A Three-Pole 1.2–2.6-GHz RF MEMS Tunable Notch Filter With 40-dB Rejection and Bandwidth Control

This paper presents a high-performance three-pole tunable notch filter with frequency and bandwidth control. The filter is implemented using suspended-stripline resonators and planar 3-bit RF MEMS capacitive networks. A tuning range of 1.1-2.7 GHz with a 40-dB rejection bandwidth of 115±25 MHz is demonstrated with a passband insertion loss <; 0.8 dB. A 40-dB rejection bandwidth of 26-126 and 24-200 MHz is demonstrated at 1.6 and 2.0 GHz, respectively. The filter introduces no noticeable distortion of wideband code-division multiple-access (WCDMA) waveforms with a power of 25 dBm at frequencies corresponding to the 30-40 dB nulls and at the - 3-dB and - 6-dB passband frequencies. At the - 0.5-dB passband frequency, the filter can handle up to 30 dBm of WCDMA power with no measurable distortion. To our knowledge, this filter represents state-of-the-art tuning performance and power handling for planar notch filter designs. The application areas are in wideband cognitive radios with high interference levels.