Design and Implementation of Multiband and Broadband Microstrip Antennas for Wireless Systems

Abstract

With advancement in wireless systems, the device size is shrinking. The modern day wireless systems are termed as next generation wireless systems. The modern day, small size wireless devices are not just limited to voice conversation but also support high data rate multimedia applications like VoIP, video conferencing, wireless broadband and online gaming etc. The high data rate can be achieved by increasing the bandwidth support of the system. Antenna being important integral part of wireless system requires to support broad bandwidth. The heterogeneous technology support to wireless system is other advancement in next generation wireless systems. So the antenna for next generation wireless devices require support to larger bandwidth and support to multiple technology. This motivation leads to research presented in the thesis. The thesis is organized with four objectives. The first objective is devoted to the study of different type of techniques for multiband and broadband operation. In process for achievement of first objective, the historical development in wireless systems are considered for insight to different technology and application support. The planar antenna has advantages of being conformal, low profile, small size and ease of integration with device PCB. So the challenge is to design multiband and broadband planar antennas. The length of antenna is frequency dependent so specific techniques can achieve multiband and broadband operation. In this thesis, the different techniques which are already presented in literature for achieving multiband and broadband support to microstrip antennas are surveyed. In the next chapters, the different designs to achieve multiband operation are discussed. This is second objective of the thesis. The planar multiband antenna is designed and termed as multiband microstrip patch antennas. To start with, the planar antennas with different type of feeds are compared. The slot in patch of MPA is one method to achieve multiband operation of planar antenna. The different type of fractal shape patches are considered for multiband operation. The sierpinski carpet and sierpinski gasket shapes are discussed with limitation of each. The analysis reveals that the sierpinski carpet suffers with problem of impedance matching at the edge of the patch and sierpinski gasket suffers with the problem of non-uniform conduction at the nodes of triangles. Further the modified CPW feed with sierpinski gasket shape is considered for multiband operation of antenna. The second types of design discuss the planar broadband antennas. The Rumsey’s principle term the broadband antenna as frequency independent antennas. It is analyzed that, the bandwidth can be enhanced by increasing the substrate height and decreasing the substrate dielectric constant. The effect of different type of feeds on bandwidth of antenna is considered. The defected ground structure is another method to achieve broadband operation of planar antennas. The hybrid fractal is proposed as ultra-wideband planar antennas. The hybrid fractal comprises of sierpinski gasket and sierpinski carpet shape. The sierpinski gasket shape is performing two operations, one is to resonate at multiple frequencies and to act as impedance transformer for sierpinski carpet antenna. The different resonances are merged to obtain broadband response of antenna. The hybrid fractal so proposed offers high gain along with the wide impedance bandwidth. The planar inverted F antenna because of its inherited small size is used for modern day mobile handsets. The PIFA support to multiband and broadband operation is discussed in the thesis. The folded edge, Fractal PIFA is proposed as small size antenna for 3G mobile handsets. Further F-PIFA are made resonant at multiple band of frequencies. The MIMO concept further enhance the data rate for wireless systems without need of increasing the bandwidth. The MIMO PIFA with patches at different heights can be used to reduce correlation between two antennas. The ECC value of proposed antenna is analyzed and concluded as MIMO PIFA antenna for LTE applications.