Broadband design on dual and circularly polarized antennas for wireless communication systems

Abstract

The broadband design of dual and circularly polarized antennas demands precise wideband control of the individual orthogonal radiated polarization. The quality of polarization and its control is related to the inherent isolation between the two orthogonal modes. Dual linear polarization involves two orthogonal linearly polarized modes, while circular polarization involves two or more orthogonal linearly polarized modes with equal amplitude excitation and quadrature phasing. A balanced feed network provides the orthogonal linearly polarized modes with impedance matching, balanced power splitting and appropriate phasing. The use of a 180o broadband balun (~52.58%), and 90o broadband baluns (Type I) (~57.5%) and (Type II) (~72.46%), are compared with the conventional 180o narrowband balun (~10%) and 90o hybrid coupler (~14%). Each novel broadband balun, investigated for sequentially-rotated two- and four-point feed microstrip and dielectric resonator antennas, are shown to deliver enhanced polarization (axial ratio) bandwidth, and also enhanced isolation bandwidth for dual linear polarization.