Design and simulation analysis of rectifying metasurface antennas for SWIPT

With the rapid development of the Internet of Things and wireless sensor networks, the trade-off between enhancing information transmission and moderating device power requirements is becoming increasingly prominent. To help students understand the field‑circuit co‑design mechanism in microwave technology, this paper describes a comprehensive experimental project based on simultaneous wireless information and power transfer (SWIPT) technology. This project focuses on the joint design of a rectifying metasurface antenna, translating a cutting‑edge research topic into a feasible undergraduate teaching case.

The experiment follows two main approaches: decomposing a complex problem and simulation‑driven design. The SWIPT receiving end is divided into three modules: a circularly polarized antenna, an energy‑harvesting metasurface, and a rectifying diode. A single‑stage parallel rectifier circuit using an HSMS2860 Schottky diode was simulated in Keysight Advanced Design System (ADS), in which a harmonic balance simulation with parameter sweeps determined the optimal input impedance and load. An arrow‑shaped metasurface unit operating at 5.8 GHz was designed in CST Microwave Studio with periodic boundary conditions. A time-domain solver with open boundary conditions is used to simulate an infinite array. A lumped RC element with R = 87.81 Ω and C = 0.65 pF modeled the diode. The unit's energy-harvesting efficiency was calculated by dividing the power dissipated in the lumped element by the total incident power. The communication antenna is a circularly polarized microstrip antenna operating at 2.45 GHz, designed using the single‑feed corner‑truncation method. The antenna's reflection coefficient, axial ratio, and far‑field gain were simulated. Finally, a shared‑aperture system was built in CST using a stacked structure comprising a bottom ground, a 1.575 mm-thick middle patch antenna, and a 2 mm-thick top metasurface array. After analyzing the surface current distributions, the load resistors in the strongest coupling region were repositioned to reduce mutual interference.

The rectifier circuit achieved a peak efficiency of 65.62% at 5.8 GHz with an input power of 14.77 dBm and a load of 150 Ω. Under these conditions, the diode impedance is 87.81−j42.22 Ω. The individual metasurface unit showd S11 = −19.23 dB at 5.8 GHz and an energy-harvesting efficiency of 99.2% at normal incidence. The efficiency was above 80% for incident angles up to 50° and above 98% for polarization angles of 0°−80°, demonstrating good polarization insensitivity and wide‑angle stability. In the initial shared-aperture system, the 5.8 GHz energy-harvesting efficiency was 84.53%. The 2.45 GHz antenna had S11 = −13.45 dB, an axial ratio of 0.396 (well below 3 dB), and a maximum gain of 5.65 dBi. However, surface current analysis showed that approximately 35% of the antenna's radiated power is absorbed by the metasurface owing to strong coupling. After relocating the load resistors, the antenna performance improved significantly. S11 increased to −18.61 dB, the axial ratio remains at 1.20 (still below 3 dB), and the gain increased to 7.46 dBi. This represented a gain improvement of 1.81 dB compared to the initial design. The energy harvesting efficiency at 5.8 GHz decreased moderately to 76.10% but remains above 70% over the 5.62~5.89  GHz band. This trade‑off clearly illustrated the co‑design principle of SWIPT systems.

This experiment integrates metasurface electromagnetic manipulation, nonlinear rectifier analysis, and co‑aperture design for energy and information. The co‑simulation workflow using CST for full‑wave simulation and ADS for circuit simulation reflects real engineering practice. Trade‑off optimization helps students grasp the field‑circuit–energy‑information co‑design concept. This project provides a practical, inquiry‑based experimental case for electronic information engineering education.