A review on planar printed structures that are based on Matryoshka-like geometries is presented. These structures use the well-known principle of Matryoshka dolls that are successively nested inside each other. The well-known advantages of the planar printed technology and of the meandered nested Matryoshka geometries are combined to generate miniaturized, multi-resonance, and/or wideband configurations. Both metal and complementary slot structures are considered. Closed and open configurations were analyzed. The working principles were explored in order to obtain physical insight into their behavior. Low-cost and single-layer applications as frequency-selective surfaces, filters, antennas, and sensors, in the microwave frequency region, were reviewed. Potential future research perspectives and new applications are then discussed.

This paper describes the design, fabrication, and test of a printed planar log-periodic dipole antenna to be used as a standard gain antenna in simple, low frequency, anechoic chamber far-field antenna measurements.The design procedure is size constrained by the photolithographic printing circuit fabrication process.Maximum gain and an input reflection coefficient below -10 dB are envisaged for the frequency range 0.5-2.5 GHz.The antenna is printed on a low cost FR4 substrate, and a careful analysis, with optimization of all the antenna physical parameters namely: number, length, spacing and width of the dipoles, width of the feed line traces, feed line termination, feed balun, and substrate shape, is carried out.The good agreement obtained between numerical simulation and experimental results provides validation of the proposed antenna configuration and design procedure.

The design of a single-band singly-layered reflectarray fed by a circularly polarized 2x2 microstrip patch antenna array with corporate feeding to be used in K-band (18.7–19.2 GHz) is proposed in this paper. It is demonstrated by simulations and measurements that the axial ratio bandwidth performance of the reflectarray depends strongly on the circularly polarization purity of the feeder. Simulated and measured results revealed that the complete reflectarray exhibits good performance in terms of input impedance with -10 dB input reflection coefficient bandwidth of 19.0 %, radiation pattern with 3 dB axial ratio bandwidth of 10.55 % and 3 dB gain bandwidth of 2.64 %.

This paper presents a feasibility study of a singlylayered dual-band reflectarray for space applications.The data links should operate simultaneously at K-band downlink frequency band 17.7-20.2GHz with left-hand circular polarization (LHCP) and at Ka-band uplink frequency band 27-30 GHz with right-hand circular polarization (RHCP).The main aim is to present how a reflectarray can be designed so as to allow reconfigurability of its radiation pattern, especially in terms of beam steering to two different directions.The design is automated by means of a computational tool developed in MATLAB environment interfaced with the electromagnetic simulator CST Studio Suite by means of Visual Basic scripts.Simulation results are presented to demonstrate the efficiency of the proposed computational tool and reconfiguration strategy.

An antenna system based on a wideband printed monopole is proposed for the estimation of electromagnetic field radiation in the frequency range 0.7-3.5 GHz. Such system is envisaged to be integrated into protective vests worn by professional users in their working space environment as part of an intelligent multi-risk protection. Four dual-linearly polarized monopoles are integrated into the coat (chest, back, left and right shoulders) and an extra one in the helmet. Numerical simulation results, for the antenna system integrated into a simplified phantom model of the human torso and head indicate that the proposed solution can provide the required electromagnetic field evaluation.

This paper describes the design steps carried out to prove the concept of a wideband monopole antenna system to be used in a wearable device conceived for the evaluation of electromagnetic field radiation. Such a device is envisaged to be integrated into protective vests worn by professional users in their working space environment as part of intelligent multi-risk protection. Initially, the main characteristics of a simple straight monopole are reviewed to serve as a reference. A modified octagonal monopole antenna element is introduced, and a two dual-linearly polarized configuration of such monopoles is designed, fabricated, and tested to be used in the frequency range of 0.7–3.5 GHz. The expected radiation characteristics (input reflection coefficient and isolation between vertically and horizontally polarized ports) are confirmed experimentally. The effects of a thick lossy foam substrate layer used to mitigate the presence of the metal shield, employed in the vest lining as a Faraday cage protection, are analyzed both by simulation and experimentally. Finally, electromagnetic simulations are carried out to confirm that a system of five dual-linearly polarized monopole elements located in the chest, shoulders, back, and helmet of the user can provide an adequate estimation of the incident electromagnetic field radiation.

Design, fabrication and test of a dual-linearly polarized wideband printed planar monopole antenna is presented. The proposed configuration consists of two orthogonal CPW-fed modified octagonal monopoles with low mutual coupling. It is developed to be used in a wearable antenna system application to probe the electromagnetic field, with frequency in the range 0.7-3.5 GHz (5:1 bandwidth), incident on a professional user. The reasonable agreement obtained between simulated and experimental results has validated the proposed design approach and provided the proof of concept.

This communication proposes a novel unit cell for the design of dual-band dual-circularly polarized reflectarrays for space communications. The main advantage of the proposed cell is the use of one single layer for the antenna fabrication, hence yielding lower costs and fabrication with lower complexity in comparison to multilayer antennas. The proposed cell is used to design a dual-band dual-circularly polarized reflectarray with widely separated bands. Due to the physical symmetry, it provides very good polarization characteristics. The antenna performance is validated by far-field measurements and very good agreement between simulated and measured results has been verified.

The rectenna is a basic and fundamental element for RF energy harvesting. The development of efficient rectennas requires the implementation of some impedance matching technique between the rectifying circuit and the antenna element. An impedance matching technique inspired on the inset feeding of microstrip patches is proposed in this work. The technique keeps the size of the rectenna unchanged and does not require any additional component. An application example operating at 5.8 GHz and using a cheap FR4 substrate is presented.

This paper describes the analysis of the effects of a frequency selective surface (FSS) on the characteristics of a microstrip line fed antenna with a bow-tie slot in the ground plane for operation in the frequency range 1 to 10 GHz. The use of the FSS is proposed to miniaturize the antenna structure and increase the number of resonance frequencies and the gain. Air gaps can be inserted between the antenna and the FSS to allow for the adjustment of the resonance frequencies and increase the bandwidth. To prove the concept, antenna prototypes printed on a 30×30 mm2 FR4 low-cost substrate are designed, fabricated and tested. Good agreement is obtained between numerical simulations and experimental results, thus validating the proposed design procedure. The obtained miniaturization and multiband effects can be most convenient for multiservice wireless system applications such as WLAN, WiMAX, 4G, and 5G mobile communication systems.

The performance assessment of a two-beam electronically switchable circularly polarized reflectarray antenna based on single-layer circular microstrip patches with phase delay line stubs is presented. Preliminary numerical analysis demonstrates the reflectarray capability to switch its main beam between 9.1° and 18.2° from the boresight in K-band (17.7-20.2 GHz). A very simple preliminary model is used for the envisaged PIN diode switches. For an array with 20x20 unit-cells, the achieved gain is above 27.2 dBic and the side-lobe level is below –18.2 dB at f 0 . Moreover, a remarkably low axial ratio of 1.1 dB is obtained for the whole frequency band of operation.

This paper presents a complete and detailed description of the fabrication and measurement of the electromagnetic properties of water-based semi-solid phantoms with emphasis on the analysis of the time evolution of the complex permittivity of several samples stored in different conditions. A known recipe for a 2/3 muscle equivalent phantom is used as test material, and the several phantom sample properties are measured with an in-house developed coaxial probe technique. It is shown that the storing condition is of paramount importance to extend the lifetime of a given phantom. This behavior stems from the way the storing condition affects the water evaporation rate of the sample. In particular, while an unprotected sample can preserve its electromagnetic properties only for a few days, a very well-sealed one can last at least up to a year.

This article describes a circularly polarized 2 × 2 microstrip antenna array with corporate feeding to be used at K‐Band (18.7‐19.2 GHz) as a reflectarray feed. A design approach is proposed for the improvement of axial ratio and impedance bandwidths of circularly polarized microstrip antenna arrays with sequential rotation. A parametric analysis is also proposed to evaluate accurately the array phase center position. An array prototype has been designed, fabricated, and tested. The good agreement obtained between simulation and experimental results provides validation of the design approach and proof of the proposed concept.

This letter presents a new approach for the enhancement of the axial ratio (AR) of a single-layer circularly polarized reflectarray antenna based on a circular microstrip patch with phase delay-line stubs unit cell. The AR improvement is achieved by inserting insets around the two stubs, changing the orientation of one of them and using a mirror symmetry arrangement. Two prototypes have been designed, fabricated, and tested to proof the proposed concept in K-band. A good agreement has been obtained between numerical simulations and experimental results. The measured results confirm a remarkable AR improvement with values below 1 dB and 3dB gain and AR bandwidths larger than 23.7.

This paper presents a social spider optimization (SSO) design of a small-size microstrip antenna. Two antenna miniaturization techniques, based on the use of a Koch fractal contour and a shorting post (connecting the patch to the ground plane), are combined to enable a major size reduction. The antenna is inset fed by a microstrip line. The developed SSO algorithm is used to find out the best radius and position of the shorting post and the length of the inset feed, to achieve the desired resonant frequency with good impedance matching. Antenna prototypes have been fabricated and measured. The good agreement obtained between numerical simulation and experimental results has validated the design procedure. Compared with a conventional rectangular patch, the antenna resonance frequency is reduced from 2.45 GHz to 730 MHz, which corresponds to a remarkable miniaturization of about 70%. The proposed antenna is suitable for applications in the 700-800 MHz frequency range, such as 4G mobile communication systems.

A fast and accurate method is proposed for the design of rectennas. It combines the use of a full-wave electromagnetic simulator, for the analysis of the antenna, and a harmonic balance simulator, for the analysis of the rectifying circuit, with a single-point experimental calibration procedure. The proposed method can be used to speed up the development of general rectenna configurations. Two case studies are presented to illustrate the proposed concept. The first one is general, whereas the second is efficiency-optimization-oriented. A modified planar printed dipole without a matching network is used in both cases. An efficiency of 48% is achieved for a power density of 57 mu W/cm(2) around 5 GHz. A good agreement is obtained between simulation and experimental results.

The planning of new wireless communications networks, such as the fourth generation of mobile telephony (4G), represents a major challenge to include more and more advanced services with different quality requirements, mobility support, high transmission rates and high traffic capacities. The various environments in which these networks operate and the your associated phenomena, produce different effects in the behavior of the received signal and hence a variation in the performance of the radio links communication. Therefore, these effects should be evaluated correctly, in such a way that the sizing of the network meets the quality requirements regulated. This paper aims to establish the characterization of wireless signal coverage in indoor environments in the frequency range of 700 MHz. This band was chosen because of its allocation to be used by communication systems broadband 4G / LTE in Brazil. Thus, simulations based on the ray tracing method and measurements were made for comparative purposes. The measurements to characterize the coverage and signal behavior were carried out obtaining average values of the signal at regularly spaced intervals so as to ensure a smaller influence of fast fading phenomenon and greater spatiality therebetween. The research considered the values using artifices as virtual transmitters in the simulations, positioned at the beginning of each cross runner, who considered the same power output power measured at that point or location from the actual transmitter. Thus, the results showed a good agreement between simulated, measured and theoretical values calculated from the Friis formula, in situations with line of sight and without line of sight.

The path loss established between several wearable antennas placed on a tissue-equivalent phantom is investigated through numerical simulations and measurements. The on-body performance of a previously proposed dual-mode wearable textile antenna, designed to operate in the 2.45 GHz industrial, scientific and medical band, is evaluated and compared with a wearable textile patch antenna. Simulation results of a lambda/4 resonant wire monopole are also presented to serve as a reference. Five different scenarios for the location of the transmitting and receiving antennas are analyzed: one with line of sight (LOS), two with non-LOS (NLOS), and the remaining two in the transition between LOS and NLOS. The transmission results are evaluated with the antennas mounted on the surface of a homogeneous phantom with 2/3 muscle properties mimicking the shape and physical macroscopic properties of a human torso. A general good agreement is obtained between numerical simulation and experimental results. It is shown that in the NLOS scenario, the proposed antenna has an equivalent path loss only about 3.4 dB higher than the monopole and about 10 dB lower than the patch.

In this paper, a dual-band frequency selective surface, FSS, for WiFi applications (2.4 GHz and 5.8 GHz) is designed using the four arms star geometry associated to trapezoidal rings. The characteristics of each geometry are discussed separately and initial project equations are proposed. When associated, the resultant effects in the FSS frequency response are investigated, including the polarization and how the frequency of resonances can be adjusted. One advantage of the proposed FSS is the possibility of adjusting almost separately the frequency response associated to each geometry, with different bandwidths for each resonance. The polarization dependence is a drawback, but it can be surpassed by the use of double layer FSS, not discussed in this paper. Numerical and measured results are presented, verifying a very good agreement, with at least a rejection band of -15 dB at each WiFi bands.

In this paper is presented the implementation of a corner reflector antenna where the reflective metal plates are replaced by frequency selective surfaces, FSS, based on the four-arm star geometry. The projected antenna an aperture angle of 60° and operation at 4.0 GHz. The design steps are described and numerical and experiments. For the region within the aperture angle, the corner reflectors with metallic plates and FSS presented practically the same results. The differences between numerical and experimental results in the region outside the angle region are discussed and justified. It is concluded that the use of FSS as reflectors in the corner reflecting antenna is feasible, which is very interesting considering the characteristics of the material (low weight and reduced volume) and the simplicity of the of the FSS. In addition, the antenna proposed in this work is potentially attractive, since it is possible to use FSS reconfigurable and, therefore, if an active antenna is obtained.