Abstract
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 re-configure 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 multi-frequency 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.
Highlights
Artificial metallic structures, such as periodic holes and grooves have been reported to mimic surface plasmon polaritons (SPPs) at millimeter wave and terahertz frequencies where metals are regarded as perfect electric conductors[1]
We report multi-frequency multi-bit programmable amplitude modulation (AM) of spoof SPPs based on interdigital split-ring resonators (SRRs) and In-Ga-Zn-O (IGZO) Schottky diodes
3-D models are built in Ansys High Frequency Structural Simulator (HFSS), and their S-parameters are calculated by using Driven Mode solver
Summary
We proposed a programmable approach for multi-frequency multi-bit AM of spoof SPPs with interdigital SRRs by using IGZO Schottky diodes. Interdigital SRRs are proposed to obtain large operation bandwidth of from 37.4 to 52.8 GHz with minimized parasitic coupling and high Q-factor. Schottky diode fabricated in the SRR gap reconfigures the SRRs to metallic loops, which enables significant AM of from −12.5 to −6.2 dB at 34.7 GHz and from −26 to −8.5 dB at 50 GHz, respectively. Based on the interdigital SRRs and IGZO Schottky diodes, a dual-frequency device with cascaded SRRs was designed and fabricated, achieving 3-bit AM at 34.7 and 50 GHz with programmable bias. The proposed method provides a novel insight into multi-frequency multi-bit programmable modulation of spoof SPPs at microwave and THz regime
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