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A novel highly miniaturized wideband quadrature hybrid using slow-wave technology is proposed in this paper. In order to reduce the size of conventional branch-line/coupled-line couplers, a unique structure is utilized based on two layers of crossing strips with densely interconnecting vias. This structure makes full use of the electrical coupling and magnetic coupling in the slow-wave structure, and enhances the mutual inductance effect between parallel vias, which successfully leads to enhanced coupling strength that enabling the wideband 3-dB quadrature hybrid. Importantly, 99.4% of size reduction has been achieved as compared to conventional three-section branch-line counterpart while maintaining an equally good performance. The achieved relative planar area is only 0.003A2, which is orders-of-magnitude improvement over state-of-the-art. 

This article presents a novel architecture of load-modulated balanced amplifier (LMBA) with a unique load-modulation characteristic different from any existing LMBAs and Doherty power amplifiers (DPAs), which is named pseudo-Doherty LMBA (PD-LMBA). Based on a special combination of control amplifier (carrier) and balanced amplifier (peaking) together with proper phase and amplitude controls, an optimal load-modulation behavior can be achieved for PD-LMBA, leading to maximized efficiency over extended power back-off range. More importantly, the efficiency optimization can be achieved with only a static setting of phase offset at a given frequency, which greatly simplifies the complexity for phase control. Furthermore, the cooperations of the carrier and peaking amplifiers in PD-LMBA are fully decoupled, thus lifting the fundamental bandwidth barrier imposed on the Doherty-based active load modulation. Upon theoretical proof of these discoveries, a wideband RF-input PD-LMBA is physically developed using the GaN technology for experimental demonstration. The prototype achieves a highly efficient performance from 1.5 to 2.7 GHz, e.g., 58%–72% of efficiency at 42.5-dBm peak power and 47%–58% at 10-dB output back-off (OBO). When stimulated by a 10-MHz long term evolution (LTE) signal with a 9.5-dB peak-to-average power ratio (PAPR), the developed PD-LMBA achieves an efficiency of 44%–53% over the entire bandwidth at an average output power of around 33 dBm.