Fig. 1. The wave propagation along waveguide surface

Fig. 2. Sinusoidal impedance modulation unit structure

Fig. 3. Dispersion diagram of the proposed SPP unit

Fig. 4. The antenna structure

Fig. 5. Quad-beam LWA photos，simulated and measured S-parameters

Fig. 6. Simulated normalized far-field radiation patterns

Fig. 7. Measured normalized far-field radiation patterns

Fig. 8. The comparison of the measured and simulated antenna peak gain