Stacked configurations are possible with aperture coupled feeding, proximity feeding and co-axial feeding. Probe feeding technique is re-emerging in variety of antenna system due to its robust nature. It provides good isolation between feed network and radiating elements and due to direct contact with the radiator reduces dielectric layer misalignment difficulties. It also yields good front to back ratio which is very important where multiple arrays are located back-to-back in closed proximity. Therefore stacked configurations with probe –fed have been considered. The combination of low dielectric constant and high dielectric constant can yield good impedance behavior. The broadest bandwidth can be achieved when the first-order mode on the lower patch is considerably greater in magnitude than corresponding mode on the top patch or in other words the top patch is loosely coupled. For this the substrate of lower patch should have higher dielectric constant than the upper substrate.
fig: Parasitically Coupled Coaxial fed Microstrip Antenna
Fig: Multilayer Stacked Configuration
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