100MHz to 1 GHz high switching speed would imply a comparator that converts the sine to a square wave. I understand, that you intended a rectifier or RMS detector however.
It would have switching delay clearly above several 10 ns for a simple design. Accuracy may be improved by filtering the measurement with a higher time constant (us and above).
A simple design would be a schottky half-wave rectifier with a comparator. But amplitude response is not 1% flat without sophisticated design. Having a short PCB stub connecting the detector diode may result in several 10% of response error at 1 GHz. An impedance mateched thermal detector would be used for high accuracy requirements, but I don't expect that it's approproate here.