Tunable millimeter-wave band-stop filter using electromagnetic crystal (EMXT) surfaces

Electromagnetic crystals (EMXT), also known as photonic bandgap crystals when used in optical applications, are periodic electromagnetic structures that may consist of both dielectric and conductors. This paper presents the results of band-stop filters using the high surface impedance EMXT surfaces as the top and bottom walls of a rectangular waveguide. Fixed-tuned waveguide band-stop filters using passive EMXT surfaces with different resonant frequencies were made and demonstrated. Tunable EMXT surfaces based on InP heterostructure barrier varactors (HBV) were fabricated and used to demonstrate a proof-of-concept band-stop filter with its rejection band tuned from 31 to 36.3 GHz with a DC bias voltage from 0 to 10 V.