Abstract: A slot line band reject pass filter including a substrate of insulating material having slot line primary conductors formed thereon. One or more supplemental conductors are preferably coupled to the slot line primary conductors to achieve rejection of a desired frequency. Several embodiments of supplemental conductors are disclosed including substantially closed loop and non loop segments that extend in a range from parallel to perpendicular from the primary conductors. The supplemental conductors may be directly or electromagnetically coupled, or both.