Microstrip antenna array using photonic bandgap substrate

Photonic Bandgap (PBG) structures have been successfully applied to antenna design in order to raise the antenna radiation efficiency. In application of PBG structure in microstrip antennas design, mainly two techniques are used. One is to introduce a periodic lattice in the substrate layer. The seemingly simplest way to achieve this is to drill a periodic lattice of holes on the substrate slab. It is reported that for a single microstrip patch antenna, the radiation efficiency, backlobe and endfire radiation have been greatly improved by using a PBG substrate of drilled holes over the conventional bulk substrate [1]. It has also been revealed that PBG structures improve the antenna performance by suppressing the propagation of surface waves. This has been experimentally verified by measuring the mutual coupling between two distant microstrip antenna elements built on PBG substrate [1], or superstrate [2]. An alternative approach is focused on construction of a planar periodic lattice of metallic patch array on top of a dielectric substrate layer, and similar improvement was observed [3, 4]. By appropriately design of the element geometry and the lattice constant, an equivalent perfect magnetic conductive (PMC) surface was achieved over a limited band of frequency. Such a PMC surface can be applied in antenna design to suppress the flow of surface electric currents, which is the major source of edge diffraction, therefore improves the radiation property of the antenna.