Frequency reconfigurable log-periodic antenna design

Abstract

The concept of reconfigurable antenna is widely used as additional features of reconfigurable ability for future wireless communication system. There are various configurations of reconfigurable antenna such as monopole, dipole and log-periodic wideband antenna. The integrations of reconfigurable antennas with radio frequency (RF) switches are needed to perform the switchable ability. In this research, a logperiodic antenna (LPA) has been designed to perform a wideband frequency operation by connecting thirteen square-patch antennas using inset feed line technique. Then, the reconfigurable log-periodic antenna (RLPA) is designed by connecting positive-intrinsic-negative (PIN) diodes at every transmission lines with a quarter-wave length radial stub biasing. The representation of real PIN diodes and the locations of biasing circuits in simulation are also included. Three different subband frequencies with a bandwidth of 20% (3 - 4, 3.7 - 5, and 4.8 - 6 GHz for each band) are configured from the total of 73% bandwidth (3 to 6 GHz) of the wideband operations by switching ON and OFF of the PIN diode. Other sub-bands or narrow band can also be configured by selecting other group of patches. Validation for the LPA and RLPA is achieved by comparing the simulated and measured radiation patterns. The measured half-power beamwidth (HPBW) for LPA are 62°, 58° and 72° at frequency 3.4 GHz, 4.0 GHz and 5.8 GHz, respectively, while 73°, 67° and 72° for RLPA at the same frequency band. The simulated gain for LPA and RLPA are around 4.9 dB and 5.0 dB respectively, while the measured gain is around 5.5 dBi for LPA and 5.7 dBi for RLPA within a frequency range of 3 – 6 GHz. All the structures have been fabricated and the measurement results show accuracies of 97.5% for return loss, 80.2% for gain and 98.4% for HPBW with the simulation results.