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Digital RF technology has been developed and has been applied to below 6 GHz wireless applications. By replacing the IC die consumptive RF/analog circuit blocks by digital signal processor and circuit, digital rich/small transceivers can be realized. Since the foundation of this technology is based on the Nyquist theory, the operational frequency of the circuit has been limited by the Nyquist frequency (=1/2 of sampling clock frequency). As a result, the maximum operational RF frequency of existing digital RF technology was below 6 GHz. In this paper, a new direct digital RF technology that utilizes the higher‐order Nyquist zones is introduced. This technology enables handling RF signal in beyond Nyquist frequency range which means over 6 GHz range. The results of fabricated 26/28 GHz‐band transmitter/receiver are reviewed. Since the transceiver architecture with the proposed technologies does not require an RF local oscillator and up/down converters, it is suitable for microwave/millimeter‐wave multi‐antenna systems such as next generation satellite on‐board digital beam forming and Beyond 5G fully digital Massive multiple‐input multiple‐output systems. Proposed direct digital RF transceiver technology utilizes the higher‐order Nyquist zones and mmW signal can be handled directlyDirect digital RF technology brings compact/digital rich mmW transceivers and will realize large scale digital beam forming antennas for mmW applications Proposed direct digital RF transceiver technology utilizes the higher‐order Nyquist zones and mmW signal can be handled directly Direct digital RF technology brings compact/digital rich mmW transceivers and will realize large scale digital beam forming antennas for mmW applications

A 2 x 4 phased array antenna module has been developed for 60-GHz-band short- range high-speed wireless communication terminals. To realize the required vertical distance between the antenna elements, the module is made of five sheets of multi-layered organic substrates vertically stacked with Cu balls, and the 1 x 4 dipole array antenna is placed on both the top and bottom organic substrates. To reduce the mutual coupling between the element antennas, a monolithic microwave integrated circuit (MMIC) is flip-chip mounted on the feed line of each element antenna. The Au-stud bump flip-chip mounting technique helps achieve a lower return loss in the transition section at the MMIC than the Au-wire bonded. The placement accuracy of each antenna element in the vertical direction, 60-GHz signal vertical interconnection between the substrates with Cu balls, and flip-chip mounting of the MMIC are confirmed by 3-D computed tomography (CT) scans.