Phase approximation in linear and logarithmic frequency domain

The goal of this paper is to give a comparison between two methods for phase approximations: non-compact gain technique for linear frequency domain and the approach based on logarithmic sampling of gain for logarithmic frequency domain. The first procedure cannot be employed when the gain characteristic has slopes different from zero at zero and at high frequency. The Bode transfer functions do not satisfy the last requirement. To overpass this inconvenient, we have proposed the modified Bode transfer functions. Computer simulations are also presented.