The Design Of Miniature Combiner Based On Public Cavity

At present,the domestic mobile communication technology has already entered the 4G era and a variety of communication formats existing in a communication system has become inevitable.In order to effectively reduce the cost of mobile communication network,the major operators adopt a construction model with base station co-location.Therefore,a combiner which can separate the signal from the synthetic signal or combine multiple signals plays a key role in the multi network compatible system,so the qualities of performance indices(isolation,intermodulation,power etc.)for a combiner have a great influence on the communication system.First of all,as the basic unit of a combiner,the filter has an important role in the design of the combiner.At the beginning of this paper,the design principle of the filter is introduced concisely,then the Chebyshev model is selected for its most extensive application.According to the general design method of the cavity combiner,the parametric polynomial of the combiner is further obtained.Conbining resonant frequency,occasional coefficient and quality factor(Q),the specific parameters are calculated out with the help of simulation software.After that,the four key designing points of combiner are analyzed,namely miniaturization design,high isolation,low insertion loss and low intermodulation value.For the miniaturization design,high and low impedance line low-pass filter is adopted instead of band-pass filter;meanwhile,the public cavity is used in the design of the remaining three band-pass filters.For high isolation,the application of cross coupling can increase the suppression outside the band,so it can achieve a well isolation effect.In the aspect of designing low insertion loss,we first select circular cavity with 76 ohm impedance which has the highest Q value,and then hollow out the superfluous of the cavity,which can increase the effective volume of the cavity to increase the Q value and reduce the insertion loss.In the aspect of low intermodulation,coupling disc is used instead of direct coupling,and the material with silver inside and copper outside is selected for the device to reduce surface impedance,so it can reach a good effect on intermodulation.Finally,according to the deign method mentioned above,a four-frequency combiner,which is working on GSM,DSC1800,UMTS2100 and LTE2600 frequency band,is designed.The device is measured and analyzed,and the experimental results show that the isolation of the combiner is basically under the-65 dB,and the passive intermodulation values is also under-155 dBc,which means the device reaches the design specifications.