Research And Design Of The High-performance Compact Diplexer

In recent years, with the rapid development of wireless communication system, spectrumresources become increasingly scarce. Therefore, the communication system requires increasinglybetter performance of microwave filter and diplexer, which function as frequency selective devices. Itis a hot topic to design waveguide filters and diplexers which exhibit high performance, low cost andminiaturization. Firstly, we study the waveguide diplexer which has excellent performance. But thiskind of diplexer is large and costly. Secondly, the investigated SIW diplexer exhibits excellentperformence, successing the merits of conventional waveguide diplexer, and owns compact size andlow cost. To further minimize the dimension based on the previous SIW diplexer, a CSRR-basedstructure is introduced, and several types of SIW diplexers have been researched and fabricated.The main contribution and innovation of this dissertation are as follows.1. We study and design a Ku-band waveguide diplexer working within12.25GHz~12.75GHz and14GHz~14.5GHz. Equivalent circuit method and EM simulation are used to design diplexer rapidlyand effectively. The proposed waveguide diplexer is fabricated and measured, and we getmeasurement results as follows: in the receiving channel, IL is1.65dB, iso>72dB, RL<-20dB. In thetransmitting channel, IL is1.52dB, iso>80dB, RL<-17dB. A good agreement is achieved betweenmeasurement and simulation which verify the validity of our design and the accuracy of oursimulation.2. We propose a diplexer with band-notched characteristics, and it has a great isolation with awide operating band. The transmitting channel uses a SIW loaded with one single-ring CSRR tocreate a narrow passband below the cutoff frequency of SIW, achieving miniaturization of the filter.The receiving channel uses IO microstrip on the top layer and a CPW resonator on the bottom layer torealize broadside coupling, and introduces an upper-layer resonant structure to realize band-notchedcharacteristics. Afterwards, the microstrip T-junction is employed to complete the synthesis of thediplexer. In the receiving passband,-3dB passband is from2.56GHz to11.51GHz, notched locates at9.7GHz, max suppression is-22dB. In the transmitting passband, IL is1.52dB@13GHz, bandwidth isabout400MHz, isolation between two channels is more than20dB. A perfect agreement is achievedbetween the simulation and measurement.3. We study and design a novel lowpass-bandpass diplexer. The trasmitting channel uses a SIWloaded with a pair of double-ring CSRR to design a miniaturized bandpass filter. The receivingchannel is a lowpass filter using cross-section microstrip associated with DGS. The passband of transmitting channel locates between lowpass band and the spurious passband of receiving channel, soas to effectively utilize the selective characteristic of parasitic passband under some specific situations.In the receiving channel, the cutoff frequency of the lowpass band is1.1GHz, the center frequency ofthe spurious passband is2.97GHz; in the transmitting channel, the center frequency is2.4GHz,isolation is more than39dB. A perfect agreement is achieved between the simulation andmeasurement.4. We study and design a C-band SIW diplexer with circular CSRRs. We introduce a novelstructure to improve isolation by suppressing initial mode. We co-design the common port andchannels, which reduces the process of diplexer design. The measured insertion losses are1.75and1.62dB in the lower and upper passbands centered at3.92and4.62GHz. The isolation is higher than37dB. A perfect agreement is achieved between the simulation and measurement.5. By optimizing the structure and order of CSRR and introducing double-side loadingsimultaneously, we study how to reduce the size of SIW-CSRR carefully, and make the proposedSIW-CSRR diplexer smaller. The measured insertion losses are1.45and1.62dB in the lower andupper passbands centered at3.6and3.86GHz. The isolation is higher than30dB. A perfectagreement is achieved between the simulation and measurement.