Ultracompact CMOS 60-GHz Tapped-Line Combline BPF With Two Transmission Zeros Using Defected Ground Structures

In this paper, we propose a compact on-chip 60-GHz bandpass filter (BPF) in complementary metal–oxide–semiconductor (CMOS) technology. The CMOS BPF employs a tapped-line combline configuration with folding and overlapping to achieve a compact size. The combline BPF is realizable with low insertion loss (IL) due to capacitive loading, which reduces the physical length of the resonators and consequently reduces the resulting attenuation. Finally, defected ground slots are implemented in the ground plane under the coupled arms for additional performance enhancement and to achieve more size compactness. The measured IL and return loss of the fabricated prototype BPF are 3.2 and 31 dB, respectively, at a center frequency of 59 GHz with 14 GHz of bandwidth. The core chip area is 0.0165 mm
²
(
$0.002\times \lambda _{g}^{2}$
), which is the smallest BPF so far in the used technology.