Researchers at Georgia Tech are paving the way for the miniaturization of millimeter-wave circuits by merging antennas with active electronics. The approach allows for the simultaneous optimization of on-circuit antennas and integrated circuits (ICs), with tremendous possibilities to support the increasing use of millimeter-wave frequencies in 5G wireless communications networks as well as in military electronic systems.
Because the millimeter-wave devices that combine transmitter and receiver ICs and antennas are fabricated on conventional circuit materials, they can be produced and manufactured using conventional processes and materials. The small sizes of the combined designs encourage the use of multiple signals in antenna arrays, as well as the use of multiple-input, multiple-output (MIMO) antenna signal processing techniques to increase spectrum efficiency and wireless data rates at millimeter-wave frequencies. Work on the unique co-design technique is sponsored in part by the U.S. Army Research Laboratory (ARL), as well as by Intel Corp.
The researchers demonstrated the concept earlier this year at the 2018 Radio Frequency Integrated Circuits Symposium (RFIC) in Philadelphia. “In this proof-of-example, our electronics and antenna were designed so that they can work together to achieve a unique on-antenna outphasing active load modulation capability that significantly enhances the efficiency of the entire transmitter,” said Hua Wang, an assistant professor in Georgia Tech’s School of Electrical and Computer Engineering. “This system could replace many types of transmitters in wireless mobile devices, base stations and infrastructure links in data centers.”
Achieving high energy efficiency is one of the keys to the success of the new design approach reaching high efficiency at lower power levels. Most wireless transmitters achieve high efficiency only at high peak power levels, dropping drastically in efficiency at lower transmit power levels. This translates into low efficiency when boosting and transmitting signals with complex modulation, typical of most modern wireless communications formats.
“We are combining the output power though a dual-feed loop antenna, and by doing so with our innovation in the antenna and electronics, we can substantially improve the energy efficiency,” said Wang. “The innovation in this particular design is to merge the antenna and electronics to achieve the so-called outphasing operation that dynamically modulates and optimizes the output voltages and currents of power transistors, so that the millimeter-wave transmitter maintains a high energy efficiency both at the peak and average power.”
The integrated antennas, transmitters, and receivers are fabricated with a 45-nm CMOS small-outline-integrated-circuit (SOIC) process. The ICs are housed within flip-chip packages and mounted on high-frequency printed circuit boards (PCBs) and tested within a well-equipped RF/microwave measurement facility. Testing confirms a significant increase in efficiency with the new design and fabrication technique. The spectrally efficient antenna/transmitter co-designs should also support the use of much higher data rates at lower transmit power levels.
