Compact antennas for short range wireless communication applications
Student thesis: Master's Thesis
Related Research Unit(s)
Short range wireless communication such as Bluetooth and Ultra-Wideband (UWB) are becoming more popular within the market place and as a research area. They both enable users to exchange data and to connect telecommunications devices over a short range without the use of a “hard wired” connection. Antennas are an essential part of Bluetooth and Ultra-Wideband (UWB) devices with conflicting demands of small size and high antenna efficiency. Thus, the implementation of the elusive small antennas with acceptable gain is highly desirable. In this thesis, three different compact antennas are proposed for use in UWB and Bluetooth products. A printed pellet-shape microstrip-fed monopolar antenna suitable for compact portable devices is proposed for UWB multi-band, OFDM wireless communication use. An impedance bandwidth of 138.3% within the frequency range of 3.1GHz to 17GHz for S11 < -10dB is demonstrated. Positive gain and constant group delay are also achieved with an omni-directional radiation pattern. For UWB based on impulses, a double sided printed sickle-shape dipolar antenna with stable radiation pattern is proposed. Requirements for the antenna for this type of signal is more stringent with a consistent radiation pattern throughout the entire band considered highly desirable. The proposed antenna is optimized using genetic algorithm and the resulting antenna achieved a wide impedance bandwidth with small variations in the radiation pattern and gain across the entire UWB frequency range. This can be used in multi-band, OFDM as well as for the impulse radio modulation schemes, making it suitable for UWB triple mode use. Apart from the UWB antennas, a novel switchless active integrated antenna design operating at 2.4GHz is proposed for use in Bluetooth. Combining the power amplifier (PA), patch antenna and low noise amplifier (LNA), enabled the requirement of pin diode switch to be eliminated. By making use of the bias control in the amplifiers the operation mode could be made to toggle between transmission and reception. An isolation of 16.8dB together with 16.4dBm output power for the PA under the transmission mode and 14dB gain with 1.5dB noise figure for the LNA under reception are achieved. The size of the patch antenna is also reduced by 78.3% with -2dBi antenna gain and an omni-directional radiation pattern. This is achieved by transforming the output port of the PA and input port of the LNA to a low impedance under reception and transmission mode respectively to synthesis a shorting wall or partial shorting wall, effectively at least halving the antenna size.
- Antennas (Electronics), Wireless communication systems