Resumo em Inglês:

Abstract The amount of water deposits on the receiving dish antenna can cause additional losses and consequently contaminate the actual slant-path attenuation. Only a few research works have been reported in the literature on the measurement of wet antenna attenuation (WAA) and the technique(s) of extracting the losses from the total attenuation in tropical and equatorial climates, characterized with heavy rainfall intensities of convective kind. Therefore, the adverse effects of antenna losses due to rain on a 11. 843 GHz satellite link and the methodology of extracting the losses from the measured rain-induced attenuation have been reported in this article. A vertically polarized parabolic dish with diameter and elevation of 0.3 m and 420, respectively have been used in the study. The measured results at 11.843 GHz were frequency-scaled in order to obtain their equivalents at 18.585 and 20.2 GHz; and then compared with those reported from Malaysia and Canada. The study will provide useful information in the planning and designing of an efficient and reliable Earth-satellite communication link in tropical climates. The experimental results also can further enrich the ITU-R databank.

Resumo em Inglês:

Abstract The family of new antenna designs based on the double Moebius strip principle is proposed in this article. Three possible options of the power supply port location had been reviewed in this respect: the cut external strip with the signal port located directly in the cut area is used; the continuous rings without discontinuities are applied, with the signal port located in the gap between the strips; the power supply port is located in the interstrip area, and there is a cut in one of the strips. The radio technical parameters of the antennas were researched by means of their modelling in Ansys HFSS packet. The strip width, its thickness, the interstrip gap, as well as the radius of the cylinder within which the antenna may be enabled, were used as mechanical parameters of the antennas based on the double Moebius strip. The best results were represented by the super-broadband antennas with the port located between two strips. In particular, 2-inch (50.8 mm) frequency independent antenna based on the singular continuous Moebius ring has a bandwidth of 38.648 GHz (from 11 to 49.648 GHz), and the frequency ratio (correlation of maximum operation frequency to the minimum one) exceeds 4.5. The application of the cut in the strip helped to improve the frequency response characteristics of such antenna, having increased its frequency ratio to the value of 5.548. In fact, the synthesized antennas occupy the intermediate niche between the double strip ring and the fractal antennas in terms of their characteristics. It makes it possible to use them in integrated communication, radio location, radio monitoring and navigation, both as independent structural units and as parts of wheeled gear structures of the crewless platforms.

Resumo em Inglês:

Abstract This paper describes the design of a compact microstrip microwave diplexer based on bandpass filters and a stepped impedance resonator for 4G applications. The diplexer is composed of two band-pass filters (BPF) that operate at 1.8 and 2.5 GHz. Both bandpass filters for the receiver at 1.705-1.895 GHZ and the transmitter at 2.41-2.6 GHZ have a -3dB fractional bandwidth of 10.5 % and 7.6 % respectively. These BPF, suitable for 4G telecommunications, are examined, evaluated, developed, and simulated, yielding theoretically consistent results. With a dielectric permittivity of 4.4 and a thickness of 1.6 mm, FR-4 is employed as a substrate material. The theoretical design and simulation are used to calculate the size and position of the SIR and feed lines. The diplexer has a low insertion loss and a high isolation, and its efficiency is quantitatively analyzed using the HFSS software. This application allows us to swiftly and simply create electrodynamic structures. A diplexer prototype was developed using a typical method of fabricating PCBs, with a structural area of (47.4020x247.063=11711.28 mm2). The obtained simulation results of the proposed circuit are in good agreement with the measurements.

Resumo em Inglês:

Abstract The defects in the form of slots have been employed in microstrip antenna either on the patch or the ground plane to yield frequency reduction. However, the reported work does not provide any comparative study that highlight upon the frequency and cross-polar level reduction achieved using these various shape slot/defects. This paper provides a thorough comparative study for different compact variations of microstrip antennas obtained using various shape slots on the ground plane. Amongst all, the optimum results are obtained for the bowtie-shaped slot on the ground plane, which offers cross-polar level reduction by 30 dB with a frequency reduction of 21%. The study also reveals that the slot on the ground plane offers better results against the slot on the patch in terms of frequency and cross-polar reduction. This kind of comparative study is not available in the literature and thus this is the novelty in the present work. An empirical formulation for the resonant length at the fundamental mode frequency for different shapes of slot/defect is proposed. The frequency calculated using them closely matches with those obtained using the simulation.

Resumo em Inglês:

Abstract A Defected Ground Structure, DGS, based on matryoshka geometry is described in this paper. The proposed DGS geometry is outlined and initial design equations are presented. Four prototypes, with resonant frequencies 2.17 GHz, 2.44 GHz, 2.99 GHz and 3.73 GHz, were designed, fabricated and characterized, observing a good agreement between measured and numerical results. Also, the obtained results demonstrated the initial design equations usefulness. The resonant behavior was analyzed in terms of the current density and it is possible to observe the current density blocked at the resonant frequency. When compared with dumbbell DGS, a reduction in the resonant frequency up to 47.19% is achieved, confirming the matryoshka geometry miniaturization properties. Furthermore, still comparing with dumbbell geometry, DGS based on matryoshka geometry are more selective.

Resumo em Inglês:

Abstract In this paper, a planar near-zero refractive index material (NZRIM) consisting of an outer loop with four symmetrical quarter-rings is proposed. The quarter-rings are connected to the outer loop by two symmetrical microstrip lines on the opposite side. The backside of the substrate has mutually central split microstrip lines. By loading adjustable capacitor between the split in the center of the backside of the substrate, the resonance frequencies of the proposed NZRIM can be controlled and thus the epsilon-near-zero (ENZ) frequency bands change correspondingly. According to the specific frequency bands of its metamaterial characteristics, the proposed NZRIM can be mounted above the surface of different antennas with different operation bands for 5G applications. Results show that the proposed NZRIM can enhance the forward radiation gain of antennas.

Resumo em Inglês:

Abstract The signal digitization process of the open television system is still in progress, therefore, the study of the digital signal propagation has great importance so that broadcasters can develop and improve the transmission service. The field measurement of digital signal parameters is one of the most reliable means to analyze the signal propagation in a given area. In this work, received power measurements of a TV station digital signal in the city of Mossoró, Rio Grande do Norte, Brazil were performed. The objective is to implement interpolation methods and identify which is the most suitable for the spatial representation of power data in this region through the Mean Error (ME) and Root Mean Squared Error (RMSE) evaluation metrics. A good representation of the received power level contributes to the mapping of greater and lesser intensity of the digital signal in the region. The implementation of the interpolation methods was performed in Surfer® software (Golden Software, LLC), which provides the cross-validation report with the ME and RMSE values associated with each method. The Ordinary Kriging method with exponential variogram model obtained the lowest RMSE value (7.6083) and, therefore, the most adequate estimates.

Resumo em Inglês:

Abstract A compact, dual-band, and self-diplexing MIMO patch antenna with a shared aperture is presented for Industrial scientific medical (ISM) band and X-band communications. The structure consists of two orthogonal feed lines and a rectangular slot in a square patch. The size of the FR4 substrate is 50 × 50 × 1.6 mm3. The designed structure operates at 5.8 (ISM) and 8 GHz (X-band) frequencies independently with a simulated peak gain of 5.46 and 3.59 dBi respectively. A 13 dB of isolation is obtained for the two orthogonal ports. The obtained frequency ratio range is 1.20-1.33 over the reflection bandwidth. The design structure is fabricated and validated experimentally. The compactness and promising performance in terms of low ECC (Envelope Correlation Coefficient) (<0.1), high peak gain can make the proposed antenna a choice for current wireless devices.

Resumo em Inglês:

Abstract This paper presents an analysis of the impact of various dielectric properties material’s effects on broadband pyramidal microwave absorbers (PMA). The Computer Simulation Technology (CST) studio software simulates and analyzes the PMA over 0.7 GHz to 30 GHz frequency range. To achieve the best reflectivity performance of the PMA, different types of dielectric materials and the thickness of the base layers were analyzed and investigated. The average of four types of sample materials studied, the reflectivity level is between -50 dB and -27 dB for the desired range of frequency, 0.7 GHz to 30 GHz. The sample-4 material has a dielectric constant of 3.83, and a loss tangent of 1.52 has the best microwave absorption, absorbing microwaves above -48 dB over the frequency range of 0.7 GHz to 30 GHz. Because of its microwave absorption capability, sample-4 could be used in a microwave pyramidal absorber.