Three-dimensional transitions for multilayer active printed antenna in Ka-band

Abstract

This work is related to the development of terminal antennas for satellite communications in Ka-band (down-link 19.70-20.20 GHz and up-link- 29.50-30.0 GHz). Innovative designs are called for in order to meet the stringent requirements of ATM-Sat terminal antenna like high frequency operating band, compactness, light weight and above all low cost. A multilayer active array antenna appears to be the most suitable option for this application. Basically, it would consist of a passive patch elements array and several circuit layers with passive feeding networks and active circuit layers. To make this planar structure operate in a proper way, the indispensable transfer of power between adjacent layers must rely on robust and highly efficient 3D transitions. Further, for ease of mounting of active elements and due to their less dispersive behaviour at high frequencies, coplanar waveguides are chosen as transmission line media. The present work is concentrated on this aspect of 3D transition between coplanar lines. An extensive survey was carried out to collect information on different types of coplanar waveguides (CPW), modes of operation, parasitic modes and suppression techniques, CPW discontinuities, multilayer circuits, application of CPWs in antenna and MMIC circuits. Apart from these topics, thorough literature survey was carried out for 3D CPW transitions. It includes various categories of 3D transitions involving two coplanar lines or one coplanar line plus another type of transmission line like a microstrip or a stripline. After literature survey, work was concentrated on software simulation study. Initially a few examples from literature were simulated to build the confidence and check the applicability of the simulation tools. After gaining enough experience, the structures of interest like conductor-backed coplanar waveguides (CBCPW)-to-cover-shielded-CBCPW transitions by direct electrical contact and electromagnetic coupling were studied in detail. An exhaustive parametric study was done to maximise the transmission efficiency and bandwidth of operation of the transitions. The influence of several parameters like substrate height and its dielectric constant, via holes, air-bridge etc was investigated. The techniques for reducing the effect of parallel-plate modes were examined in these transitions.