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A novel miniaturized six-pole high temperature superconducting microstrip bandstop filter operating at S band is presented in this letter. A pseudo elliptical behavior in the frequency characteristic is introduced by designing the resonators to resonate at asynchronous frequencies and by varying the inter resonator phase difference. These filters have been installed in a cryogenic radio astronomy receiver with excellent results. Because of their sharp cut-off characteristics, the filters reduce satellite downlink interference signals by more than 40 dB while minimizing lost observing bandwidth.