X-Band Waveguide Filtering Antenna Array With Nonuniform Feed Structure

This paper proposes a novel design approach for a filtering antenna, which contains an array of 4 by 2 waveguide aperture radiation elements. Coupling matrix theory is introduced in this paper to synthesize the multiple coupled-resonators circuit. Unequal amplitude excitation is applied to the <inline-formula> <tex-math notation="LaTeX">$4 \times 2$ </tex-math></inline-formula> elements so as to obtain a low sidelobe level. To demonstrate the concept, an X-band antenna array is designed and fabricated using a three-layer waveguide structure. Measured results show that the filtering antenna array can achieve a gain of more than 15.58 dBi and a radiation efficiency of higher than 90% over the passband (9.91–10.1 GHz). The sidelobe level is −18.3 dB in the <inline-formula> <tex-math notation="LaTeX">${H}$ </tex-math></inline-formula>-plane and −21.1 dB in the <inline-formula> <tex-math notation="LaTeX">${E}$ </tex-math></inline-formula>-plane.