The Miniaturization Research Of High Performance WLAN RF Filters Based On LTCC Technology

With the continuous promotion of wireless transmission protocol IEEE802.11ac,the WLAN communication system compatible with 2.4GHz band and 5GHz band is becoming more and more popular.At the same time,communication technology keeps developing with microwave devices used in WLAN communication developing in the direction of miniaturization and high frequency selectivity.Low Temperature Cofired Ceramics(LTCC)technology is more and more widely used with its easy realization of miniaturized and high-performance microwave devices.This paper will make a research on miniaturized high-performance WLAN RF filters based on LTCC technology.The main work can be summarized as follows in two parts.The C band high suppression LTCC filters.Although LTCC technology has its unique advantage in filter miniaturization,but compared with other production process of filter design,its suppression of the near end is relatively poor.Two types of high suppression band-pass filters respectively for the RX end and the TX end of C band WLAN communication system are designed in this paper.The RX end filter adopts lumped parameter method,and increase its near end suppression by adding multilevel LC resonance and increasing multiple transmission zeros to its near end.The processed filter has good suppression at the near end of up side-band;The TX end filter adopts semi-lumped parameter method and increase its near end suppression by introducing cross coupling between non adjacent resonant cavities,and the processed filter has good suppression at the near end of low side-band.The size of the two filters is 2.0mm×1.25mm×0.95mm.The WLAN band low loss LTCC diplexer.To suppress harmonic of X band,lumped parameter structure is adopted for the duplexer,which is made up of S band low pass filter(LPF)and C band band-pass filter.Serial and parallel resonances are used to achieve transmission zeros in the two different filters,which is aimed to add isolation to the two passbands.By electromagnetic simulation and optimization,the measured result agrees well with the simulated one.The LPF's insertion loss is less than 0.45dB,the BPF's loss is less than 0.6dB,and it has good perform in isolation at the desired frequency band.The diplexer's dimension is only 1.6mm×0.8mm×0.6mm.