硅基毫米波双通带可调谐零反射滤波器研究

Dual-band filter chips can be applied to the front end of multi-standard communication systems and simplify the system architecture, reduce cost and enhance the spectrum utilizing efficiency. Conventional filters need to employ isolators or attenuators to reduce the detrimental effects including the increased intermodulation products introduced by stopband reflection. The reflectionless filter absorbs the reflection signal by the inherent component which improves the linearity related specification of the system and integration level significantly. However, the silicon-based millimeter wave dual-band reflectionless bandpass filter encountered problems including limited absorption bandwidth, the strong interaction between two passbands obtained by notch structures and large losses of the silicon-based filter. This project proposes a new reflectionless filter structure by reusing multi-mode resonator, which results in a filtering response with bandpass response and bandstop response match continuously. Meanwhile, parallel resonators or series resonant loops are adopted in the multi-mode resonator and the absorptive network, so that the zeros and poles of the two bands are not related to each other. Moreover, on-chip self-coupling structure and silicon-via free architecture are deployed to reduce the loss of the silicon-based passive structures. With the above research, we expect to improve the absorbing bandwidth, enhance absorbing efficiency during the frequency tuning and reduce the filter’s insertion loss, and implement a high-performance silicon-based millimeter wave dual-band tunable reflectionless bandpass filter. The design method will be summarized thereafter.

双通带滤波器芯片可简化多标准通信系统收发前端架构、降低成本、提高频谱利用率，但传统滤波器在使用时需要结合隔离器、衰减器以减少阻带反射信号引入的交调干扰等非理想效应，而硅基零反射滤波器自身可以吸收反射信号，在提高收发链路中与线性度相关的指标的同时，大幅提高收发前端的集成度。硅基毫米波零反射滤波器主要面临反射吸收带宽有限、陷波得到的两通带调控相互影响、硅基滤波器损耗较大的问题。本项目提出了一种复用多模谐振器的零反射滤波器结构，使得带通、带阻频带连续匹配对应；并在多模谐振器和有耗吸收网络中分别通过并联和串联谐振环路，消除两通带调谐过程中零极点的关联性；采用片上自耦合结构和无硅通孔架构，减小硅基无源结构的损耗；以期提高硅基可调谐零反射滤波器的吸收带宽、提高反射吸收率、降低插入损耗，最终实现高性能硅基毫米波双通带可调谐零反射滤波器芯片，并总结出设计方法。

滤波电路作为射频系统前端信号选取与滤除的关键部件，始终是国内外微波技术领域的研究热点之一。随着无线通信技术的迅猛发展，对滤波电路的性能指标提出了更高的要求。现有典型的滤波器的阻带存在多重反射信号，会不断注入到邻近有源电路中引发不稳定、杂散增加、线性度降低等问题。因此，研究实现具备阻带反射信号吸收能力的硅基双通带可调谐零反射滤波电路具有重要意义。. 本项目的主要研究内容如下：（1）研究实现了一种基于单个多模谐振器和吸收网络的新型双通道可调零反射滤波器。在吸收网络中，通过两个串联谐振环来引入零点，从而实现所有调谐状态下的持续反射吸收，同时带外信号的吸收网络相当于一个电阻，被复用于提供额外的传输路径，以实现谐波吸收。此电路具有两个独立的调谐范围，分别是1.45 - 1.95 GHz和2.45 - 3 GHz，6 GHz以下的最小吸收水平为-6 dB和-7.3 dB，在7.4倍频以内最小谐波吸收为-5.8 dB的S11和-13.9dB的S21。（2）研究实现将零反射的网络架构应用于V波段辐射计中的低噪声放大器部分，从而在所有频率下实现约50 Ω的输出阻抗，完全消除了输出端口的反射波，实现级间全频段内反射信号的吸收，并结合吉尔伯特混频器实现高性能的单片辐射计集成芯片。. 本项目研究实现的双通带可调零反射滤波器，具有7.4倍频以内的谐波抑制和吸收，达到同类设计中最宽的吸收范围，同时实现了双通带、宽调谐范围和所有调谐状态下的反射吸收能力。该研究成果可应用于现代多频段通信系统。