Microstrip fed annular slots in single and stacked configurations - studies of the effects of slot ground plane and back reflective plane on bandwidth and radiation characteristics

Abstract

The impedance and the radiation characteristics of single and stacked annular slots configurations were studied with emphasis on their dependence on various parameters such as: the slot width, the patch-to-slot spacing (for stacked configurations only), the form of the slot ground plane (SGP) and the presence of a back reflective plane (BRP). It was found that the impedance bandwidth is mainly controlled by the geometry of the radiating element (i.e., the slot width and the slot-to-patch spacing, where applicable) being only slightly dependent on the form of the SGP. The input impedance levels are also controlled by the same parameters but may change drastically with the form of the SGP, especially for slots in single configurations with a BRP. The radiation characteristics, however, are mainly controlled by the geometry of the SGP and the presence of a BRP. Whenever a particular application asks for a SGP larger then the wavelength the use of a SGP form able to reduce the effects of the edge diffraction is imperious and may enhance the performance capability of the radiators. Finally, the advantages of stacked configurations were presented. It can be concluded that the annular slot in a stacked configuration with a circular microstrip patch on top is a versatile element with wide impedance and gain bandwidths. All that, together with the very low level of feedline spurious radiation make this element most suitable for high performance array applications [2].