azimuthal gain plot in dB
dbz(ph, g, Rm)
dbz(ph, g) Rm=40 dB
azimuthal angles over [0,pi]
gain at ph (g is in absolute units)
minimum dB level (Rm = 40 dB by default)
dbz(ph, g, Rm) makes azimuthal plot of gdb=10*log10(g) versus phi, gain plot at -phi over [-pi,0] is added symmetrically, max-g is assumed to be unity (e.g., as in the output of gain1d), grid circles at Rm/4, 2Rm/4, 3Rm/4 are added and labeled,
add sample pgm