Application Research On Filter With Out-of-band Suppression

Bandpass filter is the important component of radio frequency receiver/transmitter system and radar system.Its function is to allow the signal within a frequency to pass,and the signal outside the band to be blocked to pass,that is,this structure has the high frequency selectivity.On the one hand,with the advent of the Internet of everything,convenient equipment require devices possess miniaturization and portability.On the other hand,with the advent of the era of 5G and smart cities,more and higher frequency bands are utilized.Therefore,devices with low insertion loss and wide stopband are the focus of future research.Currently,the latest wireless products require more agile performance,more powerful functions,and lower cost so that they can be used more efficiently in microwave circuits.It is more and more urgent for people to design the filter with the characteristic of the out-of-band suppression because of the increasing demand for harmonic suppression and the accuracy of signal transmission.Therefore,this paper has done the following work to solve these problems.In the paper,a compact bandpass filter with wide stopband and two finite transmission zeros is proposed firstly.By means of the source-load coupling structure control,two finite transmission zeros can be introduced in the combline filter response.A pair of ?/4 resonators can generate two transmission poles within the passband.Four transmission zeros on the upper stopband can be created by the source/load coupling and spurlines etched on the transmission lines,which can achieve wide stopband of the filter.But this structure still has the shortcoming of small power capacity and low quality factor.In order to solve the problem in the first innovation point,the second innovation point uses the half-mode substrate integrated waveguide(HMSIW)to realize the three-mode bandpass filter with high quality factor.The two resonant modes can be generated by the isosceles right triangle HMSIW resonator cavity,and an another resonant mode was generated by a pair of quarterwavelength coplanar waveguides(CPWs)loaded in the HMSIW,which form a three-mode bandpass filter together.Although this structure has the advantages of large power capacity and easy integration,it is larger in size and has poor out-of-band suppression.Then,in order to solve the problems above,a third-order band-pass filter with out-of-band suppression is realized based on a quarter wavelength substrate integrated waveguide(QMSIW)filter.The filter not only has good out-of-band suppression characteristics,but also meets the requirements of current filter miniaturization.At the same time,it has the advantages of large power capacity,easy to integrate and stable performance,which is suitable for microwave communication system:...