Resumo em Inglês:

Abstract This paper presents the design of a dual-band and dual-polarized microstrip antenna for global navigation satellite systems reflectometry (GNSS-R) for the L1/E1/B1 and L5/E5a/B2a bands. In order to allow advanced GNSS-R signal processing and sensing techniques, the design has been carried out for dual-band and dual-polarization operation with isolated ports to receive both left and right-hand circular polarizations. The design procedure to allow receiving both bands independently and with high isolation is described in detail. Numerical and experimental results show that the antenna presents good performance in terms of impedance matching, circular polarization purity and isolation between the ports. The measured levels of axial ratio are 0.86 dB and 1.89 dB for the L1/E1/B1 and L5/E5a/B2a bands, respectively. The measured isolation levels are larger than 30 dB and 40 dB in the L1/E1/B1 and L5/E5a/B2a bands, hence proving that the proposed antenna concept can be properly used in dual-band dual-polarized GNSS-R applications.

Resumo em Inglês:

Abstract This paper describes the development of a double-sided band-pass frequency selective surface based on Matryoshka geometry, preserving features such as miniaturization, multiband operation and stability of polarization and angle of incidence. Unlike cascaded FSSs, the proposal uses only one layer of substrate, with Matryoshka geometry on one side and a square mesh on the other, reducing volume and simplifying manufacturing by avoiding spacers. The double-sided FSS allows the frequency response to be adjusted using the geometry of the opposite face, which in this work is a square loop. With an attenuation of -10 dB, the proposed configuration offers a free band from 3.48 GHz to 9.06 GHz, compared to the original configuration, which ranged from 5.88 GHz to 7.43 GHz, with only 1.55 GHz free. Initial design equations are presented which facilitate the creation of FSSs for other frequencies and applications. An FSS has been designed, fabricated, and characterized, with good agreement between numerical and experimental results. The resonant frequency remains practically constant for different incidence angles, from 0º to 60º, confirming the angular stability.

Resumo em Inglês:

Abstract This paper presents a novel design of an X-band (812 GHz) 4-bit monolithic microwave integrated circuit (MMIC) type true-time-delay (TTD) line for wideband high-resolution imaging radar applications. The designed TTD line circuit offers a maximum time delay of 920 picoseconds (ps) using eight 115 ps delay elements and a distributed switching network. The unit delay line is synthesized using an artificial transmission line (ATL) circuit and implemented in a compact form of 18.5 mm2 using 130 nm gallium arsenide (GaAs) pseudomorphic high-electronmobility-transistor (p-HEMT) technology. The size of the switches and characteristic impedance of the transmission lines have been optimized to minimize insertion loss variation across different delay states while maintaining a flat delay response over a wide bandwidth. A basic 115 ps delay line cell is fabricated to prototype the circuit using GaAs-based MMIC processes. The final 920 ps chip layout simulation exhibited input and output return loss of better than 10 dB, insertion loss of 28±2 dB, and group delay variation of ±10 picoseconds over a 4 GHz bandwidth.

Resumo em Inglês:

Abstract To obtain a long propagation length and a small effective mode area, a new hybrid plasmonic waveguide model is proposed. We design a hybrid plasmonic waveguide composed of chiral metamaterials, silver metal at its center, and surrounded by a graphene interface using the COMSOL environment based on the finite element method. The interface thickness is 1.02nm, where three monolayer graphene were used. The waveguide properties can be achieved with the range of radius 5-60 nm, chemical potential 0.1-1 eV, and refractive index of metamaterial is -3 within the wavelength used. Moreover, we obtained a long propagation length, a small effective mode area, high power confinement, and lower loss. The results showed that the presence of graphene positively affects the waveguide properties, while increasing the chirality parameter, K, does not have a good effect. At the chemical potential 1eV, the propagation length will be 2.45mm in the absence of chirality, while it equals 0.4mm at K=1 with the used wavelength 1.55μm.

Resumo em Inglês:

Abstract A novel planar balanced-to-balanced (BTB) microstrip filtering crossover with high isolation and common-mode (CM) suppression is proposed in this paper. The circuit structure is based on microstrip transmission lines without coupling sections, which can reduce insertion loss and enhance isolation. Specific theoretical analysis of the BTB filtering crossover configuration using transfer matrix and mixed-mode scattering parameters is performed. In order to verify the validity of the theory analysis and design, a microstrip BTB filtering crossover prototype at the center frequency of 2.45 GHz is fabricated and measured with high isolation and excellent CM suppression.

Resumo em Inglês:

Abstract Resource allocation strategies in optical networks are fundamental due to bandwidth limitations, increasing data demand, and the consequent need for spectral efficiency. They allow for improving optical spectrum usage and ensure flexibility in the face of the dynamic nature of traffic and the coexistence of different services, reducing costs and contributing to the system’s reliability. In this context, this work proposes a resource allocation strategy that combines power assignment with spectrum allocation. Power assignment is done by launching the minimum required power plus a margin according to the route’s state. Meanwhile, spectrum allocation is performed through a modified version of the Min Slot Continuity Capacity Loss (MSCL) heuristic, capable of finding a set of frequency slots in a route, which results in minor allocation capacity loss. The choice of the MSCL algorithm was motivated by the possibility of increasing spectral efficiency through the reduction of physical layer penalties and the reduction of spectrum fragmentation by combining freedom degrees: launch power of light, modulation, route, and spectrum. The developed heuristic was tested on two networks with distinct characteristics and compared with two reference approaches. The results demonstrated a significant superiority in terms of reducing the blocking probability.