Compact Ka band filter in 0.13 µm CMOS using broadside coupled coplanar stripline

A K_a band bandpass filter in 0.13 μm CMOS is presented. Good out-of-band rejection and a good shape factor are facilitated by the use of broadside coupled coplanar stripline (BCCPS). The filter consists of a BCCPS section, coplanar striplines (CPS), and MIM capacitors. We derive the characteristic impedance and effective dielectric constant of the BCCPS in CMOS and apply it to the design of the bandpass filter. The realized filter has a measured 3 dB bandwidth from 25.5 GHz to 31.6 GHz (21%). The measured insertion loss is 6.9 dB and the size is 0.6 × 0.3 mm² excluding pads. The filter rejection below 18 GHz and above 41 GHz is better than 35 dB.