Design and Experimental Validation of a 12 GHz High-Gain 4 × 4 Patch Antenna Array for S21 Phase-Based Vital Signs...

Area of Science:

• Electromagnetics
• Biomedical Engineering
• Microwave Engineering

Background:

• Non-contact vital signs monitoring using microwave radar offers unobtrusive detection through clothing.
• The sensitivity of radar-based vital signs monitoring relies heavily on antenna system performance, particularly the forward transmission coefficient S21.
• Existing antenna designs may not provide sufficient gain and beam directivity for reliable detection of subtle physiological signals like heartbeats.

Purpose of the Study:

• To design, optimize, fabricate, and validate a high-gain 12 GHz microstrip patch antenna array for enhanced phase-based vital signs monitoring.
• To investigate the impact of antenna gain and beamwidth on the detectability of respiration and heartbeat.
• To provide practical design guidelines for high-sensitivity non-contact vital signs monitoring systems.

Main Methods:

• Design and progressive optimization of a 4x4 microstrip patch antenna array using techniques like coaxial feeding, slot-based impedance control, stepped transmission line matching, and mitered bends.
• Electromagnetic simulation and performance evaluation, including gain, reflection coefficient, and total efficiency.
• Experimental validation in an anechoic chamber and integration into a continuous-wave Vector Network Analyzer (VNA)-based radar system.
• Comparative measurements with different antenna types (biconical, single patch, MIMO) under identical conditions.

Main Results:

• The designed antenna array achieved a simulated gain of 17.8 dBi and a measured gain of 17.06 dBi at 12 GHz, with a reflection coefficient of -26 dB and total efficiency near 74%.
• Respiration detection was possible with moderate-gain antennas, but reliable heartbeat detection necessitated the high-gain, narrow-beam proposed array.
• The proposed array demonstrated significantly improved pulse detectability in the 1-1.5 Hz band without advanced signal processing, highlighting enhanced phase sensitivity.

Conclusions:

• Antenna design plays a critical role in the performance of S21-based biomedical radar systems for vital signs monitoring.
• High-gain, narrow-beam antennas are essential for achieving reliable non-contact heartbeat detection by increasing phase sensitivity and mitigating environmental clutter.
• The developed 12 GHz antenna array offers a practical solution for high-sensitivity non-contact vital signs monitoring, providing valuable design insights for future systems.