A Tunable Single-Feed Triple-Band LTE Antenna With Harmonic Suppression

This paper presents a single-feed planar inverted-F antenna (PIFA) that operates at three resonant frequencies within the LTE frequency range which would result in the enhancement of the antenna bandwidth and the increase of the data-rate speed. The antenna is designed to satisfy the requirements of carrier aggregation systems (intraband non-contagious type) cell-phone applications. The three resonant frequencies are independently tunable within the low-band (0.7–1 GHz), mid-band (1.6–2.1 GHz), and high-band (2.1–2.7 GHz), respectively, using varactor diodes as tuning devices. Each varactor diode represents a variable capacitor controlled by biasing dc voltage. A parallel LC harmonic-trap filter is built inside the antenna to suppress the harmonics generated by the low-band resonance, which enhances the tuning capabilities at the high-band. The antenna has a size of 375 mm², which is considered to be a low-profile design and placed on a <inline-formula> <tex-math notation="LaTeX">$100\times 66\times3.154$ </tex-math></inline-formula> mm³ RO4003C (<inline-formula> <tex-math notation="LaTeX">$\varepsilon _{\textrm {r}}$ </tex-math></inline-formula> = 3.55) printed circuit board. The measured antenna radiation patterns in each band are nearly isotropic as expected from the PIFA and the measured antenna radiation efficiency is 25–80% within the entire LTE frequency bands.