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In this paper, a 24–40 GHz broadband millimeter-wave (mmWave) down-conversion double-balanced mixer with a dual-band local oscillator (LO) buffer employing RF and IF coupled resonators is presented for 5G new radio (NR) frequency range 2 (FR2) cellular applications. The proposed mixer comprises a transformer-coupled $g_{m}$ -boosted common-gate (CG) $G_{m}$ -stage, a single-to-differential current-to-current RF capacitor-tuned coupled resonator, active switching stages with dual-band three-stage LO buffers, a current-to-voltage IF coupled resonator with gain equalization, and a wideband IF buffer with a transformer-based balun. The transformer-coupled $g_{m}$ -boosted CG $G_{m}$ -stage improves the NF and provides broadband input power matching. RF and IF coupled resonators enable an RF operating frequency range of 24–40 GHz and IF 1 dB bandwidth of more than 0.8 GHz, respectively. The implemented mixer was fabricated using a 40 nm CMOS process and characterized primarily in the 5G NR FR2 bands. The active die area was 0.654 mm2, and the mixer drew a bias current of 16 mA from a nominal supply voltage of 1.1 V. The mixer exhibited an RF operating frequency range of 24–40 GHz, noise figure of 12.4 dB, conversion gain of 1.2 dB, IF 1 dB bandwidth of 1.1 GHz, and output-referred third-order intercept point of 6.8 dBm.