referring now particularly to fig3 where like reference numerals have been applied to like parts , the center conductor 30 of the coaxial connector 28 is connected to a conductive loop 36 of rectangular configuration and defines a curved surface which is parallel to the axis of the inner conductor 11 . although a curved rectangular loop 36 has been illustrated , it is apparent that the loop 36 can have other configurations such as elliptical , round , oblong , etc ., which can define a curved or planar surface . the loop 36 is spaced away from the inner conductor 11 and is coupled to the inner conductor by electric fields . the loop 36 is analogous to an antenna . the benefit of the loop structure is that it can be located much further away from the inner conductor 11 than a conductive disk , such as shown in fig2 for equivalent coupling to the cavity . this results in a structure that has greater immunity to high - voltage levels and is able to handle greater input power . in addition , adjustment of the amount of coupling is quite simple . one merely bends the wire loop 36 to tune the coupling to the desired value . in production , this is a much more efficient method of tuning a resonant cavity coupler . the foregoing descriptions of specific embodiments of the present invention are presented for the purposes of illustration and description . they are not intended to be exhaustive or to limit the invention to the precise forms disclosed ; obviously many modifications and variations are possible in view of the above teachings . the embodiments were chosen and described in order to best explain the principles of the invention and its practical applications , to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated . it is intended that the scope of the invention be defined by the following claims and their equivalents .