A compact low sar value circularly polarized wearable antenna design for 5G applications

Abstract

Wireless Body Area Network (WBAN) is a technology that enables various devices to connect by putting them on a human body. Measurement of real-time physiological changes, medical diagnosis, and navigation are among the uses of WBAN. Monitoring the changes within the human body allows us to preserve a record of the health of patients continually, and it could be provided increased living standards for patients. In WBAN systems, wearable antennas perform the function of the transceiver structure, which allows for the transmission and reception of data and information. These antennas are designed to maintain their flexibility so that they do not restrict the mobility of the human body. Also, their structure should be strong for human body properties. A variety of flexible materials are employed as substrates in creating wearable antennas these days. This is done so that the structure of the antenna can supply flexibility. Because the human body is in a state of continual motion, it might be challenging to get the correct polarization alignment of the transceiver system, which is necessary for improved power reception. The use of circular polarization (CP) does away with the requirement that two systems be constantly aligned in order to receive maximum power. The majority of the previously represented wearable antennas are rigid, linearly polarized, massive in size, or have a very thick substrate. These characteristics make it challenging to employ these antennas in wearable applications. Specific Absorption Rate (SAR) refers to the ratio of the absorbed power to the unit mass of the tissue. Both the United States of America and the European Union have established their standards so that it is unacceptable for the power density of 1 g and 10 g of tissue to surpass specific values. The SAR value is a crucial limiting factor for wearable antennas. Because of this, a wide variety of methods are used in order to reduce the SAR value. Narrowband wearable antennas inevitably possessed a restricted bandwidth and a slow data transmission rate, particularly when coupled with communication modules. Despite this, the fifth generation (5G) of the communication spectrum helps address the shortcomings of previous generations. The 5G spectrum provides a higher and broader data transfer rate than the previous spectrum bands. The circular microstrip antenna in a coplanar waveguide structure has been chosen to operate in the 5G band. Denim and roger 5880 substrates have been used to provide flexibility and low SAR value. Denim substrate has a thickness of 0.787mm, and Roger substrate has a thickness of 0.508mm. There is a gap of 0.6 mm between the two substrates. A copper tape with a thickness of 0.035mm has been used as a conductor. A rectangular slot has been placed in the middle of the circular patch to ensure circular polarization. The performance of the coplanar waveguide antenna is simulated in free space and near the human body. The antenna showed a good fit in on-body and free space simulation. The simulation has been carried out by placing the antenna at a distance of 5 mm from the body. Although some changes have been observed in the simulation results on the body, there has been no severe change in general. There has been a slight shift in the frequency band and a light reduction in impedance matching. The use of two substrates has provided the lower SAR values. In summary, the antenna results provided circular polarization and very low SAR values in the desired band range. It has a good result in terms of impedance matching and radiation characteristics. The antenna has small dimensions and flexibility in general structure. It could be a good candidate for wearable applications.