How do I select between a cavity filter and a ceramic filter for a given frequency and size constraint?

Selecting between a cavity filter and a ceramic filter involves balancing size, insertion loss, selectivity, power handling, and cost for the specific frequency and application. Cavity filters use air-filled resonant cavities (typically machined aluminum or die-cast) as the resonant elements, providing the highest unloaded Q (5,000-20,000), lowest insertion loss (0.2-1 dB for narrow bandwidths), highest power handling (100W to multi-kilowatt CW), and best temperature stability. However, they are large: a 900 MHz cavity duplexer is approximately 200 x 100 x 50 mm. Ceramic filters use high-dielectric-constant ceramic blocks (Er = 30-90) as resonant elements, which shrink the physical size by the square root of the dielectric constant (5-10x reduction versus air-filled), but the unloaded Q is lower (500-3,000), resulting in higher insertion loss (1-3 dB). Ceramic filters are available in compact packages (15x10x5 mm for a 3-pole filter at 2 GHz) and are suitable for surface mount assembly. The selection depends primarily on the acceptable insertion loss and size constraints: if low insertion loss is critical (receiver front ends, duplexers in base stations), cavity filters are preferred. If small size is critical and moderate loss is acceptable (mobile devices, compact modules), ceramic filters are preferred.