Bifocal Reflector Research Articles

Theoretical Study of a Broadband Quasi-Optical Mode Converter for Pulse Gyrotron Devices

Theoretical investigation of a broadband quasi-optical mode converter for 330-GHz TE62 mode gyrotron application is presented. The converter consists of a Vlasov launcher and three reflector mirrors. Special considerations, including a Vlasov launcher with reasonably large aperture radius and optimized combination of two elliptic reflectors and a bifocal parabolic reflector, are the keys to achieve broadband mode converting. The optimized internal converter is well compatible with the gyrotron electron-optical system and generates Gaussian beam with efficiency higher than 80% in an extraordinary broadband range between 310 and 340 GHz. The principle of the broadband converter can also be applied to gyrotron amplifiers.

A High-Gain Multibeam Bifocal Reflector Antenna With 40° Field of View for Satellite Ground Station Applications

A theoretical design of a Ku-band multibeam offset bifocal dual-reflector antenna (BFRA) with 40° field of view (FoV) suitable for satellite ground station applications is presented and discussed. The BFRA has a nearly square aperture with a dimension of about 4.5 m (191 wavelengths at a frequency of 12.75 GHz) and was designed for the required scan angle $\alpha = 18^{\circ }$ . The antenna has a Gregorian configuration in the offset vertical plane and a Cassegranian configuration in the scanning horizontal plane. This BFRA was designed for a special application for which providing the maximum aperture efficiency (AE) (i.e., the maximum gain) is required and relatively high sidelobes are allowed. The calculated AE is greater than 52% and a directivity is about 54 dBi at 12.75 GHz within the whole FoV of 40° (which is equal to 100 beamwidths) in the scanning plane.

Bifocal Reflector Antenna for a Standoff Radar Imaging System With Enhanced Field of View

A unique multireflector bifocal antenna design for real-time standoff imaging applications is presented in this work. The antenna is used in combination with a 300 GHz radar sensor to acquire images at 8 m over a large (80 × 50 cm) field of view (FoV). The increased FoV is obtained by the use of an antenna system composed by a bifocal elliptical Gregorian with an extended subreflector to allow for fast scanning of a beam spot. The scanning is achieved by the combination of the rotation and vertical tilting of a flat small secondary mirror. The design, simulations, prototype description and experimental results of a manufactured working prototype are presented.

About a New Procedure for Offset Bifocal Reflector Antennas Synthesis

This letter presents a novel procedure for designing of three-dimensional offset bifocal reflector antennas (BFRAs). This procedure allows us to determine the reflector surfaces in analytical form as functions of two parametric variables. Initial design considerations are described. Two BFRA example designs with aperture dimensions of about 60 wavelengths are presented. One of them has a field of view of 47 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex> </formula> for the whole main reflector aperture efficiency greater than 50%. Thus, the proposed procedure is suitable for designing scanning and multibeam reflector antennas with a wide field of view in one plane.

A Bifocal Ellipsoidal Gregorian Reflector System for THz Imaging Applications

Current terahertz imagers rely on reflector systems for the beam quality and imaging speed because the cross-range span that the system can cover is limited by the beam aberrations when the antenna scans. We present the design of a Bifocal reflector system that can rapidly scan a terahertz beam for standoff imaging applications while increasing the field of view of previous designs up to 50%. The design is based in a confocal Gregorian system where the nominal reflector surfaces are substituted by shaped surfaces to reduce the beam aberrations, while not increasing the manufacture cost of the reflector antenna. We also provide a set of useful design formulas for the design of this kind of reflector systems. The beam patterns obtained by the proposed designs are numerically calculated with the commercial software GRASP and compared with those obtained with previous approaches to the same problem, showing the better performance of the proposed solution.

Evaluation of a bifocal reflector on a clinical lithotripter.

To perform in vitro and in vivo tests using a clinical lithotripter in order to determine whether a bifocal reflector is more efficient and produces the same or less tissue damage than a conventional ellipsoidal reflector for electrohydraulic lithotripters. A standard ellipsoidal and a novel bifocal reflector were tested on a Tripter Compact lithotripter (Direx Medical Systems, Petach Tikva, Israel). The bifocal reflector was constructed by joining two sectors of two rotationally symmetrical ellipsoidal reflectors having different distances between their foci. The F1 foci of the sectors coincided, creating a separation between the F2 foci. The fragmentation efficiency of the reflectors was compared using kidney-stone models. Shockwave-induced trauma was evaluated in vivo by treating both kidneys of six healthy dogs. One kidney was exposed to shockwaves generated with the conventional reflector, and the other kidney was treated using the bifocal reflector. Pressure measurements were obtained for both reflectors using needle hydrophones. The new design appeared to be more efficient than the conventional reflector in breaking up kidney-stone models. Tissue damage did not increase when using the bifocal reflector. The use of bifocal, instead of standard ellipsoidal, reflectors should be considered as an alternative to improve extracorporeal shockwave lithotripsy.

An offset bifocal reflector antenna design for wide-angle beam scanning

A synthesis procedure and performance results for an offset dual reflector with perfect focusing at \pm 8\deg of beam scan are presented. This bifocal antenna extends the theory of the previously reported symmetric system to an offset design. Approximations, such as the smearing of points into a focal ring, are eliminated, as is blockage. The offset design affords greater design flexibility, although the synthesis is more complex. Computed and experimental results demonstrate the improved beam-scanning performance of this antenna.

Offset bifocal reflector antenna

AbstractThe design principle and construction of an offset bifocal reflector are discussed and some test results are presented. the reflector surface is designed in a three‐dimensional configuration, and four typical bifocal reflector antennas characterized by the vertical and horizontal cross sections of the subreflector are derived. Mapping of the coordinate system set up on the horn feeder is accomplished with a geometrical optics technique, and it is found that an antenna with low distortion cross‐polarization degradation attributable to asymmetry is possible.A 1.3 m bifocal reflector antenna at 14/11 GHz with a beam separation of 9° was designed and fabricated, and its radiation properties were measured with offset feeding, which is useful in constructing a multibeam antenna. the radiation properties within this beam separation angle are equivalent to those of a single pencil‐beam antenna such as the Cassegrainian; the cross‐polarization level is less than ‐30 dB in the worst case.

Bifocal dual reflector antenna

A bifocal dual reflector antenna is similar to and has better scan capability than a classical Cassegrain reflector antenna. The method used in determining the reflector surfaces is a modification of a design method for the dielectric bifocal lens. Computed radiation characteristics of the bifocal reflector system are compared with those of a classical Cassegrain reflector system. The results confirm that the bifocal reflector has superior scanning performance.

Parallel Plate Optics for Rapid Scanning

Rapid scanning using a paraboloid antenna is unsatisfactory; rapid movement of the antenna is mechanically impractical, while motion of the feed near the focus requires long focal length for good optical results. Another attack on the problem is to place the feed between parallel plates which produce a line source near a bifocal reflector. The energy flows along the geodesics of the mean surface between the parallel plates; the problem of shaping the plates so that a circular feed motion produces an oscillating beam at the line source becomes a problem in differential geometry and the calculus of variations. If the mean surface is assumed to consist of two developable surfaces joined along part of their boundaries, the unique solution of the optical problem is a circular disk along the edge of which the feed moves, joined to a section of a 60° cone which is straightened out at the large end to obtain a straight line source. This is the RCA solution of the problem. If the surface is assumed to consist of a surface of revolution which provides a feed circle, and attached to it a circular disk a diameter of which is the aperture, under certain natural restrictions no exact solution of the optical problem is possible, but several approximate solutions exist. Dielectric introduced between the plates of such a surface of revolution scanner effects a great improvement in the optics.