Wideband Substrate-Integrated Waveguide-Fed Endfire Metasurface Antenna Array

A vertically polarized substrate-integrated waveguide (SIW)-fed endfire metasurface antenna array is proposed for wideband operation. Each of the metasurfaces consists of <inline-formula> <tex-math notation="LaTeX">$3\times 3$ </tex-math></inline-formula> rectangular patches and is printed on the two surfaces of a single-layered substrate with a thickness of <inline-formula> <tex-math notation="LaTeX">$0.16\lambda _{0}$ </tex-math></inline-formula> (where <inline-formula> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the wavelength at 32.65 GHz in free space). The antenna is fed at one side of metasurface by an open-end SIW for wideband endfire radiation. The proximity-coupled interdigital strips are introduced between the SIW and metasurface for fault-tolerant coupling. The wideband operating mechanism is revealed by studying the propagation mode and multiple resonant modes of metasurface. To verify the proposed antenna, a <inline-formula> <tex-math notation="LaTeX">$1\times 4$ </tex-math></inline-formula> array is presented with uniform excitation including two SIW Y junctions and an SIW T junction. Moreover, the connected SIW Y junction improved the impedance matching at the low frequencies based on the cavity mode analysis. The proposed design shows that the measured impedance bandwidth (10 dB return loss) is 26.6–38.7 GHz (37%) with the achieved gain of 9.1–13.8 dBi.