Design of a K-Band Chip Filter With Three Tunable Transmission Zeros Using a Standard 0.13- $\mu\hbox {m}$ CMOS Technology

A novel bandpass filter (BPF), which is fabricated with a commercial CMOS process, demonstrating a low insertion loss in the passband and multiple transmission zeros in stopbands, is presented for 24-GHz automotive ultrawideband (UWB) radar systems. The filter combines a second-order asymmetrically compact resonator filter with a source-load coupling mechanism to realize three transmission zeros; two zeros are arranged in the lower stopband, and one zero is located in the upper stopband. To achieve a compact layout size and a low insertion loss, a semilumped approach, which is accomplished with mixed utilization of high-impedance coplanar waveguide lines and lumped capacitors, is used to construct the chip filter. A K-band experimental prototype that has a very compact size of 0.35 × 0.8 mm² was realized. The average insertion loss in the filter´s passband is about 2.7 dB, the return loss is greater than 15 dB within the frequencies of 24-27.5 GHz, and the attenuation levels at the three transmission zeros all greater than 35 dB.