Impact of phase modulator on the performance of Costas loop

Abstract

 In the present work, a modified Costas loop is presented with the help of mathematical modeling and numerical simulation. The voltage-controlled oscillator output phase along with frequency is controlled using the input control voltage. The modified loop is tested as frequency demodulator circuit where the improvement in sideband attenuation is clearly visible using an additional phase control arrangement. Numerical simulation result leads to a similar conclusion when the ratio of third harmonic to first harmonic and the ratio of first sideband attenuation to carrier are obtained for different proportions of the phase control. Noise bandwidth and lock range of the modified loop are investigated with special emphasis on the dependence of these parameters on the phase modulator gain. Lock range of the loop is evaluated analytically. An excellent demodulation capability of the loop has been reported in the presence of the additional phase control. Analytical results coupled with numerical findings presented are in good agreement.