AbstractThis paper reports an active integrated antenna which combines the antenna function with the millimeter‐wave MMIC technology. TJI addition to a high carrier frequency, the compactness of the circuit is extremely useful for applications to automobile radar and wireless LAN.To realize low‐cost millimeter‐wave subsystems, this paper describes an active integrated antenna making use of the slot antenna and the second harmonic of the FET oscillator. The input impedance of the slot antenna is included in the design of a strongly coupled active integrated antenna array. The oscillation frequency of the array was evaluated by a large signal analysis.In the case of a two‐element active integrated antenna using a harmonic, the second harmonic operating frequency of 39.3 GHz was obtained. The phase of the radiation of the fundamental mode was adjusted so that different radiation patterns for different modes were obtained. Also, in the uniplanar‐type four‐element array, a large signal analysis was carried out including the discontinuities in the coplanar waveguide. Through the present trial fabrication, the fundamental data for fabrication of millimeter‐wave monolithic active integrated antennas