How do I insert a background image at the centre of Polar plot?

Also, how do I change the straight line into smooth line? please find the attached file,Thanks Code:

• rho = [ -0.65-0.65-0.66-0.66-0.67-0.67-0.68-0.68-0.69-0.69-0.70-0.70-0.70-0.71-0.71-0.71-0.72-0.72-0.72-0.72-0.73-0.73-0.73-0.73-0.73-0.73-0.73-0.73-0.73-0.73-0.73-0.73-0.73-0.73-0.73-0.72-0.72-0.72-0.72-0.71-0.71-0.71-0.70-0.70-0.69-0.69-0.69-0.68-0.68-0.67-0.66-0.66-0.65-0.65-0.64-0.63-0.63-0.62-0.61-0.61-0.60-0.59-0.59-0.58-0.57-0.56-0.56-0.55-0.54-0.53-0.53-0.52-0.51-0.50-0.50-0.49-0.48-0.47-0.47-0.46-0.45-0.44-0.44-0.43-0.42-0.42-0.41-0.40-0.39-0.39-0.38-0.38-0.37-0.36-0.36-0.35-0.35-0.34-0.33-0.33-0.32-0.32-0.31-0.31-0.31-0.30-0.30-0.29-0.29-0.29-0.28-0.28-0.28-0.28-0.27-0.27-0.27-0.27-0.27-0.27-0.27-0.26-0.26-0.26-0.26-0.26-0.26-0.26-0.27-0.27-0.27-0.27-0.27-0.27-0.27-0.28-0.28-0.28-0.28-0.29-0.29-0.29-0.30-0.30-0.30-0.31-0.31-0.32-0.32-0.32-0.33-0.33-0.34-0.34-0.35-0.35-0.36-0.36-0.37-0.37-0.38-0.38-0.39-0.39-0.40-0.41-0.41-0.42-0.42-0.43-0.43-0.44-0.44-0.45-0.46-0.46-0.47-0.47-0.48-0.48-0.49-0.49-0.50-0.51-0.51-0.52-0.52-0.53-0.53-0.53-0.54-0.54-0.55-0.55-0.56-0.56-0.56-0.57-0.57-0.58-0.58-0.58-0.58-0.59-0.59-0.59-0.59-0.60-0.60-0.60-0.60-0.60-0.60-0.60-0.60-0.60-0.60-0.60-0.60-0.60-0.60-0.60-0.60-0.60-0.60-0.59-0.59-0.59-0.59-0.58-0.58-0.58-0.57-0.57-0.56-0.56-0.56-0.55-0.55-0.54-0.54-0.53-0.53-0.52-0.51-0.51-0.50-0.50-0.49-0.49-0.48-0.47-0.47-0.46-0.46-0.45-0.45-0.44-0.43-0.43-0.42-0.42-0.41-0.41-0.40-0.40-0.39-0.39-0.39-0.38-0.38-0.38-0.37-0.37-0.37-0.36-0.36-0.36-0.36-0.35-0.35-0.35-0.35-0.35-0.35-0.35-0.35-0.35-0.35-0.35-0.35-0.35-0.35-0.35-0.35-0.35-0.35-0.35-0.36-0.36-0.36-0.36-0.36-0.37-0.37-0.37-0.38-0.38-0.38-0.38-0.39-0.39-0.40-0.40-0.40-0.41-0.41-0.41-0.42-0.42-0.43-0.43-0.44-0.44-0.45-0.45-0.46-0.46-0.47-0.47-0.48-0.48-0.49-0.49-0.50-0.50-0.51-0.51-0.52-0.53-0.53-0.54-0.54-0.55-0.56-0.56-0.57-0.57-0.58-0.58-0.59-0.60-0.60-0.61-0.61-0.62-0.63-0.63-0.64-0.64 -0.65]
• polarplot(rho,'k', 'lineWidth', 3)
• rlim([-0.8 0])
• pax = gca;
• pax.ThetaColor = 'black';
• pax.RColor = 'k';
• pax.LineWidth = 0.5;
• pax.GridColor = 'black';
• pax.RAxisLocation = 0;
• pax.GridLineStyle = '-';
• pax.GridAlpha = 0.15;
• pax.FontSmoothing = 'on'
• pax.RAxisLocation = 0;
• pax.ThetaZeroLocation = 'top';
• pax.ThetaDir = 'clockwise';
• %pax.ThetaTick = 0:30:360;
• pax.ThetaTickLabels = {'0','30','60','90','120','150','180','150','120','90','60','30'};
• pax.FontSize = 12;
• pax.FontWeight = 'bold';

[Amal George M]

For a better understanding, elaborate on what is meant by "smooth line" and "straight line". Did you mean the radial lines corresponding to different angles?