This paper presents a comprehensive review of symmetrically shaped antennas in terms of antenna size, dielectric materials, resonating band, peak gain, radiation pattern, simulating tools, and their applications. In this article, flower shape, leaf shape, tree shape, fan shape, Pi shape, butterfly shape, bat shape, wearable, multiband, monopole, and fractal antennas are discussed. Further, a survey of previously reported bandwidth enhancement techniques of microstrip patch antenna like introduction of thick and lower permittivity substrate, multilayer substrate, parasitic elements, slots and notches, shorting wall, shorting pin, defected ground structure, metamaterial-based split ring resonator structure, fractal geometry, and composite right-hand/left-handed transmission line approach is presented. The physics of these techniques has been discussed in detail which is supported by circuit theory model approach.

The progress in mobile communication and the internet of things facilitates multiple features. The trending technology demands wider bandwidth so that user experiences uninterruptedly. The wider bandwidth and the isolation are two key characteristics of modern device antennas. The design of an ultrawideband (UWB) and four-port MIMO antenna is presented in this study. The semicircular monopole patch is modified by including a guitar shape slot on a radiator and a half-circle slot in the lowered ground plane. The structural transformation affects the current path and enhances impedance matching, resulting in a broader bandwidth. The UWB monopole is replicated to construct a four-port multiple input and multiple output (MIMO) antenna. The separation between the interelement is less than the quarter wavelength. As a decoupling structure, the implicit mutual coupling in the MIMO elements is minimized by parasitic elements on the radiator and defected ground plane (DGS). A novel mesh-like structure embedded in radiating plane and DGS couples the current from an excited antenna and suppresses through the DGS correspondingly and improves the isolation. The overall geometry of the antenna is 45×45×1.6 mm3. The UWB MIMO has a measured impedance bandwidth of 113% between 4.5-16.4 GHz and greater than 20 dB of isolation throughout the bandwidth. Besides the mutual coupling reduction, radiation characteristics and all MIMO diversity parameters are studied. The performance of MIMO diversity characteristics is relatively good, with envelope correlation coefficient0.002, diversity gain.10, mean effective gain<-3 dB, total active reflection coefficient<-10dB, channel capacity loss <0.2 bps/Hz, and multiplexing efficiency<-0.5. The experimental and simulated findings are in line and make the projected design suitable for UWB MIMO applications.

A low-profile printed six-port ultrawideband (UWB) antenna with a novel decoupling structure for enhancing port-to-port isolation is analyzed in this paper. Six symmetrical pyramidal form UWB antennas with defective ground structures interspersed with parasitic components served as a unique decoupling structure in the proposed design. The grounded branches and modified rectangular stubs on the ground plane generate closed and open current distribution channels, causing the uniform current flow to be disrupted and the coupling effect to be neutralized. The projected six-port antenna has an electrical dimension of $0.68\times 0.89 \times 0.01\,\,\lambda ^{3}$ ( $\lambda $ is computed using a lower frequency of 2.9 GHz), having a below -10 dB impedance bandwidth of 116% from 2.9 to 11 GHz. Across the impedance bandwidth, the average port-to-port isolation is better than 20 dB. The antenna design has acceptable radiation properties with a peak gain of 8.3 dBi at a frequency of 7.5 GHz. Further, the projected design is also exposed to the time domain characteristics and diversity metrics. Among the different ports, the values of the group delay and fidelity factors are less than 1.5 ns and more than 0.92, correspondingly. The values of the diversity parameters such as ECC < 0.075, DG approximately 10 dB, MEG $ < -3$ dB, TARC $ < -10$ dB, CCL < 0.3 bps/Hz, and ME $ < -2$ dB ensure that the projected design is appropriate for the MIMO applications. The designed antenna is fabricated and measured, and the results are in line with the simulation.

The 5th generation (5G) network was planned to provide a fast, stable, and future-proof mobile communication network to existing society. This research presents a highly compact arc shape structure antenna resonating at 28 GHz for prospective millimeter-wave purposes in the 5G frequency spectrum. The circular monopole antenna is designed with a radius of 1.3 mm. An elliptical slot on the radiating plane aids in achieving an enhanced bandwidth resonating at the frequency of 28 GHz. Including an elliptical slot creates new resonance and helps improve the bandwidth. The antenna has an ultra-compact dimension of 5 × 3 × 1.6 mm³, which corresponds to an electrical length of 0.46λ × 0.28λ × 0.14λ, where λ is free space wavelength at the resonant frequency. The projected antenna has an impedance bandwidth of 15.73 % (25.83–30.24 GHz). The antenna has a good radiation efficiency of 89%, and the average gain is almost 4 dB over the entire impedance bandwidth. The simulated and experimental S11 findings are in good agreement.

This work presents a quad-port Multiple Input Multiple Output (MIMO) wideband antenna that operates in the terahertz (THz) frequency range is designed and analyzed. To improve MIMO performance, a defective ground structure (DGS) is used. A rectangular metallic patch was altered by adding parasitic elements to the radiator with the lowered ground plane on a polyamide substrate in order to achieve the wideband THz operating frequency. The THz antenna was turned into a MIMO antenna by replicating horizontally and vertically with a spacing of 0.05 λ and 0.002 λ, respectively (λ calculated at 1.7 THz). The designed THz MIMO antenna, comprising 40 μm × 46 μm × 2 μm, operates across the 1.7-10.4 THz frequency region. The THz MIMO antenna provides isolation of more than 20 dB in the frequency range of 2.8-10.4 THz and more than 10 dB for the frequency of 1.7-2.7 THz. Isolation augmentation is accomplished by establishing different local current channels using the antenna's DGS. The MIMO diversity properties of the proposed THz MIMO antenna are analyzed and found to be ECC<0.004, DG ~ 10 dB, TARC < -10 dB, MEG < -3 dB, and CCL<0.23 bps/Hz over the antenna's operating frequency.