Zig–Zag-Array Superconducting Resonators for Relatively High-Power Applications

Since power handling of superconducting resonators is severely limited by current density saturation, it is proposed to form resonators having their incident power and resulting currents divided within interior arrays of "basic resonators" (A properly designed array of basic resonators acts as a single resonator.) Though other forms of basic resonators may also be attractive, in this paper, in all examples, the basic resonator used is a "zig-zag resonator" having a fundamental resonance at f
₀
. This type of resonator is attractive because it is relatively compact and tends to keep the energy confined to a region close to the surface of the substrate. This latter is important so that even if a large number of basic resonators are used, energy will not be radiating out to the normal-metal resonator housing, which would greatly lower the unloaded Q. The use of parallel and cascade connections of basic resonators are analyzed and are found to both yield an increase in power handling proportional to the number of basic resonators used. However, these two types of connections have different characteristics with regard to introducing spurious modes, and it is found that it will usually be desirable to use both types of connections within an array. A sizable number of computed explorative examples are presented containing as many as 64 zig-zags. Calculation of the current densities within the zig-zags shows them to be remarkably uniform throughout the arrays. Measured high-temperature superconductor resonator results are presented, which confirm the principles involved. Unloaded Q's measured at 77 K were consistently well above 100 000. This array technique should also be useful for some relatively high-power planar normal-metal filters.