If the desired antenna is used for a receiving a wave with a single or odd number of reflections, such as a bistatic radar where separate antennas are used for transmit and receive as shown in Figure 6, then opposite circularly polarized antennas would be used for maximum signal reception. In this case buy antennas of opposite polarization sense (one left hand and one right hand).
That's another reason why even number of reflection corner reflectors for radar targets are used.I think it is probably caused by the reflected signal being the opposite circular polarisation. I.E it changes left hand to right handed circular polarisation.
Les.