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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.
In 2001, the Boeing 9-77 Indoor Compact Range successfully passed the range certification process. In preparation and during the On-Site Review in October 2001, RCS data on a pair of ultraspheres for the dualcalibration were collected. In this paper, we analyzed the data with regard to uncertainty analysis. An empirical approach for compensating the systematic error is presented.
The accurate measurement of static Radar Cross Section (RCS) requires precise calibration. Conventional RCS calibration objects like plates and cylinders are subject to errors associated with their angular alignment. Although cylinders work well under controlled alignment conditions, and have very low targetsupport interaction, these devices may not always suitable for routine outdoor ground-plane RCS measurements. We seek a design which captures the low interaction mechanisms of a cylinder, yet can be easily aligned in the field due to its excellent angular insensitivity. In a sense, this target has the best characteristics of both the cylinder and the sphere. This paper will describe the design of a "hypergeoid", a new calibration device based on a unique body of revolution. Calculations and measurements of some elementary hypergeoids are presented.
The National RCS Test Facility (NRTF) has a variety of unique test capabilities. Looking to further expand our testing options at the Mainsite test facility, the NRTF began developing a pit/pylon and rotator shroud test bed capability that would allow for radar cross section (RCS) measurement of test articles that are physically too small to accept a rotator. To reach the desired background RCS levels, the use of an expanded polystyrene foam column was not a viable option. In order to maintain the integrity of the calibrated system and enable the measurements of test articles with and without rotator bays on the same pit/pylon, a pit/pylon and shroud combination was required. Other important considerations that influenced the viability of a pylon system include cost effective mounting/dismounting of test articles, safety of the test articles and personnel, and the effective determination of backgrounds due to a stable and low observable pylon system. Our primary goal was to design and fabricate an inhouse system that met the needs of potential customers while satisfying our own clutter and background criteria. This paper documents the fabrication of the pylon and rotator shroud test bed. The results of an RCS characterization are also presented demonstrating the system’s ability to meet the desired RCS background goals.
Free space, coherent radar cross section measurements on a moving target trace a circle centered on the origin of the complex (I,Q) plane. Noise introduces only small random variations in the radius of the circle. In real measurement configurations, additional signals are present due to background, clutter, targetmount interaction, instrumentation and the average of the time-dependent system drift. Such signals are important contributors to the uncertainty in radar cross section measurements. These time-independent complex signals will translate the origin of the circle to a complex point (I0,Q0). Such data are then defined by the three parameters (I0,Q0), the center of the circle, and st, the radar cross section of the target. Data obtained when a target is moved relative to its support pylon can be separated into phasedependent and phase-independent components using the techniques of (1) three-parameter numerical optimization, (2) least-median-squares fit, (3) adaptive forward-backward finite-impulse response procedure, and (4) orthogonal distance regression applied to a circle fit. We determine three parameters with known and acceptable uncertainties. However, the contribution of systematic errors due to unwanted in-phase electric signals must still be carefully evaluated.
We present a methodology for the design of foam columns useful for the support of targets during static outdoor radar cross section (RCS) measurements. The methodology uses modal solutions along with genetic algorithms to optimize the design of a homogeneous column with resistive layers that provides minimal scattering over the design bandwidth. The methodology widens the design space, allowing for better design trades between electromagnetic and structural column performance. Results are presented for two representative design cases (broadband and spot-frequency narrowband), and the performance of the optimized column design is shown to be significantly better than that of the baseline foam column. Further design improvements are also suggested, including the use of the Born approximation for non-axisymmetric columns.
The bistatic radar signature of military systems is of interest for various applications including performance evaluation of semi-active missile systems, surveillance systems, and survivability assessment. While bistatic radar cross section (RCS) measurements have been made for high frequencies at several U.S facilities, there has been little reported work in low frequency bistatic RCS measurements. This paper presents the results of recent low frequency coherent bistatic RCS measurements from 210 MHz to 1.99 GHz at bistatic receiver angles of 0°, 35°, 70°, 120° and 145°. These measurements were successfully completed at the Naval Air Systems Command Weapons Division Etcheron Valley Range (EVR), formerly known as Junction Ranch (JR), China Lake, California This paper describes the process and provides results of low frequency bistatic RCS measurements on a hemisphere-capped cylinder target. Comparisons are presented of measured data to predicted results from moment method models of the calibration object and the cylinder target. Methodologies used in optimizing RCS data quality are also provided.
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 included development and integration of the 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 provided phase trimming and a small amount of electrical delay while the WOMBAt provided longer optical delays using commercial-off-the-shelf (COTS) components typically manufactured for the telecommunication industry. By integrating the WOMBAt with the AAMTV, a highly flexible test environment was achieved that included system calibration, multi-frequency scanning, and antenna pattern analysis. This paper presents antenna pattern results showing less than 0.7 dB of amplitude variation over the frequency range from 9 to 10 GHz at each of the measured nominal steering angles. The beamformer was steered to greater than ±69 degrees with an observed beam squint from 9 to 10 GHz of less than 1 degree.
Determination of Scan Element Pattern (SEP) and of Scan Impedance (SI) of wideband arrays is desirable, in addition to patterns and gain. Scan Element Pattern gives array gain versus scan angles and frequency, while Scan Impedance is the impedance versus scan angle and frequency that must be matched. Some organizations have been measuring SEP in transmit mode, with all elements terminated and the center element driven. This procedure gives erroneous results, as the mutual couplings are all passive. The way of properly measuring SEP is to place the array in a gain measurement setup as a receive antenna, so that all elements are terminated and properly excited. The nominal center element is connected to the receiver; the Scan Impedance mismatch is included in SEP. Knowledge of Scan Impedance is important, as it controls the impedance matching possibilities. It is however difficult to measure. Network analyzers (HP8510) measure impedance both (S11 and S22) by transmitting a signal and measuring the reflected signal, thus do not allow operation in a mode with all elements excited. A full feed network can be employed, with the network modified to allow measurement of the current and voltage at the center element. This method is seldom used. Because of the importance of SI, use is often made of waveguide simulators, and simulation codes. The infinite array Floquet unit cell codes must be used with caution as these codes omit edge effects; these may be very important in some types of coupled arrays. A planar array code is used to simulate both transmit (single element excited) SEP, and receive SEP. Data on SEP and SI are presented.
Software GPS receiver development has been undertaken. We are particularly interested in improving the GPS signal-to-noise/interference ratio using a beam forming techniques. The phase relationship among the antenna array elements requires careful calibration. In this study, we will report a phase calibration technique for a 2 by 2 GPS antenna array using both simulated and real GPS signals. This technique is based on the GPS signalprocessing algorithm developed for the software GPS receiver. A four-channel digital data collecting system was used in the experiment. For a simulated GPS signal, the experiment was conducted in an anechoic chamber in which a GPS simulation system was facilitated. For real GPS signals, we conducted the experiment on a rooftop to receive the signal from GPS satellites. The calibration verified the coherent nature of the signals among the elements. The results also allowed the source's direction to be determined.
Many system applications require very high gain antennas with extremely narrow beams that must scan electronically over a limited angular range, which in terms of beamwidths is very wide (several hundreds of beamwidths). Large, array-fed reflectors can provide high gain, large aperture, but their scan capability is limited to a few beamwidths. A conventional array, however, is capable of obtaining wide scan performance but required a very large number of elements making them prohibitively expensive. Here a novel hybrid, reflector-array antenna approach is presented that can yield the performance of the full array yet with much fewer elements and controls. To prove the concept and to verify theoretical findings, a two-dimensional hybrid reflector antenna was designed, fabricated and tested. This paper describes the results of this testing.
Accurate UHF phased array antenna patterns are difficult to achieve due to high level multipath present in the far field measurement test range. Special range geometry’s and source arrangements have been devised over the years to mitigate the measurement errors produced by test range multipath. In this paper we will describe new measurement results achieved using Aperture Synthesis illumination method designed to optimize and control the influence of ground reflections and in turn reduce quietzone amplitude ripple. Measured phased array patterns at 418, 434, 449, and 464 MHz will be shown for a 64- element array.
Two cylindrical phased array antennas were characterized at the NAVSEA Crane.s Active Array Measurement Test Bed (AAMTB) facility. The antennas include the Full Performance Antenna (FPA) and the Ultra Light Antenna (ULA) that are intended for land mobile test sites for the United States Department of Defense. These air breathing, low-cost antennas are candidates for a new communication system. Crane.s role as the program Technical Advisor (TA) includes integration and performance testing at the component level, antenna level, and system level. This paper discusses issues related to the antenna-testing phase including pattern measurements, G-F, and high power safety concerns. The final goal of the integration and testing phase was to verify that the antenna RF performance specifications were met. To this end, conventional cylindrical near-field pattern testing was adequate for many items such as beam width, pointing angle, and side lobe levels. However, two issues required additional effort: G-F measurement and high-power transmit safety concerns. Since the majority of required measurements could be made using the near-field chamber and the antenna required special controllers and prime power sources, it was desirable to make all measurements in the same location. Hence, a new measurement process was required for G-F using a near-field range and the high-power safety concerns needed to be addressed.