基于双方环结构的超宽带平衡滤波器设计

Design of Ultra-Wideband Balanced Bandpass Filter Based on Dual-Square Ring Configuration

平衡滤波器因具有卓越的抗噪声及抗电磁干扰能力而在繁杂频谱环境下的低噪通信系统中显得至关重要。该文提出了一款具有共模抑制特性的平衡滤波器,通过差共模理论结合导纳矩阵及传输矩阵完成了分析设计。该滤波器中心频率为1.4 GHz,相对带宽可达74.3%,覆盖2G、GPRS、3G及4G LTE频段。同时该滤波器的边带具有两对传输零点,故其具有理想的边带滚降速度及边带抑制水平。滤波器全差模通频带内共模信号抑制水平均优于10 dB,差模阻带抑制优于20 dB,电路尺寸仅为0.17λ_(g)×0.17λ_(g)。

Owing to the excellent noise immunity and electromagnetic interference immunity characteristics,balanced filters has become vital key building block in low-noise communication systems in complex spectrum circumstance.In this paper,a balanced bandpass filter with common mode suppression is proposed and designed by using differential/common mode theory,admittance matrix and transmission matrix analysis.The centered frequency of presented balanced filter is located at 1.4 GHz and its fractional bandwidth can reach 74.3%,which cover 2G,GPRS,3G,and 4G LTE bands.Since two pairs of transmission zeros is introduced separately lower and upper sideband,the developed balanced bandpass filter is of high roll-off rate and sharp shirt.In presented balanced bandpass filter,10 dB of common mode suppression within differential mode passbands is achieved.The differential mode out of band suppression level is higher than 20 dB,and the circuit size of exploited balanced filter is only occupies 0.17λ_(g)×0.17λ_(g).