Design and holistic evaluation of dual-band circularly polarized smartphone antenna for direct-to-device non-terrestrial networks

Sammanfattning

Direct-to-Device (D2D) communication in Non-Terrestrial Networks (NTNs) enables smartphones to connect directly to satellites, extending wireless coverage beyond terrestrial networks. This thesis presents the design of a smartphone antenna optimized for NTN operation, followed by a link budget analysis and Electromagnetic Field (EMF) exposure assessment. The proposed solution is a dual-band circularly polarized antenna operating in the S-band NTN frequency ranges. The antenna is specifically optimized to provide radiation towards the upper hemisphere, while satisfying the size constraints of a smartphone. In addition, a linearly polarized C-band antenna is obtained as an extension of the S-band structure, enabling additional functionality. The antenna performance is evaluated in terms of impedance matching, radiation characteristics and efficiency, and its impact on system performance is evaluated by a link budget analysis based on a Low Earth Orbit (LEO) satellite scenario. The results demonstrate that the optimized S-band antenna achieves data rates ranging from several kbps to several Mbps, depending on transmit power and elevation angle, demonstrating its suitability to enable NTN communication with significant data rates. In the C-band, the system can provide additional connectivity, supporting low data rate services, due to higher propagation losses and reduced antenna gain in the skywards direction. Electromagnetic exposure is assessed through Specific Absorption Rate (SAR) simulations. The results show that SAR levels remain within international limits when using certain duty cycle transmission period, needed at certain phone positions relative to the body and higher transmit power levels. The findings provide insights into the trade-offs between antenna design, link performance, and user exposure in the context of smartphone-based NTN communication.