Effects of EBG reflection phase profiles on the input impedance and bandwidth of ultrathin directional dipoles

A comprehensive study of the effects of the reflection phase profiles on dipole antennas is presented with the ultimate objective of designing ultrathin printed dipoles (as thin as one hundredth of the wavelength). Dipole driving-point impedance and bandwidth are studied as function of various electromagnetic bandgap (EBG) reflection phase profiles. It is demonstrated that although many different reflection phase profiles can be generated for a certain antenna height, it is the profile that satisfies a specific range of reflection phase angles that is required to achieve good antenna performance. Such optimum EBG phase profiles are generated for a number of antenna heights and their influence on a dipole antenna impedance and bandwidth are also studied. Finally, an actual EBG structure and a printed dipole antenna are designed, fabricated and tested. The overall antenna height for this case was 0.03λ. The computed and measured results show that efficient printed dipoles on ultrathin grounded dielectric substrates can be developed that will substantially reduce the sizes and weight of large arrays.