Study On Microwave Devices And Circuits Based On Substrate Integrated Waveguide

Substrate integrated waveguide(SIW)is a kind of planar microwave transmission line.In recent years,SIW is not only used to develop microwave or millimeter-wave circuits,but also extends to environmental detection applications,such as humidity,gas and temperature.This dissertation gives a detailed study on the key technology of high performance SIW-based humidity sensors,including a miniaturized complementary split ring resonator(CSRR)loaded half-mode substrate integrated waveguide(HMSIW)humidity sensor with graphene oxide(GO)sensing films,a SIW humidity sensor based on layed black phosphorous(BP)and several flexible substrate SIW-based humidity sensors.Also,a passive microfluidical frequency-agile SIW-based two-way power divider is proposed and studied.The main contents are summarized as follows:Firstly,a miniaturized HMSIW resonator humidity sensor with GO sensing material is proposed.The optimum region of coating GO sensing film in the resonator was determined using electromagnetic simulation tools.Using drop-coating process,the same amount of GO dispersion is deposited on the same area of the different regions of the HMSIW cavity.The properties of humidity sensors,such as relative humidity(RH)sensitivity,humidity hysteresis,temperature and long-term stability were measured and discussed in detail.The humidity experimental results show that the introduce of GO material can significantly enhance the humidity sensitivity of the sensors.In addition,when GO films were deposited on the central conducting patch of the CSRR(i.e.the strongest magnitude of the electronic fields),the sensor shows a high sensitivity of up to 772 k Hz/%RH in the humidity range of 11.3% to 84.3% and 3.415 MHz/%RH in the high humidity range(>84.3% RH),and an ultra-low humidity hysteresis(0.07% RH)in the range of 11.3% to 97.3% RH.The proposed humidity sensors have the advantages of compact structure,low losses,high sensitivity,low humidity hysteresis and excellent long term stability.Thus,this structure provides a feasible method for the design of miniturized microwave humidity sensor with high sensitivity and ultra-low humidity hysteresis.Secondly,a SIW resonator humidity sensor using black phosphorus(BP)as sensing films is proposed.The proposed structure consists of a SIW cavity resonator operating at S-band and a folded sensing slot opened on the top plane.A model diagram is given to explain the physical mechanism of interaction between BP and water molecules at microwave frequencies.The humidity sensing experiments show that the humidity sensitivity of the SIW resonator sensor with BP layer is 197.67 k Hz/%RH,which is about 40 times larger than that of the SIW sensor without sensing material.It is worth noted that the great sensitivity enhancement of the sensor using BP sensitive layers only introduce a small increase in dielectric losses.The proposed device has merits of low cost,wide humidity response range and easy implemention.Thus,it is promising to be integrated with RF front-ends for environment monitoring applications.Thirdly,a flexible SIW-based humidity sensor using polyimide(PI)substrate is proposed.The electromagnetic models of the flexible SIW sensors with different bending radius are presented.Also,the influence of the bending substrate on the electromagnetic properties of the resonant cavity of the sensor was studied.Using nanodiamond as humidity sensing material,the humidity sensing characteristics of the sensors were tested.The humidity experimental results show that the humidity performance of the bending sensors are better than that of the flat sensors.There is a small difference which can be neglected in the humidity characteristics for the sensors with different bending radius.The proposed scheme can be a candidate for detecting some chemical solution in a cylindrical container,such as the concentration,composition and dielectric constant.Fourthly,a novel SIW-based microfluidically frequency-agile SIW-based two-way power-divider is proposed.Also,the equivalent circuits corresponding to the topology diagram are presented.The formulas of the electromagnetic scattering parameters are deduced in detail,such as return losses,insertion losses and isolation between the output ports of the power-divider.Five water-injection microfluidical plastic tubes which is mounted on the surface of the SIW printed circuit board are used to change the operating frequency of the power-divider.By controlling the presence of water in the microfluidical tubes,the power-divider can operate at five central frequencies to achieve a tuning step of about 275 MHz and a frequency-agile range of 1.2 GHz.The proposed passive frequency-agile power divider has advantages of miniaturization,low cost,simple structure and easy integration with other planar circuits.Compared with most traditional power-dividers which are necessary to change the operating frequency using active devices,this structure provides a novel approach for the design of passive frequency-agile power-dividers.