Reconfigurable MIMO Antennas Using RF Switches for Wireless Communication Systems

Abstract

This dissertation is dedicated to implementation of various reconfigurable antennas namely i) polarization diversity antenna ii) frequency macro- and micro-tuning antenna, and iii) frequency reconfigurable and MIMO antennas capable of providing frequency and isolation reconfigurability. The design details of the proposed antenna, along with computer simulation and measurement results, are given. First, a small reconfigurable patch antenna was proposed to achieve polarization diversity for digital multimedia broadcasting system at 2.6 GHz. To obtain polarization diversity, a pair of on-slit PIN-diodes was inserted in each diagonal of a cross-shaped patch. The antenna produces left-hand circular polarization, right-hand circular polarization, or linear polarization, depending on the PIN-diode status. Second, a reconfigurable PIFA antenna using a switchable PIN-diode and a fine-tuning varactor was presented for mobile communication applications. Selection of operating modes was achieved by switching the PIN-diode between radiators and tuning the varactor on an antenna�s shorting line. Mode I, with the PIN-diode off and tuning the varactor, operated for USPCS (1.85�1.99 GHz), WCDMA (1.92�2.18 GHz), and WLAN (5.15�5.825 GHz). Mode II, with the PIN diode on and the fixed 0-V varactor, operated for USPCS and m-WiMAX (3.4�3.6 GHz). Third, a frequency reconfigurable PIFA using real PIN-diodes was presented for mobile-WiMAX applications. This antenna not only altered the frequency band of the mobile-WiMAX using PIN-diode switching, but it also had a small profile using capacitive load within an FR4 dielectric constant substrate. Depending upon whether the diodes are on or off, the antenna operated over 2.3 to 2.4 GHz, 2.5 to 2.7 GHz, and 3.4 to 3.6 GHz for worldwide mobile-WiMAX bands. Last, a reconfigurable MIMO PIFA was presented for three worldwide m-WiMAX bands. In order to achieve low mutual coupling, i.e., high isolation, a band-notched quarter-wave slot line on the ground plane was used between the two reconfigurable antennas. By adjusting the PIN-diode biases, the proposed antenna simultaneously obtained the operating frequency and isolation reconfigurability for the three operating bands.