Pejman Rezaei's research while affiliated with Semnan University and other places

A circularly polarized patch array antenna with a metasurface having a polarization conversion feature at 4.975 THz frequency is proposed. The structure consists of a fully metalized grounded patch array with a metasurface on top of the antenna and separated from the array antenna by a silicon dioxide layer. The modified antenna is placed between a symmetrical surface of 11 rows of 25 fishbone-shaped gold metasurface and a ground plane. The optimal antenna structure dimensions have been examined and provided for the designed array. The performance of an array antenna has been investigated from various aspects including gain, bandwidths of impedance, and axial ratio. Placing the metasurface on the microstrip antenna array causes the radiation waves of the antenna source to be converted from the linearly polarized form to circularly polarized waves, which improves the impedance and bandwidth of the axial ratio. In addition, a transmission line model is provided to show how to achieve a suitable axial ratio, which provides a high gain as well. The overall size of the final antenna is 400 × 400 × 3.3 μm³ and provides a gain of 16 dB in the operating bandwidth of 4.71–5.2 THz (i.e., 10%).

The main goal of the designed research is to find a powerful tool for adjusting and tuning polarization in microstrip patch antennas. That surely this practical platform, it is the same as graphene. In fact, the right- and left-hand circular polarization and linear polarization can be achieved by turning on and off the chemical potential in the cuts created on the diagonal edges of the antenna. In the structure of the antenna, a triangular and square scheme of gold has been worked. One of the important features of the presented structure is frequency reconfigurable. According to the requirements of the design, the central frequency of the antenna is set at 0.67 THz. Silicon-Dioxide is considered as the substrate of the design. In the range of 0.65 THz through 0.7 THz, the matching and polarization are suitable. S 11 is less than -14 dB for all types of polarization. Radiation efficiency is estimated about 50%. Eventually, the outputs of return loss, S 11 sweep, axial ratio, radiation efficiency, 2D and 3D far-field radiation patterns, E-field distribution, and current density distribution have been reported.

In this research, two graphene-based THz patch antenna structures for satellite communication and 5G applications is reported. In the unit cell analysis, it can be pointed out that the patch is made of graphene and the substrate is made of silicon dioxide. While its dielectric permittivity is 3.7. The operating frequency of the MIMO antenna is designed at 0.6 THz. In the plan of MIMO reconfigurable antenna, cells are arranged vertically. Reconfigurable conditions can be achieved by changing the chemical potential or in other words the bias voltage of graphene patches. The amount of chemical potential in the original project of both quad-port MIMO reconfigurable antennas is considered to be 0.6 eV. In the results of the first antenna, S 11 is less than -10 dB in the range of 0.58786 THz through 0.63112 THz. In the results of the second antenna, S 11 is less than -10 dB in the range of 0.57814 THz through 0.63391 THz. In the results of the first antenna, maximum efficiency is reported about 65%. In the results of the second antenna, maximum efficiency is reported about 72%. Finally, peak realized gains, radiation efficiencies, far-field 2D radiation patterns, VSWRs, current distributions, envelope correlation coefficients (port1-port2, port1-port3, port1-port4), and diversity gains (port1-port2, port1-port3, port1-port4) have all been reported over the operating frequency band for two antennas.

Ridge gap waveguide is one of the new technologies in the field of waveguides. Their advantages include being planar, low cost of construction, shielding by metal without the need for problems related to packaging, the formation of a narrow gap enclosed between two metal plates, realization of the texture on one of the metal plates and lower losses. These structures have no mechanical connection. While electric currents must flow in them. In this article, two graphene-based ridge gap waveguide coupler structures are presented. The designed structures are used in the THz band. By using graphene in the THz frequency band, frequency reconfigurable can be achieved. S-parameters curves, phase difference diagrams and e-field distributions are reported for two graphene-based ridge gap waveguide couplers.

Substrate Integrated Waveguide (SIW) technology by application of the planar construction process obtains a catchy means for integrating planar and nonplanar circuits. Further, it is hard to realize the negative coupling needed to create a compact quasi-elliptic bandpass filter based on a single-layered SIW structure. The presented work proposes a specific planar and negative coupling configuration that provides two transmission zeroes at 5.03 GHz and 6.26 GHz. This article presents a fourth�order quasi-elliptic filter. The proposed filter is also wide-band. This structure is implemented in SIW knowledge. The SIW filter has a central frequency of 5.5 GHz. The perfect bandwidth is 0.7 GHz. It is realized on a single-layer substrate from Rogers Ro4003. The Thickness of the substrate is considered as 0.508 mm. The measured outcomes of this filter, which show an excellent selectivity, and a low insertion loss of about 1.9 dB, agree suitably with simulation results. The designed filter's innovation provides these features: compact, low cost, wide-band, good selectivity, low insertion loss, and agreement between simulation and fabrication.

In this paper, a graphene-based substrate integrated waveguide antenna is presented. The designed structure is considered very desirable for THz applications. The antenna is operated at a central frequency of 1 THz. While the structure is realized on a silicon dioxide substrate. The SIW antenna displays frequency reconfigurable capability due to the special properties of graphene in the THz regime. The designed structure also provides the ability to miniaturize and compress. While the S11 frequency response is less than −12 dB for the target range (0.1 through 2 THz). Finally, a complete report of magnetic field distribution, current density, electric field distribution, radiation efficiency, 2D & 3D radiation pattern, and graphene-based substrate integrated waveguide antenna input impedance is investigated and studied.

In this article, the design of a microstrip leaf-shaped patch antenna based on a semi-metal substance called graphene is studied. Configuration of the antenna is considered in a method that each of the various sections of the antenna dependent on chemical potential variations can make available a specific radiation status for the far-field of the antenna. Basic aspect of the present plan is to regulate the antenna polarization only by variation of the Fermi energy quantity of its graphene layer. In a way as if it's main physical construction stays unchanged. With this idea, it is achieved the possibility of achieving an antenna with an advantageous matching range in the limit of 0.3 through 1 THz, which can control its polarization in three modes (RHCP, LHCP & LP) for the range of 0.5–0.7 THz with the axial ratio less than 3dB. Remarkably, the physical structure of the antenna produced it feasible for us to attain circular polarization by attaching leaf-shaped layered patches at its edges.