A Study of the Spiraphase and Anisotropic Substrates in Microstrip Antennas

Book excerpt: Two subjects are discussed in this interim report; the spiraphase antenna and the use of anisotropic substrates in microstrip antennas to decouple the radiation and scattering modes. It was observed that the spiraphase, a multi-arm spiral structure can be used either as a reflector or directly as a transmit and/or receive antenna. The bandwidth of the reflector case is much more limited; however, improvements are possible by understanding the mechanism that limits the bandwidth. The broadband nature of the spiraphase used directly as a transmit and/or receive antenna was established. The development of spiraphase into a microstrip antenna is discussed. The use of anisotropic substrates, or other substrates with 'exotic' materials, was found to be useful in decoupling the radiation and scattering modes in the microstrip antenna. This decoupling process is made possible because the use of anisotropic material nullified the foundation on which the reciprocity, or the equivalence of receiving and transmitting patterns of antenna rests. (Author).