Fully Integrated Multimode Orbital Angular Momentum Wave Generation at 360 GHz Using SiGe BiCMOS

This article presents a fully integrated multimode orbital angular momentum (OAM) transmitter using a circular slot cavity antenna, capable of concurrently operating three orthogonal OAM modes ( $|l_{\text {oam}}| =0$ , 1, and 2) while maintaining a common phase center. This allows the use of passive gain elements like lenses or reflectors for directivity enhancement. Additionally, the transmitter takes advantage of high-order cavity modes eliminating the complex multiphase feeding network. Detailed studies about the angular momentum (AM) of the radiated electromagnetic (EM) wave and the correlation between the antenna mode and OAM/SAM mode are provided in this article. The single-element transmitter is composed of a 120-GHz oscillator and a p-i-n diode frequency tripler interfacing with harmonic filtering networks. The transmitter can generate OAM waves at 360-GHz signal with a peak radiated power of −8.1 dBm and a dc-to-THz efficiency of 0.1%. It also exhibits a wide-frequency tuning range of 14.2%. The chip is fabricated in the GlobalFoundries 90-nm BiCMOS process. Apart from transmitter design, this work also introduces a method for measuring OAM amplitude and phase distribution that does not require Tx/Rx frequency and phase coherency, simplifying the measurement process and ensuring accurate characterization of OAM modes. Its ability to operate in multiple OAM modes simultaneously, combined with its compact and efficient design, highlights its potential for future secure high-capacity communication applications.