High-temperature Superconducting Linear Phase Filter For WCDMA Communication System

Filters, which are made of high-temperature superconducting material, have a highquality factor. Then high temperature superconducting filters (HTS filter) are with thefollowing advantages. First, HTS filter has low insertion loss and improved edge steepness,which is irreconcilable to enhance noise immunity of receivers. Second, because of HTSfilter’s near-zero insertion loss, receiver sensitivity can be greatly improved as well as callquality. And the coverage area of the base station is also increased，which is ncessary toreduce the number of base stations. At the same time, the whole HTS filter system is alsowidely used in the following respects, such as satellite communication as well as militaryelectronic warfare.In the meantime, in the fields of radar, astronomy exploration and otheradvanced technology HTS filter system is indispensable.This paper is mainly for thedevelopment of high-temperature superconducting linear phase filter in the WCDMA3Gmobile communication system. HTS filter has been less concerned about linear phase filter.At present, the same frequency band transmission is sued in China Mobile TD-SCDMAstandard transmitter. So there is more research on high-power superconducting filters. AndHTS filter study with China Telecom CDMA2000standard, is also relatively abundant, whileChina Unicom with WCDMA technology research in superconducting filter is not so in-depth.With the rapid development of the third generation mobile communications, WCDMAsystems require wider bandwidth, therefore, the band edge steepness is not only steep, thereare but also strict requirements on the front end of the linear phase filter indicator.With respect to the design of conventional linear phase filter, the more the filter orders are,the steeper edges are. However, the group delay distortion will increase with the increase ofthe sharpness of the filter. Because of the problem of group delay distortion, high frequencysignal can cause a significant phase distortion after passing the filter. The quality of thedemodulated digital mobile communication system decreases as well as the error rate ofcommunication increases. Currently, the external balanced method and the self-equalizationmethod are common used to solve the program of filter group delay distortion. As to theexternal balanced method, it is necessary to introduce an external group delay equalizer.Therefore, the circuit area of the superconducting filter is increased, which is not conducive tominiaturization integration.While there are higher requirements for tuning devices. The self-equalization method can solve this problem exactly. So self-equalization method is applied inthis study of high-temperature superconducting linear phase filter.This work was designed and fabricated based on WCDMA system with twospecifications of high-temperature superconducting linear phase filters.The center frequency is both1950MHz, filter bandwidth is20MHz, and60MHz respectively.The actual testingresults are greatly matched the design requirements.The insertion loss is less than0.2dB. Andthe return loss is also better than18dB.The group delay characteristics are also good.