A novel design is introduced for dual-band operation at 28/38 GHz for improving microstrip antennas. Also, the design support circularly polarized antenna that works in millimetre band applications. This proposed antenna is attached to a circular hole in the centre of the patch with four slits embedded in the corners. Also, small holes are etched at sides of the patch to achieve the resonant frequencies and improve the return loss value with achieving very wide band at 38 GHz. A single-feed circularly polarized antenna at 28 GHz and 38 GHz with return loss − 30 dB and − 42 dB, respectively, which makes it suitable for operation at 5 G wireless communication designs. A single element design can cover the frequency ranges of 27.6–28.3 GHz at 28 GHz with bandwidth 2.5% and 35.2–47.2 GHz at 38 GHz with very wide bandwidth 32.4%. Simulated results show that the proposed antenna has good circular polarization in both frequencies of left-hand circular polarization (LHCP). On the other hand, MIMO antenna with four ports is constructed. The four ports are arranged at the corner and middle of substrate with dimension 100 × 75 × 0.508 mm3. Meanwhile, resonant implementation frequencies in a millimetre wave of the MIMO achieved more mutual coupling minimization that effectively accomplished <− 36 dB. In addition, the numerical and experimental results are achieved to evaluate the performance of both single- and four-port MIMO antennas. The diversity gain (DG), envelop correlation coefficient (ECC), total active radiation coefficient (TARC) and channel capacity loss (CCL) also are calculated, and the results are suitable for 5 G applications.