Three kinds of ESD protection circuits for RF ports were designed in a 0.18 μm SiGe BiCMOS process. The linearity of the RF circuit could be significantly improved through series multistage diodes without affecting the ESD protection capability. Through the series LC resonance network and large inductances in the ESD diode path, the insertion loss of ESD protection circuit in the RF port could be significantly reduced, and the linearity could also be improved. Simulation results showed that the input 1 dB compression point could be improved to 18.9 dBm through the two-stage series diode structure. At 16 GHz, the series LC resonant network design and the series large inductance design could reduce the insertion loss by 0.5 dB and 0.9 dB, respectively.