RESUMO
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.
RESUMO
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.
RESUMO
Microwave ablation is commonly used in soft tissue tumors, but its application in bone tumors has been barely analyzed. Antennas to treat bone tissue (~3 cm2), has been lately designed. Bone tumors at pathological stage T1 can reach 8 cm wide. An antenna cannot cover it; therefore, our goal is to evaluate the thermal performance of multi-antenna arrays. Linear, triangular, and square configurations of double slot (DS) and monopole (MTM) antennas were evaluated. A parametric study (finite element method), with variations in distance between antennas (ad) and bone thickness (bt) was implemented. Array feasibility was evaluated by SWR, ablated tissue volume, etc. The linear configuration with DS and MTM antennas showed SWR ≤ 1.6 for ad = 1 mm−15 mm and bt = 20 mm−40 mm, and ad = 10 mm−15 mm and bt = 25 mm−40 mm, respectively; the triangular showed SWR ≤ 1.5 for ad = 5 mm−15 mm and bt = 20 mm−40 mm and ad = 10 mm−15 mm and bt = 25 mm−40 mm. The square configuration (DS) generated SWR ≤ 1.5 for ad = 5 mm−20 mm and bt = 20 mm−40 mm, and the MTM, SWR ≤ 1.5 with ad = 10 mm and bt = 25 mm−40 mm. Ablated tissue was 4.65 cm3−10.46 cm3 after 5 min. According to treatment time and array configuration, maximum temperature and ablated tissue is modified. Bone tumors >3 cm3 can be treated by these antenna-arrays.
Assuntos
Neoplasias Ósseas , Micro-Ondas , Neoplasias Ósseas/diagnóstico por imagem , Neoplasias Ósseas/terapia , Osso e Ossos , Análise de Elementos Finitos , Humanos , Micro-Ondas/uso terapêutico , TemperaturaRESUMO
In this article, a combination of rectangular loop array and slot radiator for multiband applications is presented. The antenna is configured by arranging, concentrically, a set of rectangular loop radiators excited by electromagnetic coupling provided by a dumbbell slot. The size of the loops is calculated to obtain the desired resonant frequencies, which are almost independent of the adjacent rings. The exciting slot is designed to operate in a wideband frequency range to cover the upper desired resonance. In addition, to obtain directive radiation patterns, a reflector shaped like a box is introduced, giving a stable gain, radiation pattern shape, and port matching at the selected frequencies. The configuration presents great results, since to the authors' knowledge, even a similar configuration given in the open literature presents some disadvantages compared to this one; moreover, not just any structure can be employed as the resonating elements, obtaining multiband behavior at the same time.
RESUMO
Direction finding (DF) systems are used to determine the direction-of-arrival (DoA) of electromagnetic waves, thus allowing for the tracking of RF sources. In this paper, we present an alternative formulation of antenna arrays for modeling DF systems. To improve the accuracy of the data provided by the DF systems, the effects of mutual coupling in the array, polarization of the received waves, and impedance mismatches in the RF front-end receiver are all taken into account in the steering vectors of the DoA algorithms. A closed-form expression, which uses scattering parameter data and active-element patterns, is derived to compute the receiver output voltages. Special attention is given to the analysis of wave polarization relative to the DF system orientation. Applying the formulation introduced here, a complete characterization of the received waves is accomplished without the need for system calibration techniques. The validation of the proposed model is carried out by measurements of a 2.2 GHz DF system running a MUSIC algorithm. Tests are performed with a linear array of printed monopoles and with a planar microstrip antenna array having polarization diversity. The experimental results show DoA estimation errors below 6° and correct classification of the polarization of incoming waves, confirming the good performance of the developed formulation.
RESUMO
The opportunistic exchange of information between vehicles can significantly contribute to reducing the occurrence of accidents and mitigating their damages. However, in urban environments, especially at intersection scenarios, obstacles such as buildings and walls block the line of sight between the transmitter and receiver, reducing the vehicular communication range and thus harming the performance of road safety applications. Furthermore, the sizes of the surrounding vehicles and weather conditions may affect the communication. This makes communications in urban V2V communication scenarios extremely difficult. Since the late notification of vehicles or incidents can lead to the loss of human lives, this paper focuses on improving urban vehicle-to-vehicle (V2V) communications at intersections by using a transmission scheme able of adapting to the surrounding environment. Therefore, we proposed a neuroevolution of augmenting topologies-based adaptive beamforming scheme to control the radiation pattern of an antenna array and thus mitigate the effects generated by shadowing in urban V2V communication at intersection scenarios. This work considered the IEEE 802.11p standard for the physical layer of the vehicular communication link. The results show that our proposal outperformed the isotropic antenna in terms of the communication range and response time, as well as other traditional machine learning approaches, such as genetic algorithms and mutation strategy-based particle swarm optimization.