Research And Design Of Non-reflection Filter Based On Thin Film IPD

The rapid development of the national economy and the advent of the 5G era have put forward higher requirements for RF/microwave systems.As one of the most important components of RF front-ends,the performance,size,functionality,and the cost of filters will be used as important criteria to judge their quality.Traditional filters work through transmitting in-band signals without loss or very little loss,and reflecting out-of-band signals back to the signal source.But these signals reflected back to the signal source will damage the system performance.However,the reflectionless filters can absorb the reflected signals through the internal lossy components to improve the linearity of the system.The components made in the thin film IPD process not only have smaller parasitic parameters and higher reliability,but also are very conducive to high-frequency applications.They can meet the requirement of high process accuracy in designing reflectionless filters.In this paper,the design of the reflectionless filter based on the thin-film IPD process was studied in depth.Combining the theory of Morgan's reflectionless filter,the process of designing reflectionless filters based on a symmetric dual two-port network was studied.A reflectionless low-pass filter as well as a high-pass filter that can be applied to the S band was proposed,which can achieve small in-band insertion loss,and whose return loss in the entire frequency band can reach more than 14 d B,indicating that the absorption of the reflected signals can reach more than 95%.On this basis,in order to improve the out-of-band suppression,the cascade of two reflectionless low-pass filters was adopted of which the design,processing and testing are then carried on the thin-film IPD process.The actual measurement shows that the out-of-band suppression of the filter can reach 35.81 d B.The size is only 1220?m ×650?m × 87.71?m.In addition,the suppression gain branch and the parallel form of two lager resistors were introduced to obtain a new circuit which was then cascaded.The introduction of the new structure not only reduces the power and error of a single lossy component,but also avoids the failure caused by overheating which can further affecting the absorption of reflected signals,while improving the out-of-band rejection and return loss of the filter.In order to make the reflectionless filters applicable to microwave high frequency,this paper introduces the conversion method from lumped LC reflectionless filters to microstrip reflectionless ones.The entire filter has good reflectionless performance,but the out-of-band suppression performance is insufficient.In response to this problem,this paper proposed an improved new microstrip reflectionless bandpass filter topology by introducing coupled transmission line structure.The impedance values and electrical lengths corresponding to this topology are given in the paper.ADS simulation shows that the topology can be applied to filter design on different substrates and under different center frequencies.Finally,a microstrip reflectionless bandpass filter with a center frequency of 23 GHz and an out-of-band rejection of up to30 d B was designed.HFSS simulation shows that the improved filter can significantly improve the out-of-band suppression,which verifies the effectiveness of the structure.