A resonator refers to an electronic component that generates a resonant frequency, commonly divided into quartz crystal resonators and ceramic resonators. The function of generating frequency has the characteristics of stability and good anti-interference performance, and is widely used in various electronic products. The frequency accuracy of quartz crystal resonators is higher than that of ceramic resonators, but the cost is also higher than that of ceramic resonators. Resonators mainly play a role in frequency control, and all electronic products require resonators for frequency transmission and reception. The types of resonators can be divided into two types based on their appearance: direct insertion and surface mount.

Metal waveguides and metal resonators are widely used in the decimeter wave, centimeter wave, and longer millimeter wave bands. Due to the fact that the cross-section of the waveguide and the size of the resonant cavity are similar to the wavelength, for example, when a rectangular waveguide operates in TE01 mode, its wide edge size is greater than half the wavelength. Therefore, in the short millimeter and submillimeter wavelength bands, the size of the metal waveguide and resonant cavity is too small to manufacture. It is even more impossible to apply metal waveguides or resonant cavities in the infrared or visible light bands, where the wavelength is in the micrometer range. Therefore, dielectric waveguides and dielectric resonators have rapidly developed and gained wide applications. Although the size of dielectric waveguides and resonators is also on the order of comparable wavelengths, they are easy to make into small sizes using microfabrication methods. For example, optical fibers and waveguides with cross-sectional dimensions in the micrometer range belong to dielectric waveguides.