A folded SIR filter with embedded feed slot for wide spurious suppression

This paper proposes a design of folded stepped impedance resonator (SIR) filter with cross-coupled structure for size reduction and improved spurious suppression in the stopband. The design concept is demonstrated by using four SIR resonators with the fundamental frequency, f₀, of 5.3 GHz. For a comprehensive treatment of the filter with open stubs and embedded slot feeds, the spurious response can be suppressed. The measured results are in good agreement with the simulated predictions, which an insertion loss of 0.3 dB in the passband and a shape factor of 3.5 has been achieved. Moreover, the wide range response of the upper stopband is better than -20 dB extended up to 28 GHz (5.3 f₀).