A resistive bridge, NOT the transformer kind, has 6dB of insertion loss which absorbs much of the reflected power, so the VSWR the transmitter "sees" is ~1.5:1 or less, regardless of what the load is past the bridge.
Because of its loss it is switched in until a tuning solution is found, then switched out to operate.??
73, Don N2VGU
Donald S Brant Jr