I prepared a waveguide filter based on LTCC(the volume of the filter is 35mm×35mm×2mm). The input microstrip is on the top surface of the filter. And the output microstrip is on the bottom surface of the filter. How can I measure the filter by a VNA?
I have to say this is a very strange arangement for LTCC filter. Can you please explain how you intend to connect it to the rest of the circuit once you overcome the measuring problem? This can give you the hint how to arange the measurements. If you would have some transitions etc. you can measure your filter with them, they are going to be present in the final circuit anyway!