A 43–84GHz, Wideband Frequency Doubler With a Symmetric, AC-Terminated Transformer Balun

This paper presents a frequency doubler with wide tuning range, high efficiency, and high harmonic rejection ratio for E, V, and U-band applications. A novel transformer balun architecture is used to generate a well-balanced differential signal, employing the AC-termination method at the input winding, combined with a capacitor array in a symmetric layout, resulting in minimal amplitude and phase imbalances. Additionally, a dual-resonance methodology for input matching is utilized to maximize the covered bandwidth. The proposed doubler covers 43–84 GHz, corresponding to a 64.6% 3-dB bandwidth, and achieves a peak output power of 5.2 dBm at 1-dBm input power while maintaining a peak total efficiency of 19.7%. Both the fundamental and third-harmonic rejection ratios are larger than 37 dBc and 33 dBc over the operating frequency, respectively.