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A multilayer aperture antenna array in millimeter-wave band is presented in this article. The antenna array is based on glide-symmetric holey gap-waveguide technology combined with E-plane insertion gaps for a low-cost and low-loss design. The radiating part of the antenna array is formed by an array of sixteen aperture antennas, grouped in four sets of 2x2 antenna subarrays in E-plane configuration. The 2x2 subarrays are fed by a one-to-four corporate feeding network in E-plane with holey gap-waveguide technology. The antenna array has been manufactured with high precision stereolithography (SLA) and subsequent metal plating. This design procedure yields a low-cost and low-weight manufacturing process for functional prototypes. The complete array has been manufactured and measured, comparing its performance with the simulation results. Measurements show an input reflection coefficient below -10 dB which ranges from 68 GHz to 74 GHz. The measured radiation patterns suit adequately the defined ones in the design stage. Moreover, gain above 19 dBi in the entire operating frequency band is achieved with a 74.1% mean antenna efficiency.

In this article, two novel efficient leaky-wave antennas (LWAs) with stable radiation patterns operating in the 60 GHz band are proposed. The LWAs are implemented in groove-gap waveguide (GGW) technology. To mitigate the beam squint due to the dispersive nature of LWAs, complementary-dispersive prisms are coupled to the LWA radiation aperture. The antennas are implemented in fully metallic purely holey periodic structures, resulting in a more cost-effective and robust manufacturing process compared to previously reported pin-based structures. Two prisms are proposed, one with mirror symmetry and one with glide symmetry. When the prism possesses a glide symmetry, much fewer holes are required while maintaining a similar performance, which even further decreases the fabrication costs. The complex propagation constant is optimized for low sidelobe levels (SLLs) with tailored hole diameters and waveguide dimensions, thus for the first time demonstrating the capability of using glide-symmetric holes to control the leakage rate. Two prototypes with mirror- and glide-symmetric prisms are theoretically synthesized and validated by the simulated and experimental results. A frequency bandwidth of 11% is achieved for both prototypes with the beam squint within ±0.9° (mirror) and ±1.7° (glide), SLLs below −15 dB (mirror) and −13 dB (glide), total efficiency almost 90%, and realized gain of 17 ± 0.5 dB at a fixed observing angle. The developed antennas are intended for mm-wave point-to-point communications.

Mobile communications are growing and the number of users is constantly increasing at an accelerated rate, as well as the demand for the services they request. In the last few years, many efforts have focused on the design and deployment of the new fifth generation (5G) cellular networks. However, novel highly demanding applications, which are already emerging, need to go beyond 5G in order to meet the requirements in terms of network performance. But, at the same time, as the Earth does not allow us to increase the carbon footprint anymore, the energy consumption of the communication networks has to be critically taken into consideration. A multi-objective approach for addressing all these issues is therefore required. This work develops a cellular network framework that allows the evaluation of different system parameters over dynamic traffic patterns, as well as optimizing the different conflicting objectives simultaneously. The novelty relies on that the optimization process integrates key performance indicators from different layers of the network, namely the radio and the network layers, aiming at reaching solutions that account for the power consumption of the base stations, the total capacity provided to mobile users and also the signaling cost generated by handovers. Moreover, new metrics are needed to evaluate different solutions. Starting from the well-known energy efficiency merit factor (bits/Joule), three new merit factors are proposed to classify the network performance since they take into account several network parameters at the same time. These indicators show us the ideal working point that can be used to plan the point of operation of the network. These operation points are a medium-high power and capacity load and a low signaling load.

This paper presents a compact and low-loss V-band waveguide phase shifter based on glidesymmetric pin configuration. This kind of higher symmetry permits the control and improvement of the electromagnetic behavior or radiofrequency devices, as it is the case of the proposed phase shifter. The study of the dispersion diagram of the phase shifter unitary cell demonstrates that the pin configuration is a proper option for introducing a phase shift in a waveguide-based system. There is a significant increase in terms of phase shift when using a glide-symmetric pin distribution compared to its corresponding nonglide- symmetric configuration. Through this paper, the key geometrical parameters are also determined. The complete phase shifter is composed of an optimized cascade of tailored unitary cells so that the desired final phase shift value is achieved. A prototype has been manufactured in order to validate the theoretical approach through the comparison of phased shifters with both non-glide-symmetric and glide-symmetric configurations. The measurement results demonstrate the higher performance and compactness of the glidesymmetric phase shifter. For the same distance, the glide-symmetric version of the phase shifter provides more than 60% of phase shifting compared to the non-glide-symmetric phase shifter. Both phase shifters have a good impedance matching between 46 and 60 GHz and an insertion loss lower than 1 dB, thus clearly enabled as a 5G technology., This work was supported in part by the Spanish Research and Development National Program and FEDER under project TIN2016-75097-P, in part by the Universidad de Málaga, under Grant PPIT.UMA.B1.2017/15, in part by the Universidad de Granada under Project PPJI2017.15, and in part by the Universidad de Granada through the grant program ``Becas de iniciación a la investigación'' from the Plan Propio de Investigación.

The upcoming high-speed wireless communication systems will be hosted by millimeter and sub-millimeter-wave frequency bands. At these frequencies, electromagnetic waves suffer from severe propagation losses and non-line-of-sight (NLOS) scenarios. A new wireless communication paradigm has arrived to resolve this situation through the use of reconfigurable intelligent surfaces (RIS). These metadevices are designed to reconfigure the wireless environment in a smart way. Traditional RIS designs based on the implementation of 2-D configurations have been considered up to now. However, 3-D structures enable an extra degree of freedom in the design that can be taken as an advantage for the development of improved RIS structures with advanced functionalities. This article proposes the implementation of a novel electronically-reconfigurable RIS based on the use of 3-D graphene meta-atoms. The reconfigurability lies on the graphene conductivity, easily tunable with a biasing voltage. Different conductivity values vary the meta-atom electromagnetic response, modifying the RIS functionality. A multi-objective optimization framework determines the optimal phase state of each meta-atom to accomplish the desired RIS performance. The operation of the RIS as an efficient beam steerer/splitter, absorber and polarization selector is validated with full-wave results.

This letter presents a closed-form integral-equation formulation that models the director tilting in nematic liquid crystals. The proposed formulation is computationally efficient compared to numerical methods and provides a physical insight on the matter. Our previous work is generalized from the one-constant approach to all the possible cases that cover the elastic constants. These constants determine in great extent the electrical properties of the liquid crystal, and subsequently, the response of the reconfigurable devices that take use of it. Therefore, a more precise but still simple modeling of their influence is pursued here. Simulations show good agreement with numerical implementations. In comparison, the error in the estimation is considerably reduced when using the integral-equation formulation, specially as the polarization voltage or the dielectric anisotropy decreases., IEEE Microwave and Wireless Components Letters

A reconfigurable phase shifter in waveguide composed by glide-symmetric holey unit cells is presented in this paper. The hole depths of this kind of holey unit cell are modified to allow a phase shift variation in the waveguide. The adjustment of the hole depths in the unit cell is achieved by the insertion of screws in the holes that are implemented as through holes. This advantage in implementation of reconfigurable elements inside the holes is added to the low-dispersive behaviour of the holey glide-symmetric unit cells. Both features make possible the design of a reconfigurable phase shifter in waveguide with flat phase shift responses. The phase shifter design proposed in this work provides a maximum phase shift of 90° with good impedance matching from 50 GHz to 75 GHz.

This paper presents the applicability of using the time-gating technique to propagation measurements in order to recreate new scenarios. This technique, which has been studied previously in antenna measurements, is applied in propagation measurements to modify and tune the reflections that a particular propagation scenario exhibits. A new configuration for shielded chambers is proposed, where half of the chamber is covered with absorbers (anechoic chamber) and half without absorbers (reverberation chamber). This configuration and the time-gating technique allow the study of the propagation environment for the new recreated scenarios.

This paper analyzes thoroughly the dispersion and filtering features of periodic holey waveguides in the millimeter-wave frequency range. Two structures are mainly studied depending on the glide and mirror symmetries of the holes. A parametric study of the dispersion characteristics of their unit cells is carried out. Glide-symmetric holey waveguides provide a higher propagation constant and a low dispersion over a wide frequency range regarding hollow waveguides. This property is particularly useful for the design of low-loss and low-dispersive phase shifters. We also demonstrate that glide-symmetric holey waveguides are less dispersive than waveguides loaded with glide-symmetric pins. Furthermore, we perform a Bloch analysis to compute the attenuation constants in holey waveguides with mirror and broken glide symmetries. Both configurations are demonstrated to be suitable for filter design. Finally, the simulation results are validated with two prototypes in gap-waveguide technology. The first one is a 180$^{o}$ phase shifter based on a glide-symmetric holey configuration that achieves a flat phase shift response over a wide frequency range (27.5\% frequency bandwidth). The second one is a filter based on a mirror-symmetric holey structure with 20-dB rejection from 63 GHz to 75 GHz.

This work was supported in part by the Spanish Research and Development National Program under Project TIN2016-75097P and Project RTI2018-102002-A-I00, in part by "Junta de Andalucia" under Project B-TIC-402-UGR18 and Project P18.RT.4830, and in part by the Predoctoral Grant FPU18/01965., In this brief, we present a low-loss mechanically reconfigurable phase shifter implemented in gap-waveguide technology for mm-wave frequencies. The proposed design gives a practical implementation of tuning elements inside the waveguide providing alternatives to the use of the E-plane split waveguide at high frequencies in order to avoid leakage losses. The depicted phase shifter design is based on a H-plane split waveguide. The phase shift is controlled by means of a tuning screw, which exerts pressure on a flexible metallic strip inserted inside the waveguide. The flexible strip bends with different curvature radii and determines the phase shift at the output port. Cost-effective manufacturing and simple implementation of the flexible metallic strip are achieved by means of the gap-waveguide design. A prototype has been manufactured for validation purposes. Good impedance matching is achieved from 64 GHz to 75 GHz providing a 15.8% impedance bandwidth. The results show a maximum phase shift of 250° with a maximum and mean insertion loss (IL) of 3 dB and 1.7 dB, respectively., Spanish Research and Development National Program TIN2016-75097P RTI2018-102002-A-I00, Junta de Andalucia B-TIC-402-UGR18 P18.RT.4830, FPU18/01965

Two cost-effective implementations of a leaky-lens antenna at 60 GHz are proposed for high-throughput 5G communication links. The leaky-wave feed is realized in gap-waveguide technology, where the radiation from the slit is controlled with glide-symmetric holes. The beam-squint of the leaky-wave radiation is mitigated, owing to the coupling of a complementary-dispersive prism. Here, two prisms are implemented, one with glide-symmetric holes, and another with substrate-integrated-holes (SIHs), both integrated in parallel plates with the leaky-wave feeding. Thanks to glide symmetry, better control of the leakage rate, lower costs, and better tolerance to manufacturing are achieved in comparison with the non-glide holey counterpart. In addition, the SIH-based design exhibits a substantially enhanced bandwidth with even better robustness. In the analysis of the leaky-wave feed, more accuracy and reduced computational time is achieved by using a multi-mode method. Both antennas show stable radiation patterns, featuring high efficiency, high gain, and low side lobe levels.

This paper presents the compact design of a substrate-integrated waveguide (SIW) antenna based on H-plane aperture structure. The antenna is composed by a coaxial feeding and an aperture. In this aperture inner metallic vias are introduced acting as partially detached walls in order to form 4 adjacent subapertures at the end of the aperture antenna. Thus, the field from the feeding is divided in different wavefronts that are composed at the antenna aperture to get an endfire radiation. In this manner, a flatter wavefront is generated to achieve high directivity. Additionally, some periodic parallel strips are printed after antenna aperture to improve the impedance matching with the air. The proposed antenna has impedance matching below -10 dB from 34 to 36 GHz with nearly constant gain between 13 and 15 dBi. A prototype is manufactured to validate the proposed antenna design.

This paper presents the applicability of using structures to control the phase shift in a waveguide phase shifter. By means of dispersion diagrams, different phase shift unit cells are analyzed. Glide symmetry is also applied to some of these unit cells to evaluate its effects in the propagating modes. Then, unit cells with best dispersive behaviour are selected to design two waveguide phase shifters, one by pinned unit cells and the other by holey pinned unit cells. Both waveguide phase shifters are well matched in the frequency range from 50-75 GHz with insertion losses lower than 0.5 dB. The phase shift produced by both waveguide phase shifter is also evaluated. Pinned waveguide phase shifter is more dispersive compared to the holey waveguide phase shifter, producing a phase shift deviation over 180° of ±50° and ±10°, respectively.

This work has been supported by the the Spanish and Andalusian goverments, and FEDER, under contrats TIN2016-75097-P, RTI2018-102002-AI00 and B-TIC-402-UGR18. Francisco Luna also acknowledges support from Universidad de M ' alaga. The authors thankfully acknowledges the support provided by the Supercomputing and Bioinformatics center of the University of Malaga., Network densification with deployments of many small base stations (SBSs) is a key enabler technology for the fifth generation (5G) cellular networks, and it is also clearly in conflict with one of the target design requirements of 5G systems: a 90% reduction of the power consumption. In order to address this issue, switching off a number of SBSs in periods of low traffic demand has been standardized as an recognized strategy to save energy. But this poses a challenging NP-complete optimization problem to the system designers, which do also have to provide the users with maxima capacity. This is a multi-objective optimization problem that has been tackled with multi-objective evolutionary algorithms (MOEAs). In particular, a problem-specific search operator with problem-domain information has been devised so as to engineer hybrid MOEAs. It is based on promoting solutions that activate SBSs which may serve users with higher data rates, while also deactivating those not serving any user at all. That is, it tries to improve the two problem objectives simultaneously. The resulting hybrid algorithms have shown to reach better approximations to the Pareto fronts than the canonical algorithms over a set of nine scenarios with increasing diversity in SBSs and users., Spanish goverment, Andalusian goverment, European Commission TIN2016-75097-P RTI2018-102002-AI00 B-TIC-402-UGR18, Universidad de Malaga, Supercomputing and Bioinformatics center of the University of Malaga

This communication presents the design of a two-port electronically tunable phase shifter at K band. The phase shifter consists of a 3 dB hybrid coupler loaded with reflective phase-controllable circuits. The reflective circuits are formed by varactors and non-sequential impedance transformers which increase the operational bandwidth and the provided phase shift. The final phase shifter design is formed by two loaded-coupler stages of phase shifting to guarantee a complete phase turn. An 18 GHz phase shifter design with dynamic range of 600 degrees of phase shift is depicted in this document. The prototype is manufactured and validated through measurements showing good agreement with the simulation results., This work has been partially supported by the TIN2016-75097-P, RTI2018-102002-A-I00, and EQC2018- 004988-P projects of the Spanish National Program of Research, Development, and Innovation and project B-TIC-402-UGR18 of Junta de Andalucía

This document presents the design of an array of helix antennas in axial mode based on higher symmetries. These higher symmetries permit, for a given frequency, the miniaturization of the antenna. Therefore, an array formed by this kind of miniaturized antennas presents lower mutual coupling among the constituting antennas. A comparison is made between the performance of antenna arrays formed by conventional and glide-and-twist-symmetrical helix antennas. The results show a decrease in mutual coupling in the glide-and-twist-symmetrical helix array, regarding to the conventional helix array, for the same element spacing. Moreover, better radiation performance is achieved in terms of directivity and gain in the miniaturized helix array.

This paper presents a radiofrequency (RF) energy harvesting system based on an ultrawideband Archimedean spiral antenna and a half-wave Cockcroft-Walton multiplier circuit. The antenna was proved to operate from 350 MHz to 16 GHz with an outstanding performance. With its use, radio spectrum measurements were carried out at the Telecommunication Engineering School (Universidad Politécnica de Madrid) to determine the power level of the ambient signals in two different scenarios: indoors and outdoors. Based on these measurements, a Cockcroft-Walton multiplier and a lumped element matching network are designed to operate at 800 MHz and 900 MHz frequency bands. To correct the frequency displacement in the circuit, a circuit model is presented that takes into account the different parasitic elements of the components and the PCB. With an input power of 0 dBm, the manufactured circuit shows a rectifying efficiency of 30%. Finally, a test is carried out with the full RF energy harvesting system to check its correct operation. Thus, the RF system is placed in front of a transmitting Vivaldi antenna at a distance of 50 cm. The storage capacitor has a charge of over 1.25 V, which is enough to run a temperature sensor placed as the load to be supplied. This demonstrates the validity of the RF energy harvesting system for low-power practical applications., This research was funded in part by the project TIN2016-75097-P of the Spanish Research and Development National Program, and in part by the project TEC2017-85529-C3-1-R of the Ministerio de Economía y Empresa.

This paper presents an analytical expression that models the tilt angle of directors in a nematic liquid crystal (LC), depending on its elastic properties, its dielectric anisotropy, and the quasi-static electric field applied. The analytical solution obtained is fast and easily computable in comparison with numerical estimations and is of special interest in radiofrequency; for instance, for the LC modeling in full-wave electromagnetic simulators in the design process of electronically tunable devices, such as microwave phase shifters or electronically steerable antennas for satellite communications. Subsequently, a comparison is made between numerical approaches (self-implemented shooting method) and the analytical formulas when varying the parameters of the LC, being demonstrated its usefulness. The average LC director is then obtained and used to form the full permittivity tensor that completely characterizes the electrical properties of the material. Finally, an electromagnetic simulation is carried out to show the capabilities of the LC as a tunable phase shifter. It is shown that only 5 cm of a commercial 200-mm LC mixture is necessary to achieve 360 of the maximum variable phase shift at the 30-GHz band, This work was supported in part by the Spanish Research and Development National Program under Project TIN2016-75097-P, and in part by the Ministerio de Economía under Project TEC2017-85529-C3-1-R.