Miniaturized cavity filter based on TM010 mode dielectric resonators
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摘要: 现用于4G基站的介质腔体滤波器都采用TE01δ模介质谐振腔，虽然其品质因数Q值很高，但体积较大。为了小型化介质腔体滤波器，创新性地使用了TM010模介质谐振腔，虽然其Q值比较低，但同样能满足高带外抑制的要求。对TM010模介质谐振腔的端口耦合和两腔之间的磁耦合、电耦合进行分析研究，创新性地使用了介质窗的形式产生电耦合，避免了使用飞杆，易于加工，降低制造成本。最后设计了一个8腔TM010模准椭圆函数介质腔体带通滤波器，在通带(TD-LTE频带，2570~2620 MHz)两端分别设计两个传输零点以提高带外抑制。调试结果表明，TM010模介质腔体滤波器不仅能满足低插损、高带外抑制的要求，而且其体积大幅度缩小。Abstract: The dielectric cavity filter used for 4G base station usually adopts TE01δ mode dielectric resonators. Its quality factor Q value is very high, but its size is relatively large. In order to miniaturize the dielectric cavity filter, TM010 mode dielectric resonator is innovatively used. Although its Q value is relatively low, it can also meet the requirements of high band rejections. In this paper, the port coupling, magnetic coupling and electric coupling between two resonators are analyzed. Dielectric openings are innovatively used to create electric couplings, which are easy to machine and reduce manufacturing costs. Besides, an 8-pole quasi-elliptic function filter with two pairs of transmission zeros that can improve the close-to-band rejection slopes is designed and its passband is 2570 MHz to 2620 MHz, TD-LTE band. The debugging results show that the TM010 mode dielectric cavity filter can not only meet the requirements of low insertion loss and high band rejections, but also reduce its size greatly.
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图 1 TM010模圆柱介质谐振腔几何结构
Figure 1. Geometry of TM010 mode cylindrical dielectric resonator
图 3 TM010模与TE01δ模介质谐振腔尺寸比较
Figure 3. Comparison of the size of TM010 mode and TE01δ mode dielectric resonator
图 7 空气窗耦合结构及对应的耦合系数
Figure 7. Coupling structure with an air opening and corresponding coupling coefficient curve
图 8 介质窗耦合结构及对应的耦合系数
Figure 8. Coupling structure with a dielectric opening and corresponding coupling coefficient curve
图 9 介质腔体滤波器的总体结构以及它的回波损耗和插入损耗
Figure 9. The overall structure of the filter and its return loss and insertion loss
图 10 T1和T2面上的电场大小分布
Figure 10. Magnitude of the electric field on the T1 and T2 surfaces
表 1 4G基站介质腔体滤波器的主要技术指标要求
Table 1. Technical specification of the 4G base station dielectric cavity filter
technical specification working frequency/MHz return loss/dB insertion loss/dB out-of-band suppression/dB power capacity/W expected value 2570~2620(±0.5) ≤ -10 ≥ -1 ≤ -40 @ 2500~2565 MHz ≤ -40 @ 2625~2695 MHz ≤ -60B @ 1880~1920 MHz ≥ 100 
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表 2 端口的外部品质因数Qe
Table 2. Loaded quality factor of the port
d/mm Qed Qer 7.00 56.90 57.51 7.10 55.07 55.80 7.16 53.76 54.50 7.20 52.99 53.74 7.30 52.11 51.83
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表 3 谐振腔之间的开窗宽度以及调谐螺钉的长度(单位: mm)
Table 3. The width of the openings between resonators and the length of the tuning screws (unit: mm)
d01 l12 l13 s14 l23 l34 l45 l56 s58 l67 l68 l78 d8L 9.51 17.74 3.63 15.16 17.57 13.73 15.12 14.43 18.66 16.84 2.53 18.1 9.64 screw_l1 screw_l2 screw_l3 screw_l4 screw_l5 screw_l6 screw_l7 screw_l8 7.678 6.347 6.721 7.053 6.938 6.73 6.315 7.559
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表 4 4G基站介质腔体滤波器的仿真指标
Table 4. Simulation results of the 4G base station dielectric cavity filter
technical specification working frequency/MHz return loss/dB insertion loss/dB out-of-band suppression/dB power capacity/W 3D simulation results 2570~2620(±0.5) ≤-10 ≥-1 ≤-50 @ 2500~2565 MHz ≤-48 @ 2625~2695 MHz ≤-60 @ 1880~1920 MHz ≥ 1000
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