The Study Of Microwave Circuit For Wireless Multi-band Communications

The task of this paper is the research of optimal design of multi-band multi-section transformer considering the characteristic impedance discontinuities、a novel wideband WILKINSON divider using parallel branch lines and2X2switch matrix for WiMAX relay station applications. In this paper, theoretical analysis combining with electromagnetic simulation is used to design these units.A dual-band two-section、tri-band three-section and hex-band six-section impedance transformers are designed, in which the characteristic impedance discontinuities of the corresponding transmission line is involved. Based on the transmission line model and microstrip line theory, design equations of the proposed transformers are derived, and the effect of the microstrip "step" is included. By the method of genetic algorithm, the design parameters of the proposed transformers are obtained for the purely resistive source and load impedances, as well as the frequency-dependent source and load impedances, respectively. Finally, electromagnetic simulations of the microstrip circuit based on the above design parameters are implemented with the commercial software ADS, and the numerical examples prove the validity of the proposed design.A novel wideband branch line Wilkinson divider is proposed. Branch lines are introduced to replace multiple resistors used in the multistage Wilkinson divider to increase the bandwidth of a single-stage Wilkinson divider. To demonstrate its performance, a modified single-stage Wilkinson divider with four branch lines has been fabricated and measured. Results show that the measured input return loss, output return loss, and isolation are better than12.4,12, and11dB, and simultaneously, the isolation better than15dB is achieved from18to37GHz.A2X2Switch Matrix operating at the3.3-3.8GHz frequency band is presented. The design is based on PIN diode·switch elements. The achieved isolation is below80dB, while the insertion loss is less than2dB for the full frequency band. The proposed2X2Switch Matrix is used as the antenna switching element in the RF Front-End of a WiMAX Relay Station, supporting both Time-domain Transmit and Receive and Simultaneous Transmit and Receive operation in Time Division Duplexing mode.