Microstrip patch antenna power balance by a mixed time frequency method

A novel method is presented to determine the power balance of an arbitrary-shape microstrip antenna. The finite-difference time-domain (FDTD) method is used to solve Maxwell´s equations. The solutions of the electromagnetic fields are then Fourier-transformed. The near-field Poynting vector flux is calculated through a closed area surrounding the antenna. The radiated power in the free space and the surface wave power losses are also calculated. The summation of these two terms is then compared to the power delivered by the generator to the antenna. The antenna is assumed to be lossless. A comparison is made between the results obtained in this way and by Alexopoulos´ (1981) method, associated with the FDTD method for the determination of surface currents. The radiation pattern is obtained by means of the equivalence principle near the antenna. The radiation pattern obtained according to the equivalence principle is very similar to the one derived from Alexopoulos´ method.<>