Low-Pass Filter Based Integrated 5G Smartphone Antenna for Sub-6-GHz and mm-Wave Bands

To maintain the compactness of future 5G smartphones, integration of sub-6 GHz and millimeter-wave (mm-wave) bands is a challenging task due to the large frequency ratio. We, therefore, propose a single-fed triple-band antenna with a large frequency ratio. The proposed antenna is composed of a microstrip patch radiator with an inverted U-shaped slot for dual-band operation in the mm-wave frequencies (28 and 38 GHz). A meandered radiating structure is linked to the microstrip patch radiator through a compact microstrip resonant cell (CMRC) low-pass filter (LPF), which is used for the integration of these structures to be operated at 3.5 GHz. A compact size of 22 mm
$\times10$
mm
$\times0.508$
mm for the proposed antenna was realized by incorporating the radiator slot, an LPF, the truncated ground, and a meandered line structure. Wide, decoupled −10 dB bandwidths of 12.9%, 5.8%, and 2.4% at 3.5, 28, and 38 GHz, respectively, were realized for the proposed MIMO antenna without utilizing an external decoupling structure. A detailed safety study with respect to specific absorption rates and power densities was analyzed in data, reading, and talking modes. Finally, the measurements were performed in an anechoic chamber, and the measured results were in a good correlation with the simulation results.