Large-Signal Analysis and Characterization of a RF SOI-based Tunable Notch Antenna for LTE in TV White Space Frequency Spectrum

The demand for spectrum resources has increased dramatically with the explosion of wireless mobile devices and services. The Cognitive Radio (CR) associated with TV white space frequencies defined between 470 MHz to 790 MHz is one solution to excel the spectrum resources shortage and address LTE low bands. The antenna design to cover such a wide band is a twofold challenge. First Electromagnetic fundamental limits impose a tradeoff between antenna efficiency, miniaturization and its frequency band wideness, secondly to be implemented in portable device (around 10 cm typical length) the antenna miniaturization needs is to be strong such as in λ/6 (where λ is the wavelength at 500 MHz). Thus, frequency reconfigurable antennas are suitable candidates and can be easy integrated. In this paper a compact frequency-agile notch antenna for LTE low-band using TV white space frequencies is designed and fabricated. The 18 x 3 mm notch size (area dedicated for the antenna) is only λ/33 at 500 MHz. The antenna aperture tuning is provided by a SOI CMOS tunable capacitor. The novelty of this paper is to present not only classical metrics (gain, return loss…) but also the experimental characterization of parameters that are usually used for active RF components. The non-standard tunable capacitor RF non linearity analysis is carried on and analyzed. The simulated and experimental performances are presented and demonstrate antenna tuning operation from 800 MHz down to 500 MHz. The slot electrical near field distribution is also investigated to confirm acceptable electrical field within the tunable component. High linearity is validated with measured ACLR levels lower than -30 dBc up to 22 dBm input power in the considered frequency range.