Miniaturized, Low-Profile, Triple-Band Microstrip Antenna and its Four-Antenna Module for Smartphone Applications

A miniaturized, low-profile, triple-band, and four-port multi-input multi-output (MIMO) microstrip antenna module (MAM) is proposed for smartphones. First, a planar integrated L-shaped capacitively coupled feeding probe, a stepped slot, and a grounding via are sequentially exploited. As a result, TM0,1, TM1,1, and quasi-TM2,0 modes are independently manipulated to make a microstrip antenna (MA) operate in the 2.4-GHz WLAN, fifth-generation (5G) N78, and N79 bands, respectively. Both good impedance matching and radiation properties are realized with a small volume of $28.4\times 28.4\times 1$ mm3. Then, a triple-band four-port MIMO MAM is constructed by sequentially rotating the proposed antenna element. As a validation of the concept, the proposed integrated four-port antenna module with an electrical volume of only $0.48\lambda _{\text {L}} \times 0.48\lambda _{\text {L}} \times 0.008\lambda _{\text {L}}$ is fabricated and experimentally tested, presenting a good consistency between the measurements and simulations. Without adding any extra decoupling structures between antenna elements, port isolations are better than 15.9 dB and envelope correlation coefficients (ECCs) are lower than 0.07, respectively. Compared with the existing triple-band four-MAMs, the proposed one is with the advantages of small volume, easy integration, and high isolation for 5G smartphone and terminal applications.