Miniature differential-mode dual-band antenna module embedded with broadband balun

A miniaturized dual-band differential-mode antenna with a broadband 1:1 balun is integrated in a 1-mm thick multi-layer PCB substrate. A broadband balun for the 2.5 GHz and 5.2 GHz dual-band, was designed and fabricated with a broadside-coupled line structure. With a proposed deembedding method, mixed-mode S-parameters of the unit balun were extracted with measured data. Simulated and measured return losses were better than 12 dB in the dual-band. With the balun, a miniaturized dual-band antenna embedded with lumped-elements was integrated. The lumped elements were also used for impedance-matching with the balun. The size is 60 % smaller than the half-wave dipole antenna. Measured return loss of the integrated antenna connected to a coaxial cable was 15.3 dB at 2.5 GHz and 24.1 dB at 5.2 GHz. Measured gain was almost omni-directional in both the bands. The maximum gain was -0.5 dBi at 2.5 GHz and 1.1 dBi at 5.2 GHz.