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MTI Technology and Engineering Ltd. in Israel has installed an antenna test facility for the development and production testing of communication link antennas. Link antennas are typically high gain, medium size (< 2 ft) and medium to high frequency (10 to 50 GHz), with strict requirements on sidelobes, back-radiation and cross-polarization. Production testing is typically done on the main cuts. The facility is also used for PTMP and WLL antennas down to 2 GHz. This is an ideal requirement for a small size compact range. The ORBIT/FR single reflector compact range with a cylindrical quiet zone of a size 4 x 4 ft (diameter x length) was selected. The performance is compliant to international regulations (e.g. FCC, ETSI, DTI-MPT), and has a cross polarization as low as –40 dB for 0.4-m antennas. The total chamber size is 31 x 18 x 15 ft (L x W x H). The positioner system is roll over model tower over azimuth over lower slide. The instrumentation is Agilent 8530 based. The system was installed and qualified in late 2002. Qualification was performed from 2 to 50 GHz for quiet zone field probing and antenna sidelobe level accuracy testing. A system description, as well as an excerpt of the qualification data are presented in the paper.
New taper chamber feed section was created for numerical analysis. To launch the undisturbed electromagnetic wave into the test zone, newly designed dual polarized aperture-matched blade mode bowtie (ABB) antenna was designed and implemented at the vertex of the feed section of the tapered chamber. For the accurate calculation, wall type absorber samples are obtained and measured. These values are included for realistic configurations. From the simulated time domain result, field distributions at the aperture of the feed sections are investigated. Determination of the usable spaces for different frequencies is discussed. Also, cross-talk levels are presented since the feed antenna designed for dual polarization.
Sub-millimeter wave holograms can be used as collimating elements in compact antenna test ranges. The fabrication of very large holograms can be facilitated using a modified hologram illumination with amplitude taper. The modified illumination also removes the current polarization limitation to a vertical polarization in the hologram operation. Shaped beam illuminating the hologram is achieved with a dual reflector feed system with two shaped hyperbolic reflectors. In this paper, the design of the quasi-optical reflector feed system with developed ray-tracing based reflector synthesis procedure is described. Simulation and measurement results of the dual reflector feed beam at 310 GHz are presented. The measured quietzone of a demonstration hologram fed with the dual reflector feed system is also shown.
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 National RCS Test Facility (NRTF) has designed, fabricated, and implemented an efficient and robust calibration procedure and test body applicable to pylon based monostatic RCS measurements. Our unique calibration test body provides physical separation between the calibration device and pylon allowing the pylon to be outside the range gate of the calibration device. This separation reduces the calibration device uncertainty due to target support contamination and interaction. Spectral analysis and feature extraction of rotational dihedral/dipole data allows further rejection of background noise and clutter that possess different angular dependencies from those of the dihedral/dipole. Due to the significant reduction in the achievable crosspolarization isolation that occurs with a small degree of positioning error in dihedral/dipole roll angle, a data driven search algorithm has been developed to select the two dihedral/dipole angles used by the polarimetric distortion compensation algorithm.
This paper presents results from a tracking and classification radar that is contained in a coffee-can sized cylinder that sits directly on the ground. The 50 mW radar operates in the 3.1 to 3.6 GHz band using horizontal polarization. The results from earlier radar propagation channel studies will be discussed, including propagation characteristics as a function of polarization and frequency band. The design for this radar that exploits the channel propagation characteristics will be described. Data from tracking of vehicles and humans will be presented. Examples of the range profiles of groups of humans and of moving vehicles will be shown. We will also show a test of the capability of such a system to track humans through building walls.
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.
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 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.
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.
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 (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.
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.
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.
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.
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.
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.
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.
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.
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.