BROADBAND CAVITY BACKED LOW PROFILE SPIRAL ANTENNA

Abstract

Designing a wideband antenna for use in UWB system is a major challenge and has attracted the interest of many antenna engineers. A spiral structure appears to be promising for wideband application due to its broadband impedance characteristics and compact size. This thesis focused on the design of a broadband (2-18GHz) cavity-backed spiral antenna. The design of two types of planar spiral antenna (Equiangular and Archimedean spiral) is presented in this thesis. Two professional electromagnetic simulators, Ansoft HFSS (Finite Element Method based) and CST MWS (Finite Integral Time Domain based), are used as analysis tools to obtain antenna performances. A detailed characterization of all antenna components and parameters is provided. The microstrip tapered balun used for feeding section of spiral antenna is designed and simulated in Ansoft HFSS. The bidirectional beam of the planar spiral antenna is transform to the unidirectional beam by backing the spiral antenna with an empty cavity. The performance degradation due to cavity resonances is discussed and their suppression is also demonstrated. A comparison of the two types of spiral antenna is also presented. This thesis also focuses on the miniaturization of the radiating aperture of the Archimedean spiral antenna and size reduction of the radiating aperture is achieved by meandering the outer turns of Archimedean spiral antenna. The Archimedean spiral antenna and the meander arm spiral antenna were also fabricated and tested for return loss and VSWR. The measured VSWR ≤ 2 for majority of the band, ensuring proper impedance matching of the microstrip tapered balun with the input impedance of antenna.