In this brief, a millimeter-wave (mm-Wave) wideband frequency quadrupler is demonstrated in a 55-nm CMOS technology. It cascades two injection-locked frequency doublers (ILFD). Each of them consists of an oscillator gain stage realized by an injection-locked oscillator (ILO) and a frequency doubler implemented by a push-push pair. A tail feedback loop is proposed and applied in the second ILFD. It effectively boosts the injection current for the second ILFD. Therefore, both the operating bandwidth and output power (Pout) of the circuit are prominently improved. In addition, transformer-based high-order resonators are used to reduce the phase variation of their impedance around 0° and hence extend the locking range of ILOs. According to the measurement results, a frequency range of 30.8 ~ 40 GHz is achieved. The maximum Pout is up to -7.1 dBm without additional buffers. The circuit also attains a wide 3-dB frequency bandwidth of Pout, which is from 32 to 38.4 GHz. The harmonic rejection ratios of the frequency quadrupler are 16.5 ~ 25.9 dBc at the second-order harmonic and 31 ~ 45 dBc at the fundamental and third-order harmonics over the entire operating bandwidth. The core area occupies only 0.24 mm².