Abstract
M.Ing.
This work considers a dual band electronically steerable parasitic array radiator (ESPAR) antenna system. This system is designed with one actively fed radiating element and N-parasitic radiating elements. The radiation pattern can be electronically controlled by means of the loads terminating the parasitic elements. The antenna system is designed as ESPAR to have a minimum number of controlling elements thereby minimising the power consumed.
The dual band operation of this antenna is for the frequency bands of the wireless local area network (WLAN), which are 2.412-2.482 GHz for IEEE 802.11b/g (known as the 2.4 GHz band) and 5.15-5.825 GHz for IEEE 802.11a (known as the 5 GHz band). In the upper band, only the 5.8 GHz sub-band was considered. The dual-band capability was targeted by conducting a structural parameter modification on the antenna system. The structural modification involves optimisation of the length of the active element, the length of the parasitic element, the distance of the parasitic element from the active element and most importantly, by application of a loading technique on the elements.
The loading was done by using optimisation tools, such as fminsearch, fminbnd and the genetic algorithm. The specific circuit that was used for the loading was a series connection inductors inserted into the antenna’s elements at positions found via a global optimization.. The method used was to first identify the optimal length per specific resonant frequency and consider the optimal length with respect to both resonant frequencies. The second step was to load the three resulting optimised different monopoles, and the loading with results closest to the requirements. The optimum monopole of the three in the second step was then used as the fixed input parameter for the main optimisation of ESPAR antenna. Using a ground plane with a skirt, an acceptable return loss performance has been achieved for the antenna's main building
M.J. Bembe ii
block, a monopole element, in both frequency bands. The challenge was found in steering of the beam in different directions; it was then concluded that the usage of more elements could provide the necessary freedom for the optimisation process.
Six elements were arranged symmetrically close to the active fed element in order to achieve a dual band resonance, with different designs meeting the requirements differently. This is the first report showing an ESPAR antenna optimisation which includes the loading of elements with lengths and distance optimisation.