A method to design blended rolled edges for compact rangereflectors

A method to design blended rolled edges for compact range reflectors with arbitrary rim shape is presented. The reflectors may be center-fed or offset-fed. The method leads to rolled edges with minimal surface discontinuities. It is shown that the reflectors designed using the prescribed method can be defined analytically using simple expressions. A procedure to obtain optimum rolled parameters is also presented. The procedure leads to blended rolled edges that minimize the diffracted field emanating from the junction between the paraboloid and the rolled edge surface while satisfying certain constraints regarding the reflector size and the minimum operating frequency of the system     

Performance trade-off between serrated edge and blended rolled edgecompact range reflectors

The performance trade-off between serrated edge and blended rolled edge compact range reflectors is investigated. The edge diffracted fields which contribute to stray signals in the quiet zone have to be minimized. Consequently, an iterative approach has been developed to design serrated edges such that the edge diffracted rays from the serrations can be kept as far away as possible from the desired quiet zone area. Performance of various designs based on the number and size of serrations have been studied using a physical theory of diffraction solution. In addition, an optimized blended rolled edge design with the same size as the serrated edge reflector has also been evaluated for comparison. Finally, numerical results are presented in this paper to address the performance trade-off issue among the various designs. It is clearly shown from this study that the blended rolled edge reflector performs significantly better, which should offset the increased cost needed to construct a rolled edge reflector versus a serrated one     

Curved edge modification of compact range reflector

For many years, the compact range has successfully been used to design and evaluate many electromagnetic radiation and scattering systems. However, it has had limited use for large structures because of the large discrepancy between the reflector and target zone sizes. The limitation results from the large edge diffracted signal which emanates from the termination of the reflector. Previous attempts to solve this problem have involved using serrated edges to diffuse the diffracted field. While this reduces the edge diffracted field in the target zone, it is not eliminated. In addition, one has introduced many new corners which also diffract into the target zone. A curved edge modification is presented which reduces the edge diffraction by an order of magnitude or more and in the process does not create new mechanisms which perturb the plane wave in the target zone. Using this curved modification, one is able to design a compact range reflector whose target zone cross section approaches the size of the reflector parabolic surface. This makes the compact range ideal for scale model measurements since larger targets (antennas) can be measured. It also makes it more practical to consider systems which can measure full scale vehicles.     

Compact range reflector edge treatment impact on antenna andscattering measurements

Compact range measurements with a serrated edge and a blended, rolled edge reflector are compared. This is done by using simulated antenna pattern and backscattered field measurements. The measurement errors caused by stray signals emanating from the edge termination of reflector are discussed. It has been found that different stray signal sources impact on the measurement accuracy from different aspect angles. In addition, the measurement accuracy achievable with different reflector systems is dependent on the characteristics of the antenna or scatterer under test. From these findings, one will be better able to understand how well these two types of reflectors will perform in terms of accurately providing the proposed measurements. Consequently, one will be able to choose the best reflector design for his/her application     

Feasibility of compact ranges for near-zone measurements

The purpose of this paper is to demonstrate the feasibility of using compact range reflector systems to make near-zone radiation or scattering measurements. This can be achieved by designing the compact range to provide a uniform spherical wave incident upon the antenna or scatterer under test. The basic design technique is demonstrated using the Scientific Atlanta reflector system which has been modified by adding an elliptic rolled edge to improve the uniformity of the incident wave. The near-zone range design is validated (from around 50 ft range to the far zone) by probing the field in the measurement volume and by comparing measured backscattering patterns from a circular cylinder with those calculated by the geometrical theory of diffraction (GTD). All the advantages of a conventional far-zone compact range are now made available by our demonstrated variable-zone (adjustable continuously from 50 ft to infinity) compact range.     

Extending the low-frequency limits of the compact-range reflector

Traditionally, the compact-range is not considered a viable method for conducting low-frequency (VHF/UHF) antenna or RCS measurements, because of the limited electrical size of the collimating-reflector system. Normally, compact-range measurements are conducted in the extreme near field of the collimating system, where the main reflector size is on the order of 25 to 30 wavelengths minimum, with edge treatments of at least four wavelengths at the operating frequency. This mode of operation limits measurements to the high UHF band (500-800 MHz) and above, for even the largest sized reflector systems. L or S bands are more commonly the low-frequency limit. Recent research with compact ranges indicates that acceptable VHF/UHF measurements can be conducted in the quasi-far-field region of the collimating system, with reflectors as small as five wavelengths, and with electrically short edge treatments. A good user knowledge of this mode of operation is required to maximize its utility. A qualitative measure of acceptable quiet-zone performance must also be established. This paper addresses the theory of operation, practical implementation, and inherent limitations of the non-conventional use of the indoor compact range for conducting low-frequency measurements     

Pattern measurements of reflector antennas in the compact range andvalidation with computer code simulation

The measurements were performed at the University's compact range facility. They demonstrated: (1) the excellent dynamic range that can be achieved with antenna pattern measurements in a compact range facility; and (2) the excellent validation achieved for the calculated patterns of two 8-ft diameter reflector antennas. The compact range has a rolled edge modification to its reflector and uses a pulsed radar system to eliminate the clutter interference such that a dynamic range of more than 80 dB can be obtained. The measured far field patterns of two 8-ft reflector antennas, a prime focus fed antenna and a Cassegrain antenna, at 11 GHz were compared with those calculated by Ohio State University's Reflector Antenna Code. The computer code simulation's approach is also briefly described     

An improved main reflector design for compact range applications

Compact ranges offer many advantages over other types of ranges, and as a result much effort is being directed toward the improvement of their performance. The use of concave edge contours and blended rolled edge terminations to reduce the unwanted energy diffracted into the target zone from the termination of the main reflector is discussed. The proposed shaping of the edge contour minimizes the diffracted fields by virtue of reducing the spread factor; whereas, the blended rolled edge terminations reduce the diffracted fields by creating a smooth transition in the reflected field. Two design examples are treated in order to illustrate these concepts.     

Stray signal requirements for compact range reflectors based on RCSmeasurement errors

The authors present a performance criterion for compact range reflectors such that their edge diffracted stray signal levels meet a reasonable radar cross section (RCS) measurement error requirement. It is shown by example that one of the significant error sources is the diffracted fields emanating from the edges or junctions of the reflector. This measurement error is demonstrated by placing a diagonal square flat plate in the target zone and rotating it to appropriate angles. These angles are determined by bisecting the plane wave and stray signal directions. This results in a peak bistatic measurement of the edge diffracted stray signal. It is proposed that the diagonal flat plate be used to evaluate new reflector designs as well as existing systems. A reasonable stray signal performance level has been developed so that new reflector systems can be characterized in terms of an RCS measurement error requirement     

Compact antenna test range without reflector edge treatment and RF anechoic chamber

There are several types of CATRs (compact antenna test ranges) used in antenna-pattern measurements. An offset reflector is generally used to generate the quiet zone of a CATR. Serrated edges, rolled edges, or R-cards are generally chosen along the reflector's edge to reduce the edge-diffraction field inside the quiet zone of the CATR. In order to reduce stray signals from the environment, a high-quality RF anechoic chamber is required for a CATR. In this paper, a new type of CATR, without either a reflector edge treatment or an RF anechoic chamber, is developed. A commercially available DBS (direct-broadcast satellite) reflector antenna, without edge treatment, is used as the reflector antenna of the CATR to generate the quiet zone of the antenna test range. In order to improve the quiet zone's performance, the fields due to feed spillover, edge diffractions, and other stray signals are gated out by the ITDAMS (impulse time-domain antenna measurement system). The RF interference in the environment can also be reduced by time synchronization and pulse integration of the impulse time-domain antenna measurement system. In order to verify the capabilities of the proposed CATR, three kinds of antennas (a low-directivity horn antenna, a high-directivity 60 cm direct-broadcast satellite reflector antenna, and a 25 cm Ka-band Cassegrain LMDS - local microwave distribution system - antenna) were measured by the proposed CATR. The antenna-pattern results agreed quite well with those of a near-field range and a far-field range.     

用UTD方法评估一种紧凑场反射器的目标区特性

讨论了一种紧凑场反射器的边缘绕射情况,并用一致性几何绕射方法(UTD)对该反射器的目标区准平面波指标作了评估,给出了目标区大小与工作频率之间的关系.     

A measurement technique for modeling the effects of feed support struts on large reflector antennas

A measurement technique is described in which frequency scaled models of struts are placed in the near-field region of an offset reflector. In this compact range environment the excitation of the strut model is by plane waves, as would be encountered in the axisymmetrical reflector situation. Far-field radiation patterns are recorded, with and without the strut model in place, and, because of the low sidelobe levels associated with offset reflector antenna systems, it is possible to isolate the far-field response of the strut model. This technique is particularly useful for determining the real effects of structures that are difficult to analyze mathematically, such as latticed struts or metallic geodetic radomes.     

Offset dual-shaped reflectors for dual chamber compact ranges

The application of the theory of the synthesis of offset dual-shaped reflectors to the design of compact ranges is examined. The object of the compact range is to provide a uniform plane wave with minimum amplitude and phase ripple over as large a volume as possible for a given size reflector. Ripple can be lowered by reducing the edge diffraction from the reflector producing the plane wave. This has been done either by serrating or rolling the edge. An alternative approach is to use dual offset-shaped reflector synthesis techniques to produce a reflector aperture distribution that is uniform over most of the aperture, but with a Gaussian taper near the edge. This approach can be used together with rolling and/or serration if desirable. The amount of phase and amplitude ripple obtained with two different dual-shaped reflector designs is studied as a function of position in the plane wave zone and reflector size in wavelengths. The amount of both transverse and longitudinal (z-component) cross polarization is studied     

Theoretical analysis of tuning properties for a phase-tunable DFBlaser

The device consists of a conventional or a λ/4-shifted DFB (distributed-feedback) laser monolithically integrated with an external waveguide section with separate electrodes for phase control. Tuning curves are presented for threshold current, frequency, linewidth, and output power. The analysis demonstrates a generally higher side mode suppression and larger frequency tuning range but also a larger linewidth for the λ/4-shifted device compared to the device with a conventional DFB section     

The ohio state university compact radar cross-section measurement range

The ElectroScience Laboratory at The Ohio State University has recently installed a new radar cross-section measurement system. The system uses a Scientific Atlanta compact range reflector (an offset parabolic reflector) to generate a far-field plane wave in the confines of a40 times 20 times 60ft anechoic chamber. The system uses a computer controlled microwave frequency synthesizer and a multichannel computer controlled receiver. The target support/positioning system and an optical target alignment system are also interfaced to the computer. The parameters of the system are 1) operation from 1 to 30 GHz (eventual operation to 96 GHz has been confirmed by field probing); 2) a plane wave volume (test area volume) of 1.3 m diameter; and 3) a sensitivity of -50 dBsm. Of particular importance is the ability of the system to measure phase as well as amplitude. This permits vector subtraction of the background and system calibration using a reference (sphere) target. The development of this system and the performance characteristics obtained so far will be discussed. Some results which demonstrate the system performance will be shown. Of particular interest is the broad-band measurement of both amplitude and phase. This permits conversion of the results to the time domain. Examples will be shown in which the various system components (antennas, reflector, walls, ceiling, etc.) are separated in the time domain by this technique. The development of the range is continuing and planned future improvements will also be discussed.     

Ka 波段紧缩场天线的设计

设计了一个Ka 波段紧缩场天线。馈源设计结合角锥喇叭在反射面边缘照射电平下降快与波纹喇叭波瓣宽度宽的特点,通过给角锥喇叭加扼流套的改进设计来实现对反射面的照射。反射面采用锯齿型边缘来降低边缘的绕射作用,并进一步在无法加工锯齿部位贴附三角形吸波材料来减小绕射对静区特性的影响。暗室内采用平面测量结果表明,Ka 波段紧缩场天线静区特性满足设计指标要求。     

An improvement in electrical characteristics of a short backfire antenna

A short backfire (SBF) antenna is considered to be a favorable option for a compact and high efficiency shipboard antenna in maritime satellite communications. Though the SBF antenna has many attractive characteristics, it has a demerit of narrow frequency bandwidths because of its leaky cavity operation in principle. The electrical characteristics of a conventional SBF antenna have been improved by changing its main reflector from a flat disk to a conical plane and by adding a second small reflector. Frequency bandwidths of 20 percent for VSWR's under 1.5 can be obtained by the improved SBF antenna.     

Performance of a rectangular-waveguide-excited short backfire antenna employing a conical main reflector

The letter presents experimental results at X-band for a short backfire antenna employing a conical reflector, which is excited by a rectangular waveguide. It is shown that the use of a conical main reflector can lead to a compact antenna having a directive gain of 16.7?18.3 dB, sidelobe level below 13.8 dB and input VSWR better than 2.5 over a 20% bandwidth from 9?11 GHz.     

Hybrid PO-MoM analysis of large axi-symmetric radomes

Over the last three decades, intensive work has been done to develop techniques aimed at accurate and efficient analysis of antenna radome systems. Some applications involve radar operating in the millimeter wave range and for those cases the radome size can be on the order of one hundred wavelengths or so in length. For practical simulations of such large radomes, a hybrid physical optics-method of moments (PO-MoM) technique is presented for accurate and efficient analysis of electrically large radomes. The procedure combines the method of moments (MoM) for modeling the tip region of the dielectric radome and ray optics in conjunction with physical optics (PO) for treating the flatter smooth section of the radome. Calculated far-field patterns using the new technique agree well with measured data for a reflector antenna radiating in the presence of a large radome. The computational time for simulating the performance of a 46λ reflector in the presence of an 88λ long radome was a mere 4 h on a 233 MHz PC     

Frequency-dependent characteristics of current distributions onmicrostrip lines

The spectral-domain analysis using Chebyshev's polynomials as basis functions is used to obtain the frequency-dependent characteristics of current distributions and the effective relative permittivities of an open microstrip line. The results obtained are compared to other available results. To obtain accurately the current distributions requires a larger number of basis functions. Both longitudinal and transverse current distributions on the strip are shown for wide ranges of frequency (0⩽h/λ₀⩽1)