Frequency-scanning grating-reflector antenna for multibeamsatellite communications

The analysis and design of a circularly polarized frequency-scanning grating-reflector antenna is presented. The antenna is intended for a multibeam satellite communication system, covering 3.1° north-south and 7.2° east-west with 25 spot beams. Frequency scanning is used for the north-south coverage, while the east-west coverage is obtained by the use of a cluster feed. The grating reflector consists of a planar frequency-scanned reflection grating with a quasi-periodic lattice geometry. The frequency-scanned grating reflects the incident field into a diffracted field composed of the first-order diffracted grating lobe. A focus-feed position for the diffracted field is obtained by a proper design of the quasi-periodic lattice geometry. Design principles for the planar grating-reflector antenna are presented together with an analysis method for predicting copolar and cross-polar radiation patterns. The analysis method is verified by experimental results     

A novel frequency-scanned reflector antenna

Theoretical and experimental results are presented for a frequency-scanned antenna composed of a line source and a frequency-scanned reflection grating that is shaped to a cylindrical reflector. The principle considering is to select the grating geometry such that the first higher-order diffracted wave propagates and serves as the frequency-scanned beam. An analytical solution for the cylindrical reflector geometry that gives a line focus is given. The grating structure considered consists of an array of dipoles placed over a ground plane. The design of the dipole grating for optimum blazing (i.e., for optimal power conversion from the incident wave to the diffracted wave) is discussed. For the theoretical analysis Floquet's theorem and the method of moments are used     

Frequency-scanned reflection gratings with integrated polarizer

A frequency-scanned reflection grating (blazed grating) with polarizer properties is investigated. The grating structure considered consists of a periodic array of double-dipole elements etched on a dielectric substrate and placed over a ground plane. The two dipoles within a periodic cell are displaced and tilted from each other. Numerical results are presented showing that this grating structure can be designed to have the property of efficiently converting the power of an incident linear polarized wave into a circular polarized diffracted wave. A design is also outlined where the grating acts as a twist reflector, converting an incident linear polarized transverse electric wave into a first-order diffracted transverse magnetic wave. The theoretical analysis is based on Floquet's theorem and the method of moments. Experimental results verifying the numerical results are also presented     

Frequency-scanned gratings consisting of photo-etched arrays

Frequency-scanned gratings consisting of periodic arrays of thin conducting elements are investigated. The principle used is to let the first higher-order diffracted wave propagate and serve as the frequency-scanned beam. The grating structures are designed for optimum blazing to the desired diffracted wave (i.e., for optimal power conversion from the incident wave to the diffracted wave) by the use of an iterative optimization process. Both reflection and transmission gratings are considered; the elements investigated are single dipoles and crossed dipoles. The theoretical analysis is based on Floquet's theorem and the method of moments. Several numerical examples are presented showing that this type of grating structure has a high blazing efficiency and is suitable for frequency scanning. The theoretical results are verified by comparison with experimental results     

A millimeter-band planar lens based on an inhomogeneous medium with forced refraction

A millimeter-band planar lens designed on the basis of an inhomogeneous medium with forced refraction, which is formed by a periodic grating of metal strips placed on the surfaces of a dielectric plate, is considered. The possibility of application of this lens as the basis for the design of a multibeam receiving antenna for a radio imaging system is analyzed. The structure of an antenna consisting of a planar lens and a multichannel feed is proposed. The results of the design of a planar lens based on an inhomogeneous medium with forced refraction are presented. A multichannel feed in the form of an array of E-plane horns is analyzed and the results of simulation of this feed with the help of an approximate technique and numerical solution of an electromagnetic problem are given. The design of the multibeam antenna and its experimental characteristics are presented. The possibility of computer correction of radiation patterns of the multibeam antenna is considered.     

Radiating Mechanisms in a Reflector Antenna System

The radiating mechanisms of a reflector antenna system are discussed. Means of computing the various component fields are given, including aperture radiation, direct feed radiation, and diffracted radiation. An offset parabolic reflector antenna system fed with a corrugated horn is treated as an example. Means of reduction of the undesired components of radiation are suggested.     

Millimeter-wave double-dipole antennas for high-gain integratedreflector illumination

A double-dipole antenna backed by a ground plane has been fabricated for submillimeter wavelengths. The double-dipole antenna is integrated on a thin dielectric membrane with a planar detector at its center. Measured feed patterns at 246 GHz agree well with theory and demonstrate a rotationally symmetric pattern with high coupling efficiency to Gaussian beams. The input impedance is around 50 Ω and will match well to a Schottky diode or SIS detector. The double-dipole antenna served as the feed for a small machined parabolic reflector. The integrated reflector had a measured gain of 37 dB at 119 μm. This makes the double-dipole antenna ideally suited as a feed for high-resolution tracking or for long-focal-length Cassegrain antenna systems     

Antenna factor of compact antenna range for EMC measurements above1 GHz

A formula is proposed for measuring the antenna factor of an offset-fed parabolic reflector operated as a compact antenna range (CAR) by considering the plane-wave approximation and field-distribution in the collimated region. The antenna factor is determined from the half power beamwidth (HPBW) of the feed, the physical geometry of the reflector and a field-distribution correction factor. The proposed formula is in good agreement with the measured results using a standard double-ridged horn antenna as the feed. The formula can be used to design CARs for EMC applications     

G/T maximization of a paraboloidal reflector fed by a dipole-diskantenna with ring by using the multiple-reflection approach and themoment method

A 1.8-m paraboloidal reflector fed by a dipole-disk antenna with a beamforming ring is optimized for high G/T at L-band by using the moment method (MM) and the multiple reflection (MR) approach. The MR approach is based on using MM to calculate the radiation and scattering patterns of the feed, using physical optics plus uniform geometrical theory of diffraction (UTD) to include the reflector, and in addition to include the mutual interaction (multiple reflections) between the reflector and the feed by using the expression for the sum of an infinite geometric series. The MR approach is shown to be equally accurate as a MM solution of the complete antenna with reflector, provided the reflector is in the far field of the feed, and the MR approach is much faster. As a result of the calculations using the MR approach, design curves are presented showing how the G/T varies as a function of antenna geometry, size, and elevation angle, all for a given noise profile of the surrounding sky and ground. The computed radiation patterns and G/Ts are compared with measurements for several elevation angles and surrounding terrain     

Diffraction corrections to the cylindrical wave radiated by a linear array feed of a cylindrical reflector antenna

A phase-steered linear array feed for a parabolic cylindrical reflector antenna is considered. The nearly cylindrical wave radiated from this line feed in the Fresnel zone is expressed in terms of the isolated-element pattern. The correction to this wave due to diffraction from the endpoints of the line feed and from the grating formed by the array elements is also derived.     

A scattering matrix-based beamformer for wide-angle scanning in hybrid antennas

This paper presents a new approach to beamforming in hybrid antennas. Using a scattering matrix model for the hybrid antenna system, a bidirectional transformation is developed that relates the signals at the hybrid system feed to the signals that would be present in a planar array at the location of the reflector aperture. For example, the received fields at the feed of a hybrid antenna system may be transformed into the fields at the reflector aperture, and these reflector aperture fields may then be processed as if they were received by a planar or linear array. Similarly, the desired field or current distribution across the reflector aperture when transmitting may be transformed into the required field or current distribution at the hybrid system feed. This method allows standard linear or planar array analysis and synthesis techniques to be used with the hybrid system. Examples are provided for transmit and receive weight synthesis.     

Radiation properties of a planar dielectric waveguide loaded withconducting-strip diffraction grating

A dielectric planar waveguide periodically loaded with conducting strips is considered as a possible antenna for millimeter-wave range. We show that separating the grating from the waveguide leads to the reduction of radiative attenuation of the waveguided radiation and substantial narrowing of the angular spread of the diffracted radiation     

A Dual-Mode Millimeter-Wave Folded Microstrip Reflectarray Antenna

A dual-mode folded microstrip reflectarray antenna was developed and demonstrated in this paper. The proposed folded reflectarray antenna contains three parts: a planar main reflector, a planar subreflector, and printed feed antennas. The main reflector is used to produce twisted reradiated fields and to provide phase compensation for focusing. The subreflector parallel with the main reflector is made of a substrate printed with high-density metal grid lines, which is transparent to perpendicularly polarized fields, but would reflect the parallel ones. Three fixed-position patch antennas with polarization parallel to the grid lines are created for the radar mode, so that the radiation beam is switchable. Another patch with perpendicular polarization is designed for communication. A simple approach was proposed for simulating and designing the folded reflectarray. Measured results show good agreement with the calculated ones.     

The dielectric-filled parabola: a new millimeter/submillimeterwavelength receiver/transmitter front end

A design is presented for a semi-integrated millimeter/submillimeter wavelength receiver/transmitter front end incorporating a planar antenna and a solid-state device in an efficient feed structure which can be matched directly to high f-number optical systems. The feed system combines the simplicity and robustness of a dielectric substrate lens with the high gain of a parabolic reflector in a single structure that is termed a dielectric-filled parabola. The same fundamental unit can be configured as either a heterodyne or direct detection mode receiver, a power transmitter or a frequency multiplier by changing out the solid-state device and/or the integrated antenna. The structure can also be used with a small integrated antenna array in a multibeam or imaging arrangement. Design and fabrication details for the feed system are given. These are followed by beam pattern and impedance measurements taken on a microwave model when dipole, bow-tie, log-periodic, and log-spiral antennas are used as the integrated feed elements     

Physical optics analysis of four-reflector antenna

A four-reflector physical optics analysis procedure is presented. Theoretical characteristics of the National Aeronautics and Space Administration/Jet Propulsion Laboratory (NASA/JPL) 64 m antennas computed from this procedure were found to be in excellent agreement with experimental observations. TheS-band horn fields will subsequently be carried through all four reflectors (resulting in a transmission viewpoint of final antenna system beams) to account fully for all nearfield, cross polarization, and higher order mode generation effects caused by various intentional asymmetries in geometry. This appears to be the first time such a complete and rigorous analysis has been performed on such a complex antenna system. The analysis techniques presented are useful in many ongoing ground station antenna research and development efforts, including high-efficiency shaped reflector and beam waveguide feed designs and microwave metrology (holography) applied to large reflector surface measurements.     

A theoretical study of a mulit-element scanning feed system for a parabolic cylinder

This paper is a theoretical investigation of a method of scanning a beam of an antenna consisting of a fixed reflector and an array of elements illuminating the reflector by appropriately controlling the phase and amplitude of the signal radiating from each element. For the purpose of determining the feasibility of such a systems the two-dimensional problem is explored where a specific antenna geometry and an element radiation pattern are assumed. It was found that although the system exhibits similar performance to a system with a single radiating element when radiating a beam on axis, it could be scanned some eight beamwidths off axis without significant deterioration in characteristics. Interestingly, it was discovered that there is a separation (about0.7lambdain this case) between the feed elements where the sidelobes become dramatically high, analogous to grating lobes in a phased array.     

Design and experimental investigation of a multibeam integrated reflector antenna of the millimeter wave band

A multibeam integrated reflector antenna operating in the millimeter wave band is considered. The antenna consists of a radiating array, a planar mirror, and a multichannel feed. The results of simulation of a radiating array of slots in a metal screen are presented. The array is manufactured on the basis of a medium with forced refraction, including a double-slot array, which can radiate along the normal to the array plane. Operation of the array in the multibeam mode is analyzed. It is shown that application of a medium with forced refraction increases the array aperture efficiency in this mode. The results of the design of a planar two-layer mirror are presented and the mirror’s quality indices are estimated. A multichannel radiator designed as an array of planar H-plane horns is studied. The results of simulation of such a radiator with the help of an approximate technique and numerical solution of an electromagnetic problem are considered. The design of the multibeam antenna and its experimental characteristics are presented.     

Novel Gaussian beam method for the rapid analysis of largereflector antennas

A relatively fast and simple method utilizing Gaussian beams (GBs) is developed which requires only a few seconds on a workstation to compute the near/far fields of electrically large reflector antennas when they are illuminated by a feed with a known radiation pattern. This GB technique is fast, because it completely avoids any numerical integration on the large reflector surface which is required in the conventional physical optics (PO) analysis of such antennas and which could take several hours on a workstation. Specifically, the known feed radiation field is represented by a set of relatively few, rotationally symmetric GBs that are launched radially out from the feed plane and with almost identical interbeam angular spacing. These GBs strike the reflector surface from where they are reflected, and also diffracted by the reflector edge; the expressions for the fields reflected and diffracted by the reflector illuminated with a general astigmatic incident GB from an arbitrary direction (but not close to grazing on the reflector) have been developed in Chou and Pathak (1997) and utilized in this work. Numerical results are presented to illustrate the versatility, accuracy, and efficiency of this GB method when it is used for analyzing general offset parabolic reflectors with a single feed or an array feed, as well as for analyzing nonparabolic reflectors such as those described by ellipsoidal and even general shaped surfaces     

A magnetic current loop array in a reflector antenna

A magnetic current loop antenna array is designed, implemented, and measured. Radiation pattern, input impedance, and efficiency of the array are presented. The array is intended as a feed in a reflector antenna. Using a 360 mm solid dish, the overall gain of the reflector antenna is 24.6 dB at 9 GHz. The tolerance in placing the feed at the focal point of the dish is high. The present feed is low cost, self-supportive, robust, and easy to manufacture. It is an ideal substitute for the horn in a TVRO or VSAT antenna     

Pattern synthesis of the offset reflector antenna system with lesscomplicated phased array feed

The performance degradation of an offset reflector antenna with off-axis scanning feed and distorted reflector surface can be improved by using a phased array feed. Generally, both analog attenuators and phase shifters are used in phased array feed. Yet, it seems to make the feed system very complicated. In this paper, a phase-only gradient search (POGS) algorithm is developed to optimize the performance of offset reflector antenna systems using phased array feed that is equipped with phase shifters only. This technique not only can greatly simplify the complexity of phased array feed, but also can provide the reflector antenna with better antenna gain and sidelobe level control capability. Simulation and experimental results are presented to illustrate the excellent performance of offset reflector, with limited beam scanning capability, can be obtained by using this less complicated phased array feed