Suzhou Maite Technology Introduction: What kinds of filters can be divided according to their structural forms?

According to the realization mode of resonator, it can be divided into lumped element and distributed parameter filter. The distribution parameters are divided into printed circuit (microstrip, suspended microstrip line), mechanical cavity, dielectric resonator and so on.

1. Lumped (LC) filter: It is suitable for applications below 3GHz. This kind of filter uses the design method of microwave lumped elements to realize the resonant circuit, which makes the filter have a small volume, a structure that is easy to install, and no parasitic passband (or far away). At the same time, it has the advantages of flexible design and short development cycle. However, due to the low Q value of lumped inductance element, the insertion loss of this kind of filter is large and the relative bandwidth cannot be made very narrow (generally > 3%), which limits its application in situations with low insertion loss, high squareness, narrow band and high power.

2. Dielectric filter: Generally, the Q value of dielectric resonator is 2~3 times or 10~20 times that of lumped element (TEM mode, TE01 δ mode, Dielectric Loaded Cavity), so that this kind of filter can realize narrow-band filtering (1% to 1‰). However, the parasitic passband is close (TEM mode is about 2~3f0, TE01 δ mode is about 1.12f0), and this kind of filter is mainly used in situations where both near-end noise suppression of passband and small volume are required.

3. Cavity filter: Resonators are all made up of mechanical structures, which makes them have a fairly high Q value (thousands or even tens of thousands), which is very suitable for applications requiring low insertion loss (< 1dB), narrow band (< 1%) and high power (up to 300W or higher) transmission. This kind of filter has a large volume and parasitic passband, which has high processing cost and long production cycle.

4. Crystal Filter: Shi Ying material has piezoelectric effect, and the crystal resonator made of special corner cutting has a very high quality factor (105 order of magnitude), and the constructed filter has excellent selectivity, and the fractional bandwidth can be 0.1~5‰.

5. Microstrip circuit filter: This kind of filter is widely used at low cost and without excessive volume requirements. Especially above 3GHz, the overall performance is better than that of LC filter. The dispersion effect of suspended microstrip line combined with printed board technology is very small, and it is smaller than metal cavity and has good repeatability, which makes it widely used in broadband filters and multiplexers.