To improve the response performance of superconducting infrared detectors, we propose using a photonic antenna with a microdetector in conjunction with a nanostructure. In this paper, we report on the evaluated properties of a slot antenna and microstrip lines for the design of a midinfrared detector with a phased-array nanoslot antenna. We also explain the fabrication process for the detector. The antenna and microstrip line were designed for operation at a wave center near 5 mu m. By measuring spectral reflectance characteristics, clear absorption by the antenna and the microstrip resonator was observed. To evaluate the validity of our process, we fabricated a midinfrared detector, which has structures composed of slot antennas and microstrip lines. We confirmed that the superconductivity of the superconducting detector was generally maintained in good condition after the fabrication process of midinfrared detectors.