Design and performance of an electrically small slot loop antenna with a miniaturized superconducting matching circuit

In order to realize a small superconducting receiver, we designed an electrically small slot loop antenna with a miniaturized impedance matching circuit. The area of the slot loop antenna is 4 mm × 4 mm on MgO substrate at a frequency of 2.4 GHz. By applying 2-pole bandpass filter technique, we propose a design theory of the miniaturized impedance matching circuit that consists of coplanar waveguide (CPW) quarter and half wavelength transmission lines of meandering geometry and the impedance inverting circuits (J inverters). By using electromagnetic field simulator, we realized the circuit which matches the small radiation resistance R_a=0.776 Ω of the electrically small slot loop antenna to the feeder impedance Z₀=50 Ω, and attained the normalized bandwidth of 3%. We also made a preliminary experiment on this miniaturized antenna using a YBCO thin film on MgO substrate.