The present invention discloses an antenna and an active antenna system, so as to reduce complexity and power consumption of an antenna device, and reduce production costs. The antenna includes: an antenna array, a multichannel front-end, a multi-beam receiving network, and a multi-beam transmitting network; the antenna array includes w antenna elements, wherein w is a natural number greater than or equal to 2; the multi-beam transmitting network is configured to perform beamforming processing on j transmit signal beams, to obtain m transmit signals, wherein j is a natural number; the multichannel front-end is configured to convert w first radio-frequency signals received by the w antenna elements into n received signals, and convert the m transmit signals obtained by the multi-beam transmitting network into w second radio-frequency signals, wherein both n and m are natural numbers less than or equal to w; and the multi-beam receiving network is configured to perform beamforming processing on the n received signals generated by the multichannel front-end, to obtain k received signal beams, wherein k is a natural number.