Multi Frequency Multi Bit Amplitude Modulation of Spoof Surface Plasmon Polaritons by Schottky Diode Bridged Interdigital SRRs

Multi-frequency multi-bit programmable amplitude modulation (AM) of spoof
surface plasmon polaritons (SPPs) is realized at millimeter wave frequencies
with interdigital split-ring resonators (SRRs) and In-Ga-Zn-O (IGZO) Schottky
diodes. Periodic SRRs on a metal line guide both SRR mode and spoof SPP
mode, the former of which rejects the spoof SPP propagation at the SRR
resonant frequencies. To actively modulate the amplitude of spoof SPPs, IGZO
Schottky diodes are fabricated in the SRR gaps, which continuously reconfigure
SRRs to metallic loops by applying bias. Interdigital gaps are
designed in SRRs to increase the capacitance, thus red shifting the resonant
frequencies, which significantly broadens the operation bandwidth of multifrequency
AM. Thus, cascading different kinds of interdigital SRRs with
Schottky diodes enables multi-frequency multi-bit AM programmable. As a
demonstration, a dual-frequency device was fabricated and characterized,
which achieved significant multi-bit AM from -12.5 to -6.2 dB at 34.7 GHz and
from -26 to -8.5 dB at 50 GHz independently and showed programmable
capability.