ELECTROMAGNETIC SIGNAL FILTER, FILTERING METHOD AND DELAY CIRCUIT

摘要

PROBLEM TO BE SOLVED: To provide a small and inexpensive short wave filter which is adversely proportional to the desired frequency by filtering the electromagnetic signals propagated into a metallic casing through at least one frequency selection surface that is enclosed in the metallic casing. SOLUTION: A plurality of metallic repetitive patterns 24 are printed on the frequency selection surfaces 18 and 20 having thickness of 1-5 mil by means of a thin film technique. The surfaces 18 and 20 are buried into a solid dielectric material 22, and the material 22 and both surfaces 18 and 20 are completely surrounded by a metallic casing 12. Every pattern 24 has a shape that is resonated with the prescribed frequency and accordingly serves as a band elimination filter. When an electromagnetic signal 30 under propagation meets one of both surfaces 18 and 20, the energy belonging to one or more frequencies corresponding to the resonance frequency of one or more of patterns 24 are absorbed by the patterns 24 and then reflected by the Snell's refraction law. Thus, it seems that the surfaces 18 and 20 never exist against all frequencies except for the resonance frequency.