The channel bandwidth in HT20 mode is 20 MHz, and the channel bandwidth in HT40 mode is 40 MHz. Two neighboring 20 MHz channels are bundled to form a 40 MHz channel. One channel functions as the main channel, and the other as the auxiliary channel. The main channel sends Beacon packets and data packets, and the auxiliary channel sends other packets. When the HT40 mode is used in the 2.4 GHz frequency band, there is only one non-overlapping channel. Therefore, you are not advised to use the HT40 mode in the 2.4 GHz frequency band.

Two neighboring 20 MHz channels can be bundled into a 40 MHz channel. If the center frequency of the main 20 MHz channel is higher than that of the auxiliary channel, 40MHz-minus is displayed; otherwise, 40MHz-plus is displayed. For example, if the center frequency 149 and the center frequency 153 reside on two 20 MHz channels, 149+ indicates that the two 20 MHz channels are bundled to form a 40 MHz channel.