By integrating the interdigital structure into a conventional open-loop resonator, a compact mixed electric and magnetic coupling bandpass filter is designed and fabricated for the first time. Due to the high intensity inner coupling capacitor, which is generated by interdigital lines, not only did the size of the filter sharply decrease, but the electric field was strengthened. Therefore, by properly adjusting the ratio of electric and magnetic coupling, the transmission zeros very close to the passband is obtained readily. Based on mixed electric and magnetic coupling, a fourth-order bandpass filter with multiple transmission zeros is realized without requiring either a cross-coupled path or source-load coupling. For design purposes, the equivalent-circuit model is also derived and verified. Advantages of this filter include its miniaturized size of only 0.06λ0 × 0.045λ0, its sharp cutoff slope, as well as the tiny discrepancies between simulation and measurement.