A compact package whose inner walls can be located near a radio frequency circuit without changing the characteristics of the radio frequency circuit has a planar circuit on the bottom of the package, which is enclosed with metal walls. A high impedance plate is formed in two dimensions on the metal plate of a lid. The high impedance plate has a dielectric sheet on which is formed a conductor sheet on which is formed a two-dimensional periodic array of right hexagonal metal patches. The high impedance plate blocks surface propagation of electromagnetic waves in a certain frequency band (band gap). The operating frequency of the planar circuit is set within the band gap, so that the lid and the planar circuit can be put close to each other with no change in the operation characteristics of the planar circuit.