negative values on polar plot (decibels polar plots )

[yadin]

hi every one can you please
can you help me to fix these polar plot in db's
so that the center is at the minimun negative number in voltagedb
about [-50]
and the maximun is at zero
how can i see values on the axies like showing that the axes start at
-40 -30 .....0
than you
import wx
import os
from wx.lib.colourdb import *
from pylab import*
angteta = [ 4.36332313e-003, 3.18522588e-001, 6.32681854e-001,
9.46841119e-001,
1.26100038e+000, 1.57515965e+000, 1.88931892e+000,
2.20347818e+000,
2.51763745e+000, 2.83179671e+000, 3.14595598e+000,
3.46011524e+000,
3.77427451e+000, 4.08843377e+000, 4.40259304e+000,
4.71675230e+000,
5.03091157e+000, 5.34507083e+000, 5.65923010e+000,
5.97338936e+000,]

voltage = [ 0.00363471, 0.26569155, 0.52562334, 0.76330428,
0.93673361, 1. ,
0.93321713, 0.75733232, 0.5185449 , 0.25840091,
0.00363471, 0.26569155,
0.52562334, 0.76330428, 0.93673361, 1. ,
0.93321713, 0.75733232,
0.5185449 , 0.25840091,]

#voltagedb = 20*log10(voltage)
voltagedb = [-48.7906044 ,-11.51244516, -5.58650713, -2.34604603,
-0.56767793, 0. ,
-0.60034598, -2.41427014,
-5.7042726 ,-11.75411924,-48.7906044 ,
-11.51244516, -5.58650713, -2.34604603, -0.56767793,
0. ,
-0.60034598, -2.41427014, -5.7042726 ,-11.75411924,]
polar(angteta,voltagedb)

show()