Substrate Integrated Waveguide-Based Full-Duplex Antenna With Improved Out-of-Band Suppression

Abstract

This brief presents a self-diplexing antenna with harmonic-suppression capability. The suggested antenna operates at 7.8 and 9 GHz and maintains a harmonic suppression of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.17f_{1}$ </tex-math></inline-formula> (where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{1}$ </tex-math></inline-formula> is the lower resonant frequency.) The isolation between two ports is more than 22 dB. The substrate-integrated waveguide (SIW) is used in the construction of the cavity-backed planar duplexing antenna. Starting from a microstrip patch antenna with undesirable high-frequency harmonics, a series of vias are used to suppress those harmonics. Finally, a slot (rotated over 45°) is used to bring the higher order mode to lower frequencies. Moreover, the size reduction in this design is achieved using capacitive slots. Consequently, the proposed antenna suppresses the second, third and fourth harmonics by using two pairs of slots and shorting pins. Besides having a low-profile and offering harmonic suppression, it provides independent frequency tuning in the operating frequency bands by means of capacitive slots. The proposed antenna is built and tested, displaying a reasonable match between the simulation and measurement performances, in this way validating the suggested concept.