Optically Multiplexed Beamformer Architecture (WOMBAt) was developed and characterized at the Crane Naval Surface Warfare Center Active Array Measurement Test Bed (AAMTB) facility. The project includes development and integration of the true-time delay (TTD) WOMBAt photonic beamformer with the Active Array Measurement Test Vehicle (AAMTV). The AAMTV is a 64-channel transmit-receive (TR) module based phased array beamformer that is integrated with the AAMTB facility 12’x9’ planar near-field scanner. The AAMTV provides phase trimming and a small amount of delay using electrical components while the WOMBAt provides longer delays using commercial-off-the-shelf (COTS) optical components typically manufactured for the telecommunication industry. By integrating the WOMBAt with the AAMTV, a highly flexible test environment was achieved that includes system calibration, multi-frequency scanning, and antenna pattern analysis. Phase I receive tests for this system were previously described and presented to AMTA[1] in 2002. This paper will describe the results of reconfiguring the AAMTV into a transmit architecture for Phase II. WOMBAt successfully demonstrated wideband TTD in both receive and transmit configurations at angles greater than the system goal of ±65º while exceeding all other system level performance goals. System level performance included a beam squint of less than 1.1º for receive and 0.5º for transmit, a worse case amplitude variation of 2.4 dB receive and 1.6 dB transmit and differential delays of less than 3.5 picoseconds.
The Intelsat-IX spacecraft carries a C- and Ku-Band payload. It provides coverages from five different orbital locations over Atlantic (AOR) and Indian (IOR) ocean regions. The feed arrays for the C-band multifeed offset parabolic reflector antennas were designed, manufactured and tested by EADS Astrium GmbH in Munich, Germany. Design drivers for the antenna subsystem were the high power requirement for the transmit antenna and stringent isolation specification for both transmit and receive antennas. The final designs feature as many as 145 feed horns and up to ten switches. Due to the complexity of the beam forming network and the large number of SCRIMP (Short Circular Ring loaded Horn with Minimized Cross-Polarization) horns at every feed array a special test philosophy was introduced in order to detect any malfunction of the array at an early stage of the antenna assembly and integration. This paper will present details of the applied test sequence starting at the initial beam forming network measurements and the intermediate near-field feed testing under extreme environmental conditions up to the final antenna testing in a compact range at unit and at spacecraft level. The used inhouse data evaluation software platform allows the evaluation of any measurement at any stage of the testing sequence independent of the actual applied losses and /or design error allocations.
The existing planar near-field antenna test range at Alcatel Space (ASP) in Toulouse has recently been enlarged and the frequency bandwidth increased to 18.5 GHz to allow for the testing of large fully integrated space flight antennas. This upgraded test range, including a specific reconfigurable reflector antenna support tool, will be described. The range assessment method, carried out with a Ku-band single reflector antenna, will be outlined: error budgets obtained with the NIST 18-term method as well as absolute gain measurement and inter-comparisons with compact antenna test range (CATR) measurements will be presented. Typical applications for L-Band and C-Band antennas will be presented with error budgets. Comparisons with simulated data will further demonstrate the range performance.
The recent launch and successful orbiting of the EO-1 Satellite has provided an opportunity to validate the performance of a newly developed X-Band transmitonly phased array aboard the satellite. This paper will compare results of planar near-field testing before and after spacecraft installation as well as on-orbit pattern characterization. The transmit-only array is used as a high data rate antenna for relaying scientific data from the satellite to earth stations. The antenna contains distributed solid-state amplifiers behind each antenna element that cannot be monitored except for radiation pattern measurements. A unique portable planar near-field scanner allows both radiation pattern measurements and also diagnostics of array aperture distribution before and after environmental testing over the ground-integration and pre-launch testing of the satellite. The antenna beam scanning software was confirmed from actual pattern measurements of the scanned beam positions during the spacecraft assembly testing. The scanned radiation patterns on-orbit were compared to the near-field patterns made before launch to confirm the antenna performance. The near-field measurement scanner has provided a versatile testing method for satellite high gain data-link antennas.
Bistatic radar cross sections of targets are computed from field measurements on a cylindrical scan surface placed in the near field of the target. The measurements are carried out in a radio anechoic chamber with an incident plane-wave field generated by a compact-range reflector. The accuracy of the computed target far field is significantly improved by applying asymptotic edge-correction techniques that compensate for the effect of truncation at the top and bottom edges of the scan cylinder. The measured field on the scan cylinder is a “total” near field that includes the incident field, the field of the support structure, and the scattered field of the target. The background subtraction method determines an approximation for the scattered near field on the scan cylinder from two measurements of total near fields. The far fields of metallic sphere and rod targets are computed from experimental near-field data and the results are verified with reference solutions.
Bistatic radar cross sections of targets are computed from field measurements on a cylindrical scan surface placed in the near field of the target. The measurements are carried out in a radio anechoic chamber with an incident plane-wave field generated by a compact-range reflector. The accuracy of the computed target far field is significantly improved by applying asymptotic edge-correction techniques that compensate for the effect of truncation at the top and bottom edges of the scan cylinder. The measured field on the scan cylinder is a “total” near field that includes the incident field, the field of the support structure, and the scattered field of the target. The background subtraction method determines an approximation for the scattered near field on the scan cylinder from two measurements of total near fields. The far fields of metallic sphere and rod targets are computed from experimental near-field data and the results are verified with reference solutions.