AMTA Paper Archive
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Ground Vehicle Tracking Performance of Low-Cost 3.5 GHz Ground Wave Radar
This paper will discuss the design and performance of a small step-frequency homodyne monopulse radar. The radar is designed to sit on the ground and penetrate weedy foliage to observe moving vehicles. It operates with horizontal polarization near 3.3 GHz with approximately 500 MHz bandwidth. Only 8 dBm power is needed. We will show the results of tests done with a corner reflector and with a walking human. Tracking performance in both range and azimuth will be shown.
Error Analysis of Circular-Polarization Components Synthesized From Linearly Polarized Measurements
A usual way of performing pattern-measurements on circularly polarized antennas is by measuring the linear components of the field and mathematically converting those to the left-hand and right-hand circular components. These synthesized circular components are sensitive for a number of factors: The exact orthogonality of the measured linear components, the measurement-accuracy of both phase and amplitude of the measured linear components, the polarization-pureness (or the accuracy of the description of the polarization-characteristics) of the probe, etc. This paper analyzes these factors, using a computer-model. An indication on the requirements to be imposed on the measurement-equipment is provided.
A Truck-Based Multifrequency SAR Platform
The growing need for a mobile radar system able to conduct measurements away from fixed radar ranges has prompted System Planning Corporation (SPC) to develop a mobile MkV radar system. Planned helicopter-based SAR measurements generated a requirement for a ground-based platform to verify functionality of X-band and VHF/UHF data collection and processing systems. Accordingly, SPC developed TruckSAR, a DGPS-equipped mobile testbed to collect side-looking and normal-incidence SAR data. Interleaved step chirp data were collected at 9.0-9.3 GHz (HH polarization) and 150-450 MHz (HH, VV, HV, and VH polarization). The system is self-contained and is proving useful for applications beyond ground and foliage penetration SAR investigations. This paper describes the TruckSAR hardware and data analysis systems. Results of measurements are presented, along with observations of challenges in data interpretation. Promising extensions of this mobile ground-based radar are also discussed.
Broadband, Dual Linearly-Polarized Antenna With Controllable Beamwidth
The OSU/ESL has been developing a broadband, dual-polarized dielectric horn antenna (DHA). This antenna has some attractive characteristics such as dual-polarization, good antenna isolation and stable beamwidth. By adjusting the geometry, the beamwidth of the E- and H-plane patterns can also be controlled independently. Critical design issues that affect the DHA performance include launch structure, lateral-wave elimination and dielectric constant will be addressed. A design example will be provided with a prototype DHA antenna constructed and tested for 2~14 GHz frequency range with a 110o beamwidth in both Eand H-planes. The antenna isolation was found to be greater than 30 dB for this prototype. The new DHA antenna could have wide applications in which broadband, dual-polarization operation, independent E- and H-plane beamwidths are desired.
Broadband Dielectric Probe for Near Field Measurements
A novel broadband dielectric rod probe design that has the characteristics of broad bandwidth; symmetric probe pattern; low RCS; low antenna clutter and dual polarization operation is discussed. The RCS level reduces the interaction between the probe and antenna under test (AUT). The lower antenna clutter level improves the sensitivity in detecting responses from wide angles with greater time delays. During the transmission mode, the rod is excited with a broadband microwave launcher from one end. The radiation then occurs at the other terminal of the rod. Measurement results of the far-field patterns, RCS and reflection coefficient for a prototype rod probe (DRP) are presented.
Experimental Studies With Comparisons to Computational Model for Automobile Antennas
A series of experimental and theoretical tests designed to develop techniques for reliable computational modeling of automobile antenna performance is presented. The results from the experimental measurements are compared with the results of computational techniques to verify their accuracy and reliability. The Electromagnetic Surface Patch (ESP5) code, a theoretical Method of Moment (MoM) general-purpose code developed at the Ohio State University, is used for computational modeling. We progress from the simple geometry of a single square plate and a monopole, to the more complex structure of a small copper-coated plastic model of an automobile. The computational simulation and measurements are configured with both a monopole antenna mounted at the center of the automobile roof and a backlite heater grid FM antenna. The input impedance, pattern, and polarization are all measured. Comparisons between the results of the computational simulations are presented, as well as the procedures used to measure the antenna characteristics and compare the experimental data with the measured data.
Advanced Compact Antenna Test Range Quiet Zone Characterization and Extension Techniques
Telecommunication satellites capacity growth has lead to a new generation of antennas , larger in size and with extremely sharp performance in terms of gain , cross polarization and coverage isolation (frequency re-use). In order to test such kind of antennas (the largest one is a Ku-band 3.6 m diameter and 6 m focal length reflector antenna) Alcatel Space Industries has implemented several innovations in its Compact Antenna Test Range (CATR): - a powerful and flexible machine has been invested , which provides 6 degrees of freedom (the machine has been called “6DOF Table”) in a wide range of motion to any satellite, allowing to bring any antenna of this satellite into the quiet zone - thanks to this new machine a series of accurate scanner probing has been performed , not only in the central plane of the quiet zone , but also on an eight meter range along the Angle Of Arrival (AOA) of the CATR - the quiet zone has been extended by one meter in height thanks to defocusing techniques; this extension has been modeled with GRASP 8 and tested using the vertical degree of freedom of the “6DOF Table” and a very accurate scanner. - In addition , the Cross polarization of the quiet zone has been tested with high dynamic ranges, using very high purity gridded horns . An average Cross polarization isolation better than 55 dB has been evidenced.
Accurate Gain Calibration With Corrugated Horns
A method is presented for calculating the gain of corrugated conical horns. It is based on basic symmetry conditions of circular or conical waveguide mode fields. This formulation allows to derive the radiation pattern over a complete sphere form two principal polarization patterns (E- and H-plane patterns). This method can be applied for both theoretical or experimental patterns, respectively. The theory has been verified experimentally with measurements carried out on two different ranges. The results agreed within 0.05 dB or less in all situations.
Quasi-Optical Waveguide Modeling Method for Scattering Matrix Measurements in the Near Millimeter and Submillimeter Wave Regions
Earlier (AMTA'97, AMTA'98), we have proposed a new low-cost laboratory method named the quasi-optical waveguide modeling (QWM) method to study power and amplitude-phase scattering characteristics of objects, in particular the RCS of targets or their scale models, in the near millimeter (NMM) and submillimeter (SMM) wave regions. A specific feature of this technique in that an investigated object (or its scale model) is mounted inside a quasi-optical waveguide structure in the form of a hollow dielectric waveguide (HDW), in which the scattering characteristics of the waveguide dominant HE11 mode are determined. These characteristics are related to the wanted scattering characteristics of the test object in free space by definite relationships. At the same time the HDW serves several functions: it forms a quasiplane incident wave within the scattering area where test object is placed, performs the low-loss and low-distortion transmission of the scattered wave carrying information of the object being tested to the receiver, effectively filters the unwanted modes arising at the scattering on the test object, and insulates the measurement area from the ambient conditions containing parasitic sources. In this paper we consider the possibility of using the QWM method to study polarization backward scattering characteristics of physical objects, in particular the complex elements of the scattering matrix with relative phase (SMR). A quasi-optical polarimetric micro-compact range (PMCR) based on the circular HDW and quasi-optical devices has been developed and built. The measurement results of the SMR and backward scattering patterns of a reference object as a square metallic cylinder obtained in the PMCR for the different linear polarization basic sets at the 4-mm wave band are presented. The comparison between the experimental results for the reference object and the theoretical data calculated by the geometrical theory of diffraction have shown a good agreement, and demonstrated the possibilities of the QWM method, and its good perspectives for backward scattering polarization characteristics modeling in the NMM and SMM wave regions.
Numerical Analysis of a Novel Tapered Chamber Feed Antenna Design
Tapered chambers have long been used for far-field antenna and RCS measurements. Conventional taper chambers used commercial antennas such as horns or log-period dipoles as wave launchers. One problem of this approach is the movement of the phase center associated with the antenna design. The positioning of the antenna inside the chamber is also critical. Undesired target-zone amplitude and phase distortion are caused by the scattering from the absorber walls. A novel feed antenna design for a tapered chamber is proposed here to provide broadband and dual polarization capabilities. This design integrates the absorber and the conducting walls behind the absorbers into to ensure a stationary phase center over a wider frequency range. In such a design, the dielectric constant of the absorber is utilized to maintain a clean phase front and a single incident wave at high frequencies. The conductivity of the absorber is also utilized to shape the field distribution at low frequencies. As a result, a wider frequency range can achievable for a given chamber size. One trade-off of this design is its reduced efficiency could be associated with the absorber absorption. Some simulation results from a 3-D FDTD model of a prototype design will be presented.
Correcting Dual Port Probe's Port-to-Port Calibration Using Near-Field Measurements
When a dual port probe is used for near-field measurements, the amplitude and phase difference between the two ports must be measured and applied to the probe correction files so that the measurements and calculations will have the same reference. For dual port linear probes, the measurement of this “Port-to-Port” ratio is usually accomplished during the gain or pattern measurements by using a rotating linear source antenna.1 When a dual port linear probe is used to measure a circularly polarized antenna, the uncertainty in this Port-to-Port ratio can have a significant effect on the determination of the cross polarized pattern. Uncertainties of tenths of a dB in amplitude or 1-3 degrees phase can cause changes in the cross polarized pattern of 5-10 dB.2 3 The paper will present a method for measuring the Port-to-Port ratio on the near-field range using a circularly polarized antenna as the AUT (Antenna Under Test). The AUT does not need to be perfectly polarized nor do we need to know its correct polarization. The measurements consist of two separate near-field scans. In the first measurement the probe is in its normal position and in the second it is rotated about the Z-axis by 90 degrees. A script then calculates the Port-to-Port ratio by comparing the crosspolarization results from the two measurements. Uncertainties in the Port-to-Port ratio can be reduced to hundredths of a dB in amplitude and tenths of a degree in phase. Measurements were taken at TRW’s Large Horizontal Near-field Antenna Test Range.
New Antenna Design and Measurement for Automobile Applications Using Genetic Algorithm
New automobile antennas must be developed to satisfy the growing requirements of the automobile industry. The uses of GPS band antennas for vehicle applications are growing very rapidly in the modern telecommunication area. In automobile antenna design, there exists geometrical constraints and several requirements for antenna specifications, for example, a Right-Hand Circular Polaization (RHCP) for a GPS antenna. In this paper, a new antenna for the automobile applications is designed using a Genetic Algorithm. It is well known that the GA can be used efficiently in the designing of various antennas. The GA searches the solution space of the possible antenna geometries satisfying the design goals. The design goals are RHCP with low cross polarization, a low SWR, and an omni-directional gain pattern in the upper-half plane. These design goals will be included in the cost function. The GA produces a set of new optimal antenna geometries. A series of experimental tests of the new antennas is presented, and the results are compared with the theoretical prediction. The ESP 5, a theoretical Method of Moment (MoM) general-purpose code developed at the Ohio State University, is used for an analysis tool.
VHF Capability and RCS Measurements from Long Cylinders
In order to better understand the capability and limitation of the radar in the VHF band, we present the results from RCS measurements on simple calibration objects of sizes from small to large. Though the uncertainty for measuring a small object is usually well behaved to within +0.2 dB, the greatest difficulty for a large object is the lack of knowledge on the distribution of the incident field. Some qualitative ideas may be obtained from fieldprobes along a few directions. Yet, a thorough investigation of the field in 3-D as a function of the frequency and polarization is generally beyond time and budget constraints. For the special cases of long and thin cylinders at broadside, we find that the difference in HH-VV is very sensitive to ka, which allows us to distinguish them apart.
Wide-Band Dual Polarized Probes for High Precision Near Field Measurements
High precision near field measurement systems in dual polarization have stringent requirements on the probe performance in terms of radiation pattern shape, on-axis and off-axis polarization purity and port-to-port isolation. In general, these specific requirements can be fulfilled using single polarized probes for narrow frequency bands (about 10% relative bandwidth) and using mechanical rotation for polarization diversity. Consequently, several sealed probes and complicated procedures are necessary to cover the operational frequency band of most common antenna applications leading to inefficient and time-consuming measurement procedures. SATIMO has developed high precision wide-band, dual polarized near field probes covering the frequency range from L to Ka-band to overcome this problem. Two different probe technologies have been applied, each particularly well suited for the appropriate low (L to X-band) and high (X to Ka-band) frequency range. The low frequency probe design is based on a compact corrugated horn with capacitive orthogonal excitations. The high frequency probe design consists of an axially symmetric corrugated horn, a square to circular wave-guide transition, and a wide-band, high isolation ortho-mode junction (OMJ) exciting the orthogonal polarizations. Probes in C-band and Ku-band have been delivered to and tested by ALCATEL SPACE INDUSTRIES in their planar near field antenna test range in Toulouse. The C-band probes have operational bandwidths of 25% covering the entire commonly used transmit and receive frequency bands for C-band communication satellites. The Ku-band probes have operational bandwidths of 40% covering the entire commonly used transmit and receive frequency bands for Ku-band communication satellites.
Ultra-Wide Band and Ultra-Wide Angle (UWB/A) SAR Antenna Design and Analysis With Measured Results
Ultra-Wide Band (UWB) antenna descriptors have been used to design an optimal Log Periodic Dipole Array (LPDA) antenna for the Army Research Laboratory’s (ARL) BoomSAR. Although dispersive in nature, the LPDA design offers improvements over existing antennas with broader beamwidth, higher efficiency, and improved off-boresight polarization performance. In the UWB/A SAR application, it is important that the antenna polarimetric spectral response remains coherent and uniform over the aspect angles used in the image formation process. This paper describes the process by which these goals were achieved and presents measured results from the BoomSAR of trihedrals and cylinders that validate the approach.
How to Choose an Antenna Range Configuration
Choosing the proper antenna range configuration is important in making accurate measurements and verifying antenna performance. This paper will describe the steps involved so the antenna engineer can select and specify the best antenna range configuration for a given antenna. It will describe the factors involved in choosing between near-field systems versus far-field systems, and the different scan types involved. It will explain the advantages of each type of antenna range and how the choices are affected by such factors as aperture size, frequency range, gain, beamwidth, polarization, field of view, sidelobe levels, and backlobe characterization desires. This paper will help the antenna engineer identify, understand, and evaluate the applicable characteristics and will help him in specifying the proper antenna range for testing the antenna.
Outdoor Broadband RCS Measurements of Model Scale Aircraft
In real life, most radar targets are located outdoors. Here we present results from outdoor broadband RCS measurements at the X-, Ka- and W-band of “Holger”, a metallized model-scale aircraft with cavities. RCS vs. angle data in the wing plane (0° elevation) were recorded at discrete frequencies (9, 35 and 94 GHz) in both horizontal (HH) and vertical (VV) polarizations. ISAR data at 7-13, 32-38 and 92-97 GHz were acquired. Results from a 104.1 m ground range and a 162.7 m free space range will be compared.
Portable Dechirp-On-Receive Radar
Sensor Concepts Inc. has prototyped a fast, lightweight, dechirp-on-receive radar called the SCI-Lr to provide the capability of a range instrumentation radar in a highly portable package. The small weight, size and power requirements of the SCI-Lr allow a variety of new deployment options for the user including in a small general aviation aircraft or on a mountaintop that is accessible only by four wheel drive. Pulse rates up to 20 KHz enables investigation of high Doppler bandwidth phenomenon such as ground vehicle microdoppler features. The dual integration from dechirp-on-receive matched filtering in fast time and Doppler processing in slow time provides high sensitivity with low output power. Planned enhancements of waveform bandwidth up to 2 GHz , frequency operation between .2 and 18 GHz and pulseto- pulse polarization switching will provide high information content for target discrimination. The flexibility provided by the hardware is augmented by software tools to examine data in near real time to monitor data quality and sufficiency. A variety of applications are being investigated including RCS measurement, SAR and ISAR imaging, Ground Moving Target Indication, and signature collection for ATC.
Simultaneous Axis Motion Applications in Antenna and Radome Measurements
This paper describes the use of simultaneous axis motion for various antenna, RCS, and radome applications, and the use of off the shelf hardware to support the corresponding measurement requirements. This is particularly relevant to polarization, low reflectivity target characterization, and radome measurements. Specific motion profiles required to accomplish various classes of tests are discussed, along with the implications on the mode of operation of the measurement system in order to achieve the most efficient collection of the required data. These simultaneous axis motion requirements may typically be user defined from the available set of axes composing the positioning system. Evaluation of the speed and real time tracking capability of the multiple axes are examined as they relate to the accuracy of the measurements that are required.
Uncertainty Analysis for Spherical Near-Field Measurements
A general approach is introduced for estimating uncertainties in far-field parameters obtained from spherical near-field measurements. Although the analysis is incomplete at present, we expect that as the measurement radius increases, our results will transform smoothly into the far-field case, where uncertainties depend on the on-axis gain and polarization of the probe and on the measurements in the far-field direction of interest.
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