Filtenna design with selectivity enhancement for modern communication system

Abstract

This thesis presents filtenna design with selectivity enhancement for modern communication systems. Filtennas are designed to simplify the radio frequency (RF) front-end, reduce cost and eliminate signal losses. Two filters, (Filter A and Filter B) and two filtennas, (Filtenna A and Filtenna B) have been designed to overcome a few drawback such as decrease in the peak gain, poor selectivity, increase in feeding area and structure complexity of the existing filtennas. Filtenna A and Filtenna B are designed based on Filter A and Filter B, respectively, by using filter synthesis technique. All designed structures were simulated using Computer Simulation Technology (CST) Microwave Studio and validated through fabrication and measurement of the prototypes. Firstly, an improved technique for creating sharp selectivity of a T-shaped stub bandpass filter (Filter A) is designed. The T-shaped stub is loaded with vertical resonators to produce good selectivity at both edges of the passband at 3.6 GHz. The advantage of this filter is the potential ability to adjust the center frequency and the bandwidth to suit the system demands. Secondly, a novel and compact second order Chebyshev bandpass filter (Filter B) with sharp selectivity is designed to operate at 5.8 GHz. The sharp selectivity is obtained by using U-shaped resonators and Defected Ground Structure which are responsible for the rejection at the higher and lower band edge, respectively. The advantage of this design is size compactness. About 56% area reduction is achieved over the second order Hairpin bandpass filter. Thirdly, the T-shaped stub bandpass filter is synthesized with a microstrip patch antenna to form a T-shaped stub fed filtenna (Filtenna A) with enhanced selectivity. The advantage of this design is that it maintains the same bandwidth as the conventional patch antenna with enhanced gain and good out-of-band suppression. The fourth design involves the synthesis of the second order Chebyshev designed filter with a U-shaped patch (Filtenna B). The designed filtenna operates at 5.8 GHz and has sharp selectivity as no degradation of the peak gain. The superiority of the proposed design over the conventional patch antenna is verified by a 99 % decrease in the out-of-band suppression and a 11.86 % increase in the gain performance. The designed filtennas address the limitations faced by existing filtennas and can be used in Wireless Local Area Network (WLAN) application.