19.1 A fundamental-frequency 114GHz circular-polarized radiating element with 14dBm EIRP, −99.3dBc/Hz phase-noise at 1MHz offset and 3.7% peak efficiency

Circular-polarized (CP) radiation is found to be a viable choice for imaging/sensing applications by offering faster scan time and robust source-detector alignment compared to linear radiation [1]. Power-efficient generation of a low-noise, high-power mm-wave/THz circular-polarized signal in silicon continues to be a challenging task. Due to limited output power of transistors at mm-wave, power combining methods (e.g., on-chip or spatial power combining) are employed to achieve high radiated power from multiple oscillator elements [1-5]. These methods, however, require lossy passive or power-hungry active coupling networks to lock the oscillators together, thereby degrading DC-to-RF efficiency [2]. This work introduces a high-efficiency and high-power multiport element, which can concurrently perform as a resonator, a power combiner, and a radiator, thereby avoiding the coupling networks and antenna buffers (Fig. 19.1.1). This structure enables CP radiation by exciting a radially symmetric radiator with evenly spaced phases of an RF signal [3]. These elements can be employed in an array configuration to obtain higher directivity (Fig. 19.1.1).