A 50–75 GHz Quadrupler With 18.4-to-20.3 dBm Output Power and >25 dBc Harmonic Rejection

In this article, a quadrupler with high output power and harmonic rejection (HR) over a wideband is reported, based on the GaAs process. To address the degradation of odd-order HR and conversion efficiency caused by impedance and amplitude-phase mismatches in differential structures, a broadband Marchand Balun with high common-mode rejection (CMR) and an improved push-push quadrupler topology is proposed. To further enhance HR and output power, a high-frequency-selective balanced power amplifier (PA) is designed with an out-of-band HR over 55 dB. A prototype is fabricated and tested to verify the design. Experimental results demonstrate that, with a fundamental input power of 0 dBm, the quadrupler achieves an output power greater than 18.4 dBm, and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 1$</tex-math> </inline-formula>, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 2$</tex-math> </inline-formula>, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 3$</tex-math> </inline-formula>, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 5$</tex-math> </inline-formula> HR are better than 25 dBc within the 50–75 GHz frequency range.