Research On Terahertz Diplexer

Terahertz technology has great application potential and scientific value in the military and other fields.In broadband communications,imaging systems,astronomical observations,the value of researching can not be underestimated.In the past ten years,terahertz technology has gradually arouse people's attention,and the related terahertz devices and systems have made good progress.As a very important passive device,the diplexer plays an indispensable role in the terahertz communication system and naturally has its research value.In the terahertz band,it is generally not used for the design of diplexers,considering that transmission line structures such as microstrip lines and strip lines have large radiation loss and dielectric loss.For the waveguide,it has excellent characteristics compared with the former and is very suitable for the terahertz band.The diplexer structure which used in this thesis is based on waveguides.The specific scheme is to realize diplexing by connecting two bandpass filters with a T-type power tap.The high-performance of diplexers largely depends on the performance of the filter.Therefore,the research in this thesis focuses on the design of various types of filters.The core idea is to add an appropriate zero point to the filter transmission characteristic curve,making the filter the out-of-band suppression performance be improved.The design methods which include:cross-coupling structures,addition of suppressing resonators,the use of over-mode resonators,etc.This thesis starts from the traditional microwave filter theory,the pattern matching method will be adopted to analyze the synthesis process of the direct coupling filter,the initial value of each filter parameters will be sloved,and it will shorten the time of simulation optimization.At the same time,on the basis of understanding the generalized Chebyshev filter synthesis method,it is applied to a specific integrated example,and a complete solution matrix process will be given.The specific processes which include: solution of characteristic polynomials,extraction of coupling matrix,simplification,etc.,And the matlab programming will be uesd to verify,it will greatly simplify the theoretical calculations in the design process.Due to the higher frequency of the diplexer designed in this thesis,the center frequencies of the two diplexers are located at 210 GHz and 240 GHz and 400 GHz and 440 GHz,respectively.It is necessary to consider the processing errors synthetically,and carry on the tolerance analysis to the simulation result.The test results show that the insertion loss of the WR-4.3 band diplexer is less than 1.89 dB,the return loss is greater than 14.6dB,The insertion loss of the WR-2.2 band diplexer low channel filter is less than 3.92 dB,the return loss is more than 15 dB,the insertion loss of the high channel filter is less than 4.05 dB,the return loss is more than 10.5dB,and the isolation between the whole passband output ports is greater than 46 dB.The research results of this thesis have certain reference and engineering value to the design of terahertz cavity diplexer.