Design of wideband outdoor base station antennas

Abstract

This thesis presents a study on the enhancement of a magneto-electric dipole, which is composed of two short circuited patches and a - shaped probe feed operated at centre frequency 2.15GHz. The antenna was designed based on the complementary antenna concept for achieving excellent electrical characteristics (i.e. stable gain, low back lobe, wide bandwidth, low cross polarizations, and nearly identical E- & H- plane radiation patterns. The objective of this thesis is to reduce the size of the antenna by folding technique, and preserve its wide bandwidth and excellent performance over the frequency band. By employing the folding technique, the height of the proposed antenna is reduced to 14mm (0.1λ), which is reduced by over 50% comparing with original design. In the past, size reduction is achieved by many different methods, such as fully or partially loaded by high dielectric substrate, folded patch with shorting walls or shorting pins, etc. However, all the above methods are difficult to fabricate and not cost effective since expensive dielectric substrate is employed. In this thesis, the most cost effective method for the size reduction will be presented. For the proposed antenna, a wide impedance bandwidth of 49% (SWR≤ 2) is achieved. The maximum antenna gain is ~8dBi. Low back lobe, low cross polarization are also be achieved.