1：Experimental Design and Method Selection:

The antenna design involves an annular open-loop radiator fed by a 50-Ω printed monopole with an impedance transformer, fabricated on an FR4 dielectric substrate. A slit in the ground plane and an air gap on the loop are used to enhance impedance matching and generate circular polarization through travelling-wave distribution. Simulations are conducted to analyze performance.

2：Sample Selection and Data Sources:

The antenna is designed and simulated; no physical samples or external datasets are mentioned.

3：List of Experimental Equipment and Materials:

FR4 dielectric substrate (dielectric constant 4.4, loss tangent 0.02), dimensions 50×50×1 mm3.

4：4, loss tangent 02), dimensions 50×50×1 mm3. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: The antenna geometry is defined with specific parameters (e.g., W=50 mm, r1=13.8 mm, r2=15.8 mm, θ=22°, lt=10 mm, wt=1.5 mm, lf=6 mm, wf=3 mm, lg=14 mm, ls=9.2 mm). Simulations are performed to obtain S11, axial ratio, gain, and radiation patterns.

5：8 mm, r2=8 mm, θ=22°, lt=10 mm, wt=5 mm, lf=6 mm, wf=3 mm, lg=14 mm, ls=2 mm). Simulations are performed to obtain S11, axial ratio, gain, and radiation patterns. Data Analysis Methods:

5. Data Analysis Methods: Simulated results are analyzed for impedance bandwidth (S11 < -10 dB), axial ratio bandwidth (3-dB AR), gain, and radiation patterns using simulation software (not specified).