shown and the balun circuit bu fig3 illustrates how interdigital structures ids of the balun circuit bu can be arranged in an interlocking finger configuration on the underside of the cover de in order to realize a balun functionality for example these interdigital structures ids can correspond to the inductive element ie of the balun circuit bu for example fig4 a illustrates an interconnection of resonators in a ladder type arrangement ld of the filter circuit fi in this example three series resonators sr are connected in series and a respective parallel resonator pr in a parallel path connects the signal path sp to ground m fig4 b illustrates an alternate configuration of the filter circuit fi which is composed of resonators r arranged in a lattice type structure lt in contrast to the filter circuit ld in fig4 a which is embodied in an unbalanced fashion the filter circuit lt in fig4 b is embodied in balanced fashion the lattice type structure lt can comprise coupled resonators gr which have been deposited e g in an scf stack crystal filter arrangement on the substrate su the balun functionality however is realized by means of the balun circuit provided for this purpose therefore the coupled resonators gr do not have.