A millimeter-wave (mm-wave) antenna with enhanced gain for new 5G networks is introduced in this work. A rectangular slot antenna operating at the fundamental mode of the desired frequency band is utilized in this study. The antenna gain is improved by employing a Frequency Selective Surface (FSS). The FSS-based reflectors are designed at the same fundamental mode of the antenna and added under the antenna at a specific distance to achieve the required gain enhancement with a suitable dimension of 25 × 25 × 5 mm³. The antenna gain is increased by around 5.3 dBi when the FSS-based reflectors are added under the antenna. The antenna and the FSS are fabricated and tested. The antenna has tested outcomes without FSS with S₁₁ ≤ -10 dB from 26 GHz up to 29.8 GHz and realized gain of around 4.5 dBi within the entire frequency band and radiation efficiency of around 93 %. While the antenna with FSS has achieved bandwidth with S₁₁ ≤ -10 dB from 25.5 GHz up to 30.8 GHz and realized gain around 10.3 dBi at 28 GHz and radiation efficiency around 90 %. The simulated and tested outcomes have the same trend which validates the suggested antenna to be operated in the new 5G applications. All simulation results are completed using the CST Microwave Studio.

This paper proposes the design of a compact sub-6 GHz four-port flexible antenna for utilization in 5G applications. A two-arm monopole with a coplanar waveguide feed line printed on a flexible substrate was proposed to shape the single-element antenna. The single element was designed, fabricated, and measured first; then, four copies of the single element were organized on a single flexible substrate to compose the four-port antenna. The MIMO antenna was simulated, fabricated, and experimentally measured. All the simulations and measurements of the flexible single element and MIMO antennas are presented. The presented MIMO antenna showed good impedance characteristics, with a deep level of −24 dB from 3 to 4.12 GHz. The antenna had omnidirectional and bi-directional patterns in the φ = 0° and φ = 90° planes. As an important parameter evaluation for MIMO, the mutual coupling between the different ports was investigated. The diversity gain (DG), the total active reflection coefficient (TARC), the mean effective gain (MEG), the envelop correlation coefficient (ECC), and the channel capacity loss (CCL) parameters were investigated and showed good performance. All the obtained simulation results were in a high degree of agreement with the measurement results, supporting the usage of the suggested antenna in 5G communications.

This paper presents the design and analysis of a new compact quad-band metamaterial absorber (MMA). The proposed structure is constructed as an array of 12x13 unit cells, each one is based on a combination of interlaced I/square resonators supporting four distinct resonant frequencies. The proposed metamaterial unit cell is printed on FR-4 substrate with thickness 1.5 mm and size 20 mm × 20 mm. The MMA structure exhibits four distinct absorption peaks at 2.248, 2.878, 4.3 and 5.872 GHz with absorption rates of 96, 93, 93, and 95 %, respectively, under normal incidence. This design achieves a negative permittivity and permeability that is applicable for S-band and C-band operating frequencies. The MMA unit cell structure has a 3-dB bandwidth of 78, 89, 144 and 202.6 MHz. The proposed structure has compactness of 0.15 λ0 × 0.15 λ0 with thickness of 0.0112 λ0, where λ0 is the free-space wavelength with respect to the lowest resonance frequency (2.248 GHz). The input impedance, surface currents and electric field distributions are shown to illustrate the mechanism of the structure. The design has been fabricated showing a good agreement between simulated and measured results. The proposed absorber structure can be used in different applications such as electro-magnetic protections, as well as military and medical applications. All simulation results are performed using the Computer Simulation Technology (CST), Microwave Studio 2018 software and Mathwork simulation tool MATLAB ver. 2011.

This letter presents a triple-band antenna with circular polarization (CP) behavior embedded in a lossy tissue for bio-telemetry applications. The triple bands are the Industrial, Scientific, and Medical (ISM) (868-868.6 MHz and 2.4-2.4835 GHz) bands and the midfield band at (1.824-1.98) GHz. These bands are used for physiological information telemetry, power-saving, and wireless power transfer (WPT) in medical devices. CP behavior at three bands is the key feature of the designed implantable antenna, compared with literature dual-band CP antennas. Moreover, the size of the designed antenna is compact of 50.8 mm$^{3}$. Finally, the specific absorption rate (SAR) and link margin are calculated for the consideration of health safety and reliable communication aspects.

In this paper, single-layer ultra-Wide Band (UWB) microstrip patch antennas loaded with asymmetrical U-shaped slot in both microwave and millimeter wave applications are presented. These novel antennas cover a fractional bandwidth around 40% in both microwave and millimeter applications. The applications cover the C-band (4–8) GHz, V-band (40–75) GHz, and W-band (75–110) GHz. In addition to that, it is the sole article that cover the bands (5.15–5.825) GHz and (8.025–8.4) GHZ for WiMaX and ITU band applications, respectively. Moreover, it covers three bands for Automotive radar applications within (71–76) GHz, (81–86) GHz, and (92–95) GHz, in addition to further 5G/mm-wave applications at 60 GHz. Each antenna is coaxial fed and implemented on a Roger 5880 substrate with relative dielectric constant of 2.2, thickness of $1.575~mm$ and loss tangent of 0.0009. They operate over the frequency band (5.5–9.5) GHz for microwave band and (55–95) GHz for mm-wave band. To achieve either a notch in other bands or develop a multi-band structure, the conventional ground is replaced by two different structures. The first ground is an array of patches and the other is a mushroom ground. The first ground results in a notch within the band (73–79) GHz while the second one achieves a multi-band within (55–68) GHz and (81–95) GHz. Both antennas are simulated and verified using Finite Difference Time-Domain analysis (FDTD); CST Microwave Studio and Finite Element Method (FEM); Ansoft HFSS. For microwave band, the antenna is fabricated and measured for verification. Concerning the mm-wave version, three different types of ground planes are presented; traditional, periodic structure of patches and mushroom. The structure with periodic patches conducts the same band as the traditional ground plane does. This is a prestep for the design of the notches. The mushroom ground is carried out for multi-band applications. The average gain of the antennas is 7 dB.The measured two dimensional cuts of the radiation pattern, radiation efficiency, and reflection coefficient of the microwave version are presented and are in good agreement with the simulated results while for the mm-wave antenna the same parameters are simulated with two different methods and are in good agreement.