Design Of Miniaturized Bandpass Filtering Directional Couplers

In recent years,with the rapid development of mobile communication technology,higher requirements in many aspects such as miniaturization and integration have been put forward for wireless communication systems,especially for microwave terminal equipments.In microwave terminal equipments,both directional couplers and bandpass filters are important components,and they are often designed separately and cascaded using transmission lines.However,this method often brings problems such as large volume,narrow bandwidth,and high insertion loss.The above problems can be solved by researching miniaturized filtering directional couplers that can integrate coupling and filtering functions.In view of this,with the support of the Natural Science Foundation of China（61571075）,this thesis studies four band-pass filter directional couplers,and the main results are as follows:（1）A trans-directional coupler with band-pass filtering characteristics is proposed and fabricated,which has the advantages of small size and wide bandwidth.The circuit structure is analyzed by the method of odd-even mode analysis,and the theoretical formulas and design steps are given.The actual measurements show that the relative bandwidth of the coupler with return loss and isolation greater than 10 d B is 41.7 %,and within this bandwidth range,the phase difference of the output ports is 90 ° ± 5 °,and the amplitude imbalance between the output ports is less than 0.8 d B.（2）A miniaturized filtering trans-directional coupler with wide passband,wide stopband response is proposed and fabricated.The circuit structure is analyzed by the method of odd-even mode analysis,and the theoretical formulas and design steps are given.The actual measurements show that the relative bandwidth of the coupler with return loss and isolation greater than 10 d B is 34 %,and within this bandwidth range,the phase difference of the output ports is 90 ° ± 5 °,and the amplitude imbalance between the output ports is less than0.5 d B.In addition,good stopband characteristics are formed on both sides of the passband,and the high frequency band has a stopband width of up to 5 f₀.（3）A filtering quadrature directional coupler based on inductively loaded parallel coupled lines is proposed and fabricated,which has the advantages of wide passband,wide stopband and small volume.The circuit structure is analyzed by the method of odd-even mode analysis,and the theoretical formulas and design steps are given.The actual measurements show that the relative bandwidth of the coupler with return loss and isolation greater than 10 d B is 48 % respectively,and within this bandwidth range,the phase difference of the output ports is 90 ° ± 5 °,and the amplitude imbalance between the output ports is less than 0.8 d B.In addition,good stopband characteristics are formed on both sides of the passband,and the high frequency band has a stopband width of up to 2.64 f₀.（4）A frequency-tunable broadband filtering trans-directional coupler is proposed and fabricated.The circuit structure is analyzed by the method of odd-even mode analysis,and the theoretical formulas and design steps are given.The actual measurements show that the frequency adjustable range of the coupler is from 1.3 GHz to 1.9 GHz,and at the tuning center frequency,the return loss is greater than 20 d B,and the isolation is greater than 14 d B.The relative bandwidth of the coupler with return loss greater than 10 d B is 40.1 % ～ 52.9 %,the relative bandwidth of the output port phase difference satisfying 90 ° ± 10 ° is 29.7 % ～35.7 %,and the amplitude unbalance between the output ports is less than 1 d B.The relative bandwidth is 31.1 % ～ 45.3 %.In addition,good stopband characteristics are formed on both sides of the passband of the tuning frequency,and the high frequency band has a stopband width of 2 f₀ ～ 2.75 f₀.