V. V. Srinivasan

Dual Circularly Polarized Spherical Phased-Array Antenna for Spacecraft Application

Design aspects of an active spherical phased-array antenna (SPAA) operating in dual circularly polarized (CP) mode are discussed here. Dual CP configuration with good cross-polarized isolation enables frequency reuse using polarization diversity. This design also implements sharing of the resources like amplifiers and phase shifters in an optimal way to reduce mass, power requirement, and cost of the antenna. The antenna is hemispherical in shape and maintains required effective isotropic radiated power (EIRP) over a hemispherical coverage area. Detailed analysis including the effect of failure of a few of the elements of the array and the measured results of the antenna at X-band are discussed here. This antenna has been used for transmission of payload data from a low Earth orbit satellite of ISRO.

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.

Design Aspects of a Compact Dual Band Feed Using Dielectric Rod Antennas With Multiple Element Monopulse Tracking

Monopulse tracking using multiple horns is an attractive and low-cost option for a ground station feed. In this paper, a compact design of this type of feed operating in dual band is discussed. This design uses dielectric rod elements as radiators. Four elements in 2 × 2 array configuration operate for downlink reception and tracking application. One single element with high gain at the center of the array operates for uplink using high power. This allows some design flexibility with respect to independence in configuring the two chains and also provides some inbuilt isolation between them. However, there are issues in this configuration with respect to the mutual coupling between the elements. These are addressed in detail and an optimum design with measured results of a tracking feed operating in 3.4 to 4.2 GHz for downlink and 6.3 to 6.8 GHz for uplink for an 11-m diameter dual shaped Cassegrain antenna is presented here.

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.

Integrated Quadrifilar Helix at C-band for spacecraft omni antenna system

In this paper, design of a circularly polarized (CP) Quadrifilar Helix antenna (QFH) is discussed. QFH provides a circularly polarized cardioid-shaped radiation pattern with a high front-to-back ratio, better circular symmetry in the pattern and very good cross-polarization discrimination over wide coverage. Realization aspects and the measured results of the QFH are discussed here. This antenna is proposed to be used for transmission of satellite telemetry data with Omnidirectional coverage in C-band for Indias all upcoming GEO-Stationary and navigational satellites.

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.

Characterisation of X/S large, high gain, ground station antenna in outdoor test range

It is important and tedious job to characterize large, ground station antenna within specified confidence limit. This requires an extensive measurement program to characterize large antennas (10 mtrs and above). In this paper various aspects of testing and optimizing the antenna performance in outdoor test range (> 5 kms) are discussed. This can be used as a reference guide by other antenna engineers for the optimisation of antenna performance in outdoor test ranges for high gain antennas.

Synthesis and Realisation of a Shaped Beam () for Airborne Microwave Remote Sensing

A shaped beam in the elevation plane is advantageous for a remote sensing radar antenna. The shaping is required to compensate for the path loss variations due to slant range. A radiation pattern synthesis method which combines analytical and numerical techniques to derive the array excitation coefficient is discussed. The use of this algorithm to synthesise a shaped beam for an airborne microwave remote sensing antenna, alongwith measured results is also presented.