A new photonic band-gap structure has been developed using a periodic array of metallic rods. Structures have been designed and built that operate in the 75–110 GHz frequency range. A periodic structure shows a high-pass transmission characteristic, while the addition of a defect to the structure adds a bandpass response. Measured responses show good agreement with theoretical simulations. A defect mode operated in the reflection mode showed a quality factor Q of 461. This new metallic structure is considerably smaller than comparable dielectric photonic band-gap structures, and should be useful for building compact, inexpensive filters with operating frequencies ranging from 1 GHz to 1 THz.