Which of the following is a disadvantage of multiband antennas?
They present low impedance on all design frequencies
They must be used with an antenna tuner
They must be fed with open wire line
They have poor harmonic rejection✓Bonne réponse
Explication
A single-band antenna presents a bad mismatch at its harmonics and therefore radiates them poorly, which is useful. A multiband antenna is deliberately matched on harmonically related bands, so transmitter harmonics falling there meet little attenuation and get radiated.