Compact Dual Band Bandpass Filter Using Novel E-Type Resonators With Controllable Bandwidths

A compact microstrip dual band bandpass filter (BPF) using novel E-type resonators is presented in this letter. The E-type resonator is a short-circuited stub loaded hairpin resonator, two passband frequencies of which can be regulated by adjusting the characteristic impedance and electrical length of the hairpin and the stub. By combining pseudo-interdigital coupling structure, the coupling coefficients of two bands can be adjusted to a desired value in a relatively wide range. In addition, hook feed line is introduced to obtain desired external coupling degrees for two bands. Thus, controllable fractional bandwidths (FBWs) can be achieved. Two two-order 2.45/5.25 GHz dual band BPFs with 3 dB FBW 7%/7% and 5%/5%, respectively, are designed. The measured result agrees well with the simulation.