Polarisation is the orientation of the electric field vector with time. Select the correct answer in relation to the polarisation of the uniform plane wave:a.The axial ratio of a linearly polarised signal is 1b.The axial ratio of an elliptically polarised signal is ∞c.A circularly polarised signal has an axial ratio 1d.A circularly polarised antenna receives a signal from the horizontally polarised antenna with minimum strengthe.A vertically polarised antenna receives signal with a horizontally polarised antenna with a PLF=0.25

Let's go through each option:

a. The axial ratio of a linearly polarised signal is 1: This is correct. In a linearly polarised signal, the electric field vector maintains a constant orientation, so the ratio of the major to minor axis (the axial ratio) is 1.

b. The axial ratio of an elliptically polarised signal is ∞: This is incorrect. An elliptically polarised signal has an axial ratio between 1 and ∞, but it is not necessarily ∞.

c. A circularly polarised signal has an axial ratio 1: This is correct. In a circularly polarised signal, the electric field vector rotates in a circle, so the major and minor axes are equal, giving an axial ratio of 1.

d. A circularly polarised antenna receives a signal from the horizontally polarised antenna with minimum strength: This is correct. A circularly polarised antenna can receive signals from both horizontally and vertically polarised antennas, but the signal strength will be reduced compared to receiving from a similarly polarised antenna.

e. A vertically polarised antenna receives signal with a horizontally polarised antenna with a PLF=0.25: This is incorrect. The Polarisation Loss Factor (PLF) between a vertically polarised antenna and a horizontally polarised antenna is 0, because they are orthogonally polarised and cannot receive each other's signals.

Therefore, the correct answers are a, c, and d.