Mohammad Akbari

This manuscript proposes the design of a 28 GHz antenna system that is capable of generating at the same time five orbital angular momentum (OAM) modes with aligned far-field antenna patterns. The antenna system includes a radial line slot antenna (RLSA), based on radial waveguide technology, which is fed by two Butler networks: one is 8×8 and the other is 16×16. The Butler matrix networks are able to generate various progressive phase states for the RLSA to enable simultaneous generation of five concentric OAM beams with right hand circular polarization (RHCP). The proposed design could be utilized for increasing spectral efficiency by multiplexing a separate data stream onto each transmitted OAM beam and performing partial-aperture OAM reception in line-of-sight (LOS) communications in 6G. The experimental results performed on the antenna prototype reveal the effective performance of the proposed antenna system.

The manuscript presents the design and characterization of a wideband front-end receiver, based on hollow waveguide technology, for the wireless access point (WAP) applications. The Ka-band receiver is comprised of a low-loss beam-switching antenna network (BSAN) with two-dimensional (2D) scanning property. For demodulation, the receiver uses an efficient six-port network (SPN) that is composed of four 90° hybrid couplers and a 90° phase shifter. To suppress the phase imbalance on the entire band of interest, 27 GHz to 33 GHz, a frequency-independent phase shifter with a minimum phase error is suggested. The SPN receiver is integrated with antenna-in-package in waveguide technology to decrease the insertion losses and noise levels at the first stages. To determine the SPN phase errors, a theoretical and experimental analysis of real-time wireless data transmission utilizing phase-shift keying (PSK) and quadrature amplitude modulated (QAM) signal is conducted. Besides, channel capacity along with beamformer influence on channel performance improvement are determined.

A novel high-efficiency 8-beams dual-polarized array antenna using an 8×8 beamforming network is studied and developed at 60-GHz. Two 4×4 Butler matrices are employed as base beamformers, and two 4×8 pattern control networks are utilized for increasing the number of the radiating elements and suppressing sidelobes in the proposed dual left/right-hand circularly-polarized (LH/RH CP) beamforming network. This beamforming network is implemented in hedgehog and hollow waveguide technologies using the diffusion bonding technique. Diffusion bonding, also known as diffusion welding, is a solidstate joining process that is based on the atomic diffusion of elements at the joining interface. The progressive slot technique is used as a traveling-wave antenna for generating a wideband axial-ratio at 60-GHz band from 57 GHz to 64 GHz. The sidelobes are suppressed to lower than -19 dB across the visible scanning range. The operating bandwidth of the system is 10.75% at 60- GHz, and the radiating efficiency of the system is above 90% for each port. The beamforming network is fabricated and measured. The simulated and measured results show a good agreement.

This manuscript introduces a low loss beamformer with a capability of two-dimensional scanning in elevation and azimuth directions at 30 GHz for 5G applications. The proposed beamformer is based on the broadband and highly-efficient rectangular air-filled coaxial line. The beamformer is fed by four standard waveguides (WR-28) as the input ports. Correspondingly, each of the input ports using specific transitions is connected to the coaxial beamformer network. Ultimately, the coaxial transmission lines, in the radiating part of the beamformer, feed a 2×2 waveguide antenna array. The structure is aptly called a waveguide-coaxial-waveguide beamformer. The total dimensions of the fabricated prototype are 60 mm × 60 mm ( corresponding to 6λ × 6λ). The beamformer is able to generate four fixed beams, one in each quadrant at an elevation angle of 25° from the broadside to the array axis. The results demonstrate that the proposed passive beamformer has a radiation efficiency greater than 90% over the frequency bandwidth of interest. Good stability of the radiation pattern and maximum gain over the desired bandwidth were achieved while maintaining sidelobes level of less than 20 dB.

This paper presents four different approaches utilized in beam tilting that are based on the phase gradient (phase shifting) surfaces. Each approach is individually analyzed and then compared to other techniques. Beam tilting is obtained through various techniques by transforming the phase distribution of Fabry-Perot cavity antenna (FPCA) in the near-field region by means of inexpensive and passive surfaces including wedge-shaped dielectric lens (WSDL), discrete multilevel grating dielectric (DMGD), printed gradient surface (PGS), and perforated dielectric gradient surface (PDGS). To enhance efficiency in the millimeter-wave (MMW) band, the FPCA is fed through printed ridge gap waveguide. In addition, considerable enhancement in radiation performance of the antenna at 60GHz is acquired by a partially reflective surface (PRS), including a gain enhancement from 6.5 dB to 22 dB. To validate the suggested methodology and performance of the designs, several prototypes are chosen for fabricating. A satisfactory agreement between the numerical results and experimental ones is achieved. The proposed designs are also applicable for millimeter-wave frequencies especially the narrower band communication system.

This manuscript focuses on the design of a transparent circularly polarized (CP) antenna subarray integrating with CubeSat’s solar panels. The sub-array antenna employs two techniques including the Fabry_Perot cavity (FPC) and sequential rotation-feeding network. These techniques are used to generate CP along with a high level of directivity over a broad bandwidth. The main aim here is to propose a multi-functional antenna with the high radiation properties as well as the capability of power harvesting, simultaneously. To harvest power using a solar panel the transparency requirement should be satisfied. Hence, the proposed design is sputtered with the thin layer of indium-tin-oxide (ITO) with a thickness of 200nm. However, it seems to be sacrificed a large amount of conductivity at the frequency band of interest (x-band). Correspondingly, the performance of conductivity and transparency both the materials of ITO and copper as coated on the proposed design is determined. Alternatively, as an optically transparent conductor (OTC), a combination of both coating layers, including ITO and copper with thicknesses of 200nm and 5nm, respectively, are applied. In the scattering point of view, the proposed design is also capable of suppressing the radar cross section (RCS) for the space missions with the aim of space-based observations.

Advanced! electromagnetic (EM) surfaces, namely meta-surfaces, are designed for multifunctional purposes. A glass material with a chessboard configuration is exploited to realize non-absorbing coating for backscattering reduction. Simultaneously, a solar cell is implemented above the metallic target for light energy harvesting using the transparency feature of the coat. Therefore, two separated aims are obtained in one structure using the plexiglass material and mono solar cell. Initially, EM wave interactions with both materials are determined. Then, by the use of the wave interactions and scattering theory, two different surfaces are investigated analytically with the aim of transparent backscattering reduction cover. Next, an optimization algorithm is employed to achieve the minimum reflection from the adjacent surfaces. To validate the design performance, a prototype is manufactured. The proposed chessboard cover with plexiglass material is numerically and experimentally analyzed and compared together, having an acceptable agreement. The experimental results indicate a 75% bandwidth for backscattering reduction. In addition, the proposed structure can give promising opportunities to enhance the scattering properties with simultaneously power harvesting, which could generate critical advantages for real-world applications.

This paper proposed a wideband, efficient and high gain circularly polarized (CP) array antenna based on gap waveguide technology for 30 GHz frequency band applications. The antenna sub-array is a 2 ×2-slot groove gap waveguide (GGW)-based cavity-backed antenna. The antenna is fed by a ridge gap waveguide (RGW). Two corners of the radiating slots are truncated to obtain CP radiation and some corrugations are introduced to the radiating layer to suppress the surface waves between neighbor sub-arrays. The planar 16-way feeding network based on RGW is utilize to feed the sub-arrays. The feeding network is multi-level sequential phased with a quadrature phase shift. To validate the array antenna performance, a prototype of the antenna has been manufactured using standard milling technology. The measured reflection coefficient bandwidth is about 22 % covering from 28.3 to 35.3 GHz and a measured 3-dB axial ratio bandwidth of about 21.8 % is achieved from 27.8 to 34.6 GHz. The maximum measured gain is 23.5 dBi which is occurred at 30.75 GHz.