Christos Kalialakis

Small H-shaped antennas for MMIC applications

A small short-circuited H-shaped GaAs monolithic microwave integrated circuits (MMICs) patch antenna is presented. Resonant at 5.98 GHz, it is the lowest frequency MMIC patch antenna reported that we are aware of and is intended for short-range communications (e.g., vehicular). Initial experimental and theoretical characterization of the proposed structure has been carried out on soft microstrip substrates. It has been shown that the size of an H-shaped patch antenna can be reduced to as low as one tenth of that of a half wavelength patch antenna resonant at the same frequency, saving valuable substrate space. The resonance frequency, radiation patterns and gain have been investigated. Ground plane truncation effects, which are important for MMIC applications, have been examined using the finite-difference time-domain (FDTD) method.

Analysis and design of integrated active circulator antennas

A study on the analysis and design of active integrated antennas based on active quasi-circulators is reported in this paper. The antenna consists of a novel hybrid active circulator and a short-circuited quarter-wavelength microstrip antenna, which combine to form an active antenna with transmit and receive action at the same frequency. A full-wave model of the configuration using the extended finite-difference time-domain method is devised to analyze its operation, to study parasitic electromagnetic coupling effects, and to derive design guidelines. Experimental results for a hybrid model are also presented.

Evolutionary Algorithms Applied to Antennas and Propagation: A Review of State of the Art

A review of evolutionary algorithms (EAs) with applications to antenna and propagation problems is presented. EAs have emerged as viable candidates for global optimization problems and have been attracting the attention of the research community interested in solving real-world engineering problems, as evidenced by the fact that very large number of antenna design problems have been addressed in the literature in recent years by using EAs. In this paper, our primary focus is on Genetic Algorithms (GAs), Particle Swarm Optimization (PSO), and Differential Evolution (DE), though we also briefly review other recently introduced nature-inspired algorithms. An overview of case examples optimized by each family of algorithms is included in the paper.

Harmonic Radiation from Varactor-Loaded Microstrip Antennas

Novel results are presented for the radiated harmonics from varactor loaded microstrip antennas. Results are given for rectangular half wavelength and quarter wavelength microstrip antennas. The effect of the tuning range is also investigated.

A Novel Ultra-Lightweight Multiband Rectenna on Paper for RF Energy Harvesting in the Next Generation LTE Bands

This paper introduces a novel compact ultralightweight multiband RF energy harvester fabricated on a paper substrate. The proposed rectenna is designed to operate in all recently released LTE bands (range 0.79–0.96 GHz; 1.71–2.17 GHz; and 2.5–2.69 GHz). High compactness and ease of integration between antenna and rectifier are achieved by using a topology of nested annular slots. The proposed rectifier features an RF-to-dc conversion efficiency in the range of 5%–16% for an available input power of −20 dBm in all bands of interest, which increases up to 11%–30% at −15 dBm. The rectenna has been finally tested both in laboratory and in realistic scenarios featuring a superior performance to other state-of-the-art RF harvesters on flexible substrates.

Performance analysis of a ultra-compact low-power rectenna in paper substrate for RF energy harvesting

In this paper the experimental results of a compact low-power rectenna in paper substrate, designed to operate in the Wi-Fi band, are presented. The complete prototype, based on an annular slot antenna and a single-diode rectifier, features a weight of 1.5 grams and shows an RF-to-dc conversion efficiency in the design band of about 40 % for a −10 dBm available input power, of about 28 % at −15 dBm, and in the range [10, 22] % at −20 dBm, corresponding to an output DC voltage in the order of 320, 240 and 60 mV respectively. Additionally, the rectenna features an efficiency higher then 7 % in the whole band 1.8–2.7 dBm for a power density estimated around 3 µW/cm2.

Design of a ultra-compact low-power rectenna in paper substrate for energy harvesting in the Wi-Fi band

This paper presents the design of a novel rectenna based on a tapered annular slot and a single-diode rectifier, optimized to operate in the Wi-Fi band and in presence of low input power (Pavs=-15 dBm). In order to obtain a compact layout a double-layer architecture has been considered, according to which the interior metal surface of the annular slot is employed as ground plane for the rectifying circuit placed on the other side of the substrate. As a result, a rectenna with an active area of only 40 × 33 mm2 and an efficiency included between 26.5 and 28% has been obtained. The antenna has been fabricated in paper substrate and tested in the anechoic chamber. Then, the rectifier has been designed and optimized within the Advanced Design System suite. Finally, the rectenna performance has been discussed and compared to the State of the Art (SoA).

Evolutionary design of a dual band E-shaped patch antenna for 5G mobile communications

Fifth generation (5G) wireless technology is a promising solution for multi-Gbps data rates in future mobile communications. The new devices are expected to operate at millimeter wave frequencies. To address the 5G requirements novel antennas have to be developed. In this paper the Teaching-Learning-Optimization (TLBO) algorithm is applied in order to design a dual-band E-shaped patch antenna. The geometrical parameters of the aperture-coupled antenna are the inputs of the optimization algorithm. The method gives acceptable design solutions achieving simultaneously S11 minimization and low VSWR at the frequencies of interest (25GHz and 37GHz).

Combined effects of finite diversity switch isolation and antenna mutual coupling on spatial diversity

The effects of certain non-ideal conditions on spatial diversity are examined. Diversity switches are microwave components that can be found in spatial-diversity systems. The effects of the finite isolation are treated, along with the effect of mutual coupling between the antenna elements. The mutual coupling is demonstrated for the case of dipoles and rectangular microstrip antennas. Closed-form expressions are provided for the correlation efficient of two-branch diversity schemes.

Mutual coupling effects on the MIMO capacity using dual band Wi-Fi double-T printed antennas

The use of a T-Shaped dipole antenna in a MIMO context is investigated. The antenna operates in the two Wi-Fi bands (namely 2.4GHz and 5.25 GHz). The mutual coupling between two T-Shaped dipole elements is reported for several different arrangements. The effect of the mutual coupling on the MIMO capacity is studied and indicative capacity results are given for Rayleigh fading channels.