Investigation on the performance of an optically generated RF local oscillator signal in Ku-band DVB-S systems

We investigate a way to externally generate the local oscillator (LO) signal used for downconversion of the K_u-band (10.7-12.75 GHz) RF signal received from a phased array antenna (PAA). The signal is then translated to an intermediate frequency (950-2150 MHz) at the output of the mixer of standard LNBs (Low Noise Block) of a DVB-S (Digital Video Broadcasting-Satellite) reception system. The LO is generated optically by heterodyning of two lasers. We analyze the impact of the laser parameters (optical power and linewidth) on the quality of the generated LO (i.e. phase stability and carrier-to-noise ratio). In addition, a complete system analysis is presented for a 25×64 elements PAA system. We also report the progress on the development of the distributed feedback (DFB) lasers to be used in the heterodyne process. We analyze and experimentally demonstrate that, in order to have an optically-generated LO with equivalent performance to the one of an electronic LO, the laser linewidth should be in the order of tens of Hz, with a maximum relative intensity noise (RIN) of -123 dB/Hz and a minimum optical power of 0.125 mW.