of the microstrip line through the substrate to the ground plane 12 is indicated at 106 normally the distance d is selected so as to allow the peaks of the magnetic fields of the resonator and microstrip to coincide this will produce a coupling maximum with respect to the transverse position of the resonator and the coupling will be relatively insensitive to variations in the offset distance d therefore the value of the coupling may be easily controlled by controlling the height h of the resonator above the microstrip substrate in the present embodiment this can be easily effected by varying the height of the dielectric spacers 66 the net resonator microstrip coupling is the difference between the positive and negative couplings due to magnetic fields on both sides of the resonator center line as can be seen in fig3 in particular the coinciding resonator microstrip magnetic field lines running in the opposite direction produce positive coupling as is the case on the right in fig3 the coupling magnitude is reduced in amount by the negative coupling produced by the magnetic fields running in the same direction i e on the left in fig3 although the coupling between resonator and microstrip line can be effected by merely extending a linear portion of the.