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This paper deals with different aspects of the on-ground antenna pattern characterization of the MIRAS radiometer for ESA’s SMOS mission. Various technical challenges of the project are briefly described. Special attention is given to the effect of multiple reflections between the antenna under test and the measurement probe. A series of antenna measurements of the MIRAS radiometer antennas is now on-going at the DTU-ESA Facility. The main objectives of these are to investigate the accuracy of the forthcoming antenna characterization, to find solutions to the already known problems, to identify new possible difficulties, and to establish an optimal measurement strategy, which should allow for the tight error requirements and minimize the overall time of the measurement campaign.
As known, spacecraft antenna design is an everdemanding task, due to the tight requirements on performance and the small available space. Moreover, the trend of installing array antennas onboard makes this task even more complex. For this reason, every antenna design must be verified against its installation constraints, in term of pattern distortion, due to interaction with spacecraft structure, inter-antenna coupling with nearby antennas, which can be remarkable due to the reduced available space, and generation and propagation of passive inter-modulation products (PIM), that can seriously affect the performance of transponders. For the above reasons, a Design Framework has been developed in the frame of an ESA contract. In this activity, European universities, industry and research centers cooperated in order to integrate within a single environment different prediction codes providing the required modeling capabilities. The system is able to guide the user from the antenna design phases through antenna installation simulation. The framework also allows for storage and management of experimental data in the more common formats or in user-defined ones, making able the designer to validate its numerical models with measured data obtained from intermediate breadboards. A validation activity is in progress and comparisons between simulation and measurements are reported, together with main characteristics of the design system. The system has been applied, among others, in the design and compatibility analysis, of Galileo 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.
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.
We introduce a new calibration standard geometry for use in a static RCS measurement system that can simultaneously offer multiple “exact” RCS values based on a simple azimuth rotation of the object. Called the “cam,” the new calibration device eliminates the problem of frequency nulls exhibited by other resonantsized cal devices by shifting the nulls through azimuthal rotation. Furthermore, the “cam” facilitates the use of dual-calibration RCS measurements without the need to mount a second cal standard. The “cam” is practical to fabricate and deploy; it is conducting, composed of flat and constant-radius singly-curved surfaces, and is compatible with standard pylon rotator mounts. High-accuracy computational results from moment-method modeling are presented to show the efficacy of the new standard.
New results are presented on using small spheres mounted on a foam tower for calibration. Subtraction of the foam tower response is found to be necessary and sufficient for the dual-calibration method to work.
Coherent radar cross section measurements on a target moving along the line-of-sight in free space will trace a circle centered on the origin of the complex (I,Q) plane. The presence of additional complex signals (such as background, clutter, target-mount interactions, etc.), which do not depend on target position, will translate the origin of the circle to some complex point (I0,Q0). This type of phase-dependent I-Q data has been successfully analyzed. However, the presence of outliers can introduce significant errors in the determination of the radius and center of the IQ circle. Hence, we implement a combination of a robust and efficient Least-Median Square (LMS) and an Orthogonal Distance Regression (ODR) algorithm is used (1) to eliminate or to reduce the influence of outliers, and then (2) to separate the target and background signals. This technique is especially useful at sub-wavelength translations at VHF, where spectral techniques are not applicable since only a limited arc of data is available. We analyze data obtained as an Arrow III target moves relative to its supporting pylon. To demonstrate the effectiveness of the technique, we introduce rf interference signals into S band data and show that the uncontaminated parameters can be recovered with acceptable uncertainties.
Over the past few years, range certification activities have become more commonplace, as industry, government and academia have embraced the process and acted to implement documented procedures at their facilities. There is now a significant amount of documentation laying out the process, as well as templates to assist ranges in developing their range books. To date, however, there have been fewer examples of useful tools to assist the ranges in better understanding how the process will affect their specific range. The authors have developed a first generation MATLAB toolbox designed to provide ranges a “what-if” capability to see the impact of specific range errors on the range’s operations. Included within the toolbox are several types of additive and multiplicative errors, as well as means of modeling various aspects of radar operation.
A single tapered resistive strip (R-Card) has been used in the past in several applications related to antenna designs and ground bounce reduction for far-field ranges. Several antenna designs use single tapered R-Card to significantly reduce the diffracted fields from the antenna to achieve low side lobe performance and also maintain stable phase center location across wide frequency bandwidth. Single layer R-Card fences have also been successfully designed and used to reduce the ground bounce stray signal in far field ranges. Recently, a multilayer tapered R-Card concept has been investigated and implemented in two different applications for interaction reduction due to performance requirements. One of the applications is to use multilayer R-Card fences to reduce the groundbounce effect between two antennas for GPS applications. The second application is to embed the multilayer R-Card with the Styrofoam target support column used in RCS measurements to reduce the interaction between the target-under-test and the metallic azimuth rotator underneath the Styrofoam column. In both applications, the multilayer R-Card concept, with different resistance distributions and proper spacing, has been designed and evaluated such that it behaves as an absorber to reduce the interference/interaction between two antennas or two scattering objects. The design and evaluation of this new multilayer R-Card concept will be presented in this paper.
Occasionally, antenna patterns have discontinuities or “glitches” in them. While most of these glitches are obvious to a human looking at the plot, it can be difficult for a computer to automatically identify glitches while ignoring sidelobes and other real features of the antenna pattern. This paper will present a technique for accurately identifying and removing antenna pattern glitches through the use of higher order derivative information.
System Planning Corporation (SPC) is pleased to announce our new instrumentation radar measurement system denoted the Cheetah radar line. This radar system is based around the new Agilent PNA series of network analyzers. The PNA operates from 0.1 to 67 GHz and is utilized for making gated CW or CW RCS and Antenna measurements. The PNA has a built in synthesizer that allows the unit to be used without costly external synthesizers and external mixers. The PNA also has four identical receiving channels, two signal and two reference, that permit simultaneous co and cross pol measurements to be made. PNA IF bandwidth is selectable from 1 Hz to 40 kHz to optimize measurement sensitivity, dynamic range and speed. Using the segmented sweep feature of the PNA a single frequency sweep can be broken into segments, to further optimize the sensitivity, dynamic range, and speed. Each segment can have its own start and stop frequency, frequency step size, IF BW and power level. SPC has developed the high speed RF gating, low noise RF preamplifiers and high speed digital timing system, which allow maximum sensitivity, full up gated CW or CW radar measurements using the PNA. SPC has coupled the system to the CompuQuest 1541 RCS and Antenna Data Acquisition and Data Analysis Processing Software. This exciting new product line offers reduced cost and improved performance over current network analyzer based systems using the HP 8530, 8510, etc. Performance improvements are in the reduced noise figure, sensitivity, dynamic range and measurement speed. Measurement speeds are increased by at least a magnitude of order over the older systems and in some cases a couple of orders of magnitude.
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.
This paper describes the new ORBIT/FR StingRay Gated-CW radar implementation that provides both performance and speed improvements over those previously utilized and fielded in RCS measurement systems. The radar is implemented using one or multiple pulse modulators used to provide gating of the transmit and receive signals, in conjunction with the new class of Performance Network Analyzer recently introduced by Agilent Technologies. The radar features an order of magnitude improvement in speed over that previously offered using implementations with the Agilent 8510 or 8530 network analyzer/receiver. In addition, base sensitivity improvements are realized, and the radar is more flexible with user selection among many IF bandwidth settings now available. The physical profile of the radar is also improved, meaning that additional performance gains may be realized by creating a more efficient packaging scheme where the radar may be located closer to the radar antennas, either in a direct illumination configuration or in a compact range implementation. These factors, when considered in aggregate, result in the new ORBIT/FR StingRay Gated-CW radar offering that provides a higher performance-to-cost value trade-off than was previously available to the RCS measurement community.
Upcoming space exploration missions will have microwave instruments operating well beyond 100 GHz. Test techniques and instrumentation have to keep up with these developments. Although most of these instruments operate in a few narrow bands, a test engineer, faced with the combined requirements of a range of instruments will prefer full octave band coverage. As a goal, he would like to have the same functionality as at lower frequencies, i.e. sweep or step frequency capability, high dynamic range in the order of 80 dB, coherent, computer controllable and compatible with existing receiver equipment (HP8530). A concept based on a Backward Wave Oscillator, locked by PLL to a synthesizer was chosen. On the receiver side, sub-harmonic mixing was applied. The 110-170 GHz band was chosen as a first step to test the concept. The realized equipment has unsurpassed performance in terms of band coverage and dynamic range. In fact, all the requirements were achieved.
The ongoing rapid introduction of new and enhanced electronic products, especially in the area of wireless communications, put an increasing burden on manufacturers in regard to demonstration of product compliance with applicable EMC standards. Wireless communication systems use higher operational frequencies than ever before and PCs, a commodity item in many regions of the world, use clock frequencies in excess of 2 GHz. These technical innovations require emissions measurements above 1 GHz to minimize interference of products with communication systems. The accelerated technical innovation presents a real challenge for national and international standardization bodies which have to determine suitable limits, reflecting the necessary protection, along with the specifications for test measurement equipment and test procedures. At this point in time (May 2002), only very few general EMI standards do contain requirements for emissions measurements above 1 GHz. For instance CFR 47 Part 15 calls out emissions limits up to 40 GHz; the accompanying measurement standard, ANSI C63.4-2000, includes a generic procedure to perform the measurements. However, currently there is no criterion available for the validation of the test site above 1 GHz, similar to the normalized site criterion for the 30 MHz to 1000 MHz frequency range. Therefore, the test environment, which has a significant impact on the test results, cannot be qualified against an independent reference. The international standardization community, i.e., CISPR/A/WG1, is actively working on a verification criteria and procedure for test sites above 1 GHz to address this shortcoming. The following paper presents an alternative method for evaluating a test site above 1 GHz. Test data is presented and discussed which resulted from measurements, conducted to determine the suitability of an existing site for measuring emissions above 1 GHz.
We have developed the spherical near-field measurement system using a photonic sensor as the probe of the spherical scanning. Because the photonic sensor is a few gram of weight and a few mm in length, the measurement system can be compact and simple. The probe compensation is not needed because the photonic sensor can be considered as an ideal infinitesimal electric dipole antenna in the spherical near-field measurements as well as the planar near-field measurements as shown before. To demonstrate the validity of the system, we have measured the antenna patterns of a microstrip antenna on a finite printed board at 5.85 GHz. The measurements by the photonic sensor agreed with the one by the far-field method.
A measurement technique for Effective Isotropic Radiated Power (EIRP) using planar near-field scanning has been demonstrated earlier. In this paper I show how we at MI Technologies have implemented using the spherical near-field method the measurement of EIRP and a vector phasor quantity analogous to Effective Area that we call Antenna Receive Response. This technique is applicable to all antennas, including active antennas.
This paper will discuss the application of alignment techniques and tools in a near-field testfacility. Standard alignment telescopes are not directly applicable in a general purpose near-field set-up because of limited dimensions of such a facility, where a direct target is not available and is often to close to the antenna to be in the focus region of the telescope itself. Self-made optical tools will be presented to overcome this problem, including some estimates about the required and obtained accuracies. Using these tools is demonstrated as a fast and accurate way to align an antenna to the measurement set-up.
This paper describes the installation and implementation of a Cylindrical Near-field Test Facility at Chelton Radomes Ltd, Stevenage, (formerly British Aerospace Systems and Equipment Ltd.), in the UK for the testing of large radome/antenna combinations. Test site commissioning and validation activities to determine measurement accuracy & repeatability for the radome performance parameters of transmission loss and boresight error, are discussed. Test data from actual measurements are presented.
While probe arrays are now recognized to allow rapid and accurate near-field measurements, the interaction with the Antenna Under Test (AUT) is still sometimes considered as a potential limitation, especially for electrically large directive antennas [1]. Based on numerical simulations, this paper reports the results of a thorough investigation of the interaction mechanism and analyses its impact on the far-field pattern accuracy. The most often, interaction effects can be maintained at an acceptable level, thanks to an appropriate design of the probe array element and structure. However, the efficiency of a posteriori compensation schemes has also been investigated. The Pattern Coherent Averaging Technique (PCAT) [2], which is well known for compensating plane wave deviations in the quiet zone of antenna far-field test ranges or interactions from single probe near-field facilities, also proved very efficient to reduce the interaction effects with a probe array.