This article presents K/Ka-band four-element four-beam phased-array transmitter (TX) and receiver (RX) front-ends. Hybrid-packaged technology is employed, consisting of one TX/RX 65-nm CMOS beamformer and four 0.1- $\mu \text{m}$ GaAs power amplifiers (PAs)/low-noise amplifiers (LNAs). Each beam maintains a full connection to every antenna element without degrading array gain. A compact and symmetrical layout floor-plan is proposed to reduce signal routing complexity. Signal distribution and combination are performed through two optimized tree-type and rectangular-shaped beamforming networks to improve the beam-to-beam consistency and isolation. The TX/RX CMOS beamformer provides an energy-efficient solution by adopting low-power phase/amplitude controls. The second harmonic trap is co-optimized with the transformer-based matching to enhance linearity in the TX. A new L-type inductor-enhanced matching network is devised in the RX to broaden bandwidth. In addition, the digital circuit introduces a voting mechanism to improve fault tolerance. Utilizing fan-out wafer-level chip-scale packaging, both hybrid-packaged TX and RX front-ends occupy an area of 50 mm2. The proposed TX demonstrates a measured small-signal gain of 23.5–26.5 dB across 17.7–20.2 GHz. The output 1-dB compression point ( $P_{\text {1dB}}$ ) and the maximal power-added efficiency (PAEMAX) reach 21.2–23.2 dBm and 26%–30%, respectively. The proposed RX achieves a measured average gain of 24 dB across 27.5–30 GHz with a minimal noise figure (NF) of 3.1 dB. Both TX and RX exhibit uniform performance across all channels, while consuming a maximal power of 2600 and 264 mW, respectively, equivalent to 162.5–16.5 mW per element per beam.