Sensor and estimating method

A sensor comprising:

• a transmit antenna including N transmit antenna elements, each of the N transmit antenna elements transmitting a transmit signal to a predetermined range within which an organism is likely to exist, N being a natural number of two or greater;
• a receive antenna including M receive antenna elements, each of the M receive antenna elements receiving N receive signals including reflection signals generated as a result of some of the N transmit signals transmitted from the N transmit antenna elements being reflected by the organism, M being a natural number of two or greater;
• circuitry;
• and
• a memory, wherein
• the circuitry calculates an N×M first matrix having complex-number transfer function components, each of the complex-number transfer function components representing propagation characteristics between a transmit antenna element and a receive antenna element, from the N receive signals received by each of the M receive antenna elements for a predetermined period,
• the circuitry extracts a second matrix corresponding to a predetermined frequency range from the first matrix, the second matrix representing components influenced by a vital sign including at least one of respiration, pulse, and motion of the organism,
• the circuitry estimates a position of the organism with respect to the sensor by using the second matrix,
• the circuitry calculates a first distance indicating a distance between the organism and the transmit antenna and a second distance indicating a distance between the organism and the receive antenna, based on the estimated position of the organism, a position of the transmit antenna, and a position of the receive antenna,
• the circuitry calculates a radar cross-section value with respect to the organism by using the first and second distances, and
• the circuitry estimates a posture of the organism by using the calculated radar cross-section value and information indicating associations between radar cross-section values and postures of the organism stored in the memory.