An antenna apparatus includes an antenna element, a switch with a common terminal that is electrically connected to the antenna element side, a first signal path provided between a first input/output terminal of the switch and a first communication circuit, and a second signal path provided between a second input/output terminal of the switch and a second communication circuit. The first signal path includes a radio-frequency circuit and a phase shifter, and the RF circuit has an impedance that is open or shorted in a second frequency band as seen from the antenna element side. In a state in which the first input/output terminal and the second input/output terminal are both electrically connected to the common terminal, the phase shifter provides a phase shift, and the impedance in the second frequency band of the first signal path as seen from the common terminal is open.

An antenna apparatus includes an antenna element, a switch with a common terminal that is electrically connected to the antenna element side, a first signal path provided between a first input/output terminal of the switch and a first communication circuit, and a second signal path provided between a second input/output terminal of the switch and a second communication circuit. The first signal path includes a radio-frequency circuit and a phase shifter, and the RF circuit has an impedance that is open or shorted in a second frequency band as seen from the antenna element side. In a state in which the first input/output terminal and the second input/output terminal are both electrically connected to the common terminal, the phase shifter provides a phase shift, and the impedance in the second frequency band of the first signal path as seen from the common terminal is open.

A receiver receives signals and noise over a frequency spectrum of a desired received signal. The desired received signal is spread using code division multiple access. The received signals and noise are demodulated to produce a demodulated signal. The demodulated signal is despread using a code uncorrelated with a code associated with the desired received signal. A power level of the despread demodulated signal is measured as an estimate of the noise level of the frequency spectrum.