The expressions for calculation of return stroke electromagnetic field components are given. The basic element for field calculations is the line channel arbitrarily placed in a free space. For perfectly conductive ground it is possible to calculate and examine fields from more geometrically complicated lightning structures (inclined, tortuous, branching) using this more simple model. Some examples of space waveform variations for several simple lightning models with one-segment vertical, inclined, horizontal and three-segments inclined adjacent channels are discussed. The special attention is called to the fact that the variable limits of integrating in the expressions given differ from ones applied in the usual field calculation practice. All examples discussed are given for the fixed distance 50km in order to exclude the waveform variations caused by distance changing.