This article represents the effects of dielectric substrates on the performances of piezoelectric transducer (PET) tunable bandpass filters. The filter consists of two open loop resonators that are coupled by a magnetic coupling. A capacitive cross coupling between input and output port is introduced, which produces two transmission zeros in the lower and upper stopbands. Three dielectric substrates with various dielectric constants are used as perturbers, and their effects on the coupling coefficient and quality factor of the microstrip filter are analyzed. A PET tunable filter with each substrate as a perturber is fabricated and measured.