questions on applliacion of LTCC Lowpass filter from Mini-circuits

Now I am dealing with a tranceiver. I am planning to use the LFCN-95+ and LFCN-400+ in series to get a better bandstop. However, I don't know where the signals fall in the stop band finally end. Do they just store in the input microstrip, or just radiate by the microstrip? If the case is the latter, do I need to provide some screen box for each filter? It might be agony for me, because the filters are so small.

In general, you can not connect two lowpass filters in series and have them perform well. The problem is that they are reflective, and the line length between them can resonate at some frequency and cause a passband.

You can put the two lowpass filters in series if there is some loss in between them, like a 3 dB pad, or some other isolation like a single gain stage. If you are just hooking them up in series, you should carefully analyze them before doing the layout.

Rich

It's radiated by microstrip line, so you need made some cavity design.

Very true. RF currents can easily leak around the chip filters, and still show up at your destination.

You can either channelize the board (put it into a metal housing with narrow channels); use metal shield cans; or put one lpf at one end, and the other lpf at the destination end of the board. In the later case, you need some isolaton or resitive loss between the two lpf's to keep the line from resonating.