Filter construction and oscillator for frequencies of several gigahertz

A radio-frequency filter (400, 500, 600) comprises a base plate (401, 603) and an electrically conductive ground plane in connection with it, a predetermined number of inner conductors (403A-403G, 501, 502, 601) attached substantially perpendicularly to the base plate which have a first end and second end, and an electrically conductive casing (402, 503, 602) which is connected at one side to the base plate and substantially surrounds said inner conductors. A first end of each inner conductor is in contact with said ground plane and a second end is in contact with said electrically conductive casing so that the resonators comprising the inner conductors, ground plane and casing function as half-wave resonators.