A simple millimeter wave and terahertz (THz) receiver scheme that uses subwavelength focusing of electromagnetic beam on the point-contact detector area with waveguide dimensions is studied. A detection system with such an optical coupling scheme is implemented, where the signal to be detected is coupled to a detector through a mesoscale dielectric particle lens based on terajet effect. We have experimentally demonstrated an enhancement of the point-contact detector sensitivity higher than 6 dB and with 1.5 times decreasing of the noise equivalent power value. The results show that the proposed method could be applied to reduce the size and increase the sensitivity of various THz systems, including imaging, which would enable significant progress in different fields such as physics, medicine, biology, astronomy, etc.