High--temperature superconducting (HTS) films have low surfaceresistance in the microwave region. This indicates that HTS passivemicrowave devices, for example, filters and antennas, are promisingfor commercial use. For superconducting filters, low insertion loss,sharp skirt property and high attenuation value out of band areimportant, and for superconducting antennas, electrically smallantennas and super-directive high--gain antennas are useful. It isknown that the elliptic filter has a sharp skirt property comparedwith that of a Chebyshev filter. We examined a cross- coupled filterwhich is one type of elliptic filter. The insertion loss of thefilter was approximately 0.3 dB. The skirt property of the four-resonator cross--coupled filter was almost equal to that of an eight-resonator hairpin filter. We also examined a cryocooler coolingsystem for superconducting antenna and measured the relative gaindirectivity and power capability of an HTS antenna. The gain of theHTS patch antenna was approximately 10 dB larger than that of anormal conducting antenna. The large gain of the HTS antenna wascaused by the low surface impedance and enhancement effect of thedielectric window of the cooling system.
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