Cavity and LTCC filters

Hi,

can anybody clarify the main difference between cavity and LTCC filters in mmWave field? They both seem to have a high Q.

Do you mean LTCC as in
https://www.minicircuits.com/products/LTCC-Ceramic-RF-Filters.html ?


Do you have the circuit where you intend to use a high Q filter?

I believe LTCC is a surface mount unit while cavity filters are more like a wave-guide like structure. Integrating cavity filters into a PCB requires different mounting techniques while LTCC can be made as SMT and soldered like a classic component.

1. The term cavity is a broad one: traditionally microwave filtering/resonant cavities are made of metal, containing just air, compressed air, or a gas, sometimes liquid, or a solid that may melt to absorb heat and thus solve heat management.

2. But a dielectric or diamagnetic piece of material is also a cavity that resonates (high Q) at certain frequencies while showing high insertion loss on most of the input frequency band, literature reference Microwave Engineering 4th ed. D.Pozar.

3. LTC or LTCC filters is the marketing denomination of some manufacturers for microstrip built, lump components, that may include operational amplifiers, building blocks tagged as filters.

4. One can build filters with capacitors and inductors (SMD, ..) or/and transmission lines only. Or you can combine LC and microstrip lines with small resonators placed nearby tracks, acting as capacitors, but with higher Q.

Have at the following selection guide

5. Cavity only filters have higher frequency selectivity, but they may also have an overall higher insertion loss, requiring pre-amplifier, and my generate more output signal power, but may also produce more noise and/or harmonics, requiring additional output stages.

6. Now most of UHF spectrum has been auctioned to mobile operators but there are still some UHF channels available for TV broadcast. The CATV head end shown in following link


is built with one UHF amplifier per UHF channel. Each amplifier has a cavity filter at the input and another at the output.


7. The Klystron shown here

has cavities filtering the electron beam, what Mr Dehn mentions as bringing the electrons to same velocity.

Hope it helps

JohnBG
jgb2012@sky.com