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A tri-band superconducting filter at L-band comprising three high-pole single-band sub-filters with sharp band-edges is presented to meet the high selectivity requirement. Matching junctions with high-impedance branch lines are used to connect the sub-filters and to reduce the channel interactions. MgO and LaAlO3 substrates are utilised in the design and fabrication procedure to reduce the filter size and achieve a high performance. The whole filter has a compact size of 43 × 39.1 mm, and the measured results match well with the simulations.