Antenas

A low-cost and highly efficient printed Yagi antenna structure with high radiation efficiency is presented. The proposed prototype consists of two stacked planar layers. The first layer electromagnetically couples energy to the printed Yagi array parasitic elements located on the second layer. A reduced-size 60-GHz prototype (1.0687 0.8015 cm ) is designed to operate over the Industrial, Scientific, and Medical (ISM) band. The measured impedance bandwidth is more than 5 GHz with a gain of 10 dB measured at 60 GHz. With these features, this antenna achieves a low profile that makes it suitable for millimeter-wave monolithic microwave integrated circuits (MMICs) packaging as well as for short-range wireless communications and imaging applications.

In the frame of the multi-segment System for Broadband Ubiquitous Access to Internet Services and demonstrator (SUITED) project, a phased array antenna has been designed with the ability to scan the beam over a certain angular range, especially at very low elevation angles. All the antenna parts were realized and measured, and their predicted performances were achieved. The antenna is fully integrated. The methods for adjusting amplitude and phase of each antenna element were also developed, including auxiliary hardware compatible with the standard antenna control board and auxiliary software for parameter settings. The methods were successfully tested in an anechoic chamber. Flexibility in adjusting phase and amplitude characteristics enables optimization of the radiation pattern. SUITED is funded by the European Union under the Information Society Technologies (IST) program, aiming to make a significant contribution towards the understanding and development of IP-based mobile networks, consisting of both satellite and terrestrial (UMTS, GPRS, W-LAN) components.

To obtain wide bandwidth and high gain at millimeter wave frequency, Antipodal Fermi-Linear Tapered Slot Antenna (AFLTSA) is proposed. The proposed antenna achieves wide bandwidth from 23 to 33 GHz as well as flat gain of 14.5 dBi over wide operating frequency band. It achieves the side lobe level of -8 dB in H Plane and -16 dB in E plane. Proposed design also achieves the front- o-back ratio of -20 dB and symmetric pattern.

En general, els animals escullen les millors taques del seu hàbitat per tal d'aprovisionar-se de menjar (Stephens i Krebs, 1986). Les aranyes no són una excepció; Misumena vatia (Clerck, 1757), una aranya cranc de les flors, augmenta el seu èxit reproductiu escollint les flors que atreuen més insectes (Morse i Fritz, 1982; Fritz i Morse, 1985). Efectivament, la disponibilitat de menjar pot afectar les aranyes; una mancança d'aliment pot reduir la seva supervivència, el seu creixement o la seva fecunditat .

Recently, non-orthogonal multiple access (NOMA) has been developed as an alternative to orthogonal multiple access (OMA) to fulfill the need of connecting massive number of devices with high requirements of 5G wireless communication. In this work, two types of transmitter antenna selection (TAS) are employed-in down link NOMA amplify and forward cooperative relay system over Rayleigh fading channels-to enhance the bit error rate (BER) performance. The first TAS, which is based on maximum ratio combining at relay is applied on the first hop, and the second TAS with maximum likelihood and successive interference cancellation detection based on minimizing average BER at mobile end user is applied on second hop. The obtained results reveal that the proposed TAS schemes enhance the performance of NOMA cooperative relay system significantly compared to other TAS that were used as a reference in this work, namely antenna random selection scheme and equal gain combining of all antennas.

Recently, the interest in implantable antennas has significantly increased because of their attractive and diverse medical applications. As the human body is a hostile environment for implantable antennas, where it absorbs most of the antenna's radiation, designing implantable antennas has become a challenging task. Despite the many efforts that have been made to construct successful designs of robust performance against the complicated human body environment; more efforts are still needed to overcome the current challenges. This paper aims to review recent advances in designing implantable antennas and upcoming research progress in the area of implantable antennas. To achieve this aim, the main differences in performance between antennas in free space and lossy media are emphasized firstly. Then, the main antenna's designs proposed for implantable applications are surveyed and categorized based on critical design parameters. Finally, the main characteristics of existing designs are summarized, and future needs are highlighted.

A quad-band circularly polarised (CP) patch antenna for 7.1/7.6/7.9/8.6 GHz for UWB/5G applications are proposed in this paper. By designing the patch antenna with an inverted U-shaped radiator, I-shaped and L-shaped strips which are all rotated by 45ᵒ at the horizontal axis. The measurement of -37.51 dB of return loss for 8.6 GHz frequency was obtained. A microstrip line feed technique was used for feeding which is one of the contacting schemes used in the feeding methods. A conducting strip is connected directly to the edge of the microstrip patch. It provides a simple planar structure since the conducting strip is smaller in size when compared to the patch. The substrate FR_4 epoxy has high electrical insulation, good mechanical strength, better wear, and corrosion resistance. The measured 3 dB AR information is 5.63% (6.9-7.3 GHz), 5.26% (7.4-7.8 GHz), 5.0% (7.8-8.2 GHz) and 3.50% (8.4-8.7 GHz) severally. This antenna can be used in UWB/5G applications which offer high-speed data transmission.

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"The IEEE802.11g standard is widely used in both industrial and
domestic applications because of its compatibility with numerous
equipments. Because some telemetry systems need long range
links, building a directional antenna is a simple way of increasing
the range of such equipments. Microstrip is a proven antenna
technology: easy to build, low profile, light weight, low cost and
flexibility in terms of radiation pattern and polarization.
Adjustments to meet the main requirements are made during the
design of the antenna. The expected results can be previewed with a
series of simulations.
"

Ao longo dos anos, a tecnologia microstrip tem mostrado grande sucesso na concepção de antenas.
Com inúmeras aplicações em microondas e ondas milimétricas, reúne várias vantagens que lhe
proporcionaram grande sucesso: baixo peso, baixo custo e grande flexibilidade na escolha do diagrama de
radiação e polarização pretendidos. Porém, esta tecnologia possui algumas desvantagens, como por
exemplo, largura de banda estreita. Este tipo de projectos requer a utilização de software de cálculo que,
apesar dos seus rigorosos modelos matemáticos, acabam por gerar resultados simulados que muitas das
vezes têm diferenças quando comparados com resultados experimentais. O que geralmente acontece é que
as curvas simuladas e experimentais correspondentes ao factor de reflexão das antenas (S11) têm formas
semelhantes, mas encontram-se desfasadas em frequência. Este facto pode ser particularmente
constrangedor em aplicações de banda estreita, em que a falta de sintonia pode fazer com que a antena não
tenha o desempenho desejado.
Neste trabalho é apresentada uma técnica experimental para sintonia fina de antenas baseadas em
elementos microstrip. Este tipo de técnicas apenas é passível de ser aplicado em antenas onde se possam
modificar os elementos através de fresas para circuitos impressos ou através do processo fotolitográfico. Este
trabalho estuda dois tipos de abordagem: diminuir ligeiramente o tamanho dos elementos para aumentar a
frequência de ressonância da antena; adicionar um pequeno pedaço de cobre a cada elemento (o que torna
os elementos electricamente maiores) ou adicionar finas camadas de um superstrato à antena para aumentar
a frequência de ressonância da antena.
Ambos os processos são validados apenas com recurso a simulações por software. A antena em
causa é um agregado de 4x4 elementos rectangulares, impressos num RT/Duroid 5880 com 3,175 mm. Esta
antena foi projectada para uma aplicação de telemetria da Marinha Portuguesa. Este sistema de telemetria é 2
baseado no padrão IEEE 802.11g (f0 = 2.442 GHz, LB = 84 MHz = 3.4%) e requer um alcance de cerca de 10
km, o que requer que antena tenha pelo menos um ganho de 16 dBi. A antena foi projectada e optimizada
com recurso ao software ENSEMBLE. Após o fabrico do protótipo efectuou-se a medida do parâmetro S11, o
qual mostrou que a curva característica se encontrava deslocada 34 MHz (1.4 %) em relação à frequência
central do padrão.
O estudo baseado nas simulações permitiu determinar as regras para compensação do desvio em
frequência, quer superior quer inferior.