Miniaturised microstrip dual-band bandpass filter using novel symmetric double-spiral resonators for WLAN application

A miniaturised dual-band bandpass filter (DB-BPF) centred at 2.45/5.70 GHz using novel symmetric double-spiral resonators is proposed. The measured and simulated results of the proposed DB-BPF are in good agreement with each other except for a slight frequency shift downwards in the measurement. According to the measurements, the measured 3 dB bandwidths are 6.53% (2.35-2.51 GHz) at 2.45 GHz and 4.2% (5.61-5.85 GHz) at 5.70 GHz; the insertion losses including the loss from SMA connectors are <;0.8/1.2 dB and the isolation between these two passbands is better than 20 dB from 2.54 to 5.59 GHz. The circuit area of the fabricated prototype is very compact, being only 7.7 × 9.4 mm.