Superconducting planar filters using dual-mode cross-slotted square resonators

Passive microwave filters based on high temperature superconducting (HTS) f ilms are very promising for telecommunication applications. Filters based o n a dual-mode configuration present the appealing combination of high power handling capability and excellent miniaturization. Here a new kind of dual -mode filter based on cross-slotted square resonators is presented. The nov elty of this structure is related to the use of a pair of unequal crossed s lots formed on a square patch resonator, so that the size of the device can be significantly reduced. Single stage dual-mode filters are designed with a commercial 2.5D software at frequencies of interest for satellite commun ications. Prototypes based on a square resonator with 6 mm side operating a t 3.7 GHz are fabricated using Nb double-sided films grown on 10 x 10 x 0.5 mm(3) LaAlO3 substrates. The response is measured at 4.2 K and the nonline arity is investigated observing the power degradation. The effect of additi onal cuts, opportunely realized on the conductor surface, is discussed in r espect to the size reduction and the maximum circulating power. It is found that the resonant frequency can be reduced from 3.7 to 3.3 GHz without aff ecting the power handling capability.