Terahertz Microstrip Elevated Stack Antenna Technology on GaN-on-Low Resistivity Silicon Substrates for TMIC

In this paper we demonstrate a THz microstrip stack antenna on GaN-on-low resistivity silicon substrates (ρ < 40 Ω.cm). To reduce losses caused by the substrate and to enhance performance of the integrated antenna at THz frequencies, the driven patch is shielded by silicon nitride and gold in addition to a layer of benzocyclobutene (BCB). A second circular patch is elevated in air using gold posts, making this design a stack configuration. The demonstrated antenna shows a measured resonance frequency in agreement with the modeling at 0.27 THz and a measured S11 as low as −18 dB was obtained. A directivity, gain and radiation efficiency of 8.3 dB, 3.4 dB, and 32% respectively was exhibited from the 3D EM model. To the authors' knowledge, this is the first demonstrated THz integrated microstrip stack antenna for TMIC (THz Monolithic Integrated Circuits) technology; the developed technology is suitable for high performance III-V material on low resistivity/high dielectric substrates

Design and Analysis of a Retroreflective Array for IR Application

This research investigates the adaptation of a Van Atta style of retrodirective array designed to work at 2 GHz to work in the infrared spectrum of 8-12 μm centered at 30 THz. The Computational Research and Engineering Acquisition Tools and Environments (CREATE) software suite and high performance computing (HPC) resources of the HPC Modernization program were utilized to model and simulate multiple steps of an adaptation process to illustrate and examine the incremental performance changes of frequency scaling the design. Two different substrate materials, germanium and hafnium oxide, are evaluated as the dielectric materials, and a comparison of the broadband performance of scaled designs using both dielectric materials shows that hafnium oxide provides better performance than germanium for this application. In addition, both gold and aluminum are evaluated for use in scaled designs. The results suggest that the cost savings and oxide bonding benefits of aluminum outweigh the slight performance advantage of gold. The Van Atta array concept is adaptable to IR wavelengths and microfabrication. Improved final broadband performance of the scaled design is a factor of approximately three and a half better than the 2 GHz design

An investigation of nanoscale materials and their incorporation in patch antenna for high frequency applications

The rapid development in the polymer-based electronic contribute a strong determination for using these materials as substitute to the high-cost materials commonly used as medium substrate in the fabrication of Microstrip Patch Antenna (MPA). Antenna technology can strongly gain from the utilisation of low-cost, flexible, light weight with suitable fabrication techniques. The uniqueness of this work is the use of variety of common but unexplored different polymer materials such as Polyethylene (PE), Polypropylene (PP), Polyvinyl chloride, (PVC) Polystyrene (PS), Polystyrene fibre (PSF) as the substrates for the design and fabrication of different MPAs for communication and sensing applications in millimetre wave (MMW)region. Electrospinning (ES) technique is used to reconstruct PS and produced PSF material of low dielectric constant. A co-solvent vehicle(comprising 50:50 ratio) of Dichloromethane (DCM) and acetone was utilised with processing condition of solution infusion flow-rate of 60μL/min and an applied voltage of 12± kV yielded rigid PSF substrates. The PSF Produced has complex permittivity of 1.36±5% and a loss tangent of 2.4E-04±4.8E-04 which was measured using Spilt-Post Dielectric Resonators (SPDR) technique at National Physics Laboratory, Teddington, London. A diamond-shaped MPAs on RT Duriod material were simulated and fabricated using photo-lithography for different inner lengths to work in the frequencies range from (1-10 GHz). The resonant frequency is approximated as a function of inner length L1 in the form of a polynomial equation. The fabricated diamond-shaped MPA more compact (physical geometry) as compared with a traditional monopole antenna. This MPAs experimentally measured and have a good agreement with the simulated results. The coplanar waveguide (CPW) diamond-shaped MPA working in the MMW region was designed and fabricated with polymer materials as substrates using thermal evaporation technique and the RF measurement was carried out using Vector Network Analyser (VNA). The resonant frequencies of the CPW diamond shaped MPAs for (PE, PP, PVC, PS and PSF) were found to be 67.5 GHz, 72.36 GHz, 62.41 GHz, 63.25 GHz and 80.58 GHz, respectively. The antenna fabricated on PSF were resonating at higher frequency when compared to the other polymers materials. In adding an air-bridge to the CPW diamond-shaped MPA the resonating frequency increased from ≈55 GHz to≈ 62 GHz. Three different shaped nano-patch antennas (Diamond shaped, diamond shaped array and T-shaped) have been designed, simulated and fabricated on Silicon substrate with DLC deposition using focused Ion Beam (FIB) technique, these antennas were found to resonate at 1.42 THz with (-19 dB return loss), 2.42 THz with (-14 dB return loss) and 1.3 THz with (-45 dB return loss) respectively

(Sub)millimeter-Wave Antennas

Disertační práce se zabývá návrhem a optimalizací kruhově polarizované anténa pro oblast terahertzových kmitočtů. V práci se věnuji zjednodušené teorii terahertzového zdroje a návrhu vhodné antény pro tento zdroj. Návrh je zaměřen na dosažení kruhové polarizace z lineárně polarizovaných antén. Abych potlačil šíření povrchové vlny na elektricky tlustém dielektrickém substrátu, věnuji se návrhu a optimalizaci specifických periodických struktur. Návrh těchto struktur je poměrně komplikovaný, protože neexistuje přímočarý vztah mezi vlastnostmi struktur s elektromagnetickým zádržným pásmem (EBG) a geometrií buňky. Abych vhodně koncentroval vyzařovanou energii do úzkého svazku, věnuji se návrhu a optimalizaci částečně odrazného plochy (PRS), které působí jako planární čočka pro terahertzovou anténu.The thesis deals with the design and optimization of circularly polarized antennas for THz frequencies. In the thesis, a simplified theory of THz sources is presented, and a suitable antenna for a THz source is designed. The design is focused on achieving circular polarization from linearly polarized antennas. In order to suppress surface waves on an electrically dense dielectric substrate, we design and optimize specific periodic structures. The design of such a structure is rather complicated since the relation between electromagnetic band gap (EBG) properties and unit cell geometry is not straightforward. In order to properly focus the radiated energy, we design and optimize a partially reflective surface (PRS) acting as a planar lens for the THz antenna.

Characterization of multi-wall carbon nanotubes and their applications

PhDCarbon nanotubes (CNT) and their applications is a field which has attract a lot of interest in the past two decades. Since the first invention of CNTs in 1991, and in view of utilising nanoantennas, the focus in many laboratories around the world has shifted to trying to lengthen nanotubes longer from nanometers to few centimeters. Eventually this could lead to CNTs’ use in sub-millimeter, millimiter wave and microwave antenna applications. In this thesis, fundamental properties of carbon nanotube films are investigated, and some applications such as the use of CNTs as absorbers or CNT doped liquid crystals are considered. The concept of frequency tunable patch antennas is also presented. Simulation and measurement results of the liquid crystal based antenna show that frequency tuning is possible, through the use of a liquid crystal cell as a substrate. Additionally, greater tuning can be achieved using liquid crystals with higher dielectric anisotropy at microwave frequencies. This can be achieved by using CNT doped liquid crystals. As mentioned, microwave and terahertz measurements of vertically aligned carbon nanotube arrays placed on the top surface of a rectangular silicon substrate are presented. The S-parameters are calculated allowing the extraction of the complex permittivity, permeability and conductivity of the samples. Theoretical models are being introduced delineating the behaviour of the multi-walled nanotube (MWNT) samples. The material properties of this film provide useful data for potential microwave and terahertz applications such as absorbers. Finally, finite-difference time-domain (FDTD) modelling of CNTs is introduced, verifying the measurements that have been performed, confirming that CNT arrays can be highly absorptive. A novel estimation of the permittivity and permeability of an individual carbon nanotube is presented and a periodic structure is simulated, under periodic boundary conditions, consisting of solid anisotropic cylinders. In addition, the optical properties of vertically aligned carbon nanotube (VACNT) arrays, when the periodicity is both within the sub-wavelength and wavelength iii regime are calculated. The effect of geometrical parameters of the tube such as length, diameter and inter-tube distance between two consecutive tubes are also examined

Millimeter-Waves Structures on Benzocyclobutene Dielectric Substrate

The need of low-loss substrate materials with stable dielectric performances is a strong requirement when working at millimeter frequencies, where standard dielectrics exhibit prohibitive losses. In this paper, the authors focus their attention on a polymer material, the benzocyclobutene (BCB), having a low dielectric constant and a low loss tangent, with a stable behavior up to THz frequencies. A specific in-house manufacture technology is described to realize millimeter-wave structures on a BCB dielectric substrate. Experimental validations on BCB-based circuits and antennas prototypes are discussed

A comprehensive survey on antennas on-chip based on metamaterial, metasurface, and substrate integrated waveguide principles for millimeter-waves and terahertz integrated circuits and systems

Antennas on-chip are a particular type of radiating elements valued for their small footprint. They are most commonly integrated in circuit boards to electromagnetically interface free space, which is necessary for wireless communications. Antennas on-chip radiate and receive electromagnetic (EM) energy as any conventional antennas, but what distinguishes them is their miniaturized size. This means they can be integrated inside electronic devices. Although on-chip antennas have a limited range, they are suitable for cell phones, tablet computers, headsets, global positioning system (GPS) devices, and WiFi and WLAN routers. Typically, on-chip antennas are handicapped by narrow bandwidth (less than 10%) and low radiation efficiency. This survey provides an overview of recent techniques and technologies investigated in the literature, to implement high performance on-chip antennas for millimeter-waves (mmWave) and terahertz (THz) integrated-circuit (IC) applications. The technologies discussed here include metamaterial (MTM), metasurface (MTS), and substrate integrated waveguides (SIW). The antenna designs described here are implemented on various substrate layers such as Silicon, Graphene, Polyimide, and GaAs to facilitate integration on ICs. Some of the antennas described here employ innovative excitation mechanisms, for example comprising open-circuited microstrip-line that is electromagnetically coupled to radiating elements through narrow dielectric slots. This excitation mechanism is shown to suppress surface wave propagation and reduce substrate loss. Other techniques described like SIW are shown to significantly attenuate surface waves and minimise loss. Radiation elements based on the MTM and MTS inspired technologies are shown to extend the effective aperture of the antenna without compromising the antenna’s form factor. Moreover, the on-chip antennas designed using the above technologies exhibit significantly improved impedance match, bandwidth, gain and radiation efficiency compared to previously used technologies. These features make such antennas a prime candidate for mmWave and THz on-chip integration. This review provides a thorough reference source for specialist antenna designers.This work was supported in part by the Universidad Carlos III de Madrid and the European Union's Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant 801538, in part by the Icelandic Centre for Research (RANNIS) under Grant 206606, and in part by the National Science Centre of Poland under Grant 2018/31/B/ST7/02369

Advanced Technologies for SIW Passive Microwave Components

The rapid growth of wireless networks and technologies of the last few decades has imposed new requirements on the performance of microwave components. There is a demand for wireless devices and sensors with high performance, high miniaturization and low production cost. Given this framework, the aim of this work is to provide a useful contribution through the study of existing techniques and the proposal of new ones. This is done by pursuing two specific lines of research: the study and analysis of compact Substrate Integrated Waveguide (SIW) resonators and filters, and the development of particularly simple and inexpensive reconfigurable antenna arrays based on an innovative amplitude beam-steering technique. Resonators are used as the basis for many different microwave devices. The achievable performance of said devices is limited by the losses of their resonators. The SIW is a planar transmission line technology which is a promising candidate for a wide array of applications. Compared to other planar technologies, the SIW offers particularly low losses and high electromagnetic performance, with an increase in the size of the components as a trade-off. In order to increase the miniaturization of SIW devices, the Half-Mode technique has been proposed, resulting in the Half-Mode Substrate Integrated Waveguide (HMSIW) topology. The Half-Mode technique can be applied multiple times to the classic square SIW resonator. With every iteration, the miniaturization factor is increased. The topologies that can be obtained are the Half-Mode resonator, the Quarter-Mode resonator and the Eighth-Mode resonator. While the SIW topology is completely closed and electromagnetically shielded, HMSIW and derived structures are partly open. For this reason, the performance of HMSIW devices suffer from the introduction of leakage and radiation losses. This work offers a study on the performance of the size reduction technique by the systematic analysis of these topologies. In a practical application, the results of this analysis are used to find which compact topology may be more convenient to employ depending on the design constraints such as frequency or kind of substrate to use. In order to mitigate the problem of losses, a few modified topologies which offer a substantial increase in the Quality Factor for only a modest increase in the size of the resonators have been proposed. An antenna array is defined as a group of antenna elements which operate concurrently. By acting on the relative phase of the signal of each radiator, it is possible to control the shape and orientation of the radiation pattern of the entire array. A phased array provides a high level of flexibility on the shape of the radiation pattern, but it is usually a complex system which requires a high amount of control elements. This work proposes an alternative technique that can be used to synthesise arrays with beam-steering properties without the use of phase shifters. The array is divided in two sub-arrays with the same amount of elements. Each sub-array is designed with a fixed phase profile and direction of maximum radiation. The pointing direction of the overall radiation beam can be controlled by adjusting the ratio of signal power being distributed between the two sub-arrays. The proposed technique manages to minimize the amount of control elements required to obtain beam-steering, since only a single power divider is needed. Fixed sub-array cells are simple to design and implement. The result is a large reduction in the complexity of the system. This work presents in detail the advantages, limits and drawbacks of the proposed amplitude-based beam steering technique. This technique is then used to design two different antenna arrays for 5G applications.The rapid growth of wireless networks and technologies of the last few decades has imposed new requirements on the performance of microwave components. There is a demand for wireless devices and sensors with high performance, high miniaturization and low production cost. Given this framework, the aim of this work is to provide a useful contribution through the study of existing techniques and the proposal of new ones. This is done by pursuing two specific lines of research: the study and analysis of compact Substrate Integrated Waveguide (SIW) resonators and filters, and the development of particularly simple and inexpensive reconfigurable antenna arrays based on an innovative amplitude beam-steering technique. Resonators are used as the basis for many different microwave devices. The achievable performance of said devices is limited by the losses of their resonators. The SIW is a planar transmission line technology which is a promising candidate for a wide array of applications. Compared to other planar technologies, the SIW offers particularly low losses and high electromagnetic performance, with an increase in the size of the components as a trade-off. In order to increase the miniaturization of SIW devices, the Half-Mode technique has been proposed, resulting in the Half-Mode Substrate Integrated Waveguide (HMSIW) topology. The Half-Mode technique can be applied multiple times to the classic square SIW resonator. With every iteration, the miniaturization factor is increased. The topologies that can be obtained are the Half-Mode resonator, the Quarter-Mode resonator and the Eighth-Mode resonator. While the SIW topology is completely closed and electromagnetically shielded, HMSIW and derived structures are partly open. For this reason, the performance of HMSIW devices suffer from the introduction of leakage and radiation losses. This work offers a study on the performance of the size reduction technique by the systematic analysis of these topologies. In a practical application, the results of this analysis are used to find which compact topology may be more convenient to employ depending on the design constraints such as frequency or kind of substrate to use. In order to mitigate the problem of losses, a few modified topologies which offer a substantial increase in the Quality Factor for only a modest increase in the size of the resonators have been proposed. An antenna array is defined as a group of antenna elements which operate concurrently. By acting on the relative phase of the signal of each radiator, it is possible to control the shape and orientation of the radiation pattern of the entire array. A phased array provides a high level of flexibility on the shape of the radiation pattern, but it is usually a complex system which requires a high amount of control elements. This work proposes an alternative technique that can be used to synthesise arrays with beam-steering properties without the use of phase shifters. The array is divided in two sub-arrays with the same amount of elements. Each sub-array is designed with a fixed phase profile and direction of maximum radiation. The pointing direction of the overall radiation beam can be controlled by adjusting the ratio of signal power being distributed between the two sub-arrays. The proposed technique manages to minimize the amount of control elements required to obtain beam-steering, since only a single power divider is needed. Fixed sub-array cells are simple to design and implement. The result is a large reduction in the complexity of the system. This work presents in detail the advantages, limits and drawbacks of the proposed amplitude-based beam steering technique. This technique is then used to design two different antenna arrays for 5G applications

Design, Analysis, and Applications of Optically-Activated Antennas and Dielectric Lenses Using Photosensitive Semiconducting Materials

PhDThe primary objective of the research is to investigate photosensitive semiconducting materials, mainly organic, and utilise them in antenna front-end systems and dynamic lenses for sub-THz applications. Mechanisms such as phase-shifting and photo-conductive switching are introduced in EM-devices to alter the antenna performance and behaviour. Using such mechanisms the devices are able to attain frequency, radiation pattern and polarisation reconfigurability. The common inorganic semiconductor, Si, and organic semiconductors such as poly 3-hexylthiophene (P3HT), [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) have been extensively studied and used in the exemplar EM-devices developed for this thesis. In this research, novelty is deployed with the use of photosensitive semiconductors as a means of ‘tuning’ dielectrics to control the propagation of the emerging beam-field of an antenna. Both organic and inorganic photosensitive semiconductors have been implemented in this work. The research begins by exploring the physical properties of such photosensitive semiconductors at microwave frequencies. Medium-resistivity Si was characterised using a conventional microstrip transmission line and the conductivity of the Si piece in dark and active states were estimated by matching its transmission characteristics with the modelled Si in CST Studio Suite. Thereafter the modelled Si was used in an antenna design to estimate the reconfigurability of the device. However, inorganic semiconductors are being replaced with organic semiconductors because of their inflexibility in device fabrication. Organic polymers, on the other hand, are light in weight, can be cast onto any surface, when blended with an organic solvent, and also photo-excited using white light. Organic polymer heterojunction 95% P3HT: 5% PCBM was characterised and changes in the real and imaginary parts of the complex dielectric constant of the organic blend are measured in the range of –0.05 to –0.55 and +0.01 to +0.52 respectively, over the sub-THz frequency-domain. In order to demonstrate EM-control of a wave using a photo-sensitive material, a two-element patch antenna array using organic polymer P3HT-PCBM is fabricated and the functionality for antenna beam steering examined. Non-optimum illumination of the organic layer on the antenna patches, led to an asymmetric and perturbed beam steer. Hence, a novel optically triggered antenna has been proposed at S-Band (2 – 4 GHz), where sodalime glass is being used as lower substrate, ITO (Indium Tin Oxide), transparent to white-light, as the ground plane and transmission lines along with patches are modelled onto the upper substrate layer (P3HT:PCBM). The estimates of the dielectric changes in the organic polymer blend due to optical excitation were used as inputs in the modelled device to show the proof-of-concept for beam steering with such a phase-shifting device. In addition, the antenna design also demonstrated that with a small change in the real part of the permittivity of the substrate it is possible to generate a maximum beam steer of 5°, using an effective phase-shifting design in CST Studio Suite. At millimetre-wave or sub-terahertz frequencies, small changes in the dielectric with excitation-region depth comparable to the wavelength are plenty to manipulate the emerging wave of an antenna or lens. Hence, an optically-activated dynamic lens is proposed and designed to dynamically control millimetre-wave transmission using optical illumination. The lens acts as a graduated gateway for phase transmission by adjusting the spatial permittivity across the lens. A nearfield measurement system is used to analyse the performance of the lens over the WR-10 (75 – 110 GHz) waveband. The phase distribution of the electric field across the face of the plane organic lens shows a similar pattern in the spatial phase-distribution of the lens plane in the active state as that projected by the illuminating source, allowing for projection-angle-induced cosine errors. Hence the dynamic operation of the lens can be beneficial for beam controlling applications in imaging, surveillance and remote sensing in the mm-wave frequency-domain.Queen Mary Doctoral College Postgraduate Research Initiative Fun