Novel broadband analog predistortion circuit for radio-over-fiber systems

A novel broadband analog predistortion circuit (PDC) is designed to linearize radio-over-fiber (RoF) systems. Dual Schottky diode is used as predistorter. The PDC with high bandwidth and small dimension is achieved by removing quarter-wavelength transformers and power dividers. Measured S-parameters show that the PDC can work from 10 MHz to up to 40 GHz. The PDC is verified using two-tone and WiFi signals in an RoF system. The spur-free dynamic range with respect to third order intermodulation distortion is improved by more than 10 dB from 1 to 5 GHz and more than 5 dB from 1 to 30 GHz, and it is found that the RoF system is limited by fifth order nonlinearity. Error vector magnitude is improved by 1 dB for WiFi signals at 2.4 and 5 GHz by using the PDC.