Compact Endfire Coupled-Mode Patch Antenna With Vertical Polarization

Abstract

Coupled-mode patch antenna (CMPA) is able to reform the beam by manipulating the phase of the fringing fields at the edges. In this paper, a method is proposed to realize endfire radiation with vertical polarization based on the concept of CMPA. Besides the phase controlled by the coupling, the asymmetric feeding introduces additional phase shift to one of the radiation slots, which makes the beam pointing to the forward endfire direction within the whole band. The ground of the antenna is truncated to be the same size of the top patch, which eliminates the undesired effect of the ground edge and ensures the symmetric patterns pointing around endfire direction. The size of the antenna itself is only <inline-formula> <tex-math notation= LaTeX >$0.26\\lambda _{0} \\times 0.44\\lambda _{0}$ </tex-math></inline-formula>, where <inline-formula> <tex-math notation= LaTeX >$\\lambda _{0}$ </tex-math></inline-formula> is the free-space wavelength at the center operating frequency. In order to block the unwanted common mode current outside the feeding coaxial cable, a quarter-wavelength balun is applied in the implementation. The fabricated antenna sample has highly selective two-pole <inline-formula> <tex-math notation= LaTeX >$S_{11}$ </tex-math></inline-formula> response with center frequency of 2.41 GHz and 10 dB fractional bandwidth of 2.5%. The simulated and measured patterns confirm the endfire radiation of the proposed antenna. The measured 3 dB bandwidth of realized gain at forward endfire is 2.5% at center frequency of 2.41 GHz, where the realized gain is 2.8 dBi and the front-to-back (F/B) ratio is 17.1 dB. The proposed endfire antenna with vertical polarization has the advantages of its inexpensive and friendly fabrication, compact and simple configuration, and high selectivity.