The invention discloses an electrically tunable four-
passband filter based on a double layered
resonator, and mainly solves the problems that the number of passbands of a traditional electrically tunable filter is small, adjustable
passband bandwidth is not constant, the out-of-
band rejection degree is poor and the volume is large. The electrically tunable four-
passband filter based on the double layered
resonator includes a pair of parallel
coupling feeder lines (1) and a pair of adjustable stepped impedance resonators (2, 3) which are arranged on an upper
microstrip medium substrate (7), and a
branch loading
resonator (4) and two
direct current biasing circuits (5, 6) which are arranged on a lower
microstrip medium substrate (8), wherein the two
direct current biasing circuits (5, 6) are connected to two ends of the adjustable stepped impedance resonators (2) and (3), thereby realizing continuously adjustability of a third passband and a fourth passband, and the
branch loading resonator (4) realizes fixing of a first passband and a second passband. The electrically tunable four-
passband filter based on the double layered resonator is small in size and high in out-of-
band rejection degree, can realize four passbands, realizes continuous adjustability of the third passband and the fourth passband under the condition that the bandwidth is basically maintained unchanged, and can be used for a
wireless communication
system.