Compact interdigital microstrip band pass filter

A compact microstrip band pass filter using interdigital coupled line and meandered electromagnetic band gap (EBG) slots is proposed in this article. The interdigital capacitor in the signal strip with meander EBG slots etched in the ground plane contributes 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, which is composed by cascading two units, has a resonant frequency of 2.8 GHz and a fractional 3 dB band width of 28.6% (2.4-3.2 GHz). A return loss of 18 dB and a maximum of 1.6 dB insertion loss in the pass-band are achieved. The filter size is 11.2 × 4.00 mm², which is 0. 172 λ_g × 0.06 λ_g, and the length of resonator is 5.6 mm, which is 0.086 λ_g, where λ_g = 65 mm is the guided wavelength at center frequency.