Compact interdigitated microstrip bandpass filter with meandered EBGs

A compact microstrip bandpass filter using interdigital coupled line and meandered electromagnetic bandgap (EBG) slots is proposed in this paper. It is a microstrip structure with meander EBG slots etched in the ground plane, and interdigital capacitors in the signal strip which contribute to the series capacitance. In addition, the finger of the interdigital is shorted to ground through via holes, which results in the shunt inductance. The combination of series capacitor and shunt inductor is useful to realize the left-handed metamaterial, and improve the frequency selectivity. The filter, consisting of three cells, has a resonant frequency of 5.2 GHz and a fractional 3 dB bandwidth of 5.7%. A return loss of 18 dB and a maximum of 1.02 dB insertion loss in the pass-band are achieved. The resonator size is 5.4 mm×3.8 mm, which is 0.15 λg ×0.11 λg, where λg is the guided wavelength at centre frequency.