High-Q 4-6-GHz Suspended Stripline RF MEMS Tunable Filter With Bandwidth Control

This paper presents a high-Q two-pole tunable filter with frequency and bandwidth control. The filter is implemented using suspended-stripline ring resonators and planar RF micro-electromechanical systems capacitive networks. A tuning range of 3.7-5.95 GHz with an absolute 1-dB bandwidth of 110 +/- 20 MHz (3.6%-1.7% fractional bandwidth) is first demonstrated with an insertion loss < 2.5 dB. The bandwidth can be controlled at any frequency, and a 1-dB bandwidth of 90-515 MHz is also demonstrated at 5.5 GHz. The measured Q(u) is 115-250 at 3.7-5.95 GHz. The measured third-order intermodulation intercept point and 1-dB power compression point are > 35 dBm (Delta f = 300 kHz) and 20 dBm, respectively. To our knowledge, this filter represents the state-of-the-art in tuning performance and Q for planar designs at 2-6 GHz.