The exact expressions for the electric field and capacitance of double sided electrode structure are derived by using the conformal mapping method. A compact analytical model for determining the parameters of the quadratic electrooptic effect in the PLZT transverse modulator is given. The uniformity in intensity modulation of double sided electrode structure caused by the excess birefringence in the region near the edge of the electrodes is improved in comparison of the calculation with the single-sided electrodes.