A Broadband Quad-Mode Dual-Band Dual-Sense Circularly Polarized Series-Fed Array Antenna for Wearable Applications

A compact, broadband, quad-mode dual-band dual-sense circularly polarized (CP) series-fed array antenna for wearable applications is presented. The proposed design integrates a two-port sequentially rotated series-fed network, four chamfered-corner crossed-slot square patches, and a ground plane on a single semi-flexible substrate. The sequential feeding network achieves a ±90° phase shift between elements at two distinct frequencies, enabling dual-band dual-sense circular polarization. To miniaturize the antenna and maintain optimal inter-element spacing, the series-fed configuration is folded, reducing cross-polarization. The polarization sense is controlled by the traveling wave direction and can be reversed by switching the excitation port, enabling quad-mode CP operation. This design enhances frequency coverage, supports multiple frequency bands, and improves polarization diversity by accommodating both left-hand circular polarization and right-hand circular polarization. These features reduce interference and ensure reliable communication with high isolation between modes. Measured results in free-space and fresh pork environments align closely with simulations. Additionally, the simulated specific absorption rate meets the US safety standard, confirming the method's suitability for wearable applications.