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.
