Filter construction and oscillator for frequencies of several gigahertz

A radio-frequency filter (400, 500, 600) comprisesa 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, andan 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.