Research On EBGs As Reflector Of Planar Inverted F Antenna In UHF Band

One of longstanding problem in planar inverted F antenna is its efficiency,which degrades as PIFA is placed too colse to the ground. In this paper, the PIFAmeticulous development process and its main research areas are reviewed. Twomodels, which contains microstrip antenna model and monopole antenna model, a-re utilized to explain PIFAs working mechanism. In addition, there designs a ki-nd of compact PIFA with capacitor structure, which has the size of one-eighth o-f the wavelength and is reduced by half size compared to traditional PIFAs. Pla-nar electromegnetic bandgap structures (EBGs) are studied by derivation of lump-ed element and transmission line equivalent circuits followed by utilizing analyti-cal formulation. Based on this approach, a code is developed that predicts the d-ispersion characteristics of these periodic structures in a matter of few seconds.Planar EBG structures containing meander sections are investigated and a methodfor development of an equivalent circuit for the meander line portion is presente-d. The analysis of the studied EBG structures begins from a simple1D geometry and is extended to more complex2D geometries. In the UHF band, a kind ofmushroom-like EBG structures with three conductors is designed, which has smal-ler unit cells and thinner thickness compared to classical mushroom-like EBG structures. This kind of mushroom-like EBG structures is used as reflector of PIF-A with capacitor structure. It is demonstrates that PIFAs with EBG ground havehigher radiation efficiency than PIFAs with PEC ground while the antenna resona-nce frequency and the radiation pattern is not found significant changes. The th-eoretical prediction is verified through measurements with good agreements. Thetheoretical explain of this phenomenon is that surface wave is suppressed by EB-G reflector while reflecting electromegnetic wave has the same phase of main r-adiation, which results in radiation efficiency enhancing. This result provides a m-ethod of improving radiation efficiency of PIFAs in the UHF band and the theo-retical analysis in this paper gives some guidance and refernce value to designPIFAs and EBGs.