A differential 4-bit 6.5-10-GHz RF MEMS tunable filter

This paper presents a state-of-the-art RF microelectromechanical systems wide-band miniature tunable filter designed for 6.5-10-GHz frequency range. The differential filter, fabricated on a glass substrate using digital capacitor banks and microstrip lines, results in a tuning range of 44% with very fine resolution, and return loss better than 16 dB for the whole tuning range. The relative bandwidth of the filter is 5.1 ± 0.4% over the tuning range and the size of the filter is 5 mm × 4 mm. The insertion loss is 4.1 and 5.6 dB at 9.8 and 6.5 GHz, respectively, for a 1-kΩ/sq fabricated bias line. The simulations show that, for a bias line with 10-kΩ/sq resistance or more, the insertion loss improves to 3 dB at 9.8 GHz and 4 dB at 6.5 GHz. The measured IIP₃ level is > 45 dBm for Δf > 500 kHz, and the filter can handle 250 mW of RF power for hot and cold switching.