Study on increasing efficiency of radio communication using tunable antenna and software-defined radio

Abstract

The demand for a software-defined radio (SDR) is increasing because it can support variety of frequency bands and modulation techniques. However, a condition of an antenna can become a bottleneck of the communication system using SDR due to less flexibility of the antenna. For example, when the SDR changes the signal frequency dynamically or the communication system faces a disturbance such as human body presence, the communication efficiency becomes small compared to the ideal state due to an impedance mismatching between the radio and the antenna. In this study, we propose a communication system that achieves high communication efficiency by integrating the tunable antenna and the SDR. The authors designed the SDR for not only to support flexible communication schemes but also to control the tunable antenna actively. We considered two practical situations that raise impedance mismatching and performed experiments whether the proposal communication system can coordinate the impedance of the antenna. We found that the proposed system can provide a near perfect match by sensing the environment and controlling the tuned circuit accurately. As a result, it was confirmed that the proposed system can improve the utility of SDR by increasing the communication efficiency under various environments.

Automic Antenna Tuners

“…During the operation, the antenna impedance can differ from 50 Ω depending on the unpredictable electromagnetic environment. This EM environment can change over time and from user to user making it difficult to optimize the RF front end for a well-defined antenna impedance (even if the antenna impedance is simply different from 50 Ω) ( [1] - [21]). Also, the presence of the user affects both input (TX) and output (RX) impedance because it is in the near field of the antenna.…”

“…In [21] a phase detector is proposed and it consists of a directional coupler and a detector. The detector is made of a 90-degree phase shifter, two limiters and a multiplier.…”