S. B. Chakrabarty

Improving the Cross-Polar Performance of an Offset Parabolic Reflector Antenna Using a Rectangular Matched Feed

This letter presents the improved cross-polar performance of a matched feed with an offset parabolic reflector antenna of low focal-length-to-diameter (F/D) ratio and higher offset angle. In the pyramidal horn, the higher order mode (TE11) has been added in correct amplitude and phase with respect to the dominant mode (TE01) . Parametric study on the secondary radiation pattern has been carried out for different values of offset angle. The numerical results have been presented on radiation pattern for both linearly polarized and circularly polarized rectangular matched feed. The design of a rectangular matched feed and its simulated secondary patterns have also been included.

Cross-Polarization Cancellation in an Offset Parabolic Reflector Antenna Using a Corrugated Matched Feed

This letter presents the design of a dual-mode corrugated matched feed to cancel the unwanted high cross polarization and beam squinting in an offset parabolic reflector antenna. The matched feed concept has been implemented in a cylindrical corrugated structure by adding a higher order HE21 mode to the fundamental HE11 mode. The designed feed was then used to illuminate a linearly, as well as a circularly, polarized offset parabolic reflector antenna, and the secondary radiation patterns were computed. Significant improvement in the cross polarization was observed when the results were compared to that of a conventional corrugated horn illuminated offset reflector antenna.

Performance comparison of a matched feed horn with a potter feed horn for an offset parabolic reflector

The present paper deals with the comparison of matched feed performance with that of the conventional potter horn when used with an offset parabolic reflector. The effect of TE21 mode amplitude on the cross polarization has been studied in order to ascertain the suitable TE21 modal amplitude. Followed this, the behavior of change of TE21 modal amplitude with offset angle (thetas0) has been investigated. The effect of cross-polarization variation as a function of (F/D) ratio has been studied for both the matched feed and the potter horn. Finally, the beam squinting phenomenon in case of circular polarization has been studied for the matched feed and the results were compared with that of the potter horn.

Broadband Conjugate Matched Feed Horn—A Novel Concept

This letter presents a novel concept for designing a broadband conjugate matched feed horn to cancel the high unwanted cross-polar components generated because of offset reflector geometry having low F/D and high offset angle. A new kind of symmetrical cascaded discontinuities is proposed in circular waveguide for broadband operation of conjugate matched feed. The designed feed has been used to illuminate an offset parabolic reflector antenna, and the secondary radiation patterns have been computed. The designs of feeds have been presented for different F/Ds. Significant improvement in the cross polarization is achieved over 10% frequency bandwidth at Ku-band.

Cancellation of High Cross-polarization of an Offset Parabolic Reflector Antenna using a Rectangular Matched Feed

Abstract This paper presents the design and the experimental results of a dual-mode rectangular-matched feed. This type of feed cancels the unwanted high cross-polarization generated by the offset parabolic reflector antenna. In order to design this feed, higher order TE11 mode has been added in correct amplitude and phase with the fundamental TE01 mode in a rectangular structure. The proposed feed was then used as a primary feed to illuminate a linearly polarized offset parabolic reflector antenna. Through experimental results, it is verified that such a feed suppresses the undesired high cross-polarization introduced by the offset geometry of an offset reflector antenna. This kind of feed is very much suitable for monopulse tracking radar.

Historical and Planned Uses of Antenna Technology for Space-Borne Microwave Radiometers

This paper reviews the historical and future uses of antenna technology for space-borne microwave radiometers. The radiometer antennas are discussed, starting from the Dicke-type radiometer, as used in the Microwave Sounder Unit (MSU), to the present-day total-power radiometer. The antennas cater to the need for very high beam efficiencies, of the order of 95% to 98%. The paper also summarizes the specifications, design issues, and the performance of various radiometer antennas.

Higher Order Mode Analysis of Dual-Post Discontinuity in a Circular Waveguide

ABSTRACT This paper presents the analysis of scattering characteristics of two radially directed posts in an oversized circular waveguide making an arbitrary angle in the transverse plane using method of moments. Electric-type dyadic Greens function has been used to compute the scattered field in a circular waveguide. Simulated data on return loss and power coupling in the dominant mode and higher order modes have been compared with the data computed using Ansoft HFSS. The data on return loss for the incident TE11 mode have been compared with experimental data for the circular waveguide loaded with two posts.

Pole discontinuity removal using artificial neural networks for microstrip antenna design

This article presents the use of artificial neural networks for the evaluation of integrals with finite number of pole singularities while formulating the integral equation for the electric surface current density. A feed-forward single-layer back-propagated artificial neural network (ANN) model has been trained to approximate the discontinuous integrand function. Generation of a soft continuous function obtained from the ANN model and closed-loop expressions for the evaluation of the integrals are presented. The proposed technique is applied to compute the input impedance of microstrip antenna and results have been compared with IE3D. Integration has been performed using n-point Gaussian quadrature rule for evaluating the reaction matrix.

Cut-off wave number and dispersion characteristics of eccentric annular guide with dielectric support

The paper presents a rigorous analysis of a uniform waveguide with circular outer conductor and eccentric inner conductor supported by dielectric slab between the inner and outer conductors. A vector finite element approach in which non-physical spurious solutions do not appear has been followed to study the cut-off frequencies of higher-order modes as well as dispersion characteristics of this guiding structure. Numerical data on cut-off wave numbers and dispersion characteristics have been presented.

Square Coaxial Beam Forming Network for Multilayer Microstrip Antenna

This paper presents the design of square coaxial beam former and its transition from square coaxial line to microstrip line. Impedance matching has been achieved by creating a groove discontinuity in inner conductor. A cone has been provided for smooth impedance transformation for required broad banding. The measured performance of the beam former has been obtained by feeding it to feed layer of the electromagnetically coupled multilayer patch antenna. Equal and unequal power divider has been designed with proper impedance transformer by changing dimensions of the inner conductor keeping same outer conductor dimensions. Smooth linear taper has been provided at impedance transformer junction. High power calculations are also presented for SCL to handle several kW of power.