What is a typical upper frequency limit for low SWR operation of 50-ohm BNC connectors?

BNC (Bayonet Neill-Concelman) connectors are highly popular in amateur radio and electronics due to their quick-connect, twist-lock mechanism. They are engineered to maintain a constant 50-ohm impedance, which minimizes Signal Standing Wave Ratio (SWR) across a wide range of frequencies. While connectors like the PL-259 (UHF connector) begin to exhibit impedance bumps and higher SWR above 300 MHz, BNC connectors are precision-machined to perform reliably up to about 4 GHz. Beyond 4 GHz, specialized microwave connectors like SMA or Type N are typically required to maintain low SWR.