Printed Planar Antenna Designs Based on Metamaterial Unit- Cells for Broadband Wireless Communication Systems

With the continuing development of mobile communications, the communication standards, which include operating frequencies and protocols, are also evolving. In order to accommodate these and future changes, antennas with characteristics of wideband and multiband are becoming a necessity. Hence, wireless communications industries are now demanding broadband antennas that are low-profile and low-volume structures. Conventional planar microstrip antennas are the most common form of printed antennas that have been used for many years. This is because these antennas offer advantages of low cost, conformability, and ease of manufacturing; however, the bandwidth of these types of antennas is highly restricted. Among different types of planar antennas, the slotted structure that offers the simplest structure is compact and radiates omnidirectionally; these features make it an excellent candidate for broadband applications

Frequency-Reconfigurable Low-Profile Omnidirectional Antennas

The high demand of today’s wireless technologies has resulted in increasing research efforts dedicated to modern antenna designs. A ”smart” antenna with abilities to tune its performance properties into a new environment can significantly increase communications reliability and decrease systems costs. Therefore, reconfigurable features have become a new standard of antenna designs, particularly when stringent performance indicators are required to keep up with increasing system demands. Owing to the radiation characteristics of antennas, an omnidirectional pattern is one that is widely sought after by antenna designers. Due to their uniform coverage, omnidirectional antennas are an ideal choice for numerous indoor or outdoor implementations. In this context, this thesis investigates substrate-integrated, low-profile, and reconfigurable design solutions for omnidirectional antennas. Firstly, the thesis discusses the development of low-profile monopoles made of shorted patches, where the main objective of this work is to find via-less alternatives for the antenna shortings. Two alternative strategies, namely quarter-wave stubs and complementary split ring resonators, are deployed in substrate-integrated monopoles and are compared with the classical shorting pins in terms of performances. Secondly, the thesis focuses on the investigation of frequency-tunable antennas. The stub-loaded monopole from the first part of the thesis is further developed to create reconfigurable antennas. This work aims to provide multi-band reconfigurable devices with independent tunability between the operating frequencies. In this part, a novel method of designing reconfigurable lowprofile monopoles is proposed based on independent magnetic current loops sharing the same thin aperture. Lastly, a circularly-polarized frequency-reconfigurable omnidirectional antenna is demonstrated as the final contribution of the thesis. The antenna operation principle is based on a combination of magnetic current sources, electric current sources, and phase compensation lines between them. Varactor-loaded slots are added to the structure to enable frequency reconfigurability. Moreover, a description of the antenna feeding aspects to maintain the circular polarization in real conditions is presented. Overall, this thesis provides different designs of high performance low-profile omnidirectional antennas. The results suggest that all the antenna designs are promising for numerous wireless applications. The benefits include simple antenna geometry, ease of fabrication, and low-profile. Importantly, the proposed design principles can be extended to other types of reconfigurable antennas.Thesis (M.Phil.) -- University of Adelaide, School of Electrical and Electronic Engineering, 201

Metasurface-Inspired Flexible Wearable MIMO Antenna Array for Wireless Body Area Network Applications and Biomedical Telemetry Devices

This article presents a sub-6GHz ISM-band flexible wearable MIMO antenna array for wireless body area networks (WBANs) and biomedical telemetry devices. The array is based on metasurface inspired technology. The antenna array consists of 2×2 matrix of triangular-shaped radiation elements that were realized on 0.8 mm thick Rogers RT/duroid 5880 substrate. Radiation characteristics of the array are enhanced by isolating the surface current interaction between the individual radiators in the array. This is achieved by inserting an electromagnetic bandgap (EBG) decoupling structure between the radiating elements. The radiating elements were transformed into a metasurface by etching sub-wavelength slots inside them. The periodic arrangement of slots acts like resonant scatterers that manipulate the electromagnetic response of the surface. Results confirm that by employing the decoupling structure and sub-wavelength slots the isolation between the radiators is significantly improved (>34.8 dB). Moreover, there is an improvement in the array’s fractional bandwidth, gain and the radiation efficiency. The optimized array design for operation over 5.0-6.6 GHz has an average gain and efficiency of 10 dBi and 83%, respectively. Results show that the array’s performance is not greatly affected by a certain amount of bending. In fact, the antenna maintains a gain between 8.65-10.5 dBi and the efficiency between 77-83%. The proposed MIMO antenna array is relatively compact, can be easily fabricated on one side of a dielectric material, allows easy integration with RF circuitry, is robust, and maintains its characteristics with some bending. These features make it suitable for various wearable applications and biomedical telemetry devices