Series-fed millimeter-wave antenna array based on microstrip line structure

This paper presents a millimeter wave series-fed microstrip line antenna array with low side lobes. For millimeter-wave beam forming applications, compact series fed arrays with very small horizontal width and low side lobes are very much required. The proposed array consists of a microstrip line with periodically placed stepped inverted-cone stub sections at a guided wavelength spacing. Surface current cancellation at each guided wavelength in an ideal microstrip line can be altered by symmetrically introducing the inverted-cone stub sections on two edges with a half wavelength offset. By controlling the dimensions and location of the inverted-cone stub sections, the equivalent surface currents can be altered and focused on the cone stub sections, resulting in an effective array radiation. The fabricated antenna array is resonating at 28 GHz and has an impedance bandwidth of 1.3 GHz. Peak realized gain of 10.2 dBi is achieved at 28 GHz and the measured side lobe levels are better than −15 dB in the E and H plane. The proposed microstrip line antenna array with low side lobes also benefits from simple fabrication and high integration ability, which makes it attractive for compact beamforming scenarios in millimeter-wave bands.