Wideband Fish-Bone Antenna Utilizing Odd-Mode Spoof Surface Plasmon Polaritons for Endfire Radiation

A wideband fish-bone-shaped endfire antenna utilizing odd-mode spoof surface plasmon polaritons (SSPPs) is proposed in this communication. Consisting of a microstrip-to-slotline converter and a differential-mode exciter, the feeding structure of this antenna can excite odd-mode signal on the SSPP structure. The fish-bone-shaped SSPP radiator can realize endfire radiation, which is equivalent to a row of small current sources. A tapering end is introduced to the SSPP radiator, realizing broader upper bandwidth. A prototype of this antenna is fabricated. Measured results exhibit that a wide impedance bandwidth of 70.3% (2.4–5.0 GHz) for $\vert \text{S}_{11}\vert < -10$ dB is obtained. Stable endfire radiation patterns and low cross polarization below −20 dB are also realized in the desired frequency band. The gain varies from 4.4 to 8.6 dBi within the whole operating band while a radiating efficiency of 90% can be observed. This antenna has a compact size of $1.36\lambda _{c} \times 0.86\lambda _{c} \times 0.012\lambda _{c}$ ( $\lambda _{c}$ is the free-space wavelength at 3.7 GHz).