Ranajit Dey

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.

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.

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.

Analysis of a Post Discontinuity in an Oversized Circular Waveguide

This paper presents the analysis of scattering characteristics of a radially directed thin post in a circular waveguide using the method of moments. Electric type dyadic Greens function has been used to compute the scattered field in a circular waveguide considering variation of current only in the axial direction of the post. Simulated data on return loss and power coupling in the dominant mode and higher order modes have been compared with the data computed using Ansofts High Frequency Structure Simulator. The data on return loss and coupling for the incident TE11 mode have been compared with experimental data.

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.

Design of a novel corrugated matched feed for an offset parabolic reflector antenna

The antennas for space-borne microwave radiometers have several specific requirements to achieve the specified radiometric accuracies, sensitivity and the desired performance of the radiometer in the space. These include high beam efficiency (≫ 95 %), high gain and low losses, low cross-polarization, low side-lobe levels, etc. [1]. The offset parabolic reflector antennas fulfills most of these requirements due to their inherent advantages of reduced aperture blockage, isolation between the reflector and the feed, lesser spurious radiation and suppressed side-lobes [2]. However, the performance of offset reflectors is satisfactory only when the larger F/D (F/D ≫1) configuration is selected. Generally, in spacecraft antennas, the available space for the antenna structure is limited, and hence the reflector with a large F/D may not be preferred. Alternatively, the use of an offset reflector antenna with a smaller F/D ratio results into high cross-polarization (when illuminated by linearly polarized feed), and beam squinting (when illuminated by a circularly polarized feed) [2]. This high cross-polarization and beam squinting degrade the overall performance of the system and restricts the use of offset reflectors for many practical applications. Thus, to overcome these limitations, an effective cross-pol suppression technique as well as beam squinting minimization technique are to be explored.

Tri-mode horn array fed multiple-beam offset reflector antenna with low cross-polarization and improved side lobes

In the present paper, the cross polarization reduction and improvement in the sidelobes have been discussed for a multiple beam offset parabolic reflector antenna illuminated by an array of uniformly excited tri-mode horns. The simulated secondary patterns have been obtained for a single tri-mode horn fed offset reflector and also for a tri-mode horn array fed multibeam offset reflector. The results are compared with a conventional potter horn and the significant improvement in the cross-polarization and sidelobes are observed.

Wideband Corrugated Conjugate Matched Feed Horn

ABSTRACT This article presents the design of a wideband corrugated conjugate matched feed horn to cancel the high unwanted cross-polar components generated in offset reflector geometry having very low F/D and high offset angle. A new kind of symmetrical cascaded discontinuities is used in circular waveguide at the throat section of the horn for wideband operation of corrugated conjugate matched feed. The feed horn is specifically designed to mitigate the cross-polarization generated in 90° offset reflector antenna system with F/D = 0.7 and 0.4. The secondary radiation patterns have been computed. Significant improvement in the cross polarization is achieved at 55–60 GHz frequency band.

Analysis and Application of Triple-Post Discontinuity in Circular Waveguide

ABSTRACT This article presents the analysis of scattering characteristics of three symmetrical radially directed thin posts in an oversized circular waveguide in the transverse plane using the method of moments. Simulated data on return loss of the dominant mode and higher-order mode TE21 have been compared with the data computed using Ansys high frequency structure simulator (HFSS; Canonsburg, PA, USA). The data on return loss for the incident TE11 mode have been compared with experimental data for an oversized cylindrical waveguide loaded with the three posts. Also, the above analysis has been applied for designing a conjugate matched feed horn, which is used to cancel the cross-polar components generated in an offset reflector antenna. The primary pattern of the conjugate feed horn has been simulated and optimized using Ansys HFSS. The secondary pattern has been calculated using a general reflector antenna software package (GRASP; TICRA Engineering Consultants, Denmark).