In this paper, the impact of decoupler type has been analyzed on the performance of planar inverted-F antenna (PIFA)-based multiple-input multiple-output (MIMO) antenna. A T-type and a loop-type decoupler have been employed for the isolation of the MIMO antennas, and the performances of the two cases have been compared. The decouplers have been selected based on their different coupling mechanisms with the dominant ground mode. The antennas have been designed for the ground configuration of a USB dongle operating at 2.45 GHz band. Characteristic mode analysis of the ground plane has been carried out, and the MIMO systems have been analysed based on the coupling among the antenna, decoupler and the dominant characteristic mode of the ground plane. It has been observed that the coupling between the decoupler and the ground mode significantly affects the radiation efficiency as well as the diversity performance of the MIMO antenna.

Here we propose an L-shaped slot-type MIMO antenna with pattern and circular polarization diversity for WLAN applications. In order to maintain a low profile, the pattern and polarization diversities have been achieved without using additional supporting structures. Both the antenna elements are located at the corners of the same side of the ground plane. One of the antenna elements produces left hand circularly polarized (CP) waves whereas the other element produces right hand CP waves in (front) +z-direction. The senses of polarizations are opposite in (backward) −zdirection. CP waves have been generated using two orthogonal current modes, excited by locating the slots on the corner of the ground plane. The quadrature phase difference between the modes has been employed using the slot geometry. In other directions, the antenna correlation has been reduced using pattern diversity. The measured results confirm the simulated ones. The measured axial ratio bandwidth (< 3 dB) and the matching bandwidth (< −6 dB) are 380 MHz and 110 MHz, respectively. The envelop correlation coefficient is less than 0.1 in the operating band.

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The paper presents a ground radiation antenna (GradiAnt) based triple-band MIMO antenna with wideband characteristics for Wi-Fi 6E applications. The GradiAnt is a novel antenna element with a series combination of inductor and capacitor in the feed loop, and dual-band characteristics have been achieved by controlling the impedance level of the antenna. By introducing a parasitic resonator within the feed loop of GradiAnt, triple-band characteristic is achieved, and significant bandwidth enhancement is realized, fully covering the Wi-Fi and Wi-Fi 6E operation bands. The resonator consists of a parasitic strip connected with the ground plane through an inductor. Two identical GradiAnts are symmetrically installed at the corners of the shorter edge of the 55 × 40 mm 2 sized ground plane for MIMO scenarios. A loop-type isolator is installed between the antenna elements to decouple the lower Wi-Fi band where the higher bands are self-isolated. The measured bands with reference to −6 dB are 2.36-2.63 GHz and 4.76-8 GHz. The isolation in the lower and higher bands is greater than 22 dB and 17.5 dB, respectively. The ECC is less than 0.03 in the lower band and 0.16 in the higher bands.