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A new strategy to filter the environmental clutter in the measured near/far zone field data due to reflections and diffractions from objects in the measurement zone is presented. The approach is based on the new concepts of Point Source Spectral Content and Local Spectral Content of the reduced field detected on the observation domain. The effectiveness and the performances of the approach has been evaluated by processing synthetic as well as real world data.
An error detection technique was developed for culling large masses of measured antenna pattern data by first removing information that is likely to be associated with the antenna. Since the maximum spatial frequency of radiation from the antenna can be determined by its electrical size, any energy outside that spatial band is not considered to be valid and may be used to flag suspicious data. This analysis can be accomplished rapidly and can be used to cull patterns containing such anomalies as spikes, notches, non-closures and multipath effects. This paper describes the method with examples from simulated and measured patterns.
We present and analyze a procedure for performing relative, ultra-wideband antenna pattern measurements in a non-ideal EM facility. Ultra-wideband, shortimpulse, TEM horn transmission measurements were performed and compared with computer-modeled radiation pattern results. These measurements allowed us to analyze radiation lobes and nulls in both boresight and off-axis antenna positions. The results show that the measurements performed in this testing environment agreed well with computer models.
This paper presents a method for correcting RCS data obtained from objects extending beyond the boundaries of the test zone into the transition region of a large compact range collimator. The technique, exploiting the non-zero irradiation in the transition regions, uses results of calculated or measured field probes in conjunction with an image-based decomposition of the target angular response to correct for the field taper. The taper correction is developed as a weighting function applied to the spatial distribution with frequency-dependent coefficients derived from the field probes; the corrected RCS response is then obtained by an inverse operation. The paper addresses the conceptual notions of the approach and the limitations inherent to the underlying assumptions. Results of tests on canonical and actual targets are shown to demonstrate the applicability of the technique.
Waveguide simulators are widely used for low cost validation of periodic microwave designs and to perform antenna measurements. We have used measurement results of a waveguide simulator to predict both Frequency Selective Surface (FSS) and reflectarray responses. For scan angles close to normal, a suitable waveguide simulator is relatively wide and measurement results are often corrupted. This is often caused by uncontrolled multi-mode operation. The work presented here describes a waveguide simulator, which solves this problem for triple-mode operation. The triple-mode waveguide simulator has three standard waveguide ports and one triple-mode port. This device can be excited on the three standard ports. It produces each of the three propagating modes at the triple-mode port separately. Simulations and measurements on a prototype show good agreement. With our current set-up, three scan angles can be predicted instantaneously and grating lobes can be studied as well.
The possibility of launching satellites with increasing volume and weight leads to a higher economy and costefficiency for the service of future communication satellites, which are equipped with platforms up to 12 m in width for a variety of different antennas. For testing the radiation characteristics of the antennas of such large antenna farms, new test facilities are required to be designed and built up. Besides near-field test facilities, compact ranges exist, which provide additionally short test campaigns according to its real time measurement capability. Usually, for communication satellite testing, the highly accurate CCR 75/60 of Astrium GmbH, Germany, was used until now. For the future large satellites, Astrium newly designed the CCR 120/100, which provides a test zone of more than 8 m in diameter. The paper shows the requirements for testing of the large satellite antennas. Further, the design criteria, the range geometry and first simulation results of the CCR 120/100 are shown.
Wide frequency bandwidth feeds are used in compact ranges when multi-octave bandwidth operation of the range is desired. Dual-ridge or quad-ridge horns have been widely used in RCS applications as well as in antenna measurement applications to achieve wide band operation. This selection is made to take advantage of the lower cost of quad-ridge horns vs. other options. In designing a compact range, one primary concern is the beamwidth of the feed over the operating band. This affects the amplitude taper across the quiet zone of the range. Another primary concern is the movement of the phase center vs. frequency of the feed. This directly affects the phase taper across the quiet zone as a result of de-focusing of the reflector. Here we present measured data of the beamwidth and phase center movement vs. frequency of a wide-band quad-ridge feed designed to operate from 2.0-18.0 GHz. Measured and predicted quiet zone performance data over this bandwidth are presented with the feed installed in a Model 5751 compact antenna test range having a 4-foot quiet zone.
This paper describes a fully automated test set-up for obtaining spacecraft payload end to end system performance including EIRP, saturation flux density, transponder group delay, phase noise, carrier to noise ratio and G/T in a Compact Antenna Test Range (CATR). The RF signals are routed to and from the appropriate antennas by RF switches under the control of the test software. Spacecraft architectures vary widely often requiring adaptation of the test software. To enable this, it was decided to use an interpreted public domain language (Tcl/TK and IncrTcl) as the basis for the test programs to achieve easy customization without the need to recompile the test code. The test set-up is being implemented in the ESTEC Compact Payload Test Range.
Transverse electromagnetic (TEM), time-domain antennas are designed to reproduce accurately the time characteristics of received impulsive fields. For minimal distortion, the antenna response to the fields must be constant in amplitude and linear in phase. We are using numerical techniques are employed to improve previous designs by simulating modifications to the original design without costly, time-consuming hardware alterations.
In some antenna applications, it is desirable to introduce an interior surface that is absorptive at one frequency, and reflective at an adjacent frequency. Even a narrow band absorber, such as iron loaded Magnetic RAM, has absorption qualities far outside its optimal absorption band. The concept is to use a conductive-backed Radar Absorber Material (RAM) covered by a band pass Frequency Selective Surface. The FSS allows the frequencies to be absorbed to pass through to the absorber while reflecting frequencies away from the pass band. The example shown in this paper was designed to absorb energy in the 2-4 GHz band, and to be reflective below 500 MHz. Design considerations include: Overall thickness; Coupling between the FSS and RAM, and Size of the FSS elements relative to the internal antenna structure. Potential applications include: broad band antennas, scatter control, and cosite interference mitigation.
Recently, remarkable efforts have been spent to develop GPR (Ground Penetrating Radar) systems able to detect shallow anti-personnel mines. In order to achieve high resolutions, large bandwidths are necessary; furthermore antennas must operate detached from ground. The paper describes how an existing surface based antenna, developed for high resolution inspection of man-made structures, has been optimized following a combined measurementssimulation approach. The novel antenna is the basic element of a polarimetric array, composed of 35 elements, that will be part of a multi-sensors demining system under development in the frame of a European Union funded project (DEMAND). Measurements have been carried out in the frequency domain, by the means of an S-parameters modal decomposition. Results concerning bandwidth, leakage, impulse response of array channels and input impedance of the basic element are reported in the paper. Comparison between measurements results and simulations are presented.
ORBIT/FR has implemented several antenna receiver systems covering a wide range of frequencies using low frequency Network Analyzers (NWA). The low frequency NWA has been utilized for low frequencies in the NWAs design frequency range (typically up to 4 GHz) as well as for higher frequencies using external transmit and LO sources, external multipliers and fundamental or harmonic mixers up to 75 GHz. Such configurations can be much more cost effective in comparison to preconfigured high-end systems. The technical advantages are user defined IF frequencies, integrated low frequency operation, simultaneous dual channel operation and narrow band high speed frequency switching. Through the right selection of external components, performance parameter as frequency range, dynamic range, sensitivity and measurement speed can be optimized in relation to cost. Also a very flexible upgrade path is possible from basic to complex systems.
This paper describes the synthesis of a symmetric dual reflector antenna for a deep space probe. The subreflector for the Cassegrain type high gain reflector antenna acts as a main reflector for a medium gain reflector antenna on the back surface. A comparison will be made between a ring focus type and a point focus type dual reflector antenna given the constraints of the medium gain antenna aperture.
Generally, microstrip patch antennas excited to radiate circular polarized waves have serious weakness for narrow bandwidth of axial ratio and impedance in comparison with others (lens, horns, and etc)[1-3]. For this reason, it has been difficult to use microstrip patch antenna for satellite communications in spite of several advantages which are low profile, light weight, ease to fabricate, low cost, and so on [4-5]. In this paper, novel microstrip patch antenna is presented for satellite communications at Ka band. The proposed antenna provides wide axial ratio and impedance bandwidth compared with conventional circular polarized (CP) microstrip patch antenna. These operating characteristics are analyzed.
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.
Active and multimode antenna measurements for the ever-growing number of wireless applications are becoming more and more important. There is a need driven by the mobile phone and Bluetooth industries among others to develop a test set-up capable of measuring active radiating devices under real operating conditions. For example, it is of great interest to measure the radiation characteristics of a mobile phone integrating the full communication system. The implementation of such measurements involves aspects of control, synchronization and receivers dedicated to multi-mode test configurations.
Requirements for pattern measurement of antennas with low directivity continue to increase. The wireless communications industry is a significant driving force behind this change, but other fields such as electromagnetic compatibility (EMC) have an emerging need of low directivity antennas that work well to microwave frequency ranges. Traditional microwave techniques used for highly directional antennas are not suitable for testing more broad-beamed or omnidirectional antennas. Spherical pattern measurement systems using dielectric support materials with low permittivity are required to obtain acceptable results. This paper will review several different spherical pattern measurement techniques proffered by the Cellular Telecommunications & Internet Association (CTIA) for testing cellular handsets. It will present a benefit analysis of each method and provide useful information for both the novice and experienced antenna user. It can be shown that with appropriate care, several different techniques can generate the same resulting data, but each method has its own unique benefits and drawbacks. Spherical surface plots of measured data will be provided to illustrate some of the pitfalls related to this type of pattern measurement, and results from a certified test site will be presented.
Sensor Concepts, Inc. has developed the SCI-Xe Portable Microwave Imaging System prototype for use in the assessment of the low observable (LO) characteristics of fielded military platforms in their native environments. The SCI-Xe is a single man deployable suitcase-size system that employs a small linear rail in order to acquire Linear Synthetic Aperture Radar (LSAR) data in the 8-18 GHz frequency range. Data collections are performed via a single button push and the data is stored on a removable harddrive for comparison to an existing database for analysis. Recent deployment of the SCI-Xe prototype has provided excellent feedback on the viability of performing repeatable field measurements using alignment techniques that do not significantly affect the overall system size and weight. The SCI-Xe employs a video camera and uses video image algorithms such as edge detection, thresholding, and overlay masks to provide a simple coarse alignment to a stored baseline position. Once positioned, a single LSAR collection is performed to provide the radar data necessary for analysis, which includes a robust image registration algorithm to first, perform a quantitative assessment of the positioning accuracy and second, align the data for further image filtering and statistical processing.
The free-space VSWR technique, which involves scanning a field probe through the quiet zone area and plotting the amplitude and phase ripples over this region, is generally used for evaluating the performance of a farfield range. In this paper, this free-space VSWR technique is simulated by the finite-difference time-domain (FDTD) method to demonstrate the relationship between the ripple amplitude and the absorber reflectivity. The commercial package named “FIDELITYTM”, based on FDTD algorithm released by Zeland Software, Inc., is used for the simulations. The pyramidal absorbers on the walls of the far-field range are modeled by using effective layer model. That is, in the FIDELITYTM simulation setup, the absorbers are replaced with several homogeneous but uniaxially anisotropic layers. The amplitude ripples for both cases of 12-in-pyramid chamber and 18-in-pyramid chamber are presented and discussed.
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.