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In this paper, a fully system-in-package (SiP) integrated V-band Butler matrix beam-switching transmitter (TX) is presented. The CMOS chips from differential process technologies are assembled on a low-temperature co-fired ceramic (LTCC) substrate carrier by flip-chip interconnects. The vertically embedded folded monopole antenna is designed and integrated into the LTCC. The array consisting of four identical monopole antennas and a Butler matrix for beam switching is realized on the LTCC for loss reduction. Four switched main beams are measured and agree well with simulation. This beam-forming TX shows the potential of the low-cost millimeter-wave SiP with CMOS chips.