A Low-Cost 60-GHz Modular Front-End Design for Channel Sounding

Millimeter-wave (mmWave) frequency bands are attractive for bandwidth (BW)-intensive applications. However, scholarly articles revealing straightforward and repeatable modular construction of mmWave front ends are scarce. Channel sounding, which is critical due to the distinct propagation characteristics of mmWaves, is predominantly done through bulky and expensive laboratory equipment due to the lack of other hardware. This work fills this gap through a modular approach to construct a 60-GHz front-end transceiver by packaging off-the-shelf chipsets and custom-designed blocks. In contrast to the typical expensive manufacturing processes for mmWave circuits, this work reports passive mmWave blocks, which are compatible with single-layer standard printed circuit board (PCB) process along with the measurement setup. Multilayer PCB stack-up is then used for system integration offering an economic and repeatable manufacturing. Distinguishing features of the developed front end are round-trip (half-duplex) communication, carrier reconfigurability within 58-64 GHz, and agent-mode operation. The front end is usable as a portable frequency-domain channel sounder. To the best of the authors' knowledge, it is the first report of a portable channel sounder, which can acquire a round-trip amplitude-frequency response of an mmWave channel without using any bulky or expensive laboratory equipment. This work further identifies the electromagnetic (EM) compatibility issues in unshielded PCBs and hardware response calibration. Furthermore, it identifies the hardware requirements to maintain channel reciprocity in round-trip communication at mmWave bands.