Novel Unidirectional Radiation Principle by Backward Field Cancellation and Its Application to Wearable IoT Devices

This letter proposes a dual-dipole system using backward field cancellation to realize unidirectional radiation pattern, which can be applied to wearable devices. First, the principle is analyzed. By assigning special excitation phases related to the antenna distance, constructive interference in forward and a radiation null in backward are produced. Second, a dual-dipole system as an implementation model is proposed, which consists of two identical dipoles connected with a parallel strip line. The arms of the two dipoles are interleaved and the special connection style guarantees the required excitation phases, independent of antenna distance. Third, three dual-dipole systems with antenna distances of 5/10/20 mm operating at 2.45 GHz are analyzed and fabricated. The measured broadside gains of 4.3/5.1/4.9 dBi and front-to-back ratios of 9.8/9.3/8.0 dB have validated the feasibility of the theory. When the proposed antenna is applied to a smartwatch/smart band/earphone, the on-hand/on-head efficiency is improved by 2.8/1.7 dB compared with a reference dipole, making it suitable for wearable IoT device applications.