It's mentioned in the end notes: For the sake of simplicity I have used "passive repeater" here to refer to microwave reflectors only, but the same term is als

It's mentioned in the end notes: For the sake of simplicity I have used "passive repeater" here to refer to microwave reflectors only, but the same term is also used for arrangements of two antennas connected back-to-back. These are much more common in VHF/UHF than in the microwave, although microwave passive repeaters of two parabolic antennas have been used in limited cases.