Page 158 - Satellite Communications, Fourth Edition
P. 158
138 Chapter Six
Figure 6.1 (a) Transmitting antenna. (b) Receiving antenna.
The antenna as a receiver is shown in Fig. 6.1b. Power P rec is trans-
ferred to the antenna from a passing radio wave. Again, losses in the
antenna will reduce the power available for the feeder. Receiver feeder
losses will further reduce the power so that the amount P reaching the
R
receiver is less than that received by the antenna.
6.2 Reciprocity Theorem for Antennas
The reciprocity theorem for antennas states that if a current I is induced
in an antenna B, operated in the receive mode, by an emf applied at the
terminals of antenna A operated in the transmit mode, then the same
emf applied to the terminals of B will induce the same current at the
terminals of A. This is illustrated in Fig. 6.2. For a proof of the reciprocity
theorem, see for example, Glazier and Lamont (1958).
