COMPACT DUAL-BAND BANDPASS FILTER BASED ON STUB-LOADED RECTANGULAR LOOP STEPPED IMPEDANCE RESONATOR
International Journal of Electromagnetics ( IJEL ), 2 (1):
27-37 (2018)Abstract
This work presents a compact dual-band bandpass filter (BPF) based on stub-loaded rectangular loop stepped impedance resonator (SLRLSIR). The proposed SLRLSIR consists of two outer open-circuited and two inner open-circuited stubs, which are designed to the central sides of the rectangular loop resonator. Owing to its symmetry, even-and odd-mode analysis methods are applied to deduce the equivalent-circuit equations and to justify the structural design. The second passband can be easily tuned by changing the two inner open-circuited stubs when the first passband is fixed at a desirable frequency. The upper stopband is improved by a pair of additional open-circuited stubs stepped impedance resonators at the I/O ports. Transmission zeros are generated between passbands and stopbands. A SLRLSIR prototype dual-band BPF with central frequencies of 2.42/4 GHz is fabricated and systematically studied. The measurement results agreed well with the simulation results.