We propose a wideband reconfigurable circular-polarized single-port antenna to realize high-density linear integration for use in ground penetrating radars. We switch PIN diodes at a T-shaped probe to change its polarization. The forward- and reverse-biased probes work in cooperation to generate circular polarization. Experiments demonstrate the working bandwidths of 20.0% and 18.6% in the left- and right-hand polarization states, respectively, with 7.2 GHz center frequency. They are wider than those of conventional reconfigurable single-port circular-polarized antennas.

A polarization switchable slot-coupled microstrip antenna using PIN diodes is proposed and studied. The microstrip feed line installed behind the ground plane is divided into two branches and each tip of the branches is connected to the ground plane through a PIN diode. One of the diodes is oriented from the tip to the ground plane and the other is oriented from the ground to the tip so that a slot in the ground can be selected to feed the patch by switching the dc bias between positive and negative. This selection contributes to switch the polarization between horizontal and vertical. In this paper, the authors investigate the polarization switching antenna theoretically and experimentally and confirmed sufficient differencce of antenna gain between horizontal and vertical polarization.

A behavioral model for ferroelectric capacitors is developed. There are two requirements for the circuit simulation model; one is to reproduce the hysteretic behavior of the polarization under arbitrary voltage history, and the other is to describe the time dependence of polarization change. A parallel element model has been proposed to meet the first requirement. This model reproduces the minor loops of the hysteresis by assuming that the ferroelectric capacitor consists of the parallel capacitors of different polarization and coercive voltages. In order to add the function to describe the time dependence of the polarization change, we propose a method of measuring the switching response for individual parallel elements and the model which describes the response. In the measurement, the voltage applied to the capacitor is raised in two steps. After the first step, the voltage is kept at an intermediate level for a period of time, then raised again to the final level and the polarization change was recorded as a function of time. Because the capacitor elements with the coercive voltage lower than the intermediate level complete switching during the first step, the polarization change of the whole capacitor during the second step is attributed to the capacitor elements with the coercive voltage higher than the intermediate level. This procedure is repeated with changing the intermediate level, and the switching response of each capacitor element is obtained by taking the finite differences between the adjacent sets of data. The measurement on a sol-gel derived SrBi2Ta2O9 capacitor revealed that the switching time depended only on the difference between the applied voltage and the coercive voltage of each capacitor element. The time dependence of the polarization change is implemented to the model by inserting a nonlinear resistor in series with each capacitor, which reproduces the polarization switching under arbitrary voltage change without any fitting parameters.