Plant Foliar Geometry as a Biomimetic Template for Antenna Design.

Plant diversity includes over 300,000 species, and leaf structure is one of the main targets of selection, being highly variable in shape and size. On the other hand, the optimization of antenna design has no unique solution to satisfy the current range of applications. We analyzed the foliar geometries of 100 plant species and applied them as a biomimetic design template for microstrip patch antenna systems. From this set, a subset of seven species were further analyzed, including species from tropical and temperate forests across the phylogeny of the Angiosperms. Foliar geometry per species was processed by image processing analyses, and the resultant geometries were used in simulations of the reflection coefficients and the radiation patterns via finite differences methods. A value below -10 dB is set for the reflection coefficient to determine the operation frequencies of all antenna elements. All species showed between 3 and 15 operational frequencies, and four species had operational frequencies that included the 2.4 and 5 GHz bands. The reflection coefficients and the radiation patterns in most of the designs were equal or superior to those of conventional antennas, with several species showing multiband effects and omnidirectional radiation. We demonstrate that plant structures can be used as a biomimetic tool in designing microstrip antenna for a wide range of applications.

Design of 4 × 4 Low-Profile Antenna Array for CubeSat Applications.

This paper presents a low-profile microstrip antenna with high gain for fifth-generation (5G) CubeSat applications. The proposed design consists of 16 miniaturized patch antennas distributed in a uniform 4 × 4 topology with a feeding network on Rogers TMM10 substrate. The antenna array was simulated in CST Studio Suite® software and fabricated for performance testing on the CubeSat structure. The prototype works perfectly from 3.46 GHz to 3.54 GHz. The simulated and measurement results reveal remarkable performance. The design obtained a measured gain of 8.03 dBi and a reflection coefficient of -17.4 dB at the center frequency of 3.5 GHz. Due to its reduced dimensions of 10 × 10 cm, this design is an excellent alternative for mounting on a CubeSat structure as it combines efficient performance with a low profile.

Time-Modulated Antenna Arrays for Ultra-Wideband 5G Applications.

This research presents the design of time-modulated antenna arrays with UWB performance. The antenna arrays consider a linear topology with eight UWB disk-notch patch antennas. The technological problem is to find out the optimum antenna positions and/or time sequences to reduce the side lobes and the sidebands in all of the UWB frequency ranges. The design process is formulated as a bacterial foraging optimization. The results show that the uniform array generates a better SLL performance whereas the non-uniform array obtains a wider bandwidth. The uniform array obtains an SLL < −20 dB from 3.37 GHz to 4.8 GHz and the non-uniform array generates an SLL < −7 dB from 2.97 GHz to 5.26 GHz. The sideband levels are very similar for both cases with a value of around −17 dB.

Coherently Radiating Periodic Structures for Feeding Concentric Rings Array with Reduced Number of Phase Shifters.

This paper presents the application of CORPS (coherently radiating periodic structures) for feeding CRA (concentric rings array) with a reduced number of phase shifters. The proposed design technique for the structure of concentric rings provides a better scanning capability with respect to other existing configurations. This design technique utilizes 2 × 3 or 4 × 7 CORPS networks depending on the configuration or the number of antenna elements in the phased array system. These CORPS networks are set strategically in the feeding network to provide several advantages with respect to others in the scanning capability and the reduction of the number of phase shifters of the array system. The contribution of this paper is the full antenna system design of phased CRA for analyzing scanning and the reduction of phase shifters. The proposed phased array reduces the number of phase shifter devices in CRA for a scanning range of ±25° in the elevation plane. Differential evolution (DE) was applied to optimize the amplitudes of the proposed system. Several design cases were analyzed using full-wave simulation results to verify the phased array model and to take mutual coupling into account. Full-wave simulation results provide radiation patterns with low SLL in all scanning directions. The proposed phased array was validated by experimental measurements of the full antenna system prototype.

Novel Design Techniques for the Fermat Spiral in Antenna Arrays, for Maximum SLL Reduction.

This paper presents novel design techniques for the Fermat spiral, considering a maximum side lobe level (SLL) reduction. The array system based on a Fermat spiral configuration considers techniques based on uniform and non-uniform amplitude excitation. The cases of uniform amplitude excitation are the golden angle and the optimization of the angular separations. The cases of non-uniform amplitude excitations consider a raised cosine distribution and the optimization of the amplitude excitations through the Fermat spiral array. In this study, the method of genetic algorithms (GA) was used in the cases to find the values of the angular separations and the amplitude excitations of the Fermat spiral array. A performance evaluation was conducted for all these design cases, considering the Fermat spiral geometry. These design cases were validated using electromagnetic simulation to take mutual coupling into account and consider the effect of the antenna element pattern in each proposed design case.

A New Scheme of Applying CORPS and Crossovers to Reduce the Number of Phase Shifters in Antenna Arrays.

This paper presents a new scheme of applying CORPS (coherently radiating periodic structures) for reducing the number of phase shifters in linear antenna arrays. This scheme can be seen as a combination of the properties of two techniques: CORPS and butler. The proposed system applies an interleaving of several blocks of 2 × 3 CORPS networks. This interleaving of two stages of 2 × 3 CORPS networks is made in a convenient way to provide the required progressive phase for beam-scanning and the level of amplitude excitations necessary for achieving the radiation characteristics of low SLL. Interesting results are provided based on experimental measurements and full-wave simulations to analyze and evaluate the performance of the feeding network based on CORPS and the reduction capability of the number of phase shifters in the antenna system. The proposed design methodology achieves a reduction capability of 66% in the number of phase shifters used in linear antenna arrays. This reduction in the complexity of the antenna system is reached maintaining a peak SLL of -22 dB with scanning ranges of until ±25°. A good design option is provided to simplify the complexity of the feeding network in antenna array applications.

Coherently Radiating Periodic Structures to Reduce the Number of Phase Shifters in a 2-D Phased Array.

This paper illustrates the application of CORPS (coherently radiating periodic structures) for feeding 2-D phased arrays with a reduced number of phase shifter (PS) devices. Three design configurations using CORPS are proposed for 2-D phased arrays. The design model of phased array for these configurations considers the cophasal excitation required for this structure to set a strategic way for feeding the antenna elements and reducing the number of PS devices. Blocks of 2 × 3 and 4 × 7 CORPS networks depending on the configuration in the 2-D phased array are set strategically in the feeding network to generate the cophasal excitation required in the antenna elements. These design configurations used for feeding the antenna elements in the planar array geometry provide several advantages with respect to others in the scanning capability and the reduction of the number of PS devices of the array system. The full-wave simulation results for the proposed configurations in 2-D phased arrays provide a reduction in the number of PSs of until 69% for a scanning range of ±25° in elevation and ±40° in azimuth. The application of the raised cosine amplitude distribution could generate radiation patterns with a SLL_PEAK ≈ -19 dB and SLL_PEAK ≈ -23 dB for the design proposed configurations in all the scanning range.

Non-Uniform Concentric Rings Design for Ultra-Wideband Arrays.

This paper presents the design of aperiodic concentric ring arrays for ultra-wide bandwidths (UW-ACRA). This design of ultra-wideband arrays considers the synthesis of concentric rings in two cases: 1) non-uniform spacing between rings with non-uniform spacing between antenna elements of the same ring (UW-ACRAelements); and 2) non-uniform spacing between rings assuming that spacing between antenna elements of the same ring to be equal (UW-ACRArings). This is in order to eliminate the occurrence of grating lobes and generating array structures with useful ultra-wideband properties. The synthesis process is carried out by the well-known method of differential evolution (DE). Wireless sensor networks can take advantage of these properties to achieve less data traffic, efficient delivery of information and better energy efficiency.

MAC protocol for ad hoc networks using a genetic algorithm.

The problem of obtaining the transmission rate in an ad hoc network consists in adjusting the power of each node to ensure the signal to interference ratio (SIR) and the energy required to transmit from one node to another is obtained at the same time. Therefore, an optimal transmission rate for each node in a medium access control (MAC) protocol based on CSMA-CDMA (carrier sense multiple access-code division multiple access) for ad hoc networks can be obtained using evolutionary optimization. This work proposes a genetic algorithm for the transmission rate election considering a perfect power control, and our proposition achieves improvement of 10% compared with the scheme that handles the handshaking phase to adjust the transmission rate. Furthermore, this paper proposes a genetic algorithm that solves the problem of power combining, interference, data rate, and energy ensuring the signal to interference ratio in an ad hoc network. The result of the proposed genetic algorithm has a better performance (15%) compared to the CSMA-CDMA protocol without optimizing. Therefore, we show by simulation the effectiveness of the proposed protocol in terms of the throughput.

Synthesis of volumetric ring antenna array for terrestrial coverage pattern.

This paper presents a synthesis of a volumetric ring antenna array for a terrestrial coverage pattern. This synthesis regards the spacing among the rings on the planes X-Y, the positions of the rings on the plane X-Z, and uniform and concentric excitations. The optimization is carried out by implementing the particle swarm optimization. The synthesis is compared with previous designs by resulting with proper performance of this geometry to provide an accurate coverage to be applied in satellite applications with a maximum reduction of the antenna hardware as well as the side lobe level reduction.

Evaluación de Rendimiento del Protocolo MAC basado en CDMA Para Redes 802.11 / Performance evaluation of MAC Protocol Based on CDMA for Wireless 802.11 Networks / Avaliação do desempenho do protocolo MAC baseados em CDMA Para Redes 802.11

La popularidad de las redes inalámbricas 802.11 se basa en gran medida en el control de acceso al medio. Sin embargo, los retos que enfrenta esta tecnología en el acceso al medio son la interferencia y las colisiones provocadas por los usuarios dentro de la misma zona de cobertura, lo que resulta en un bajo rendimiento, a pesar de que se transmite con una tasa alta de transmisión, o en tener también un rendimiento bajo en el canal cuando se tienen pocos usuarios transmitiendo. Para resolver esta problemática se propone en este trabajo un protocolo que permite manejar dinámicamente las tasas de transmisión, logrando maximizar la cantidad de información transmitida con éxito (caudal eficaz). Se proponen dos esquemas; el primero toma en cuenta lo que sucede en el canal para aumentar o disminuir la tasa de transmisión y el segundo maneja una combinación óptima de tasas de transmisión. Los esquemas propuestos son validados mediante simulación y se demuestra que el protocolo propuesto con los dos esquemas puede obtener la adaptabilidad del tráfico en la red comparado con el mecanismo de acceso al medio tradicional con tasa fija.

The popularity of 802.11 wireless networks is based on the access control of the wireless medium. The greatest challenges this technology faces, however, are interference and collisions caused by users sharing the same coverage area. These two factors can result in a low throughput, even though the signal is transmitted at a high data transmission rate, or in low channel capacity when few users are transmitting. To solve these weaknesses, this work proposes a protocol that handles transmission rates dynamically to maximize the transmission success rate. Two schemes are proposed to address low throughput and low channel capacity. The first scheme dynamically monitors the channel in real time and increases or diminishes the transmission rate accordingly, while the second administers an optimal combination of transmission rates to minimize interference and collisions. Simulations show that the protocol improves traffic transmission in the network, as compared with fixed rated mechanisms used to access the wireless medium.

A popularidade das redes sem fio 802.11 se baseia em grande medida no controle de acesso ao meio. No entanto, os desafios que enfrenta esta tecnologia no acesso ao meio são a interferência e as colisões provocadas pelos usuários dentro da mesma zona de cobertura, o que resulta em um baixo rendimento, apesar de que se transmite com uma taxa alta de transmissão, ou em ter também um rendimento baixo no canal quando se tem poucos usuários transmitindo. Para resolver esta problemática se propõe neste trabalho um protocolo que permite manejar dinamicamente as taxas de transmissão, logrando maximizar a quantidade de informação transmitida com êxito (caudal eficaz). Propõem-se dois esquemas; o primeiro leva em conta o que sucede no canal para aumentar ou diminuir a taxa de transmissão e o segundo maneja uma combinação ótima de taxas de transmissão. Os esquemas propostos são validados mediante simulação e se demonstra que o protocolo proposto com os dois esquemas pode obter a adaptabilidade do tráfico na rede comparado com o mecanismo de acesso ao meio tradicional com taxa fixa.