A Ka-Band Bi-Directional Reconfigurable Switched Beam-Forming Network Based on 4 <inline-formula> <tex-math notation="LaTeX">${\times}$</tex-math> </inline-formula> 4 Butler Matrix in 28-nm CMOS

This article demonstrates a Ka-Band bi-directional reconfigurable switched beam-forming network based on a 4 <inline-formula> <tex-math notation="LaTeX">${\times}$</tex-math> </inline-formula> 4 Butler matrix in a 28-nm CMOS process. The proposed switched beam-forming network consists of a reconfigurable single-pole, double-throw (SPDT) switch, SPDT switches, bi-directional amplifiers, and a 4 <inline-formula> <tex-math notation="LaTeX">${\times}$</tex-math> </inline-formula> 4 Butler matrix. By integrating the bi-directional amplifiers between the switches and the Butler matrix, ohmic losses of the switches and the Butler matrix are compensated. Also, isolations between beam ports of the Butler matrix are much improved by turning off the bi-directional amplifiers, resulting in a low sidelobe level. The reconfigurable SPDT switch enables dual-port excitations of the beam-forming network. Furthermore, additional 180<inline-formula> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> phase shifters, which are required for the dual-port excitation, are eliminated by inverting a balun of the bi-directional amplifier. Also, additional crossovers, which are required for a reconfigurable SP4T switch network, are eliminated by using two stages of SPDT switches. The total insertion loss of the switched beam-forming network is around 6 and 4.5 dB in transmit/receive (T/Rx) modes at 28 GHz, including the power division loss of the Tx mode. From the array factors based on the measured S-parameters, the designed beam-forming network can generate seven beams, <inline-formula> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula>14.1<inline-formula> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula>, <inline-formula> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula>30<inline-formula> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula>, <inline-formula> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula>48<inline-formula> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula>, and 0<inline-formula> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> with the array antenna gain of 6 dB in the Tx mode.