Miniaturized dual-band bandpass filter using λ/2 spiral-resonator and loaded open-stub

In this paper, a compact dual-band bandpass filter using the half-wavelength (λ/2) spiral-resonators and loaded open-stubs is proposed. First, the dual-resonances are employed by the λ/2 spiral-resonators. Secondly, the loaded open-stubs can not only adjust the second resonance for the designed limit, but also suppress the spurious for the upper stopband bandwidth extension. Thirdly, based on the λ/2 spiral-resonators with loaded open-stubs mentioned above, the spiral-coupled scheme is implemented, which employs a strong enough passband enhancement around the dual-resonances to achieve the dualband bandpass filter. Then, a filter is implemented with good frequency responses and a compact size.