Highly efficient 5.8-GHz class E(-1)frequency doubler using atransmission-line-basednotch filter

Abstract

An inverse class E frequency doubler is proposed to improve power conversion efficiency by using a transmission-line-based notch filter. The notch filter implemented using a transmission line is used at the output network in the doubler to suppress both fundamental and high-order harmonic signals by a switching-mode operation. A fourth harmonic signal is also reduced by using the quarter-wavelength transmission line at the output network. Two frequency doublers with the proposed output network are optimized at different input power values and implemented on an FR4 PCB. In the measurement results, the doubler optimized at a low driving power shows a power conversion efficiency of 26.3% and an output power of 11.2 dBm for an input power of 11.5 dBm. The signal rejection levels of the low-power optimized doubler power are -32, -40.1, and -31.7 dBc at the fundamental frequency, third harmonics, and fourth harmonics, respectively. The doubler optimized at a high driving power shows a power conversion efficiency of 24.6%, an output power of 13.7 dBm, and a signal rejection of less than -29.8 dBc, respectively.