1. Multimode Vivaldi Antenna

This research presents a multi-mode Vivaldi antenna, which is designed to operate either in a wideband mode, a wideband mode with a band rejection or a narrower pass band mode. The antenna in a wideband mode is designed to have a bandwidth of 2 – 8 GHz. In the notch band mode, the antenna has tunable narrow band rejection between 5.2 GHz and 5.7 GHz. The Vivaldi can also operate in a narrow pass band mode, which has a bandwidth of 4.6 - 5.0 GHz or 5.3 – 5.6 GHz. Other narrow pass bands at 3.6, 3.9 and 6.5 GHz can also be selected

2. Vivaldi Antenna with Integrated Switchable Band Pass Resonator

This research presents a novel reconfigurable wideband to narrowband Vivaldi antenna. A single pair of ring slot resonators is located in the Vivaldi to realize frequency reconfiguration, maintaining the original size unchanged. The proposed antenna is capable of switching six different narrow pass bands within a wide operating band of 1 – 3 GHz, offering added pre-filtering functionality. A fully functional prototype has been developed. PIN diode switches were employed at specific locations in the resonator to change its effective electrical length hence forming different filter configurations. The antenna is potentially suitable for applications requiring dynamic band switching such as cognitive radio.

3. Switched Band Vivaldi

This research presents a novel Vivaldi antenna with added switched band functionality to operate in a wideband or narrowband mode. The antenna reconfiguration is realized by inserting four pairs of switchable ring slots into the ground plane of the structure. A wide bandwidth mode from 1.0 – 3.2 GHz and three narrowband modes can be selected. A fully functional prototype with PIN diodes switches has been developed. The antenna could be a suitable solution for a multi-mode application requiring wideband and frequency reconfigurable antennas, such as in military applications and cognitive radio.

4. Vivaldi Antenna with Tunable Narrow Band Notch

This research presents a Vivaldi antenna with narrow band rejection characteristics within the 2 -7 GHz range of the operating bandwidth. The band rejection is realised by incorporating a microstrip line resonator printed on the reverse side of the radiating element. To give a narrow, tunable stop band action, the resonator is loaded with varactors. Three methods are presented: one with fixed band notching at 5.75 GHz; one with a single varactor to give a tunable band notch between 4.2 – 5.5 GHz; and another with 3 varactors and a shorting post to the ground, widening the stop band in the frequency range between 2 and 7 GHz, giving a tuning ratio, of 3.5:1. The proposed antennas have the capability of rejecting a combination of interfering signals (eg WLAN signals) within the operating bandwidth. These properties could be useful for defense applications or future cognitive radio systems in rejecting the interferers.

5. Frequency Reconfigurable Log Periodic Patch Array

This research presents a novel reconfigurable low profile log periodic patch array. The patches are fed with a modulated meander line through aperture slot. Wideband mode from 7 – 10 GHz and three selected narrow band mode at 7.1, 8.2 and 9.4 GHz is demonstrated. The wideband to narrow band reconfiguration is realized by bridging slot aperture, effectively deactivate the corresponding radiating element. Potentially the proposed method suggested here offers a very fine control of narrower pass band.

6. A Compact Frequency Reconfigurable Narrow Band Microstrip Slot Antenna

This research presents a frequency reconfigurable microstrip slot antenna. The antenna is capable of frequency switching at six different frequency bands between  2.2 GHz and  4.75 GHz. Five RF PIN diode switches are  positioned in the slot to achieve frequency reconfigurability. The feed line and the slot are bended to reduce 33% of the original size of the antenna. The biasing circuit is integrated into the ground plane to minimize the parasitic effects toward the performance of the antenna.

7. Reconfigurable Frequency and Pattern Yagi Antenna

This research presents a novel frequency and pattern reconfigurable Yagi antenna. The antenna is formed by a driver, a reflector and two directors. The introduction of switches using a PIN diode at the arms of the driver element produces three switchable frequencies at 1.25 GHz, 1.85 GHz and 2.45 GHz. By controlling the switches at the directors and reflector, the radiation pattern can be configured to omni-directional pattern or directional pattern at those three frequencies. Simulated and measured results are used to demonstrate the performance of the antenna. It was found that the gain of the antenna increases from 3.3 dB to 5 dB in a directional pattern, when compared to the omni-directional pattern.

8. Frequency Reconfigurable Wide to Narrow Band Monopole with Slotted Ground Plane Antenna

A frequency reconfigurable wide to narrow band antenna is presented. The proposed antenna is an integration of a monopole antenna (MA) and a microstrip slot antenna (MSA). The MA produces a wide frequency band from 1.66 GHz to 4.93 GHz and the MSA produces three different frequency bands resonating at 3.02 GHz, 3.89 GHz and 4.56 GHz. Simulated and measured results are used to validate the performance of the antenna. The affects using copper strip and PIN diode as switches in the measurement are demonstrated. The simulated and measured return losses, together with the radiation patterns, are presented and compared.