In this paper, we have presented the simulation results of a rectangular microstrip patch antenna at terahertz (THz) frequency ranging from 0.7 to 0.85 THz. THz electromagnetic wave can permit more densely packed communication links with increased security of communication transmission. The simulated results such as gain, radiation efficiency and 10 dB impedance bandwidth of rectangular microstrip patch antenna at THz frequencies without shorting post configuration are 3.497 dB, 55.71% and 17.76%, respectively, whereas with shorting post configuration, corresponding parameters are 3.502 dB, 55.88% and 17.27%. The simulation has been performed by using CST Microwave Studio, which is a commercially available electromagnetic simulator based on the method of finite difference time domain technique.

Rectangular Microstirp Patch Antenna Design at THz Frequency for Short Distance Wireless Communication Systems

To support the ever-increasing demand on connectivity and datarates, multiple beam antennas are identified as a critical technology for the fifth generation (5G), the sixth generation (6G) and more generally beyond 5G (B5G) wireless communication links in both terrestrial networks (TNs) and non-terrestrial networks (NTNs). To reduce the cost and power consumption, there is a marked industrial interest in adopting analogue multiple beam antenna array technology. A key sub-system in many of such antenna arrays is the circuit type multiple beamforming network (BFN). This has led to a significantly renewed interest in and new technological developments of Butler matrices, Blass matrices, and Nolen matrices as well as hybrid structures, mostly at millimeter-wave frequencies. To the best of the authors’ knowledge, no comprehensive analysis and comparison of circuit type multiple BFNs have been properly reported with focus on 5 G and 6 G applications to date. In this paper, the principle of operation, design, and implementation of different circuit type multiple BFNs are discussed and compared. The suitability of these sub-systems for 5 G and B5G antenna arrays is reviewed. Major technology and research challenges are highlighted. It is expected that this review paper will facilitate further innovation and developments in this important field.

Circuit Type Multiple Beamforming Networks for Antenna Arrays in 5G and 6G Terrestrial and Non-Terrestrial Networks

We present a hybrid dual-gain integrated external cavity laser with full C-band wavelength tunability. Two parallel reflective semiconductor optical amplifier gain channels are combined by a Y-branch in the Si3N4 photonic circuit to increase the optical gain. A Vernier ring filter is integrated in the Si3N4 photonic circuit to select a single longitudinal mode and meanwhile reduce the laser linewidth. The side-mode suppression ratio is ∼67 dB with a pump current of 75 mA. The linewidth of the unpackaged laser is 6.6 kHz under on-chip output power of 23.5 mW. The dual-gain operation of the laser gives higher output power and narrower linewidth compared to the single gain operation. It is promising for applications in optical communications and light detection and ranging systems.

Hybrid dual-gain tunable integrated InP-Si 3 N 4 external cavity laser

This work presents a 28-GHz Butler matrix based switched-beam antenna for fifth-generation (5G) wireless applications. It integrates a 1 × 4 microstrip antenna, a 4 × 4 Butler matrix, and a single-pole four-throw (SP4T) absorptive switch in a single planar printed circuit board and is housed in a metal enclosure. Co-integration of a packaged switch chip with the Butler matrix based switched-beam antenna greatly enhances the form factor and integration level of the entire system. A wideband two-section branch line coupler is employed to minimize the phase and magnitude errors and variations of the Butler matrix. The aluminum metal enclosure stabilizes the electrical performances, reduces the sidelobes, and improves the structural stability. The fabricated antenna with the metal enclosure assembled has a dimension of 37 × 50 × 6.2 mm3. With an RF input signal fed to the antenna’s input port through a single Ka-band connector, and the switching states chosen by 2-bit dc control voltages, the antenna successfully demonstrates four directional switched beams. The beam switching operations are verified through the over-the-air far-field measurements. The measured results show that the four beam steering directions are −43°, −17°, +10°, +34° with side lobe levels < −5.3 dB at 28 GHz. The antenna also shows reasonably wideband radiation patterns over 27–29 GHz band. The 10-dB impedance bandwidth is 25.4–27.6 GHz, while a slightly relaxed 8-dB bandwidth is 25.2–29.6 GHz. Compared to previous works, this four-directional switched-beam antenna successfully exhibits the advantages of high integration level and satisfactory performances for the 28-GHz 5G wireless applications.

A 28-GHz Switched-Beam Antenna with Integrated Butler Matrix and Switch for 5G Applications.

The next generations of wireless communications are promising high capacity, low latency, and high throughput, enabled by millimeter wave spectrum. Beamforming and beam steering are key requirements for millimeter wave systems due to the fundamental limitations of such high frequencies. Traditional phased array antennas are narrow band and conventional beamforming techniques are too bulky, energy hungry, and expensive to integrate into consumer electronics. Therefore, new approaches of beamforming and beamsteering are required for 5G and beyond due to shortcomings of existing technologies. Here we present a comprehensive review of the photonic true time delay units for application in beamforming of next generations of wireless communications. The prospects and progress of several photonic techniques are discussed here along with their challenges. The fundamental focus of this endeavor will be on the on-chip Silicon-on-Insulator based approaches which enable utilizing conventional CMOS fabrication process for integration with other optical components for compact photonic integrated circuit.

Photonic Beamforming for 5G and Beyond: A Review of True Time Delay Devices Enabling Ultra-Wideband Beamforming for mmWave Communications

Millimeter wave (mm-Wave) technology is likely the key enabler of 5G and early 6G wireless systems. The high throughput, high capacity, and low latency that can be achieved, when mm-Waves are utilized, makes them the most promising backhaul as well as fronthaul solutions for the communication between small cells and base stations or between base stations and the gateway. Depending on the channel properties different communication systems (e.g., beamforming and MIMO) can accordingly offer the best solution. In this work, our goal is to design millimeter wave beamformers for switched beam phased arrays as hybrid beamforming stages. Specifically, three different analog beamforming techniques for the frequency range of 27–33 GHz are presented. First, a novel compact multilayer Blass matrix is proposed. Second, a modified dummy-ports free, highly efficient Rotman lens is introduced. Finally, a three-layer true-time-delay tree topology inspired by microwave photonics is presented.

https://www.mdpi.com/2079-9292/9/8/1331/pdf

Design of True Time Delay Millimeter Wave Beamformers for 5G Multibeam Phased Arrays

In this work, we present a rigorous full-wave eigenanalysis for the study of nanoantennas operating at both terahertz (THz) (0.1–10 THz), and infrared/optical (10–750 THz) frequency spectrums. The key idea behind this effort is to reveal the physical characteristics of nanoantennas such that we can transfer and apply the state-of-the-art antenna design methodologies from microwaves to terahertz and optics. Extensive attention is given to penetration depth in metals to reveal whether the surface currents are sufficient for the correct characterization of nanoantennas, or the involvement of volume currents is needed. As we show with our analysis, the penetration depth constantly reduces until the region of 200 THz; beyond this point, it shoots up, requiring volume currents for the exact characterization of the corresponding radiating structures. The cases of a terahertz rectangular patch antenna and a plasmonic nanoantenna are modeled, showing in each case the need of surface and volume currents, respectively, for the antenna’s efficient characterization.

An Eigenmode Study of Nanoantennas from Terahertz to Optical Frequencies

A novel Green’s function-free characteristic modes formulation is introduced in this work. The desired impedance or admittance matrix is obtained utilizing and appropriately modifying the versatile finite element method. For this purpose, the generalized eigenvalue problem of the electric or magnetic field vector wave equation is formulated. In the case of the electric field wave equation, using the Schur complement, the system is reformulated and expressed only in terms of the tangential electric field over the radiating apertures, retaining the equivalent magnetic currents. Similarly, in the case of the magnetic field wave equation, the electric current density on radiating metallic surfaces is isolated using the Schur complement. In both cases, the obtained matrix is split into its real and imaginary part to yield the characteristic modes eigenvalue problem. Key advantage of the proposed formulation is that it does not require the evaluation of Green’s function, thereby the study of any arbitrarily shaped, multilayered geometry loaded with anisotropic and inhomogeneous materials is feasible. To prove the validity of the proposed methodology various classical structures, with both homogeneous, and inhomogeneous and anisotropic materials, published in the bibliography are studied. Both the eigenvalues and eigenvectors compared with the published results show good agreement.

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A Finite Element-Based Characteristic Mode Analysis

As fifth generation (5G) wireless communication systems roll out, significant challenges exist towards the design of critical hardware, that is needed in order to realize the performance goals of 5G systems. One such challenge is the development of antenna arrays with multiple beams. This work, proposes the design of a mm-Wave beamforming network based on a modified Blass matrix architecture, which is loaded with appropriately designed cross couplers. The proposed implementation shows a constant time delay in the 27.5-32.5 GHz frequency band.

A mm-Wave True-Time-Delay Beamformer Architecture based on a Blass Matrix Topology

This work aims at the establishment of a rigorous full-wave eigenmode analysis technique based on a finite element scheme for the study of terahertz (THz) or photonic/optical unbounded structures. This numerical tool follows the last decades' trend to migrate the technological knowledge from microwave to THz and photonic regimes. The performed eigenanalysis offers an insightful view of the studied structures, revealing their characteristics. For the truncation of the infinite solution domain, the first kind absorbing boundary conditions are employed, while the involved spurious modes are eliminated with the incorporation of a tree-cotree splitting formulation. The study focuses on tunable microring resonators supporting leaky-radiating wave propagation and bounded-resonating whispering gallery modes. Tunability is achieved by integrating an electro-optical layer and in turn through the enforcement of an external applied DC electric field. An innovative approach constitutes the numerical determination of the altered dielectric permittivity as a piecewise constant distribution rather than a constant mean value.

/pdf/an-eigenanalysis-study-of-tunable-thz-and-photonic-unbounded-1sdwcqwuml.pdf

Konstantinos D. Paschaloudis

Papers

Design of True Time Delay Millimeter Wave Beamformers for 5G Multibeam Phased Arrays

An Eigenmode Study of Nanoantennas from Terahertz to Optical Frequencies

A Finite Element-Based Characteristic Mode Analysis

A mm-Wave True-Time-Delay Beamformer Architecture based on a Blass Matrix Topology

An Eigenanalysis Study of Tunable THz and Photonic Unbounded Structures Employing Finite Element Method