Application of cryogenic tuning technique in an HTS filter

This paper describes a method for tuning an HTS filter at the cryogenic temperature. Sonnet software was used for simulating the distribution of current density. Dielectric tuning screws were used to regulate the redistribution of electromagnetic field, so that the response characteristics of the filter can be improved. For matching the designed result, this technique allows correcting the deviation caused by fabrication processing and non uniformity of substrate thickness and dielectric constant. 9-pole forward-coupling microstrip filter as a sample shows its response characteristics before and after tuning. The tuning result showed better performance than simulation. The insertion loss and return loss were improved and the center frequency shift towards the low end after tuning