Characterization of Wideband Antennas for Point-to-Point Communications

Antenna frequency response can be characterized in terms of effective aperture and gain. Antennas can also be characterized as a two-port network to ascertain the antenna transfer function ( $S_{\mathbf {21}}$ ). This characterization is important in point-to-point (P2P) communication, as the frequency response can vary due to changes in the radiation pattern in the physical channel. This paper presents a process to investigate the frequency response of a wideband antenna in order to identify the best orientation of the antenna for P2P communication. The process predicts the antenna’s effective aperture and gain for each orientation. An equivalent circuit for the wideband antenna is also derived to obtain the total radiated power. The frequency-variant radiation pattern is ascertained from the $S_{\mathbf {21}}$ phase obtained from the equivalent circuit. For each orientation, the $S_{\mathbf {21}}$ phase is analyzed based on the linear, minimum, and all-pass phase components, which enables the derivation of an equivalent circuit. The variation of group delay for each orientation is also obtained and compared. The measurements between two identical antennas at the two orientations with a free-space channel were then modeled for simulation in a digital system. This simulation predicts the antenna effects for the two orientations used. Finally, this process was validated by using a nonminimum-phase monopole ultra-wideband antenna.