Design and Development of Novel End-Fired Microstrip Antenna for Aircraft Collision Avoidance System

Abstract

Traffic alert and collision avoidance system (TCAS) is an airborne electronic equipment that is used to avoid mid-air collisions between two civil aircraft. In the existing TCAS system, four monopole stub elements are used as directional antenna and one blade type element is used as omnidirectional antenna. The transmitting and reeving frequencies of the TCAS antenna are 1.03 GHz and 1.09 GHz respectively. Low aerodynamic drag is urgently required in TCAS airborne system and hence, an antenna with end-fire radiation is essential. The existing TCAS antenna has some drawbacks such as low gain, wide beamwidth, poor directivity, frequency and beam tuning/scanning issues etc. An effort to resolve such issues by developing an antenna using microstrip elements is discussed in this research work and the prototype model design of a planar end-fired microstrip antenna is presented.

First, a unit element planar folded dipole antenna is presented which radiates in the end-fire direction. To improve the directivity performance of the proposed antenna, split ring resonators inspired artificial materials are incorporated in the design and those materials are loaded in the same plane of the primary dipole radiator. Thereafter, three antenna elements are proposed for the study. These are - 1) single patch single feed microstrip antenna, 2) dual patch single feed microstrip antenna and 3) dual patch dual feed microstrip antenna. It is also reported that how end-fire radiation is feasible to attain using microstrip patch antenna. Now, the antenna has to design in such a way that it can transmit the electromagnetic waves towards 360 degree surveillance region of the aircraft and hence, a beam steering multi-feed microstrip antenna is presented which also radiates in the end-fire direction. To make the antenna structure more compact with much better performance, another printed end-fired multi-layered microstrip antenna is proposed which consists of four feeding ports. A switchable power divider is then developed to feed that quad-feed antenna. The proposed antenna can scan the whole azimuth plane with proper excitation of antenna ports by that reconfigurable feeding network. An aerodynamically shaped conformal metamaterial lens based radome is designed to encapsulate the antenna inside an enclosure. Here, the suppression of surface wave in the antenna takes place, which results in gain enhancement and reduction of side lobes. This improves the directivity performance of the antenna.

To simulate and design all the proposed antennas, switchable feeding network and radome, CST microwave studio tool is used. The fabrication and measurement are also carried out to validate the simulated antenna performance and other antenna characteristics. Quite good agreement is achieved between the simulated and the experimental results. Much better performance characteristics make this proposed antenna a good candidate for TCAS application.