Design Of Filtering Power Dividers And Filtering Baluns

With the continuous development of wireless communication technology,nowadays a set of microwave wireless communication systems often need to be compatible with a variety of communication modes,which makes the RF front-end more complex,bulkier and electromagnetic compatibility problems more serious.In this context,compact,multifunctional and highly integrated passive components have been proposed and attracted more and more attention.In addition,frequency division multiplexing(FDM),noise reduction,mirror frequency suppression and interference suppression in communication systems all require filters,so filtering is an important function in passive feed network.In this thesis,the integrated design method of integrating filtering function into other passive devices is studied.The specific research work and main contributions of this thesis can be summarized as follows: 1.Dual-band unequal filtering power dividers are studied.Based on E-shaped dual-mode resonators and parallel coupling microstrip lines,a design method for dual-band unequal filtering power dividers is proposed.The conventional quarter-wavelength impedance transformers in Wilkinson power divider are substituted with a pair of E-shaped dual-mode resonators,which makes the device have filtering function in two bands.The unequal power distribution is realized by controlling the coupling strength between input/output feeder and resonators.To verify the effectiveness of this method,a dual-band unequal filtering power divider is designed.The filtering power divider consists of input and output feeder,E-shaped dual-mode resonators and isolation resistor.The final structure parameters are determined by simulation and optimization,and the dual-band unequal filtering power divider is fabricated and measured.By comparing the measured S parameters with the simulated S parameters,it is clear that the simulated results and the measurements have favorable agreement,and the performance of the dual-band unequal filtering power divider achieve the desired results.The filtering power divider has filtering function in two bands.The central frequency of the low band is 3.57 GHz,and the central frequency of the high band is 4.96 GHz.At 3.57 GHz,the insertion loss of Port 1 to Port 2 are 5.94 dB,and the insertion loss of Port 1 to Port 3 are 3.3 dB.At 4.96 GHz,the insertion loss of Port 1 to Port 2 are 5.60 dB,and the insertion loss of Port 1 to Port 3 are 3.20 dB.The filtering power divider obtains unequal power division in two bands,and the power splitting ratio of Port 2 and Port 3 are 1:2.2.Dual-band filtering baluns are studied.Based on multi-mode resonators,a designed method for dual-band filtering baluns is presented.In this method,by integrating the E-shaped dual-mode resonator and center stub-loaded ring resonator,the filtering baluns obtain filtering function in two bands.Utilizing the phase characteristic of the signal on both sides of the dual-mode resonator,the balun function is realized in two bands.In order to verify the practicability of this method,two dual-band filtering balun are designed.Their center working frequency ratios are 1.34 and 1.26 respectively.After simulation and optimization,the final geometrical dimensions of the two filtering balun are determined,and the filtering balun with a center frequency ratio of 1.34 is fabricated and measured.It is clear that the simulated results and the measurements have favorable agreement.The measured results show that the performance of the dual-band filtering balun is excellent.The filtering balun have filtering function in two bands.The center frequency of the low band is 3.47 GHz,and the center frequency of the high band is 4.70 GHz.The filtering balun accomplishes the conversion from unbalanced signal to balanced signal in two bands.In low band,the magnitude imbalance between two balanced ports is less than 0.60 dB,and the phase difference is within 180 ± 8°.In high band,the magnitude imbalance between two balanced ports is less than 0.78 dB,and the phase difference is within 180 ± 6°.