In this letter, a compact three‐port MIMO antenna with omnidirectional radiation patterns is presented for indoor WLAN applications. The proposed antenna consists of five identical monopoles, one is placed at the center and the other four are sequentially rotated around the center. The central monopole is fed by a microstrip line directly. The other four monopoles are fed by a two‐port feed network that can provide four outputs with equal amplitudes. The phases are progressively increasing in clockwise or anticlockwise direction, depending on the exciting port. All the three ports can generate omnidirectional radiation patterns with the same vertical polarization. The port isolation among the three ports is analyzed in detail. In 2.4 GHz band, the measured port isolation is higher than 15 dB.

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This work proposes a new circularly polarized (CP) 4 × 4 magneto-electric (ME) dipole antenna array using metallic walls for 28 GHz band applications. The ME dipole element is surrounded by eight metallic walls and is excited fed by microstrip line. By introducing metallic walls, the 3-dB axial ratio (AR) bandwidth of the element is increased from 23% to 36.5%. The 4 × 4 array is fed by a simple 1-to-16 microstrip power divider. In contrast to the conventional substrate integrated waveguide (SIW) power divider using two layers, the proposed microstrip divider only needs one substrate layer. The experimental 3-dB AR bandwidth of the array achieves 30.1%, ranging from 22.5 to 30.5 GHz, which falls inside the −10 dB impendence bandwidth. The measured maximum gain is 19.2 dBic.