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This paper presents the design and analysis of an improved wideband in-phase/quadrature (I/Q) network and its implementation in a wideband phased-array front-end. It is found that the addition of two resistors (Rs) in the all-pass I/Q network results in improved amplitude and phase performance versus capacitance loading and frequency, which is essential for wideband millimeter-wave applications. A prototype 60-80-GHz phased-array front-end based on 0.13-μm SiGe BiCMOS is demonstrated using the improved quadrature all-pass filter and with 4-bit phase-shifting performance at 55-80 GHz. Application areas are in wideband millimeter-wave systems.