In this paper, a miniaturized dual-band bandpass filter with high selectivity and band-to-band isolation is presented. The filter consists of two quarter-wavelength stepped impedance resonators (SIRs) which share a common grounded via-hole and two symmetrical half-wavelength SIRs which are embedded into the inner space to reduce the size of the filter. Two independent mixed coupling paths which are created by the coupling between these SIRs introduce two different passbands. Five transmission zeros (TZs) are generated near the two passbands to achieve high frequency selectivity and band-to-band isolation. To validate the design theory, a dual-band filter operating at 2.45 and 5.2 GHz was designed and fabricated. The size of the proposed filter only occupies 0.095λg × 0.109λg and the measured 3 dB fractional bandwidth (FBW) of the first and second passbands is 11.5% and 7.4% respectively. The measured results are in good agreement with the simulated results.
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