Miniaturised highly selective bandpass filter with very wide stopband using meander coupled lines

Abstract

A compact wideband bandpass filter with a very wide stopband for terrestrial radio (TETRA) band applications is proposed. The proposed filter employs two types of resonators: one is tri-section half wavelength stepped impedance resonator (SIR) and the other is stub-loaded shorted ring resonator. The proposed filter has adopted SIRs and meandering technique in achieving miniaturised size. Spur-lines and tapped feeding techniques are infused in the filter to suppress harmonics so as to achieve wide stopband. Cross-coupling is introduced in the filter for acquiring good selectivity. This highly selective filter has a miniaturised size of 0.09 × 0.12λg (28 × 36.8 mm2) with a wide stopband up to 8.75f0 (f0 is the centre frequency of filter) with 25 dB harmonics suppression level.