Design synthesis and miniaturization of multiband and reconfigurable microstrip antenna for future wireless applications

Tese de Doutoramento. Engenharia Electrónica e de Computadores - Telecomunicações. Faculdade de Engenharia. Universidade do Porto. 201

Mutual Coupling Considerations in the Development of Multi-feed Antenna Systems

In the design of any multi-port network with more than one antenna, mutual coupling between these different ports must be accounted for. In an effort to investigate and control these mutual coupling effects, we have selected three structures to be thoroughly analyzed. Furthermore, they have been fabricated and tested to develop relevant design guides for these selected structures to have minimal mutual coupling effects. These selected structures included a feed network for a multi-port antenna, a dual feedhorn for a large reflector antenna, as well as a set of Multi- Input Multi-Output (MIMO) laptop antennas. In the first study, we analyzed a 30- port radial splitter that can be used for an in-phase feeding of a 30-high power transmitter. Our objectives here have been geared towards estimating the mutual coupling between the 30 ports and exploring the port and alignment failure analysis, its graceful degradation results, and relevant efficiency performance for such high power multi-port network will be presented. In the second study, we investigated the mutual coupling of a multifeedhorn structure of a large reflector antenna in order to allow multi-beam radiation or reception. This high gain antenna utilizes integrated feeds with precise physical tight spacing and could suffer from strong inter-coupling. Mutual coupling effects here include input match deterioration, beam width broadening, and cross-polarization degradation due to the proximity coupling of these various feeds. Our study derived accurate feed location expressions as well as methods to improve the decoupling between the feeds that have been implemented. These results will be discussed. For the third study, we carried out extensive investigates into the mutual coupling effects amidst wireless laptop antennas for a MIMO system implementation. For a laptop use, it is required to determine the best location, optimum spacing, and orientations of these antennas in order to achieve the maximum benefits of the system’s diversity. First, we studied the coupling between two antennas as a function of their spacing, types, and orientations. Subsequently, we extended the study to a controlled multi-antenna system for a MIMO implementation. Design rules for such implementation have been derived and will be discussed in detail

Dual-Band Integrated Antennas for DVB-T Receivers

An overview on compact Planar Inverted-F Antennas (PIFAs) that are suitable for monitor-equipped devices is presented. In particular, high efficiency PIFAs (without any dielectric layer) with a percentage bandwidth (%BW) greater than 59% (470–862 MHz DVB-T band) are considered. In this context, two PIFA configurations are reviewed, where a dual-band feature has been obtained, in the 3300–3800 MHz (14% percentage bandwidth) WiMAX and 2400–2484 MHz (2.7% percentage bandwidth) WLAN IEEE 802.11b,g frequency bands, respectively, to also guarantee web access to on-demand services. The two PIFAs fill an overall volume of  mm3 and  mm3, respectively. They are composed of a series of branches, properly dimensioned and separated to generate the required resonances. Finally, to show the extreme flexibility of the previous two configurations, a novel dual-band L-shape PIFA has been designed. A reflection coefficient less than −6 dB and −10 dB and an antenna gain of around 2 dBi and 6.3 dBi have been obtained in the 470–862 MHz DVB-T band and the 2400–2484 MHz WLAN band, respectively. The L-shape PIFA prototype can be obtained by properly cutting and folding a single metal sheet, thus resulting in a relatively low-cost and mechanically robust antenna configuration

Miniaturized DGS and EBG structures for decoupling multiple antennas on compact wireless terminals

MIMO (Multiple Input Multiple Output) technology has been presented to significantly increase the wireless channel capacity and reliability without requiring additional radio spectrum or power. In MIMO systems, multiple antennas are mounted at both the transmitter and the receiver. When this technology is employed for a compact wireless terminal, one of the most challenging tasks is to reduce the high mutual coupling between closely placed antenna array elements. The high mutual coupling produces high correlation between antenna elements and affects the channel capacity of MIMO system. The objectives of this thesis are to design practical miniaturized structures to reduce high mutual coupling for small wireless terminals. The research is conducted in the following areas. Initially, a PIFA design and two-element PIFA array are proposed and optimized to operate at 1.9GHz. A pair of two coupled quarter-wavelength linear slits is inserted in a compact ground plane, resulting in significant reduction of the mutual coupling across antenna operating frequency band. In order to take up less space on the ground plane, instead of the linear slits, miniaturized convoluted slits are implemented between the two closely placed PIFAs. Although the convoluted slits have small area and are positioned close to the edges of the ground plane, the miniaturized convoluted slit structures achieve a reduction of mutual coupling between antenna elements and succeed in reducing the effect of the human body (head and hand) to the antennas. In order to further reduce the size of the slits etched on the compact ground plane, a novel double-layer slit-patch EBG structure is proposed. It consists of a two-layer structure including conducting patches and aperture slits placed on either side of a very thin dielectric layer. They are placed in very close proximity to each other (55μm). A two-element printed CPW-fed monopole array operating around 2.46GHz and a two-element UWB planar monopole array operating from 3GHz to 6GHz have been employed to investigate the proposed slit-patch EBG structures. The optimized double-layer slit-patch EBG structure yields a significant reduction of the mutual coupling and produces the maximum miniaturization of antenna array. Another novel convoluted slit-patch EBG structure has been presented to reduce the mutual coupling between two PIFAs operating at 1.9GHz. These results demonstrate that the slit-patch EBG structure is a feasible technology to reduce the mutual coupling between multiple antennas for compact wireless terminals

A Review on Different Techniques of Mutual Coupling Reduction Between Elements of Any MIMO Antenna. Part 1: DGSs and Parasitic Structures

This two-part article presents a review of different techniques of mutual coupling (MC) reduction. MC is a major issue when an array of antennas is densely packed. When the separation between the antennas i

Antennas and Arrays for Mobile Platforms -- Direct Broadcast Satellite and Wireless Communication

Flexibility of any proposed communication links is becoming one of the most challenging features. Direct broadcasting satellite services, for example, will be greatly enhanced by providing service-on-the-move. This market is very demanding as it necessitates the development of a low cost, low profile antenna that can be mounted on top of SUVs and minivans, which is capable of continuously tracking the satellite. Another example is the wireless antennas for laptops and smart-phones, where the antennas should fit within an extremely small volume and should be capable of addressing many services over wide frequency range. In this dissertation, both DBS and the wireless antennas are addressed. In these studies, efforts have been concentrated in developing low profile planar antennas, in particular, slot arrays. Travelling wave slotted waveguide arrays have been utilized to minimize the scanning angle range limits due to their inherent beam tilt angle. CNC machines were utilized first to fabricate the early prototypes for sub-array developments. Subsequently, a low cost fabrication technology is adopted to develop a low cost and light weight full array using substrate integrated waveguides (SIWs). The SIW is fully characterized and an excellent equivalent model has been derived to allow easy translation of metallic waveguide components to SIW. Various SIW junctions, transitions, and arrays have been developed for array feed networks including a 64 radiating SIW full array and a 32 radiating SIW array with folded feed. Meanwhile, for the wireless antennas, the utilization of reconfigurable hardware has been introduced to provide the required multi-functionality services and wide frequency coverage. Various reconfigurable antennas were developed and utilized to demonstrate their advantages compared to other design options such as wide-band or multi-band approaches. Both micro-electro-mechanical switches MEMS and PIN diodes have been successfully utilized to switch between the different configurations. The placement, control, and modeling of the switches are also discussed and novel modeling and biasing topologies are introduced. A novel and practical concept of reconfigurable multiband antenna is introduced here too, where advantages of both the multi-band and the reconfigurable antenna structures can be simultaneously achieved while supporting more services

A study of planar inverted-F antennas in a dielectric enclosure

Demand for small and low-profile antennas has greatly increased due to the desire for miniaturisation of modern-day mobile radio electronic terminals. Such an antenna is often integrated into the dielectric casing of a terminal, or independently enclosed within a dielectric radome to provide a protection from operating environments and keep the system more compact. However, the dielectric casing or radome may interact strongly with the antenna and result in losses in performance. The primary focus of this dissertation is to investigate and enhance the performance of Planar Inverted-F Antennas (PIFAs) when enclosed in dielectric casings or radomes for applications in mobile radio communications. PIFAs have attracted much interest due to their small volume, low profile structures and electrical characteristics compatible with existing specifications, making it a promising candidate for mobile radio applications. Therefore, the design of a single band PIFA on a finite ground plane, operating in the 900 MHz band is first presented. It is found that the effect of the finite ground plane must be considered to achieve an optimum performance of the PIFA. Then the performance of this antenna in the presence of a dielectric cover layer is investigated and evaluated in terms of resonant frequency, bandwidth and efficiency. In this study, the dielectric layer represents the dielectric casing of a device where the antenna is much closer to the top part of the casing than to the other side parts whose effect can then be ignored. Computer simulations of performance are based on the Method of Moments (MOM) and have been validated by measurements. This study shows that a dielectric cover layer will strongly interact with the antenna with the result that the antenna performance may move outside the design specifications.Therefore, it is concluded that the dielectric cover layer must always be taken into account in the design stage. In addition, the input and radiation characteristics of a PIFA enclosed within a rectangular dielectric radome for both the 900 MHz and 2400 MHz frequency bands are analysed using the MOM. This research concentrates on the effect of each individual part of the rectangular dielectric radome on the overall performance. It is observed that each individual part has a different degree of effect on both the input and radiation characteristics of the PIFA, and that the effect is more significant at the higher frequency band. The study indicates that the effect of the dielectric radome on the performance of the antenna can be minimised by carefully choosing its location and orientation within the radome. Another indication is that an optimised dielectric radome design can both miniaturise the antenna and at the same time improve the bandwidth without sacrificing other performance parameters such as the gain. Furthermore, an analytical approach based on the Transmission Line Model (TLM) is applied to estimate the input characteristics of a PIFA having a dielectric cover layer. The results calculated based on this approach are compared with MOM computed results. A reasonably good agreement between them has been demonstrated. It is suggested that the TLM model could form part of an efficient Computer Aided Design (CAD) tool for design engineers to provide initial design parameters.Finally, a new dual-band PIFA is proposed. A design example for the Industrial, Scientific and Medical (ISM) frequency bands of 900 MHz and 2400 MHz is given. Measurement validation of the design is presented. The influence of the dielectric cover layer on the resonant frequency, bandwidth, gain and radiation patterns of this antenna is also examined by simulation. In this study, it is found that a simple capacitive disk arrangement not only provides a single feed for dual-band operation but also gives flexibility to allow individual control of the two desired band resonances