a durable , broad - band low insertion loss rf feedthrough is formed of a straight conductor centrally supported by , hermetically sealed to and axially extending through the center of a strong , rigid , impervious ceramic disk . the ceramic disk is hermetically sealed , directly or indirectly , to the metal barrier through which the feedthrough is to propagate rf energy . the new ferrule and ferrule - less ceramic metal rf feedthroughs avoid the use of glass , conventional in existing feedthroughs . the novel feedthrough serves as the principal element of a microwave microstrip line to waveguide transition .