Compact circular polarization filtenna for wireless power transfer applications

Abstract

Nowadays, Internet of Things (IoT) electronic devices are needed to realize the fifth generation (5G) device-to-device communication. Obviously, current developments tend to focus more towards structure compactness for mobility purposes. However, the main weakness for mobile devices is its power supply. This can be improved by increasing the individual battery capacity or having external batteries. These proposed solutions will increase the weight of the devices, hence making them heavier to carry around. Most total IoT devices are also required to be multi-functional depending on different radio frequencies (RF). Commonly, the RF signal radiated is solely used for data communication. This useful RF signal can also be converted into small energy, instead of being left to disperse into the environment. This relates to wireless energy harvesting called as rectifying antenna (rectenna) which converts RF signal to direct current (DC). A generic rectenna consists of the combination of several components such as antenna, filter, diode and resistive load. The aim of this research is to develop a compact or miniaturized RF front-end component for the rectenna. Compactness can be achieved by embedding the filter into the antenna to form a filtenna. Non-contacted electromagnetic coupling technique with the circular patch antenna operated at 2.45 GHz is selected as the basic design and the simulation work was done using the Computer Simulation Technology (CST) software. To enhance the quality of propagation and the multi-functional properties, the proposed design optimized for circular polarization (CP) and wider bandwidth. Therefore, the modification of the basic design change to proximity coupled feeding technique with double layered configuration is presented. Analysis of the slot line resonator near to the transmission line on several locations is discussed to realize a filtenna. In this research, several different designs of antennas and filters are presented with different compactness, CP, and higher resonant rejection properties. All proposed designs are fabricated and validated through measurement studies. Good agreement is shown between simulation and measurement results. By having approximately 45-50 % of size reduction as compared to the conventional 2.45 GHz microstrip patch antenna, the developed antennas are compact in size with higher resonant rejection up to third harmonic and exhibit 5.2 dB gain.