A suspended microstrip fed slot antenna on high impedance surface structure

Abstract

The microstrip fed slot antenna (MSA) is widely used as an element antenna in conventional phased array antenna due to its low profile, light weight and low cost. It is usually made of a single piece of dielectric substrate with a slot etched on one side and microstrip feed line etched on the other side. On its own, MSA is not an efficient antenna. This is due to its bidirectional radiation pattern behaviour where almost half of the radiated power is wasted in the undesired direction. As a result, the overall performance of the conventional phased array antenna using MSA as an element is normally not satisfactory. To achieve an efficient phased array antenna, it is therefore crucial to design an element antenna that can deliver reasonably high gain and symmetrical radiation patterns in both E and H planes. This paper focuses on solving the bidirectional radiation problem exhibited in MSA and at the same time improving the gain, radiation pattern and return loss performance. This is done by adding a mushroomlike High Impedance Surface (HIS) structure or also known as Artificial Magnetic Conductor (AMC) underneath the MSA structure to form a new generation of MSA antenna called "Suspended MSA on HIS structure". This HIS structure acts as an efficient reflector that redirects most of the wasted energy from the undesired direction to the desired direction without interfering with the MSA return loss performance. Furthermore this helps to improve the overall radiation pattern of this new antenna in both E and H planes with a maximum gain of 10 dB in the desired direction and a maximum gain of less than -3 dB in the undesired direction. An equivalent circuit model of the antenna is also presented in this paper. An effective medium model and the simulation tool "Ansoft HFSS" [1] are used to aid the design of this antenna.