Active tuning and miniaturization of microstrip antennas

The objective of this paper is to introduce two aspects of printed planar antennas, miniaturization and tuning of the resonant frequency. When varactor diodes are used as capacitive loads for the antenna, it allows reducing the size of the antenna with an added feature of tunability. By varying the biasing voltage of the varactors, resonant frequency can be varied over wide range. The positions of the varactors also have influence on the resonant characteristics of the patch antenna. Various characteristics of patch antenna such as resonant frequency, input impedance, current distribution, cross polarization and radiation pattern for different varactor positions are studied using the full-wave finite difference time domain (FDTD) approach. Varactors are characterized by their equivalent circuits and incorporated as lumped elements in the FDTD method.