In this study, we experimentally proved the relationship between the number of subapertures and the self-focusing effect of a polarization-inverted transmitter by up-chirp signal driving. First, experiments on the focusing effect by aperture division were carried out using a prototype polarization-inverted transmitter. As a result, the beam width was improved by dividing the aperture. By increasing the number of aperture divisions, the beam width was reduced and the distance resolution was improved proportionally to the number of divisions. Finally, the beam width at the focal point was measured by changing the frequency component of the up-chirp signal driving the transmitter. Dependent on the focal point, the beam width did not change significantly. As a result, a focal point could be formed within the near field owing to the self-convergence phenomenon of the polarization-inverted transmitter and the convergence effect caused by aperture division. (C) 2018 The Japan Society of Applied Physics