INNOVATIVE PASSIVE MICROWAVE COMPONENTS FOR WIRELESS COMMUNICATION CHEUNG KING YIN MASTER OF PHILOSOPHY CITY UNIVERSITY OF HONG KONG SEPTEMBER 2010
CITY UNIVERSITY OF HONG KONG 香港城市大學 Innovative Passive Microwave Components for Wireless Communication 應用於無線通訊之創新被動微波元件 Submitted to Department of Electronic Engineering 電子工程學系 in Partial Fulfillment of the Requirements for the Degree of Master of Philosophy 哲學碩士學位 by Cheung King Yin 張經賢 September 2010 二零一零年九月
i 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
ii 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.
iv Table of Content Abstract... i Acknowledgement... iii Table of Content... iv Chapter 1 Introduction... 1 1.1 Background and Motivation... 1 1.2 Directional coupler... 3 1.2.1 Basic property of Directional coupler... 3 1.2.2 Quadrature Hybrid Coupler... 4 1.3 Impedance Transformation in RF circuit... 6 1.4 Frequency Reconfigurable Antenna... 8 1.5 Scope and Organization of this thesis... 9 Chapter 2 Dual-Band Hybrid Coupler with Extended Bandwidth. 11 2.1 Introduction... 11 2.2 Literature Review on the Multi-band Coupler... 12 2.3Proposed dual-band coupler:... 13 2.4 Circuit Description:... 22 2.5 Simulation and Measurement Result:... 24 2.4 Conclusion:... 28 Chapter 3 Dual-Band Hybrid Coupler with Source to Load Impedance Matching... 29 3.1 Introduction... 29 3.2 Literature Review on the dual-band impedance transformer and Impedance Transforming Coupler... 30 3.3 Proposed dual-band impedance transforming coupler... 32 3.4 Design formula:... 36 3.5 Circuit Description:... 50 3.6 Experimental Results:... 52 3.7 Conclusion:... 55
v Chapter 4 Frequency Reconfigurable Top-loaded Monopole Based on Fractal Geometry... 56 4.1Introduction... 56 4.2 Literature review on Frequency Reconfigurable Antennas... 58 4.2 Antenna Structure... 59 4.3Experimental Result... 66 4.4 Conclusion:... 69 Chapter 5 Conclusion and Recommendation for Future Work... 70 5.1 Conclusion... 70 5.2 Recommendation for Future Work... 71 Bibliography... 72 Appendix... 76 List of Publication... 79
vi List of Figure Figure 1 A distributive band-stop filter and its equivalent circuit... 2 Figure 2 Commonly used symbol for directional coupler... 3 Figure 3 Schematic of a branch line coupler... 4 Figure 4 Schematic of a 4X4 beamforming Network and a balanced Amplifier... 5 Figure 5 A RF system with characteristic impedance Z o connected to a load Z L... 6 Figure 6 A impedance Transforming network inserted between the system and the load... 6 Figure 7 Quarter Wavelength impedance Transformer... 7 Figure 8 Schematic of a three-section dual-band Coupler... 13 Figure 9 Even mode (a) and Odd mode (b) sub-circuit of the Coupler... 14 Figure 10 Optimized impedances versus frequency ratio... 17 Figure 11 The numerical result of the S-parameter in the lower band... 18 Figure 12 The numerical result of the S-parameter in the upper band... 18 Figure 13 The numerical result of the phase response in the lower band... 19 Figure 14 The numerical result of the Phase Response in the upper band... 19 Figure 15 S-parameters of the hybrid coupler operating at 2.2 GHz and 4.8 GHz... 21 Figure 16 Phase Response of the hybrid coupler operating at 2.2 GHz and 4.8 GHz... 21 Figure 17 Layout of the proposed coupler... 22 Figure 18 Fabricated Prototype of the three-section dual-band Coupler... 23 Figure 19 Simulated and measured insertion loss of the three-section dual-band coupler... 24 Figure 20 Simulated and measured return loss and port isolation of the three-section dual-band coupler... 25 Figure 21 Simulated and measured phase difference between port 3 and port 4 of the three-section dual-band coupler... 25 Figure 22 Schematic of proposed dual-band impedance transforming coupler... 32 Figure 23 Sub-circuit for Even mode... 33 Figure 24 Sub-circuit for Odd mode... 33 Figure 25 Asymmetric Branch line coupler... 36 Figure 26 Calculated Magnitude Response of Prototype Ⅰ... 46 Figure 27 Simulated Magnitude Response of Prototype Ⅰby ADS... 46 Figure 28 Calculated Magnitude Response of Prototype Ⅱ... 47 Figure 29 Simulated Magnitude Response of Prototype Ⅱ by ADS... 47 Figure 30 Calculated Phase Response of PrototypeⅠ... 48 Figure 31 Simulated Phase Response of PrototypeⅠby ADS... 48 Figure 32 Calculated Phase Response of Prototype Ⅱ... 49 Figure 33 Simulated Phase Response of Prototype Ⅱ by ADS... 49 Figure 34 Layout for prototype 1... 50 Figure 35 Fabricated prototype of the Dual-Band Impedance Transforming Coupler... 51 Figure 36 Simulated and measured response of Prototype Ⅰ at the Lower band... 53 Figure 37 Simulated and measured Response of Prototype Ⅰat the upper band... 53
vii Figure 38 Simulated and measured phase difference between 2 port of Prototype Ⅰat the lower band... 54 Figure 39 Simulated and measured phase difference between 2 port of PrototypeⅠat the upper band.... 54 Figure 40 Order 1-6 Hilbert Curve... 56 Figure 41 Different feeding regions in a three order Hilbert Curve Geometry for different operation frequencies... 59 Figure 42 The Top view and the bottom view of the fabricated Antenna Prototype... 60 Figure 43 Top-view and Side-View of the Antenna... 61 Figure 44The lump component model of the pin diode in forward biasing (a) and Reverse biasing (b).. 62 Figure 45 The Series (a) and Parallel (b) Configuration of the pin diode switch... 62 Figure 46 Measured S-parameter of BAR50-02V when 5 V basing is applied across the diode... 63 Figure 47 Measured S-parameter of BAR50-02V when 0V basing is applied across the diode... 63 Figure 48 Schematic of the Single pole double Throw switch... 64 Figure 49 Measured S-parameter between Port 1 and port 2 of the SPDT switch when the switch is on... 65 Figure 50 Measured S-parameter between Port 1 and port 2 of the SPDT switch when the switch is off... 65 Figure 51 the measured and simulated impedance for the Antenna... 66 Figure 52 Radiation pattern for state 1 at X-Z plane at frequency=0.85 GHz... 67 Figure 53 Radiation pattern for state 1 at Y-Z plane at frequency=0.85 GHz... 67 Figure 54 Radiation pattern for state 2 at X-Z plane at frequency=1.65 GHz... 68 Figure 55 Radiation pattern for state 2 at Y-Z plane at frequency=1.65 GHz... 68 Figure 56 Two Port Network with different terminal impedance... 78 List of Table Table 1 Frequency Bands for different Wireless Services... 1 Table 2 Measured S-parameter and phase difference... 26 Table 3 Comparison between Dual-Band Couplers... 27 Table 4 the S-parameter of the coupler... 52 Table 5 Effect of putting feeding point in different feeding Regions of the three order Hilbert Curve Geometry... 59 Table 6 ABCD matrix of some commonly used two-port elements... 76