Microwave Transmissions through Superconducting Coplanar Waveguide Resonators with Different Coupling Configurations

We design and fabricate two types of superconducting niobium coplanar waveguide microwave resonators with different coupling capacitors on high purity Si substrates. Their microwave transmissions are measured at 20 mK. It is found that these two types of resonators possess significantly different loaded quality factors; one is 5.6×10³ and the other is 4.0×10⁴. The measured data are fitted well by classical ABCD matrix approach and consequently the coupling capacitances are determined. It is found that the transmission peak deviates from the standard Lorentizian with a frequency broadening.