A comparison of feed methods for electrically small and low-profile meander line antennas

Electrically small and low-profile antennas (ESLA) have been widely studied in recent years. An antenna which is close to a back conductor can reduce the electrical effects from the backing material when installed on IC chips, human body or any metallic or lossy material. However, typical electrically and low-profile antennas have low radiation efficiency resulting in a difficulty of impedance matching to 50 Ω. For designing an ESLA, a capacitive feed (C-feed) technique has been proposed in [7] for a meander line antenna with a length of half-wavelength. Using the C-feed structure, the imaginary part of the input impedance of the antenna can be easily controlled by varying the size of the feed plate which is installed in between the radiating element and ground plane. Furthermore, a modified quarter-wavelength capacitive-feed meander line antenna (QCFMA) has been proposed in [8] for gain improvement satisfying ka = 0.435 <; 0.5, k: wave number, a: radius of a sphere surrounding the antenna. In this paper, the QCFMA is compared with the same dimension of meander line antenna with an inverted-F antenna structure (IFMA) in order to evaluate the performance of C-feed structure. As a result, QCFMA shows better radiation characteristics than IFMA, and the two fabricated antennas show good agreement with the simulated results.