Design and development of inclined longitudinal slot rectangular waveguide antenna for LCP and RCP

Abstract

One, two and three pairs of inclined longitudinal slots located at the proper place with an appropriate angle on the broader wall of the rectangular waveguide antenna have been presented in this paper. The location of proper placement of slot and its appropriate angle is one where the antenna gives maximum radiation. The slots are placed from the centre of the broader wall leaving equal distance on either side of the rectangular waveguide with an inclination angle of 39° with respect to centre axis to achieve good polarization pattern. These slots have been cut by electro-discharge machine (EDM) and antennas are designed using computer software AutoCAD 2000 for better precision. The experimental observations are carried out at designed frequency of 9.35 GHz, which gives left circular polarization (LCP). These antennas are also tested at below and above the designed frequency, i.e. at 9.3 and 9.4 GHz to study the polarization pattern and found to give right circular polarization (RCP) and LCP, respectively. It is also experimentally observed that these antennas are capable of producing left and right tilt in radiation pattern without deteriorating the impedance of the antenna. Since their VSWR values are well below the allowed value, i.e. < 2 for all the antennas, it implies better impedance matching. These antennas can find application in bistatic radar system of an aircraft. The design concepts of antenna are described and experimental results are discussed.