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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. Key Points: 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 [ABSTRACT FROM AUTHOR]

In this letter, re‐evaluation results of a 60‐GHz‐band digital beamforming antenna using a dual‐feed linear polarized 2 × 2 circular patch array antenna is reported. The extension from our previous report is providing new measurement data under the condition of all intermediate frequency (IF) signal usage by re‐fabrication, although we reported imperfect measurement results using the IF signals only 5 ch out of 8 ch in the previous report due to the fabrication error. A low temperature solder paste was newly used to prevent the warp of the multilayered substrate. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Simple calculation method of the intermodulation distortion of multiple-carrier amplifiers operating in weakly nonlinear region is presented. This method is based on the approximation that is effective when (1) the transfer characteristics of carriers are regarded as linear, and (2) the third-order intermodulation distortion ratio versus the output power has 2 dB/dB slope. As the number of the carriers n→∞, the intermodulation distortion ratio approaches the value of 10 log10(3/2) + 6 ≠ 7.76 dB higher than the third-order intermodulation distortion ratio in the case of two-carrier amplification at the same output power. [ABSTRACT FROM AUTHOR]