Dual Offset Reflector Research Articles

Investigation on a 220 GHz Quasi-Optical Antenna for Wireless Power Transmission

This paper investigates a 220 GHz quasi-optical antenna for millimeter-wave wireless power transmission. The quasi-optical antenna consists of an offset dual reflector, and fed by a Gaussian beam that is based on the output characteristics of a high-power millimeter-wave radiation source-gyrotron. The design parameter is carried on by a numerical code based on geometric optics and vector diffraction theory. To realize long-distance wireless energy transmission, the divergence angle of the output beam must be reduced. Electromagnetic simulation results show that the divergence angle of the output beam of the 5.6 mm Gaussian feed source has been significantly reduced by the designed quasi-optical antenna. The far-field divergence angle of the quasi-optical antenna in the E plane and H plane is 1.0596° and 1.0639°, respectively. The Gaussian scalar purity in the farthest observation field (x = 1000 m) is 99.86%. Thus, the quasi-optical antenna can transmit a Gaussian beam over long-distance and could be used for millimeter-wave wireless power transmission.

GO Synthesis of Offset Dual Reflector Antennas Using Local Axis-Displaced Confocal Quadrics

Abstract This work investigates an alternative numerical scheme for the solution of an exact formulation based on Geometrical Optics (GO) principles to synthesize offset dual reflector antennas. The technique is suited to solve a second-order nonlinear partial differential equation of the Monge-Ampere type as a boundary value problem. An iterative algorithm based on Newton's method was developed, using axis-displaced confocal quadrics to locally represent the subreflector surface, thus enabling an analytical description of the partial derivatives within the formulation. Such approach reduces discretization errors, as exact expressions for the mapping function and its derivatives are analytically determined. To check the robustness of the methodology, an offset dual-reflector Gregorian antenna was shaped to provide a Gaussian aperture field distribution with uniform phase within a superelliptical contour. The shaped surfaces were further interpolated by quintic pseudo-splines and analyzed by Physical Optics (PO) with equivalent edge currents to validate the synthesis procedure at 11,725 GHz.

Offset Dual Reflector Shaping Based On the Pfaffian Integrability Condition

A rigorous theory for the synthesis of offset dual reflector antennas is presented. The synthesis problem is posed as a three dimensional vector field which becomes the surface normals to one of the reflectors. The ray trace which defines the vector field is calculated from the reflection law at one reflector and a constant path length requirement. Implicit in the definition of the vector field is the mapping from the input wavefront to the output wavefront. The Pfaffian integrability condition is applied to the vector field which leads to a partial differential equation (PDE) for the input to output mapping. Integrating this PDE coupled to the PDE for the shape of the first reflector yields the desired solution. The method allows for a wide choice of the input to output mapping and combined with a judicious choice of geometry produces practical designs which outperform traditional conic section designs. The use of an explicit existence theorem in the problem formulation is innovative and leads to simpler software which give excellent results. Unlike previous work, much of the algebra is done without reference to coordinate frames, simplifying the presentation and relegating algebraic details to symbolic software. A novel method for integrating the coupled PDE's is introduced.

Prediction of Aperture Efficiency Ripple in Clear Aperture Offset Gregorian Antennas

Electrically small clear aperture dual offset reflector systems often exhibit a directivity ripple over frequency due to the interference of the diffracted field from the sub-reflector with the main beam field. This paper investigates the cause of the ripple, and presents a technique to predict the expected system directivity, including the ripple, using the feed radiation pattern augmented by an efficient simulation strategy in a clear aperture offset Gregorian system. The method allows for accurate prediction of the directivity ripple using a severely under-sampled set of simulation results. Predicted results are compared to several simulations, and agreement to better than 0.5 % is found for the majority of configurations using both analytical and full wave simulated feed patterns.

The shaped millimeter-wave antenna with offset feed and dual-reflector

The shaped millimeter-wave antenna with offset feed and dual-reflector

Leaky-Wave Slot Array Antenna Fed by a Dual Reflector System

A leaky-wave slot array antenna fed by a dual offset Gregorian reflector system is realized by pins in a parallel plate waveguide. The radiating part of the antenna is composed by parallel slots etched on one side of the same parallel plate waveguide. The dual offset Gregorian reflector system is fed by an arrangement constituted by two vias and a grid, also constituted by pins. Also this feed arrangement realizes a leaky type of radiation, this time inside the parallel plate waveguide. A prototype of the antenna has been designed, manufactured and successfully tested. The low profile, low cost and high efficiency of the antenna render it suited for a variety of radar or telecom applications.

CPTR용 카세그레인 오프셋 복 반사경의 해석

일반적으로 카세그레 인 오프셋 복 반사경(Cassegrain Dual Offset Reflector)은 위성 통신용 안테나로 사용되지만, 여기서는 CPTR(Compact Payload Test Range)을 위한 반사경 시스템으로 해석하였다. 시험 영역의 근접 전계는 물리 광학법(Physical Optics)을 적용하여 계산하였다. CPTR은 균일한 평면파 제공을 목적으로 하며, 이를 위해 최소한의 진폭과 위상 리플(ripple)을 가져야 하며, 교차 편파 또한 작아야 한다. 따라서 본 논문에서는 반사경 구조 및 시험 영역의 위치에 따른 근접 전계 패턴을 구하여 전계의 리플, 테이퍼와 교차 편파를 고찰하였다. 특히 통신용 반사경 안테나에서는 나타나지 않는 안테나 축방향의 교차 편파 성분을 고찰하였다. In general, the cassegrain dual offset reflector is used for the satellite communication antenna, but is analyzed as the reflector system for the CPTR(Compact Payload Test Range) facility in here. The near-field at the test zone of the CPTR is obtained by using the physical optics approximation. The CPTR has to provide a uniform plane wave with the minimum amplitude and phase ripple and the low cross polarization. Therefore, in this paper, the near-field pattern are calculated, and the ripple and taper of the field and the cross polarization are investigated with the variation of the reflector geometry and the position of the test region. Especially, the cross polarization of the antenna axis direction which is not found in the satellite reflector antennas is investigated.

Phaseless characterisation of compact antenna test ranges

Antenna characterisation and radar cross section measurements can be conveniently and successfully carried out by means of a compact antenna test range (CATR), whose performance is primarily assessed in terms of quiet zone size and field uniformity. CATR characterisation and diagnostics are usually performed by means of (amplitude and phase) field measurements in the quiet zone and are of timely interest either on CATR installation or on its periodic reassessments performed by manufacturers and/or users. This paper addresses CATR characterisation from amplitude-only data, an attractive topic because of the application of CATRs to the millimetre or sub-millimetre wave ranges. The approach is based on an appropriate strategy retrieving the missing quiet zone phase and facing the issue of the large electrical dimensions of the CATR. To take into account the characteristics of the collimating system as well as to keep as low as possible the number of unknowns to be sought for, it exploits the Jacobi-Bessel expansion of the aperture field. The performance of the algorithm has been tested through a wide numerical analysis against synthetic data generated by GRASP8-SE whose full version is routinely employed for CATR design. The main results related to a Gregorian dual offset reflector CATR, modelled on that proposed in the literature by Pistorius et al., and to a single offset reflector CATR, inspired by the one available at the Queen Mary & Westfield College, London (UK), are reported.

Analysis of quasi-optical power combiners by vector field measurements at 150 GHz

Abstract. A Two-dimensional quasi-optical power dividing/combining circuit has been experimentally investigated at 150 GHz. It consists of a rectangular horn antenna array as receiving/transmitting unit and a dual offset reflector setup to match the radiated field(s) to the pattern of the receiving antenna(s). To verify both design and adjustment of the quasi-optical circuit, electric field scans have been performed in selected planes and volumes of the setup. To measure the spatial electric field distribution, a vector field measurement system has been developed which operates in the frequency range between 148 GHz and 152 GHz. Excellent agreement between calculated and measured results for a horn antenna array approve the predicted results calculated under the physical optics approximation. Measured power dividing/combining efficiency of the passive structure of 63% for an inter-element spacing of 10$ \\lambda$ indicates that the power combining principle is a suitable method up to submillimeter wavelengths.

Generation of Multiple Beam Patterns Using a Mechanically Reconfigurable Smart Reflector Antenna System

In this research, a novel computational design and operation methodology for a reconfigurable dual offset contour beam reflector antenna (DCBRA) using a mechanically adjustable subreflector is presented. The subreflector is made with a thin flexible material such that it deforms by movement of a set of linear point actuators attached on its back surface. The deformable subreflector allows the electromagnetic field illuminating the main reflector to be changed leading to a different far-field radiation pattern. For the analysis, the Finite Element Method (FEM) is applied to calculate the deformed shape of the subreflector from a given configuration and movement of actuators and Physical Optics (PO) is utilized to calculate radiation patterns for both the main reflector and the subreflector. Finally a unified computation tool is developed which employs optimization techniques to synergistically combine the PO routine and the FEM code. The overall goal of the combination is to find the optimal actuation values of the actuators needed to generate a specific far-field radiation pattern related to a desired geographical footprint. Simulation results on the generation of contour beams for four different geographic regions—CONUS, Australia, Brazil, and Afghanistan—are presented.

Quasi-optical 150-GHz power combining oscillator

A quasi-optical power combiner for a five-element in-line oscillator array is experimentally investigated at 150 GHz. The combiner consists of a periodic dielectric phase grating (hologram) which transforms the near-field of a rectangular horn antenna array into a pseudo-plane wave. The horn array is excited by IMPATT oscillators operating uniformly in both amplitude and phase. A dual offset reflector set-up transforms the pseudo-plane wave to a Gaussian beam which matches the field pattern of a dual mode receiving antenna. Even though an inter-element spacing of 9.5 /spl lambda/ has been chosen, the passive structure gives a power combining efficiency of 74.1%. The power combining oscillator has been operated in both free-running and injection-locked mode. A CW output power of 78.0 mW and 83.5 mW was measured for the free-running and injection-locked oscillator, respectively, which is corresponding to a power combining efficiency of 66.5% and 71.2%, respectively.

Analysis and Design on Aperture Antenna Systems with Large Electrical Size Using Multilevel Fast Multipole Method

A full-wave procedure for designing electrically large optimized classical aperture antenna systems is analyzed using the multilevel fast mulitpole method (MLFMA). The useful design equations for optimized offset dual reflector antennas with circular apertures are also presented to allow the size and spacing of the main and subreflectors of the antenna system, along with the feed horn subintended angle, to be used as input variables of the design procedure. The radiation of feed horn is first analyzed and compared with theoretical and available measurement results. The conventional reflector antennas are simulated and analyzed for aperture blockage of the feed. Finally, the offset dual reflector antennas with circular aperture are designed and validated numerically by showing that low cross polarization and spillover losses obtained. All the simulations are made by using the MLFMA which is implemented based on the method of moments (MoM) with RWG triangular patch basis function to model any shape of reflector surfaces.

Spatial Power Divider/Combiner in<tex>$D$</tex>-Band

Five-element spatial power divider/combiners have been realized at 150 GHz. Holography is applied to couple the field pattern of an in-line rectangular horn antenna array to a pseudoplane wave. The hologram is realized as periodic phase grating. The transformation of the pseudoplane wave to a Gaussian beam is performed by phase modulation with a dual-offset reflector on the one hand, and a system of Fresnel lenses on the other hand. Both setups have been extensively examined. The analysis has been enhanced by a vector near-field measurement system. The comparison of the simulated and measured efficiencies, as well as field distributions shows good agreement.

Designing classical offset inverse-cassegrain dual-reflector antennas from combinations of prescribed geometric parameters

This paper proposes a simple procedure for the design of classical offset inverse-Cassegrain dual-reflector antennas from combinations of prescribed geometric parameters. We will provide a list of 21 parameters from which the antenna system is fully characterized. However, only five of these parameters need to be provided by the antenna designer as the remaining 16 parameters can be calculated in closed form using the equations provided here.

Reconfigurable contour beam-reflector antenna synthesis using a mechanical finite-element description of the adjustable surface

A synthesis technique based on a mechanical finite-element (FEM) surface description of dual-offset reflector (DOSR) surfaces is described. This technique is used to implement a reconfigurable contour beam for a geostationary satellite application. The mechanical finite-element description of the surface takes into account the mechanical properties of the reflector surfaces and the effect of a finite number of forces applied at control points on the surface. Mechanical adjustment is achieved using high-deflection stacked piezoelectric actuators attached to the rear of a lightweight flexible subreflector surface. Both the main and subreflector surfaces are shaped for an initial required geographical coverage zone and then the main reflector surface is assumed to be fixed in shape. The variable shape subreflector is then synthesized to achieve the desired illumination for different geographical regions and different geostationary positions. Based on a study of the effect of the mechanical properties of the subreflector surface and actuator number and placement, a practical design has been completed and the ability to reconfigure the beam has been verified.

Improvement of sidelobe characteristics of an offset dual reflector antenna with an elliptical beam

After we manufactured an offset dual-shaped reflector antenna with an elliptical beam designed by the geometrical optics approach, we found that the antenna could not provide the desired low sidelobe characteristics. In general, we often encounter the case in which the desired sidelobe characteristics are not attained because of design inaccuracy, reflector surface error, and reflector alignment error after antenna manufacturing. We here propose a newly developed method, called aperture phase distribution control by adjustment of reflector segments (APCAR). This method has been verified through improvement of sidelobe characteristics of the offset dual-shaped reflector antenna with an elliptical beam, whose aperture diameter is 1.3 m × 2.8 m. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(12): 10–19, 1999

Improvement of sidelobe characteristics of an offset dual reflector antenna with an elliptical beam

After we manufactured an offset dual-shaped reflector antenna with an elliptical beam designed by the geometrical optics approach, we found that the antenna could not provide the desired low sidelobe characteristics. In general, we often encounter the case in which the desired sidelobe characteristics are not attained because of design inaccuracy, reflector surface error, and reflector alignment error after antenna manufacturing. We here propose a newly developed method, called aperture phase distribution control by adjustment of reflector segments (APCAR). This method has been verified through improvement of sidelobe characteristics of the offset dual-shaped reflector antenna with an elliptical beam, whose aperture diameter is 1.3 m × 2.8 m. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(12): 10–19, 1999

Computer-aided design of reflector antennas: the Green Bank Radio Telescope

This paper presents an evaluation of the electrical performance of the Green Bank Telescope (GBT) reflector antenna, operating as single- and dual-offset configurations, as well as a general overview of the GBT system. The GBT dual-offset Gregorian configuration is designed for low cross polarization (XPOL) using the dual-offset reflector antenna (DORA) synthesis package code developed by the authors. The procedure implemented in DORA to upgrade an existing main reflector to a low cross-polarized dual-offset Gregorian reflector antenna is also described in this paper. All computed patterns were obtained with the parabolic reflector analysis code (PRAC) program, also developed by the authors, and with the commercial code GRASP7. The GBT radiation patterns and performance values, which include original data not available anywhere else as far as the authors know, indicate that low XPOL performance can be achieved with a dual-offset configuration, provided that a low XPOL feed is used. The GBT configuration is employed as a case example for the aforementioned procedure. However, an effort is made to present the main conclusions as generically as possible.

A ray-by-ray algorithm for shaping dual-offset reflector antennas

A novel GO method for designing dual shaped offset reflector antennas with a prescribed phase and amplitude aperture distribution is presented. This technique consists of tracing rays consecutively by solving nondifferential equations. The solutions, which simultaneously satisfy the amplitude and phase requirements, together with the total derivability condition of the surface expressed in a new discretized way, are easier to control than the other techniques in the literature. This algorithm accounts for the feed phase errors. Two examples are selected to show the good performance of the algorithm. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 20–26, 1997.

Cross Polarization and Beam Squint in Single and Dual Offset Reflector Antennas

ABSTRACT Cross polarization (XPOL) and beam squint phenomena of reflector antennas are examined in detail. Emphasis is on the explanation of the absence of XPOL and the presence of beam squint in offset parabolic reflectors illuminated by a circularly polarized feed. Linearly polarized feeds are also considered for both the offset and axisymmetric configurations. Although many of these results are known, they are presented in a single coherent treatment. In addition, the results for polarization and beam squint characteristics of prime-focus offset parabolic reflector antennas are extended to dual offset configurations based on computed data using the physical optics code, GRASP7 (TICRA, 1988).