Search

A leaky-wave antenna made of cavity-backed-slot radiating elements with open-stopband suppression is presented. The cavity-backed slots are seriesly fed by a strip. The bandwidth of the unit cell o...

A broadband technique to extract the attenuation and phase constants of the slot mode in a rectangular waveguide from either simulation or measurement results is proposed in this letter. The method is based on processing the values of the reflection coefficient of several slotted waveguides with different lengths and the same termination and feeding. The accuracy of the method can be improved by increasing the number of simulated or measured waveguides. The proposed technique is specially conceived to separate the contribution of the slot mode from other modes. An implementable structure and a measurement method to apply the extraction technique are proposed and used. Measured and simulation results of the proposed technique obtained from waveguides filled with two different materials are shown up to 10 GHz and validated using an approximate model. The proposed method can be regarded as a powerful technique to compute the propagation constants of leaky modes in leaky-wave antennas.

We describe a method for the broadband measurement of the even- and odd-mode propagation constants of symmetrical coupled transmission lines. The main advantage of the method, its simplicity, lies in the lack of need for four-port measurements. Only two-port measurements are required, and thus just a two-port vector network analyzer (VNA). The accuracy of the results can be increased at the cost of a higher number of measured coupled-line lengths. The new approach has been successfully applied for the determination of coupled microstrip lines in the 2- to 20-GHz frequency band in both simulated and experimental cases. A brief discussion about the repeatability of the microstrip launcher and the adverse effects of radiation is included.

An equivalent-circuit topology for two-port lossy non-symmetric reciprocal networks is proposed. The circuit topology is based on the eigenstate decomposition. The proposed circuit consists of two immittances and two transformers with a single complex turns ratio, all obtained from the eigenvalues and eigenvectors of the admittance or impedance matrix of the network in a straightforward way. The interconnection of the circuit elements is simple and compact, and the real parts of its immittances are always positive. To verify its behavior, the equivalent circuit of two different leaky-wave antenna unit cells is extracted: a series-fed coupled patch radiating element, and the complementary strip-slot. Simulated and measured data are provided for the study cases, highlighting the satisfactory behavior of the equivalent circuit over a very broad bandwidth. A simple asymmetry model is also proposed that can be used advantageously in the analysis and design of non-symmetric two-ports, like unit cells of leaky-wave antennas.

Two ways of increasing the working bandwidth of series-fed Cavity-Backed Slots (CBS) are presented and analysed in this contribution. One of them consists in increasing the off-set feeding distance of the slot. The other one adds a matching stub in the feeding line. Simulation results of both ways for matching the same slot are provided. Results show that the matching stub can be used along a wider bandwidth effectively, but, in this case, an asymmetric stripline or enclosed microstrip are the only option to feed the CBS.

In this contribution, a planar leaky-wave antenna capable of dual-band frequency scanning including broadside is presented. It is based on the complementary strip-slot element, which is a microstrip-fed slot with ultra broad impedance bandwidth, achieved by introducing its complementary stub on the layer of the microstrip. The mitigation of the broadside degradation is accomplished by properly designing the strip-slot and the pitch of the array and by introducing asymmetry (misalignment) in the unit-cell. The resulting structure differs from previous proposals in the broadband element on which it is based, which allows dual-band behaviour and high efficiency with an array of just five elements.

The design of an electronically steerable wideband planar traveling-wave antenna is presented. The proposed antenna has a very simple structure based on a microstrip line loaded with several radiating elements and phase shifters between them. The phase shifters are based on tunable capacitances, in order to perform a continuous phase shift between the radiating elements and control the main beam direction. The radiating elements are complementary strip slots that have a very broad impedance bandwidth, thus allowing the antenna to have two different modes of operation: maintaining the main lobe direction over a significant bandwidth, 1.71–2.17 GHz, and performing a main beam scanning over this bandwidth with a maximum angle range of $-45^{\circ}$ to 45° at 2 GHz.

Huygens' metasurfaces are electrically thin devices which allow arbitrary field transformations. Beam refraction is among the first demonstrations of realized metasurfaces. As previously shown for extreme-angle refraction, control over only the electric impedance and magnetic admittance of the Huygens' metasurface proved insufficient to produce the desired reflectionless field transformation. To maintain zero reflections for wide refraction angles, magnetoelectric coupling between the electric and magnetic response of the metasurface, leading to bianisotropy, can be introduced. In this paper, we report the theory, design, and experimental characterization of a reflectionless bianisotropic metasurface for extreme-angle refraction of a normally incident plane wave towards 71.8$^\circ$ at 20 GHz. The theory and design of three-layer asymmetric bianisotropic unit cells are discussed. The realized printed circuit board structure was tested via full-wave simulations as well as experimental characterization. To experimentally verify the prototype, two setups were used. A quasi-optical experiment was conducted to assess the specular reflections of the metasurface, while a far-field antenna measurement characterized its refraction nature. The measurements verify that the fabricated metasurface has negligible reflections and the majority of the scattered power is refracted to the desired Floquet mode. This provides an experimental demonstration of a reflectionless wide-angle refracting metasurface using a bianisotropic Huygens' metasurface at microwave frequencies., Accepted in PRB

In this contribution, we present the application of Huygens’ metasurfaces (HMS) to the arbitrary design of leaky-wave antennas (LWAs). These metasurfaces have demonstrated their capabiity to tailor the electromagnetic waves at will. We use them to design LWAs consisting on a parallel-plate waveguide in which the top cover is replaced by a HMS, which implements the desired field transformation. By introducing bianisotropy of the omega type into the metasurface, we have the required degrees of freedom to achieve arbitrary control of the LWA radiation parameters: leakage factor and pointing angle (phase constant). The theoretical derivation of the concept and the design methodology will be described. Moreover, the flexibility in the design will be highlighted with results of two examples of broadside radiation with different directivities. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 706334.

A novel planar travelling-wave ring array with polarisation agility is introduced. The array is built by applying the sequential rotation technique with the complementary strip-slot element. This element is a conventional microstrip series-fed slot with the special feature of very broad impedance bandwidth thanks to the strip superimposed into it on the microstrip layer. The feeding of the array elements and the required phase shift between them are provided by a ring-shaped microstrip line, which is terminated in two ports. Vertical linear polarisation, horizontal linear polarisation, right-handed circular polarisation and left-handed circular polarisation can be generated with this very simple planar structure, just by controlling the phase and amplitude of the excitation at the two ports. Moreover, thanks to the wide impedance bandwidth of the element, multiband behaviour is achievable. A design example that operates at three different bands (centred around 6, 9 and 12 GHz) is analysed, which presents ...

A novel microstrip log-periodic array based on the broadly-matched complementary strip-slot radiating element is proposed. The array consists of microstrip-fed log-periodically-scaled slots on the ground plane and their complementary stubs on the microstrip layer. Since the radiating element is not resonant, the analysis differs from the previously reported log-periodic arrays. Low scale factor (τ) with high radiation efficiency is possible, since the element radiation efficiency is not resonant and the relative spacing (σ) does not have to be selected for good matching, because the element is intrinsically matched. A design example with τ = 0.909, σ = 0.17 and 15 elements has been analyzed. The achieved bandwidth goes from 2.7 to 8.7 GHz, with a radiation efficiency and a gain of better than 85% and 5 dB, respectively. Moreover, the antenna can be terminated in an open circuit without affecting its performance. Simulated and experimental results show that the radiation pattern is stable over frequency. A method for computing the radiation pattern using equivalent circuits as well as results with a reflector plane for cancelling the beam in one half-space are also included. Due to the good performance, simplicity and low cost, this antenna can be suitable for broadband applications.

The complementary strip-slot radiating element is a microstrip-fed slot modified by introducing its complementary stub on the layer of the microstrip. Previous works have shown that the introduction of the stub into the conventional slot results in an ultra broad impedance bandwidth and have provided a lattice-network equivalent circuit for its precise modeling. In this contribution, an interesting property of the symmetric lattice networks is highlighted and used to illustrate why the complementary strip-slot radiates as the conventional microstrip-fed slot, thus corroborating the conclusions of previous works based on empirical results.

Pedestrian navigation in challenging areas where global navigation satellite systems (GNSSs) lack the required accuracy and availability, such as indoor and urban canyons, is becoming increasingly important. Multisensor navigation is one of the techniques that has shown promising positioning accuracy in such environments. Being able to appropriately fuse GNSS pseudoranges in a multisensor positioning system is advantageous as it allows us to make use of fewer than four detected satellite signals and to incorporate more accurate estimation models. In this study, a particle filter-based pedestrian positioning system is enhanced to use pseudorange measurements of a GNSS receiver instead of direct position solutions. By using correctly modelled pseudoranges, a single satellite visible over a certain time period might improve positioning accuracy and robustness when combined with measurements from other positioning sensors, like a foot-mounted inertial measurement unit. Additionally in this study, a statistical multipath error model for pseudoranges is integrated. Promising results have been achieved in a challenging indoor environment where blockage of satellites' signals and multipath are common issues.

This article proposes the lattice network as a beneficial alternative to T- and topologies for modeling symmetric transmission line discontinuities and components.The lattice network presents some important features, which make it a powerful tool to find realizable equivalent circuits. The limitations of the T- and topologies and the validity of the lattice network in terms of realizability are highlighted in this article through two microstrip components: a dumbbell-shaped defected ground structure and a microstrip stepped-impedance hairpin resonator. Moreover, the lattice image impedance is proposed here as a parameter that allows determining whether a branch of the network is predominant. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:636–639, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27385

Design aspects of a novel beam-reconfigurable pla-nar series-fed array are addressed to achieve beam steering with frequency tunability over a relatively broad bandwidth. The design is possible thanks to the use of the complementary strip-slot, which is an innovative broadly matched microstrip radiator, and the careful selection of the phase shifter parameters. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.

A novel planar slot radiating element with applications in series-fed arrays and significant bandwidth enhancement is presented in this communication. The structure is based on the microstrip-slotline coupling and simply consists of a microstrip-fed slot with a symmetrically-arranged strip conductor superimposed onto it. The broad impedance bandwidth (up to 16 GHz) lies in the resulting all-pass section that the strip and the slot make up. A theoretical study of the structure in terms of even and odd modes as well as a straightforward equivalent circuit are provided, which offer the required analytical tools to state the design methodology. Experimental and simulated results corroborate that the strip acts as a mere matching element that does not practically alter the slot radiation characteristics.

A planar dual-band sequentially-rotated array is proposed to cover the radionavigation bands at 1.19 and 1.57 GHz. The antenna consists of a two-port ring microstrip line that series feeds four radiating elements. The basic radiator is the so-called complementary strip-slot, a microstrip-fed slot that has its complementary stub superimposed to it on the microstrip layer, in order to cancel the slot resonant behaviour and provide ultra broad impedance matching. Thanks to this element feature, the antenna can cover the two bands and diplex them into the two ports without the need of additional passive or active components. The detailed design and results of the reflection coefficient, axial ratio and radiation patterns are provided, which confirm the good performance of this simple antenna.

Equivalent circuit topologies for two-port reciprocal nonsymmetric structures are proposed as an extension of the well-known symmetric lattice network. An eigenstate formulation approach that allows the separation of the eigenmodes in the equivalent circuit, as in the symmetric lattice network, is adopted. Four topologies based on series or parallel immittances with the combined use of some transformers are proposed. Particular cases, such as symmetric networks and parallel and series single elements, are derived from the proposed topologies. Moreover, power dissipation in these topologies is also analyzed. A modification in the reference planes is further introduced to achieve power dissipation orthogonality in the two branches of the circuit, as happens in the symmetric lattice network. Additionally, real transformation ratios for the transformers and nonnegative real parts for the immittances are obtained. Finally, the equivalent circuit is extracted for a complementary strip slot with different degrees of asymmetry. This illustrative example confirms the usefulness of the proposed topologies, which can be regarded as an extension of the symmetric lattice network, since they preserve the eigenstate decomposition.