Low-Loss 4–6-GHz Tunable Filter With 3-Bit High-$Q$ Orthogonal Bias RF-MEMS Capacitance Network

This paper presents a low-loss 4-6-GHz 3-bit tunable filter on a quartz substrate using a high-
Q
3-bit orthogonal bias RF microelectromechanical systems capacitance network. Detailed design equations for the capacitively loaded coupled lambda/2 resonators and with capacitive external coupling and source-load impedance loading are discussed. Measurements show an unloaded
Q
of 85-170, an insertion loss of 1.5-2.8 dB, and a 1-dB bandwidth of 4.35plusmn0.35% at 4-6 GHz. The measured third-order intermodulation intercept point and 1-dB power compression point at 5.91 GHz are > 40 and 27.5 dBm, respectively. The unloaded
Q
can be improved to 125-210 with the use of a thicker bottom electrode. To our knowledge, this is the highest
Q
tunable planar filter to date at this frequency range.