A design of smartwatch integrated antenna with polarization diversity is proposed. An annular ring is integrated in the framework of smartwatch, and excited by two ports. One port is fed by a coplanar waveguide (CPW) line loaded with a T-shaped matching network, and the other is fed by a coplanar strip line (CPS). The overall model of the proposed antenna has a cylindrical shape with 38 mm diameter and 7.5 mm thickness. A metallic plate is located at the backside of the antenna to mimic the shell of smartwatch. The prototype is fabricated and measured, and the measured results agree well with the numerical ones. The two ports have orthometric radiation patterns and can cover the 2.4 GHz wireless local area network (WLAN) band. The gain of the antenna is higher than 3.2 dBi in free space. The proposed antenna is also analyzed with a cubic tissue model and a wrist model in different distances between the proposed antenna and human models. The performances on body scenarios are also acceptable. The values of specific absorption rate (SAR) in the cubic tissue model and wrist model are below the limitations set by both the Federal Communication Commission (FCC) and the European Telecommunication Standards Institute (ETSI). Envelope correlation coefficient (ECC) shows proposed antenna can be used in multiple input multiple output (MIMO) applications. The influence of battery and printed circuits board assembly (PCBA) on S parameters is obvious, and gain and radiation efficiency are not much affected.

A low-profile wideband microstrip antenna is proposed based on the structure of composite right/left-handed transmission lines (CRLH TLs). The dimensions of the proposed antenna are 64 × 64 × 4 mm. The impedance matching bandwidth is 5.05-5.92 GHz (16.5%). The unit cell of the CRLH TLs is a mushroom structure. Several different resonant modes with different radiation patterns are excited to obtain the pattern diversity. Particularly, TM ₁₀ and TM ₂₀ modes are merged to realize a wideband performance with broadside radiation pattern, whereas the TM ₂₀ mode is used to realize a conical radiation pattern. The simulations and measurements are in good agreement, and the envelope correlation coefficient shows that the proposed antenna owns an excellent diversity performance.

A wrist-worn dual-band smartwatch antenna with polarization diversity is proposed for smartwatches. The antenna has a cylindrical structure with a diameter of 33.6 mm and a height of 6.8 mm. The radiated structure is inspired by composite right/left handed-transmission lines (CRLH-TLs) to realize a dual-band operation (2.4 GHz and 5.8 GHz WLAN band). The unit cell of the CRLH-TL is analyzed, and its equivalent circuit model and the dispersion curves are studied for mode analyzation. The +1 and -1 modes of CRLH TL are employed for dual-band operating, and two orthogonal-polarized modes are excited with different types of feeding structure to realize the polarization diversity with low coupling and low envelope correlation coefficients (ECC). The wrist model is built in both simulation and experiment to evaluate the performance of the antenna, which shows a good radiation and diversity performances. The measured degree of freedom (DoF) is 1.92 and the capacity is 17.39 bit/s/Hz with 30 dB SNR. The results of specific absorption rate (SAR) are also studied and they are pretty low. These characteristics of the proposed antenna make it a competitive candidate for wrist-worn wireless body area network devices.

In this letter, a broadband dual-polarized antenna with a very low profile and omnidirectional gain patterns is designed for 1.7-2.7 GHz Long Term Evolution (LTE) mobile communications. The designed antenna is constituted by a miniaturized tapered monopole for vertical polarization (VP) and four planar dipoles arranged in a ring for horizontal polarization (HP). The HP antenna is used as the metal ground of the VP antenna, which can avoid the feeding intersection and solve the problem of impedance matching degradation when distance between the HP antenna and the metal ground of the VP antenna is close. By sharing the partial structure, the designed antenna achieves a compact size of 110 mm × 110 mm × 13 mm and an extremely low height of 0.07 λ _min ( λ _min is the free-space wavelength at the minimum operating frequency). The design achieves an overlapping bandwidth of 45% (1.7-2.7 GHz) with an isolation higher than 20 dB. High efficiency, low cross polarization and good omnidirectivity in the horizontal plane are obtained. The designed antenna is fabricated and measured, and it performs a great consistency between the simulation and measurement.

A metamaterial-inspired varactor-tuned antenna with frequency reconfigurability and pattern diversity is designed. Two different versions of a reconfigurable structure are integrated into a single antenna to excite two different orthogonal patterns, which realizes pattern diversity for MIMO applications. The outer annular Composite Right-/Left-Handed Transmission Line (CRLH-TL) works at the 1 mode and provides a broadside pattern, and the inner circular radiator loaded with split ring resonators (SRR) operates at the 0 mode and radiates an omnidirectional pattern, which realizes pattern diversity. By using surface-mounted varactors, the operating frequencies for the two radiation patterns can be tuned over a wide frequency range, from 1.7 GHz to 2.2 GHz, covering the 1.71–2.17 GHz LTE band, and a low mutual coupling between the two radiators is achieved. The antenna has also been prototyped. The measured results are in good agreement with the simulation results, verifying the proposed concept. The dual-mode MIMO system equipped with the proposed antenna elements is discussed within the context of a 3-D channel model, and it shows a superior array compactness and spectral efficiency (SE) performance compared to scenarios with single-mode elements.

A design approach of a dynamic decoupling network for wearable antennas is proposed in this communication based on common/differential mode theory. A pair of inverted L-shaped antennas (ILAs) is illustrated to verify the design idea and method. Firstly, the ILAs with matching network are designed on a hand-held terminal, and the decoupling network is realized by a horizontal strip and a lumped capacitance inserted between the antenna pair, which is based on the common/differential mode theory. Then, we discuss the influence of the human body on the antenna performances, and show that the differential mode (DM) is more affected by the human body than the common mode (CM). Next, a varactor diode is employed to dynamically adjust the DM impedance, which can guarantee that the antennas have good impedance matching and isolation in the both scenarios of in free space and on human body. Finally, to verify the feasibility of the proposed method, the proposed antenna pair with the decoupling network is fabricated and tested in the free space and on human body, respectively, while the measured results agree well with our analyses. The proposed design approach shows considerable promise for the design of future MIMO antennas for wearable devices.