Compact antenna test range reflector edge treatment

The physical optics technique is used to compare the performance of single offset compact antenna test ranges with different reflector edge treatments and rim shapes. A comparison between reflector edge taper and rim serrations in controlling edge diffraction is demonstrated     

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.     

An array feed approach to compact range reflector design

A novel methodology is presented for the design of array feeds for compact range reflectors. The principal design strategy is to illuminate the rim of a standard, circular-aperture reflector with an array pattern null. This results in a reduction in the level of edge-diffracted fields present in the quiet zone. Since low-frequency performance is improved without dedicating reflector surface area to edge treatment, the potential quiet zone size is maximized. Implementation of the technique requires only a few real-valued array excitation coefficients. It is demonstrated that various quiet zone field performance trade-offs can be made by varying either the excitation coefficients or the array size. The quality of the quiet zone field is compared with that of a uniformly illuminated serrated reflector. The operational bandwidth and the effects of both random and systematic array excitation coefficient errors are evaluated     

Dual reflector feed system for hologram-based compact antenna test range

Manufacturing of large computer-generated submillimeter wave holograms with high pattern accuracy has been the main challenge in the development of hologram based compact antenna test ranges (CATRs). Illumination of the hologram with a shaped beam produced by a dual reflector feed system (DRFS) simplifies the hologram manufacturing by eliminating the narrow slots in the hologram pattern. In this paper, the design of a shaped dual reflector feed for a hologram CATR is described. The simulated and measured illumination field amplitude and phase at 310 GHz are presented and compared to the desired hologram illumination. The measured amplitude is within /spl plusmn/0.5 dB from the design objective in the most significant central region of the illuminating beam. Measurement results of the quiet-zone field of a demonstration CATR illuminated by the DRFS are presented and compared to the measured quiet-zone amplitude and phase of a hologram fed directly with a corrugated horn. The quiet-zone diameters of the both holograms are over 0.25 meters and the measured root mean squared (rms) amplitude and phase ripples are below /spl plusmn/0.4 dB and /spl plusmn/5/spl deg/, respectively. Further improvements to the hologram CATR, such as greater tolerance to manufacturing errors, are also discussed.     

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     

Enhanced compact range reflector concept using an R-card fence:two-dimensional case

Compact range reflector edge diffraction can be reduced by using an R-card fence. Well-designed R-cards (resistive sheets) placed in front of reflector edges reduce the field variations in the test zone. The keys to successful R-card design are proper choices of both the geometry and resistance profile. In this paper, a two-dimensional (2-D) version of the problem is attacked to show the basic concepts and essential considerations in designing R-cards. The complexity of a design is simplified by separating the different mechanisms associated with R-cards. Undesired mechanisms can be visualized by ray tracing and then eliminated by choosing the correct R-card geometry. The useful impact of this treatment is illustrated as it controls the transmitted energy level through the R-card; thus, the resistance of the R-card is defined based on an optimum aperture taper. Excellent performance in both the cross-range and down-range directions is presented, and the validity of the design is verified over a wide band of frequencies. The simplicity, flexibility, and low cost of this R-card fence concept provides a viable alternative to other edge treatments     

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.     

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     

New approach to compact measurements on reflector antennas

The letter describes a novel scheme for very compact measurements on reflector antennas. The measurement configuration involves a plane reflector located just beyond (and parallel to) the aperture plane, so that radiated power is reflected and refocused back into the feed. Measurement of return loss can then give information on antenna efficiency and gain. The basic concept is described and its performance confirmed by means of experiments on a 10 ft (3.048 m) diameter reflector. Possible methods of extending the performance of the scheme are briefly discussed.     

Lens-type compact antenna range

A compact antenna range is described which uses a plastic foam lens to obtain a collimated beam within which the radiation pattern of a test antenna can be measured. A novel feature is the introduction of a controlled amount of loss into the lens so that a nearly uniform electric field is measured over a high proportion of the lens aperture.     

Interpretation of compact range measurements

A novel derivation is given for the radiative coupling between two antennas. Compact range measurements are seen to be convolutions of the patterns from test and range antennas. The letter proposes that theoretical patterns should be similarly convolved for comparison, rather than attempting pattern deconvolution.     

一种新型Ku波段龙伯透镜反射器

本文对传统的龙伯透镜反射器采用有源频率选择表面（active frequency selective surface, AFSS）技术进行电磁结构的设计,用具有吸波/反射可切换的AFSS龙伯透镜反射器代替金属反射板,达到对入射电磁波的反射强度和雷达散射截面（radar cross section, RCS）大小可调、工作状态可切换的主动型龙伯透镜反射器. 仿真结果表明,在X波段内,设计的新型龙伯透镜反射器可实现吸波/反射功能的可切换以及单站RCS可调,大小相差约8 dB. 通过对龙伯透镜AFSS反射器进行实物加工与测试,测试结果和仿真结果较为吻合,实现了龙伯透镜反射器在一定频段内工作状态切换和RCS可调.

     

Design of multiple edge blinders for pyramidal horn reflector antennas

The design of multiple edge blinders for pyramidal horn reflector antennas is discussed. The blinders eliminate high sidelobes in the azimuthal plane near90degfor horizontal polarization at 4, 6, and 11 GHz. The successful design of multiple edge blinders for simultaneous operation in each of the three common carrier bands depends upon the suppression of an off-axis major lobe at 4 GHz and grating lobes which typically appear at 6 and 11 GHz. Using the blinder array factor and element pattern, it is shown that these lobes can be suppressed by properly choosing the blinder tilt anglebeta_{c}, the inclination of an individual blinder edgedelta, and an adequate number of edgesN.     

An analytical treatment of the compact range

Using reciprocity we find that a compact range can in principle measure the same return from a target as would be measured by an antenna irrespective of whether either the antenna or the target lies in the other's near or far field. Although the results depend upon the capability of the compact range to emulate the antenna's near or far fields, an expression is given for the correction necessary when this is not completely achieved.     

Hologram-based compact range for submillimeter-wave antenna testing

A hologram-based compact antenna test range (CATR) is being developed to overcome challenges met in antenna testing at submillimeter wavelengths. For the first time, this type of CATR has been built for testing of a large reflector antenna at submillimeter wavelengths. The CATR is based on a 3-m computer-generated hologram as the focusing element. This paper discusses the design and the construction of the CATR, and the verification of the CATR operation with quiet-zone tests done for the CATR prior to the antenna testing. Assembly of the CATR, testing of the 1.5-m reflector antenna at 322 GHz, and the disassembly were all done within two months in 2003. The quiet-zone field measurement results are analyzed in this paper. The CATR was concluded to be qualified for antenna testing. The antenna testing is described in a separate paper.     

An aperture-matched compact range feed horn design

The moment method and the uniform geometrical theory of diffraction are used to obtain two separate solutions for theE-plane far field pattern of an aperture-matched horn antenna. This particular horn antenna consists of a standard pyramidal horn with the following modifications: a rolled edge section attached to the aperture edges and a curved throat section. The resulting geometry provides significantly better performance in terms of the pattern, impedance, and frequency characteristics than normally obtainable. The moment method is used to calculate theE-plane pattern and voltage standing-wave ratio (VSWR) of the antenna. However, at higher frequencies, the moment method requires large amounts of computation time. On the other hand, the uniform geometrical theory of diffraction provides a quick and efficient high frequency solution for theE-plane field pattern. In fact, the uniform geometrical theory of diffraction may be used to initially design the antenna; then the moment method may be applied to "fine tune" it. In both methods, a two-dimensionalE-plane model of the antenna is used, but these two-dimensional solutions yield excellent agreement with measured data of the actual three-dimensional antenna. This procedure has been successfully applied to design a compact range feed horn.     

A compact RCS formula for a dihedral corner reflector at arbitraryaspect angles

A compact closed-form formula for the RCS of a perfectly conducting right dihedral corner reflector at arbitrary aspect angles is presented. The approach is based on a combination of ray tracing, physical optics (PO), and the physical theory of diffraction (PTD). There is good agreement between the results obtained using the closed-form formula and those obtained by the shooting and bouncing rays (SBR) technique     

Wide range suppressed harmonic response compact microstrip balun

In this paper, simple shunt open-stub units are used to design a compact balun with suppressed harmonic response. The stopband response of shunt stubs has been utilized to suppress the harmonic passbands. Design guidelines are presented with equations and graphs based on transmission line model. To validate theoretical predictions, an experimental prototype microstrip balun, with suppressed harmonic passbands up to six times the operating frequency, and occupying only 25% of the conventional balun circuit area is presented.     

High-precision measurements on a compact antenna test range

In the letter recent results of antenna measurements on a compact antenna test range (CATR) are compared with those on an outdoor range. Both results are corrected for the influences of the non-plane-wave illumination of the test antenna.     

A compact antenna test range based on a hologram

The application of conventional reflector-type compact antenna test ranges (CATRs) becomes increasingly difficult above 100 GHz. The main problems are the tight surface accuracy requirements for the reflectors and, therefore, the high manufacturing costs. These problems can be overcome by the use of a hologram type of compact range in which a planar hologram structure is used as a collimating element. This idea is described and its performance is studied with theoretical analyses and measurements at 119 GHz