Analysis of biconical microstrip antennas

Biconical microstrip antennas having a conical patch over a conical substrate are investigated. Analytical expressions for the field distribution inside the conical cavity are developed in a spherical coordinate system and used to determine the eigenvalues of the resonant modes. It is found that, in addition to the axially symmetric modes, TE modes can also resonate which are asymmetric and dependent on the azimuthal angle. For coaxial probe excitation of the cavity, analytic expressions for the field components are determined and used to investigate the antenna input parameters and radiation patterns. The special case of a conical patch microstrip antenna with a planar substrate is also studied. It is shown that, in comparison with circular disc microstrip antennas, a conical patch yields a wider impedance bandwidth and higher gain