Microwave Filters
Microwave filters are distributed, periodic in frequency response and subject to large parasitic effects. Design can be tricky with a good dosage of black magic.
Interdigital Filters
A series of quarter wave parallel coupled lines (often rods or bars) arranged to construct a bandpass filter. The lines are shorted at alternative ends and capacitivly loaded at the other.
Parallel Coupled Line Filters
Commonly used on microstrip or stripline to produce bandpass filters. Cheap, easy to produce, subject to spurious responses.
Capacitive Gap Filters
Suitable for narrowband filters, capacitive gaps are used as resonator-invertor elements.