Demodulation characteristics of a 20GHz-band direct RF undersampling receiver

In this paper, we describe the configuration of a direct RF undersampling receiver and demonstrate the demodulation characteristics of QPSK signal for Ka-Band VSAT (Very small aperture terminal). Two different clock (CLK) sources are used to compare the difference of CLK jitter effect on the EVM. In the case of the received RF frequency is 19.4GHz and the CLK frequency is 808MHz (24th undersampling) with jitter of 270fs r.m.s., the measured EVM of 2.7% is achieved. By using a conventional pulse pattern generator having jitter of 670fs r.m.s., the EVM of 4.6% is obtained and it shows the degradation of demodulation characteristics by the CLK jitter.