Compact planar multiple‐input‐multiple‐output antenna with pattern diversity based on the complementary theory

Abstract

A three‐port planar multiple‐input‐multiple‐output (MIMO) antenna system with pattern diversity based on the complementary theory is presented in this letter. Three directional antennas without any directors or reflectors are introduced as the radiating elements, which are rotationally symmetrical and sharing a small ground. The unilateral radiation pattern is achieved for each antenna element based on the complementary theory, where an electric dipole and a magnetic dipole are placed orthogonally and excited simultaneously. An inverted L‐shaped stub is used as the electric dipole. A capacitively loaded loop operated on the zeroth‐order resonant mode is applied as the equivalent magnetic dipole. The capacitive loading is realized with six periodical interdigital left‐handed series capacitors. Furthermore, a defected ground structure between each two ports is adopted to further improve the isolation. The operation mechanism of the proposed MIMO antenna is discussed and experimentally verified. The proposed MIMO antenna system has a measured fractional bandwidth of 7.2% (3.33–3.58 GHz) with |S11| < −10 dB. The port isolation is better than 15 dB and the envelope correlation coefficient is less than 0.0234 in the operation band.

Compact substrate‐integrated waveguide filtering multiple‐input multiple‐output magnetic dipole antenna with high selectivity and high isolation

“…In Pei et al, 7 a two‐port MIMO patch antenna with isolation larger than 18 dB has been presented by using a decoupling resonator to reduce mutual coupling. In Xu et al, 8 a three‐port MIMO antenna has been presented with isolation larger than 15 dB by using pattern diversity. In Zhang and Pedersen, 9 a two‐port MIMO monopole antenna with isolation larger than 22 dB has been presented.…”

Asymmetrical fed Calendula flower-shaped four-port 5G-NR band (n77, n78, and n79) MIMO antenna with high diversity performance

“…There can be different configurations of the MIMO antenna (2 × 2, 4 × 4) which are designed for specific applications and ensure good isolation between them. The MIMO antennas [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] discuss the design methodology and isolation techniques used so that the interference between the neighboring radiators' field radiation is mitigated and hence, all the required results are preserved. A square patch with rectangular ground placed orthogonally maintains isolation of more than 30 dB [1] while a T-type stub attached to the ground between two adjacent radiators [2,3,12] and a tapered feed patch MIMO antenna [4,8] observes better isolation by using rotated L-type strips.…”

“…In an F-shape inverted antenna, a Swastik-shaped repetitive etched structure is applied to improve the isolation [9], and a short stub-loaded resonator with added T-shaped junction in between dual radiating patch [10] and novel elliptical type stub in-ground helps in achieving higher [11]. A unique pair of fractal stub [13, 15, 16] multiband MIMO antenna with a T-shaped stub on the ground [14] and the dual half-cut quasi self-complementary MIMO antenna utilizes no complex decoupling structure for isolation [17]; feather-type circular-shaped loaded radiator achieves isolation by placing the two identical radiators orthogonally or adjacent to each other [18, 19] and a T-type stub etched with semicircular slot also helps in maintaining higher isolation between two radiating elements placed adjacent to each other [20]. The above-discussed MIMO antenna is of 2 × 2 configuration and also different techniques are applied to achieve better isolation in a four-port MIMO configuration.…”