The surface of the dielectric filter is covered with a metal layer with a tangential electric field of zero, and the electromagnetic waves are confined within the medium to form standing wave oscillations with geometric dimensions about half of the wavelength of the waveguide. Materials generally use the relative dielectric constant of 60 to 80 between the ceramic, the actual application of wireless communication in the dielectric ceramic filter size in centimeters.
The main advantage of the dielectric filter is the large power capacity, low insertion loss, but there are two major shortcomings: First, the larger, in the order of centimeters, compared with the integrated circuit occupied a large volume of the system; The filter is generally a discrete device, can not be integrated with the signal processing circuit, and from the filter to the signal processing chip needs to pass a non-negligible transmission line, must be impedance matching, not only complex structure and cause a certain signal attenuation.
The dielectric filter utilizes the low loss, high dielectric constant, frequency temperature coefficient and small thermal expansion coefficient of the dielectric ceramic material, which can be designed with high power and so on. The long-distance multi-level series or parallel trapezoidal lines constitute. It is characterized by small insertion loss, good power resistance and narrow bandwidth. It is especially suitable for CT1, CT2, 900MHz, 1.8GHz, 2.4GHz, 5.8GHz, portable phone, car phone, wireless headset, wireless microphone, radio, cordless phone and Integrated transceiver duplexer and so on to the level coupling filter. Media filter applied to the dielectric resonator is not the existence of nature, must be synthetic production, through a variety of materials, according to a certain proportion of casting pressure to become the current use of the dielectric resonant cavity, the production process complex also led to its price Much larger than the general metal cavity filter. In addition, due to the need to achieve high Q value of the resonant cavity to achieve the demand, and the size of the dielectric filter is also significantly larger than the traditional filter. At present (as of 2012) domestic equipment suppliers are actively developing new media filter products, but by the technical difficulty of the media filter and the development of high cost factors, the application of media filters is not very extensive.
Very wide operating frequency coverage;
Low insertion loss, high out-of-band rejection;
Up to dozens of miniaturized structural design;
Up to 0.8% ~ 30% of the working bandwidth;
Temperature range from civilian to military level;
Various forms of package structure and flexible output interface form.