Ahmed H. Abdelrahman

Transmission Phase Limit of Multilayer Frequency-Selective Surfaces for Transmitarray Designs

Many transmitarray antennas are designed with multilayer frequency-selective surface (M-FSS) type elements. The goal of this paper is to reveal the transmission phase limit of M-FSS for transmitarray antenna designs. An analytical study of the transmission coefficient of multiple conductor layers separated by dielectric materials has been carried out, and the maximum transmission phase range has been determined according to the number of layers, substrate permittivity, and separation between conductor layers. It is revealed that the -1-dB transmission phase limits are 54°, 170°, 308°, and full 360 °for single-, double-, triple-, and quad-layer FSS consisting of identical layers, respectively. Furthermore, it is shown that if -3-dB criteria is used, a triple-layer FSS is sufficient to achieve the full 360 ° phase range. The effectiveness of the analytical study has been validated through numerical simulations of several representative FSS examples.

Transmitarray Antenna Design Using Cross-Slot Elements With No Dielectric Substrate

The transmitarray antenna has received considerable attention in recent years as it combines the favorable features of the lens antenna and the array techniques. The goal of this letter is to present detailed design analysis of a multiple-conductor-layers transmitarray antenna using slot-type element with no dielectric substrate. A transmitarray antenna using quad-layer cross-slot elements has been designed, fabricated, and tested for 11.3 GHz operating frequency. The measured gain of the prototype transmitarray is 23.76 dB at 11.3 GHz. It is observed that the oblique incidence and the wave polarization have strong effect on the transmission coefficient of the slot-type element. Thus, a detailed analysis of the transmitarray considering the oblique incidence angles and the feed polarization conditions is performed with good agreement between the simulation and measured results.

High-Gain and Broadband Transmitarray Antenna Using Triple-Layer Spiral Dipole Elements

A triple-layer transmitarray antenna has been designed, fabricated, and tested at X-band. Using a spiral-dipole element, a full transmission phase range of 360 ° is achieved for a transmission magnitude equal to or better than -4.2 dB. The transmission phase distribution of the transmitarray elements has been optimized to reduce the effects of the lossy elements with low transmission magnitudes on the antenna gain, leading to an average element loss as low as 0.49 dB. The measured gain of the transmitarray prototype is 28.9 dB at 11.3 GHz, resulting in a 30% aperture efficiency. Antenna bandwidths of 9% for 1-dB gain and 19.4% for 3-dB gain are achieved in this design.

Bandwidth Improvement Methods of Transmitarray Antennas

Despite several advantages of planar transmitarray antennas compared to conventional lens antennas, they have a narrow bandwidth. The goal of this paper is to improve the bandwidth of transmitarray antennas through the control of the transmission phase range and the optimization of the phase distribution on the transmitarray aperture. To validate the proposed approaches, two quad-layer transmitarrays using double square loop elements have been designed, fabricated, and tested at Ku-band. The transmission phase distribution is optimized for both antennas, while they differ only in the transmission phase ranges. It is shown that the transmitarray antennas designed using the proposed techniques achieve 1-dB gain bandwidth of 9.8% and 11.7%, respectively. The measured gains at 13.5 GHz are 30.22 and 29.95 dB, respectively, leading to aperture efficiencies of 50% and 47%, respectively.

Single-Feed Quad-Beam Transmitarray Antenna Design

We present a design methodology for single-feed multibeam transmitarray antennas through case studies of quad-beam designs. Different far-field pattern masks and fitness functions are studied for multibeam designs, and the particle swarm optimization (PSO) technique is implemented for aperture phase synthesis. A quad-layer configuration of double square loops is used for the transmitarray elements, and a quad-beam transmitarray prototype is fabricated and tested. The effects of various approximations in unit-cell analysis are also investigated in detail. The Ku-band prototype generates four symmetric beams with 50° elevation separation between the beams and gains around 23 dB.

Analysis and design of wideband transmitarray antennas with different unit-cell phase ranges

Despite the numerous advantages of planar transmitarray antennas over conventional lens antennas, transmitarrays have a narrow bandwidth. The goal of this paper is to present a design methodology for improving the bandwidth of transmitarray antennas through control of the transmission phase range of the transmitarray elements. Two Ku-band transmitarrays using quad-layer double-square loop elements, which differ in the transmission phase ranges, have been designed and compared. It is shown that the transmitarray antenna designed using the proposed methodology achieves a 10.1% bandwidth as compared to the 7.0% bandwidth of the conventional design.

Transmitarray antenna design using slot-type element

Many transmitarray antennas are designed with multilayer frequency selective surface type elements. The goal of this paper is to present a multiple conductor layers transmitarray antenna using slot-type element with no substrate material. A quaternary-layer transmitarray antenna using cross-slot elements has been designed, fabricated, and tested for 11.3 GHz operating frequency. The measured gain of the prototype transmitarray is 22.06 dB. It is observed that the oblique incident associated with the excitation and the polarization direction has a strong effect on the antenna radiation pattern and gain.

Design of wideband unit-cell element for 5G antenna arrays

The previous generations of cellular networks are almost packed in the UHF band with a frequency range of 300 MHz-3 GHz in the radio spectrum. Recently, the Ka-band is under investigation to be commercially used in next generation of cellular systems, due to the spectrum availability and the small size of the components. The main purpose of this paper is to design a wideband antenna element at 28 GHz, so that it can be used in the antenna arrays of next generation mobile networks. The proposed unit-cell is a proximity coupled stacked patch antenna. The antenna parameters and characteristics are investigated both through simulation and measurement. The antenna achieves a measured gain of 7.1 dB at 28 GHz. The measured impedance bandwidth and 1-dB gain bandwidth are 34.48 % and 17.4 %, respectively.

Design of single-feed multi-beam transmitarray antennas

The feasibility of designing single-feed transmitarray antennas with simultaneous multiple beams is investigated in this paper. Different far-field pattern masks and fitness functions are studied for multi-beam designs, and phase synthesis is achieved using the particle swarm optimization technique. A quad-layer configuration using double-square rings is selected for the transmitarray elements, and several designs of quad-beam transmitarray antenna are studied. A Ku-band symmetric quad-beam antenna with 50° elevation separation between the beams is demonstrated.

Wideband subarray design for 5G an antenna arrays

There is a global trend towards migrating to millimeter wave frequencies in the fifth generation of mobile communications (5G) to further enhance the available capacity and data rates. Antenna arrays are usually applied to overcome the innate high path loss at the millimeter wave (mmW) frequency band. Moreover, the use of subarrays decreases design complexity and system cost. The goal of this paper is to present a design of a wideband subarray at the frequency range from 28 GHz to 32 GHz, i.e. the frequency range applied for Local Multipoint Distribution Service (LMDS), to be used in the antenna array design of next generation mobile networks. The proposed subarray consists of four radiating elements of proximity coupled stacked patch antennas. The unit-cell is first designed, fabricated and tested, which confirms the wideband coverage along the required band. The proposed subarray achieves a simulated gain that ranges between 11.1 dB and 12 dB along the frequency band from 28 GHz to 32 GHz. The impedance bandwidth and the 1-dB gain bandwidth are 30% and 21.2%, respectively.