Patent ID: 7605676

Claim:
A directional coupler comprising: coupled lines including a first line and a second line, and at least one ground plane, wherein at least one of the ground planes is a tuning ground plane and a distance, between the first line and the second line and each distance between the first line and the respective tuning ground plane are adapted so as to contribute to a desired coupling level under compensation conditions, wherein an electrical length of the directional coupler is a quarter or less of length of a wave propagated in the directional coupler, and wherein a region between the first and the second lines comprises at least partly a gas, and at least one dielectric layer is arranged between the second line and the at least one tuning ground plane, whereby each distance between the first line and the respective tuning ground plane is dependent on the respective distance between each tuning ground plane and a boundary between the gas and the dielectric layer.