The beam width-between-first-null of a uniform linear array of N equally-spaced (element spacing = d) equally-excited antennas is determined by

In a board side array of 20 isotropic radiators, equally spaced at a distance of $$\lambda /2$$, the veam width between first nulls is

Two isotropic antennas are separated by a distance of two wavelengths. If both the antennas are fed with currents of equal phase and magnitude, the number of lobes in the radiation pattern in the horizontal plane are

In the case of ground wave propagation, at far-off distances from the transmitting tower antenna, the Poynting vector is