V. K. Lakshmeesha

Design considerations for dual circularly polarized spherical phased array antenna at X-band for spacecraft data transmission

In this paper, design of a dual circularly polarized (CP) spherical phased array antenna (PAA) is discussed. Dual CP configuration is implemented to enable frequency reuse using polarization diversity. This is realized using a high performance dual CP radiating element. This antenna is capable to generate beams in both the polarizations at any specified direction over the hemisphere. Realization aspects and the measured results of the PAA are discussed here. This antenna is proposed to be used for the high bit-rate data transmission at X-band from the Indias upcoming RADAR imaging satellite RISAT-1.

Sequentially rotated microstrip array antenna at X-band for spacecraft

This paper describes design, development and test results of a broadband, light weight circularly polarized microstrip array antenna. Sequential rotation technique has been applied on the array to obtain broad bandwidth in return loss and axial ratio performance. Circularly polarized truncated corner square microstrip patch is selected as a basic radiating element in this 64 element array. The antenna array has been developed for data transmission application from Low Earth Orbiting spacecraft to the ground station. Microstrip patches and feeding network have been designed on a single microwave substrate to obtain light weight antenna. Microstrip patch, feed network, and the complete array have been analyzed on Ansoft Ensemble software. Developed array exhibits good radiation patterns, axial ratio, and return loss over required band of frequencies (8.0 - 8.4 GHz). After successfully completing all space qualification process, the array has flown in Cartosat-2 spacecraft (Indian Remote Sensing Satellite). The on-orbit performance of the array is satisfactory and matching with the ground test values.

A compact high power S-band dual frequency, dual polarised feed

A simplified approach to the design of a dual circularly polarized diplexing feed covering 2.0=2.3 GHz for satellite control ground stations is described. The system considered is easier to fabricate and has lesser tolerances than the conventional system and avoids concentrated field regions, thus enabling high-power capability to be achieved without being prone to any corona discharges. The system consists of the following components: a circular waveguide dual circular septum polarizer for both uplink and downlink frequencies; a high-power coaxial diplexing T-junction; and a high-power coaxial to waveguide transition.<<ETX>>

S-band shaped beam antenna for Indian Remote Sensing Satellite - IRS

This paper reports the development of a new shaped beam antenna for remote sensing satellite data transmission applications at S-band. For medium altitude, near earth satellites such as those used in remote sensing applications in sun-synchronous mode, data transmission link can be optimised for the whole pass of the satellite by making the antenna pattern profile vary so as to compensate for the path loss profile - i.e., the pattern profile becomes an inversion of the path loss profile. Such an antenna pattern, having all other parameters fixed, provides a uniform data level throughout the pass. The present development is for a similar application for an Indian Remote Sensing Satellite and this development provides for 6.5 dBi gain with higher polarisation purity using a shaped reflector and helical feeding system.

Antenna System of Aryabhata

This paper describes the design, evolution and performance in orbit of the on-board antenna system of Indias First Scientific Satellite, ARYABHATA launched on April 19, 1975.

A new approach to reduce the helical resonator discharge in RF filters used in spacecrafts

Helical filters are widely used in the UHF/VHF frequency range, for their smaller size and high Q. For ambient operation, the design is simple and can be realized using commercially available components. Whereas at lower pressure levels, mostly, due to degaussing property of the dielectric material there could be a sudden discharge or a breakdown inside the cavity that houses the helix and thereby the normal operation of the filter gets affected. This may lead to raise in noise floor or intermittent power output. In this paper, a new technique for suppressing such a discharge is discussed. This can be applied even to the filters that are already fabricated. Filters designed by this method were tested successfully in thermo-vacuum chambers up to 10−6 Torr without any problem and results of various tests are presented.

A composite C/S band feed for TVRO

The authors describe the development of a composite feed for S- & C-band TV reception from satellites. The specific application is significant in the Indian context where INSAT has TV transmission both at S-band and in C-band frequences. The main advantage of the composite feed stems from the fact that it halves the inventory of reflector dishes. For S-band it works in circular polarization having an N-type interface, and for C-band it has flexibility to have any polarization with the help of a dielectric plate polarizer with a waveguide interface. A very compact circular to rectangular transition has been developed for this purpose. The development has also been engineered to have a simple fabrication process. The whole unit has been qualified from both electrical and mechanical specification considerations and has been put into operation.<<ETX>>

C-Band Microstrip Planar Array for Spaceborne Microwave Remote Sensing

The C-Band Synthetic Aperture Radar (SAR), a payload element for microwave remote sensing satellites requires an antenna with special features such as high gain, a tapered shaped beam and low side-lobes inthe elevation plane and a narrow beamwidth in the azimuth plane. This paper discusses the design of the Microstrip Planar array and technology development of a quarter panel of a six panel configuration measuring 0.8 × 0.42 mts. The development strategy adopted here can be categorized under three areas. 1. The electrical design and computer synthesis of large array with reference to achieving shaped beam and low side lobe levels. 2. Realization of a low loss, high power handling feed structure. 3. Engineering of the overall antenna array to minimize the antenna system weight, support structures and deployment mechanism.

A Hemispherical Coverage, Self-Phased Etched Turnstile (SPET) Antenna

A new cavity backed printed turnstile antenna employing self phasing principle is reported. The ¿/4 deep cavity is shaped in the form of a rhombus of 0.44A side to enable formation of strip dipoles of 1+jl & 1-jl impedances to achieve turnstile action. The antenna generates a circularly polarised beam with a gain of about 5.7 dBi and ¿3 dBi coverage of nearly 180°. Axial ratio (AR) is <0.5 dB on axis and <3.0 dB at ± 90°. The unit has conveniently an impedance bandwidth of 10%. The weight of the antenna made of Mg alloy working at 1700 MHz is about 80 gms.

Antenna systems for the “Aryabhata’ mission

The onboard and ground antenna system employed in theAryabhata mission for telemetry and telecommand operations are described. The onboard antenna system common to telemetry and telecommand frequencies consists of four monopoles fed in turnstile configuration and generates a near isotropic pattern with worst dips of the order of −10 dB over approximately 0.2% of the total radiation sphere area. The ground antenna system consists of a high gain (16 dB) telecommand antenna and a telemetry array of eight medium gain Yagis (gain 22 dB).