A 28-GHz Reconfigurable SP4T Switch Network for a Switched Beam System in 65-nm CMOS

Abstract

A 28-GHz SP4T absorptive switch (SAS) and reconfigurable switch network (RSN) in the 65-nm CMOS process are presented for a switched beam antenna array. The proposed SAS has the smallest electrical size among the previous millimeter-wave SASs. The length of the $t$ -line used in the proposed SAS is only 1/3 of that of the conventional quarter-wave $t$ -line-based absorptive switch. The proposed RSN is the first CMOS millimeter-wave switch-based RSN for a $4\times 4$ Butler matrix-based switched beam transceiver. The RSN is designed based on the SAS in order to operate in both the switch and divider modes. In the switch mode for single-port excitation, the RSN acts as an SAS. In the divider mode for dual-port excitation, the RSN operates as a Wilkinson power divider. Furthermore, the proposed RSN is realized in 2/3 the size of the conventional SAS. The measured insertion loss and isolation of the SAS are 3.8 and 22 dB, respectively. All return losses of the SAS input, output, and absorptive ports are better than 10 dB from 26 to 31 GHz. The silicon area and electrical size of the SAS is 0.9 mm2 ( $0.0078\lambda _{0}^{2}$ ), including pads. The measured insertion losses of the RSN in the switch and divider modes are 4.1 and 4.3 dB, respectively. The isolation of the switch and divider modes is 24 and 25 dB, respectively. All return losses of the RSN are better than 10 dB from 21 to 31.2 GHz. The silicon area of the RSN is 0.78 mm2 ( $0.0068\lambda _{0}^{2}$ ).