Innovative passive microwave components for wireless communication

Abstract

Nowadays, there are many wireless services in the market such as WiFi, WiMAX, GSM and WCDMA whose services when combined into a single wireless unit are advantageous such as those found in access points. These services have different operating bands and follow different standards. Therefore, there is a need to study universal wireless components that is transparent to both multi-band and multi-standard operation. Multi-band with multifunction is usually required in these systems to reduce cost. In addition, a single circuit performing multiple functions and operating at multiple bands occupy smaller circuit area and possesses lower insertion loss. Two types of important microwave components are investigated in this thesis. By using various kinds of technique, those components can operate in multiple bands or provide two functions simultaneously. First, two new Quadrature hybrid coupler designs are introduced. Quadrature couplers which provide equal power division and 90 degree phase difference between their two outputs is one of the key components found in wireless communication systems with a wide range of application. A dual-band branch-line quadrature coupler with extended bandwidth using simple threesection branch line is presented. This design exhibits larger bandwidth than existing dualband designs reported in previous literatures. A dual-band branch line coupler was designed and measured to give 34.5% and 16.4 % bandwidth in the lower band and upper band respectively with amplitude imbalance less than 1dB. The achieved bandwidth is wide enough to cover wireless local area network (WLAN) and Wideband Code Division Multiple Access (WCDMA) applications. A dual-band hybrid coupler with source to load impedance transformation is also presentwith detailed design formulas. In previous literatures, couplers were either dual band or impedance transforming but not both. Antenna used for transmitting and receiving signal over the air is another important component found in wireless communication. In order to address the requirement for modern RF front-ends, Antennas needs to be compact in size and able to operate in multiple frequencies. Frequency Reconfigurable antennas with out-of-band rejection without the use of filters have found favor as a solution for the universal wireless Transceiver due to the omission of the filter and superior antenna performance. In this thesis, a new design of a Toploaded Monopole based on fractal geometry with electronic switching of the operating bands is presented. Components presented in this work can be applied to reduce the total number of elements found in modern wireless units. Consequently, lower insertion loss and smaller circuit size can be achieved.