Wideband Differential-Fed Filtering Antenna Based on LTCC for 5G Millimeter-Wave Applications

This paper presents a wideband filtering antenna based on Low Temperature Co-Fired Ceramic (LTCC) technology for 5G millimeter-wave applications. The design features a radiation patch, a driven patch and two sets of planar inverted-F antennas (PIFAs). The proposed antenna is fed by a set of differential microstrip lines through aperture coupling. Besides, two pairs of PIFA antennas generate two lower-band radiation zeros, while a set of U-shape slots etched into the ground plane creates an additional upper-band radiation zero. These structures enhance the filtering function while expanding the operational bandwidth to 24.25-29.5 GHz, efficiently covering the 5G n257/n258/n261 frequency bands. The antenna's dimensions are compact, measuring <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.56\lambda_{c}\times 0.56\lambda_{c}\times 0.1\lambda_{c}$</tex> at 28 GHz. The simulation results verify that the impedance bandwidth is 39.1% (23.21-34.5 GHz) and the antenna achieves over 13 dB of gain suppression in the out-of-band frequencies, effectively suppressing unwanted signal gain. The proposed antenna features compact, wideband and filtering characteristics, which is attractive for 5G millimeter-wave mobile communications.