Abstract
M.Ing.
This study considers improving the azimuth beam steering resolution of the circular
Switched Parasitic Array (SPA) antennas (made up of dipoles) by a factor of two or more. In
circular SPA antennas, beam steering is conventionally achieved by open-circuiting and shortcircuiting
different parasitic elements and usually only one parasitic element is open-circuited
at a time. However, such an approach results in low beam steering resolutions especially for
the SPA antennas with few parasitic elements. In order to increase the azimuth beam steering
resolution for the circular SPA antennas, two beam steering methods are proposed in this
research work.
In the first method, parasitic elements are open-circuited and short-circuited based on
different combinations of the parasitic elements and the possible switch states. The proposed
method was first validated by simulation tests using the MATLAB tool and WIPL-D. A
prototype of the circular SPA antenna consisting of five elements was then implemented. It is
noted that the simulation and measurement results match very well at 2.4 GHz.
In order to have at least two combinations (from the first method) with almost similar gain
and return loss, another simpler beam steering method was developed. The latter method is
based on simultaneously open-circuiting either two or three neighbouring parasitic elements.
The performance of the second method was studied through simulations using the circular SPA
antenna geometries consisting of five, seven and nine elements. These geometries were first
optimized (for gain and input impedance) and then modelled using WIPL-D. It was observed
that the two methods double the azimuth beam steering resolution of the circular SPA antennas
when compared to the conventional beam steering approaches of open-circuiting one parasitic
element at a time.
Variations in the structural parameters of the five elements circular SPA antenna at 2.4GHz
were also investigated. In this procedure, the effects of variations (also considered as random
errors) in the structural parameters (or antenna dimensions) on the performance of the SPA
antennas were examined. Firstly, variations in each structural parameter were modelled with
other structural parameters fixed as per specifications. Thereafter, effects of combined errors
were also investigated. The simulation results demonstrated that variations in the structural
parameter can either increase or decrease the gain and input impedance of the SPA antenna
depending on the given specifications. The gain and input impedance sensitivities per
variations in each structural parameter were computed to determine the degree at which the
gain and input impedance can vary for a predefined change (error) in the structural parameter.