In a uniform linear array, four isotropic radiating elements are spaced $$\lambda /4$$ apart. The progressive phase shift between the elements required for forming the main beam at 60° off the end-fire is

The half-power beam widths (HPBW) of an antenna in the two orthogonal planes are $${100^ \circ }$$ and $${60^ \circ }$$ respectively. The directivity of the antenna is approximately equal to

For an 8 feet (2.4 m) parabolic disk antenna operating at 4 GHz, the minimum distance required for far field measurement is closest to

A transmitting antenna radiates 251 W isotropically. A receiving antenna, located 100m away from the transmitting antenna, has an effective aperture of 500 cm². The total power received by the antenna is