| With excellent user experience of mechanical strength and aesthetics, metal-ringframe(MRF) smartphones are very popular nowadays. However, the large metal parts plays very significant impact for the antenna performance, especially when the mobile antenna is embraced by a full metal frame, the electromagnetic radiation energy would be mostly fettered near the phone instead of radiating beyond. The coupling between the antenna and the adjacent metal ring is very intensive. Therefore, it is a great challenge and hot spots for antenna engineers to design multiband and compact antennas for MRF smartphones applications.Concerning to the integrative design of antennas and metal frame for smartphones this paper takes notice of the distributed characteristics of metallic bezel in smartphones and proposes a design approach on the basis of coupled-fed principle to deal with the metal-ring-frame antenna at first. When the metal ring is modified as distributed coupling strip, the high Q value of the antenna system by metal boundary would be effectively reduced. But also, the coupling resonances of the made metal-ring frame would be applied at the operating band of mobile phone antenna. It is important that the metal-ring resonances could be used to cover the lower band radiation of antenna, which would vastly reduce the size occupation of internal antenna.Secondly, this paper put forward a six-band distributed coupling metal-ring-frame antenna. A driven monopole feeds two slots on the ground, which works as primary resonant element of antenna. While two grounding straps and two symmetric insert slits are applied to modify the coupling metal-ring frame as distributed parasitic element of antenna, which was motivated its metal-ring resonances covering the bandwidth of824-960 MHz.Thirdly, a seven-band coupled-fed antenna for the WWAN/LTE metal-ring-frame smartphone applications is proposed. Coupling excitation is driven by a 27.5×10-mm2 meandering monopole antenna on the system board, and the metallic bezel with two shorting points and two symmetric breakpoints is made as the distributed coupling element, which achieves frequency banding coverage of GSM850/900/LTE2300/2500.Fifthly, a miniaturized antenna with multi-resonances characteristic is presented for hepta-band WWAN/LTE narrow-frame and metal-rimmed smartphones. This schememakes full use of the distribution characteristics of the metal bezel border to compose a monopole slot resonance path, a monopole resonance path and a closed slot antenna resonant path which cover operation band GSM850/900/1800/1900/LTE2500.Moreover, occupying a narrow no-ground clearance of 44.5×5 mm2 on the system circuit board corner, the printed antenna owns a slim edge of 5 mm only, which could be tailored for the narrow-frame smartphone applications to gain a larger touch screen size.The reflection coefficient(S11) and the radiation pattern, efficiency and peak gain of these three proposed antennas are tested by near-field and far-field experiment. The measured results are well consistent with the simulated ones, and achieve the greater than 6 dB of return loss and more than 40% of the radiation efficiency in operating bands. In addition, the return loss of antennas with hand loaded and the SAR values of antennas with head model are also simulated or tested. With regard to all of the simulating or testing results, the antennas’ performances are still standing to meet the requirements of mobile phone communication. It is feasible that the metal-ring-frame resonances play for antenna radiation. It is also indicate that the proposed antennas are promising for practical wide band MRF smartphones with excellent aesthetic consideration and enhanced mechanic sturdiness. |
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