Abstract
This study presents a very-low-profile circular ultra-high frequency (UHF) small antenna with a radiating body transformed from a monopole. The proposed radiating body is gradually improved by analysing fundamental modes of the structure with different ground planes via characteristic mode analysis (CMA). CMAs demonstrate operating principles of the radiating body so that a magnetic feeding loop is proposed to excite the radiating body. An equivalent circuit of the radiating body and magnetic feeding loop is then established. The relationships between antenna bandwidth, and eigen value and modal significance are derived through physical insight of the CMA. A prototype of the proposed circular antenna operating at 474 MHz is fabricated and measured. It has a radius of 5.2%λ c (λ c is the operating wavelength), and a profile of 5.2%λ c The CMA of the proposed antenna with testing cable at different lengths is applied to understand the discrepancy between simulations and measurements. The analysis and performance evaluation shows that the proposed antenna can be a strong contender for compact sensors for machine-to-machine and internet of things applications.
Highlights
Small antennas play very important roles for wireless communication devices within limited spaces, but their performance and bandwidth are limited by the electrical size
The small and compact sensors for M2M and Internet of Things (IoT) applications have resulted in significant challenges for small antennas at UHF TV white space frequency bands, e.g. around 480MHz
The paper presented a very low profile circular UHF small antenna with radiating body transformed from a monopole
Summary
Small antennas play very important roles for wireless communication devices within limited spaces, but their performance and bandwidth are limited by the electrical size. Characteristic mode analysis (CMA) supported by theory of characteristic mode (TCM) becomes an attractive systematic tool to efficiently design antenna structures recently. It was proposed by Garbacz [19] and further developed by Harrington and Mautz [20, 21]. With knowledge of characteristic modes of an electrically small unmanned aerial vehicle body, the desired currents were excited by compact and low-profile feed structures to design integrated antennas [24]. The CMA is utilized in the process of designing a radiating body and a feeding structure, establishing an equivalent circuit, estimating antenna bandwidth, and analyzing difference between results of simulation and measurement.
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