Energy Reception for Mobile Radio

A radio signal may reach a receiver via several paths because of reflections from nearby objects. If the receiver is a mobile radio installation, the received field strength may fluctuate wildly because the reflected waves add with changing relative phases as the receiver moves. J. R. Pierce* has suggested a way to combat these fluctuations by using three antennas. As background for Pierce's idea consider the standing wave pattern produced when a plane wave is reflected at normal incidence from a large wall. An electric dipole antenna moving toward the wall finds nulls in the electric field repeated at half-wavelength intervals. However, these nulls occur at maxima of the magnetic field. In fact, the total electromagnetic energy density ^(e|2?| 2 + / x | # | 2 ) i s constant throughout the pattern. In Pierce's scheme, the transmitter radiates a vertically polarized wave. The receiver carriers a vertical electric dipole antenna and also a pair of loop antennas with axes perpendicular to each other and to the dipole. These three antennas receive the three nonzero field components Ez, 11 x , and Hu . The three antenna signals enter separate square-law detectors and the three detector outputs are added to * Private communication. 1779