Microwave systems have enormous impact on modern society. Applications are diverse, from entertainment via satellite television, to civil and military radar systems. New microwave applications are also presenting new design challenges to microwave circuit designers. For example, the recent trend of multi-frequency bands and multi-function operations in wireless communication systems along with the explosion in wireless portable devices are imposing more stringent requirements upon the size and capability of multi-band operation for microwave circuits....[ Read more ]

Microwave systems have enormous impact on modern society. Applications are diverse, from entertainment via satellite television, to civil and military radar systems. New microwave applications are also presenting new design challenges to microwave circuit designers. For example, the recent trend of multi-frequency bands and multi-function operations in wireless communication systems along with the explosion in wireless portable devices are imposing more stringent requirements upon the size and capability of multi-band operation for microwave circuits.

In this dissertation, we intend to address the design issues related to microwave balun -- an important microwave circuit block that converts unbalanced signals to balanced ones. Several novel design approaches for meeting the above-described challenges in microwave baluns are presented based on in-depth theoretical analysis and practical implementation. To achieve multi-band operation, two dual-band quarter-wavelength coupled transmission lines are proposed. One employed tapped stubs forming T-shaped three-section coupled lines, while another employed step impedance resonator (SIR) which also features three-section structures. The first one exhibits compact size, while the second one is good for uni-planar implementation without additional bond wires. Based on these two equivalent coupled-line units, two dual-band baluns are proposed. The analytical design equations are derived and are in excellent agreement with the numerical field solutions.

In additional to the equivalent quarter-wavelength units, a novel approach with additional stubs tapped to the balanced ports of a balun is shown to be capable of providing dual-band performance. The two stubs induce a transmission zero within a wide band and divide it into two separate operating bands. Furthermore, it is shown that the position and physical parameters of the tapped stubs can be used to tune the relations of the two bands, providing robust design flexibilities. The design parameters are derived with close form formulas. Two dual-band baluns with different topologies working for GSM and IEEE 802.11 family are designed, simulated and fabricated. The design concept of these baluns is validated by measurement results.