An endfire antenna based on periodically modulated SSPPs TL with unequal modulation periods on the two sides

In this paper, an endfire antenna operating with unequally periodic modulated even mode spoof surface plasmon polaritons (SSPPs) transmission line (TL) is proposed. The unequally periodic modulation on the two sides of the SSPPs TL introduces −1st harmonics with different phase constants. As the wave propagates, the phase on the two sides of the TL changes independently. Therefore, the phase difference of transverse component of the electric field between the two sides could be controlled. In some conditions, the employ of unequal periodic modulation modifies the reverse phase transverse component of the electric field of the even mode to in phase at the end of TL, which solves the problem of the radiation null. After theoretical analysis about the change of phase difference with the change of the modulation periods and length, the endfire radiation condition is given. Accordingly, a single-sided printed SSPPs endfire antenna is implemented. With −1st harmonic wave radiating, the antenna shows a stable endfire radiation beam from 9 GHz to 10.2 GHz with a measured peak gain of 7.8 dBi and simulated average efficiency of 90% over the operating frequency band. In addition, this SSPPs endfire antenna has a compact length of 2.4λ₀. The simulated and measured results are in good agreement during the operating band.