Mobile communication is composed of mobile terminals (mobile phones, laptops, phones, watches, etc.), wireless base stations, and core networks. The main function of the ACER station is to receive and transmit radio signals, and the signal coverage of the ACER station can reach thousands of meters to tens of kilometers. In order to realize the seamless connection of the signal, from the macro station to the indoor layout of a variety of signal receiving and receiving devices, and these devices not only need to filter the signal, but also the signal for circuit, suppression and other processing, so you need to use various types of filters, duplexers, multiplexers, combiner and so on.   

      Before 4G, each operator is busy with their own network layout, in order to achieve seamless links in every place, with their own signal strength to attract users to the network, so the probability of using high-power cavity filters is relatively large. Due to the large volume and relatively heavy weight of the cavity filter, it is not easy to miniaturize and integrate the equipment, and the iterative upgrade of the communication system, so the amount of the filter represented by the metal cavity is gradually less and less in the public network field.

       The filter in the 4G era, the metal coaxial cavity filter is the absolute mainstream, its working principle is to oscillate through electromagnetic waves of different frequencies in the cavity, retain the electromagnetic waves that reach the resonant frequency of the filter, and the electromagnetic waves of other frequencies dissipate in the oscillation, to achieve the function of filtering. This filter technology is mature, low production cost, should be a good choice for 5G, but in 5G communication, the remote radio frequency unit (RRU) and the antenna will be integrated into the active antenna unit (AAU) together with the tower, the highly integrated and miniaturized development of the base station has higher requirements for the size, weight, power and heating performance of the filter. The metal coaxial cavity filter has the characteristics of large volume, large weight, large heat and so on, and the price is relatively expensive, which will be unfavorable to the installation and commissioning and the tower load while increasing the cost. In order to solve the above problems, the industry began to pay attention to the two solutions of small metal cavity filters and ceramic medium filters.

Small metal cavity filter is a rapid commercial solution to reduce the size and weight of the filter under the premise of maintaining basic stability through process optimization, but this solution is limited by the process bottleneck, currently mainly used in the low frequency band below 2.6GHz, the future will not be large-scale coverage, only as compensation. 

Ceramic dielectric filter is made of ceramic material, no metal cavity, electromagnetic wave resonance occurs in the dielectric material, with high dielectric constant, high Q value, low insertion loss, small volume, light weight, low cost, good temperature drift resistance and other characteristics, can withstand high power, has a good frequency selection effect, easy to large-scale integration. However, the production accuracy of ceramic filter is high, and the current cost has not come down, due to the low price of ceramic powder raw materials, once mass production is achieved, the cost can be greatly reduced, so the future ceramic filter will occupy the main market of 5G filter.