To achieve wideband performance, a number of multi-band antennas have been investigated. However, many of these antennas were unable to cover 700-MHz LTE bands because of the additional space required to operate at this frequency range. Although the coupled-feed technique is a typical solution to this problem, this approach is not suitable for mobile devices that require a compact size and low profile. To meet the goal of developing a multi-band antenna in a compact size, a group of researchers from Kyonggi University in South Korea have proposed a frequency-reconfigurable antenna. It has the capability to operate in six modes, allowing various LTE and GSM bands to be covered.
The proposed antenna, which was fabricated on a 1.6-mm-thick FR4 substrate, comprises radiating elements and two PIN diodes. The antenna operates as three separate antennas—each of which generates its own resonant frequency. This enables performance in the lower-frequency 700-MHz LTE bands and the 850- and 900-MHz GSM bands as well as the higher-frequency 2300- and 2500-MHz LTE bands and 1800- and 1900-MHz GSM bands. In addition, it operates in the Universal Mobile Telecommunications System (UMTS) band from 1920 to 2170 MHz. At lower frequencies, the antenna’s peak gain varies from 0.13 to 1.59 dBi. The peak gain varies from 0.68 to 3.85 dBi at the higher frequencies.
See “Compact Frequency Reconfigurable Antenna for LTE/WWAN Mobile Handset Applications,” IEEE Transactions on Antennas and Propagation, Oct. 2015, p. 4,572.