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This article presents the first substrate integrated waveguide (SIW) phase shifter that can be reconfigured using liquid metal (LM). This digital phase shifter exhibits low insertion loss and is reciprocal and bidirectional. It incorporates a series of holes which can be filled or emptied of liquid metal, enabling us to add or remove via connections dynamically, on-the-fly. Using a collection of such holes, it is possible to create a wall along the E-plane or H-plane of the waveguide. When the wall is in place, it blocks the passage of energy. When the wall is absent, energy is able to flow. In this way, it is possible to guide the electromagnetic (EM) waves through one of three paths, having different electrical lengths. The result is a digital switched-line phase shifter that achieves coarse steps of phase change, from 0° up to 180°, in steps of 60°. By filling or emptying individual holes, it is possible to introduce reactive loading into each path. In this way, it is possible to achieve fine phase control in steps of 10°. Using both forms of reconfiguration in unison, the proposed phase shifter is able to deliver a phase shift of up to 180°, in steps of 10°. The proposed phase shifter operates at 10 GHz and exhibits an insertion loss of less than 2.3 dB over its entire operating band. Furthermore, the underlying concept of the proposed phase shifter can be readily scaled for operation in the millimeter-wave (mm-wave) band. The existing phase shifters operating in that band exhibit significant insertion losses. MM-wave phase shifters are expected to find application in 5G mobile access points.

This letter presents a new approach for reconfiguring substrate integrated waveguide (SIW) devices. It involves allowing or prohibiting the wave propagation by using a removable wall which is built from a series of drill holes. When the wall is required, the holes are filled with gallium-based liquid metal (LM), thus forming vias. When the wall is no longer required, the holes are emptied of LM. The method has been applied to a single-pole single-throw (SPST) SIW switch as well as a single-pole double-throw (SPDT) switch. Both switches perform well over a wide frequency bandwidth, approaching one octave. The SPST switch performs well from 2.4 to 4.3 GHz. In the ON-state (i.e., wall removed), the insertion loss (IL) is ≤0.5 dB. In the OFF-state (i.e., wall inserted), the isolation is 30 dB. The SPDT switch operates effectively from 4.7 to 7.2 GHz. The IL, between two connected ports, is 0.7 dB. The isolation between unconnected ports is 40 dB. The proposed approach will be applicable within a wide range of different reconfigurable microwave devices.

This article presents a systematic procedure aimed to design continuous profile stopband filters assembled with empty substrate integrated coaxial lines. The coaxial filter is made of five low-cost substrate layers, where the central boards contain the filter profile. This structure exhibits unimodal TEM operation over a wide frequency band, it is not dispersive, it is shielded and cannot be interfered from external signals, and it can be easily integrated with other planar devices. Well-known scattering inverse methods based on the coupled-mode theory have been used for the dimensional synthesis of the proposed topology. Since these dimensions are obtained analytically, no further brute-force optimizations are needed. In particular, a nine-pole elliptic stopband filter operating in the $K_{u}$ band and covering the whole bandwidth of Hispasat 1E communication satellite is shown. The final manufactured filter prototype is large in the longitudinal dimension, but due to its continuous topology, it results to be rather insensitive to fabrication tolerances and errors. Measured results are in good agreement with full-wave simulations. The proposed empty substrate integrated coaxial technology is particularly suitable to realize stopband filters with moderate or wide bandwidths for next-generation satellite applications.

Electroencephalogram is a useful interface system that translates the human electrical brain activity into voltage signals. By these means, the recorded brain waves can be employed to characterize, classify, or diagnose mental disorders. A novel neural network model to classify patients with schizophrenia based on electroencephalograms is presented. The proposed model decomposes the multichannel electroencephalogram records into a group of multivariate novel radial basis functions using a fuzzy means algorithm. The decomposition permits to extract different electroencephalogram channel information and distinguish between two sort of classes i.e., schizophrenic patients and healthy controls. Results show improved accuracy compared to classical algorithms reported in the literature i.e., Support Vector Machine, Bayesian Linear Discriminant Analysis, Gaussian Naive Bayes, K-Nearest Neighbour or Adaboost. As a result, the method presented in this paper achieves the highest balanced accuracy, recall, precision and F1 score values, close to 93 % in all cases. The model presented in this paper may be integrated in real time tools involved during the diagnostic of schizophrenia.

Presently, several million people suffer from major depressive and bipolar disorders. Thus, the modelling, characterization, classification, diagnosis, and analysis of such mental disorders bears great significance in medical research. Electroencephalogram records provide important information to improve clinical diagnosis and are very useful in the scientific community. In this work, electroencephalogram records and patient data from the Hospital Virgen de la Luz in Cuenca (Spain) were processed for a correct classification of bipolar disorders. This work implemented an innovative radial basis function-based neural network employing a fuzzy means algorithm. The results show that the proposed method is an effective approach for discrimination of two kinds of classes, i.e., bipolar disorder patients and healthy persons. The proposed algorithm achieved the best performance compared with other machine learning techniques such as Bayesian linear discriminant analysis, Gaussian naive Bayes, decision trees, K-nearest neighbour, or support vector machine, showing a very high accuracy close to 97%. Therefore, the neural network technique presented could be used as a new tool for the diagnosis of bipolar disorder, considering the possibility of integrating this method into medical software.

[EN] This letter presents a novel compact folded bandpass filter in empty substrate integrated coaxial line (ESICL) technology. To obtain these compact filters, the inverters are modified to provide a 180 degrees bend when inserted in an ESICL. As a result, the proposed filter has a more compact topology based on parallel resonators. A sixth-order Chebyshev bandpass filter operating at 3 GHz has been designed, manufactured, and measured to experimentally validate this new folded configuration. The length of the novel compact filter has been reduced by 82.2% with respect to an equivalent in-line filter, obtaining very similar results in terms of electrical response., This work was supported in part by the Ministerio de Economia y Competitividad, Spanish Government through Research Projects under Grant TEC2016-75934-C4-3-R and Grant TEC2016-75934-C4-1-R and in part by the Ministerio de Ciencia, Innovacion y Universidades through the Fellowship Program for Training University Professors.

[EN] Substrate-integrated circuits (SICs) [1] have attracted much attention in the last several years because of their great potential. The first implementation of the concept can be found in [2] as a feeding mechanism for a slot array antenna. Deslandes and Wu [3], [4] used the term substrate-integrated waveguide (SIW) to define this waveguide integrated in a substrate where the lateral walls are synthesized with metallized via holes, and the upper and lower walls are the top and bottom metallization of the substrate. Many other SICs have been developed since the appearance of the SIW. In the substrate-integrated slab waveguide [5], the guide is synthesized on a substrate by cutting an air hole in the center of an SIW, and the frequency operating bandwidth is increased. The ridge SIW [6] also increases the operation bandwidth by drilling cylindrical air holes in the middle of the SIW. The substrate-integrated nonradiative dielectric waveguide [7] uses a specific pattern of air holes as lateral walls, creating a dielectric waveguide channel that reduces the radiation losses with respect to the SIW. The half-mode SIW [8] reduces the size of the SIW by half by exploiting the fact that there is a symmetry plane along the propagation direction that is equivalent to a magnetic wall., This work was supported by the Ministerio de Economia, Industria, y Competitividad, Spanish government, under research projects TEC2013-47037-C5-3-R, TEC2013-47037-C5-1-R, TEC2016-75934-C4-1-R, and TEC2016-75934-C4-4-R and by Generalitat Valenciana under research project PROMETEOII/2015/005.

A Y-junction circulator based on empty substrate integrated coaxial line (ESICL) technology is proposed in this paper. As ESICL is a novel transmission line, many of the common waveguide devices have not yet been developed in this technology, i. e. only filters, a power divider, a 90 hybrid directional coupler or transition structures have been presented but no non-reciprocal devices. In this paper, a ferrite based circulator has been designed and fabricated to operate at a central frequency of 12 GHz. Measurements performed with the help of an electromagnet confirms the stability of the circulator response under different DC biasing fields. Also, measurements with magnets have been done to integrate the circulator in communication systems. In addition, different temperature tests from 20 C to 90 C have been carried out with the aim of checking the scattering parameters variations. The experimental results confirm the results obtained by the full wave simulations: insertion loss better than -1 dB isolation and return loss below -10 dB from 10 GHz to 14 GHz.

[EN] Substrate integrated waveguides reduce the losses and increase the quality factor of resonators in communication filters when compared with traditional planar technologies, while maintaining their low-cost and low-profile characteristics. Empty substrate integrated waveguides go one step further, removing the dielectric of the substrate. One of these transmission lines is the empty substrate integrated coaxial line (ESICL), which has the advantage of being a two-conductor structure. Thus, it propagates a transversal electric and magnetic (TEM) mode, which reduces the dispersion and the bandwidth limitation of other one conductor empty substrate integrated waveguides. Continuous profile filters, at the cost of being long structures, are very easy to manufacture and design (usually no optimization is needed), and they are highly insensitive to manufacturing tolerances. In this work, a simple continuous profile filter, with a stop band response, is designed for the first time using novel ESICL technology. The influence of the design parameters on the insertion losses and fractional bandwidth is discussed. A prototype has been successfully manufactured and measured. A sensitivity analysis shows the high tolerance of the proposed stop band filter to manufacturing errors., This research was funded by Ministerio de Economia, Industria y Competitividad, Spanish Government, under Research Projects TEC2016-75934-C4-3-R and TEC2016-75934-C4-1-R.

This paper presents a new design for size reduction of empty substrate integrated coaxial lines (ESICLs). The size enhancement is obtained by using improved impedance inverter arrangements. Taking advantage of the multilayer nature of the ESICL, a compact version of the inverters have been developed. The performance of the proposed inverter has been experimentally validated with a working prototype in Ku-band. A fifth-order 0.01-dB ripple Chebyshev filter operating at 13 GHz has been manufactured and measured. The experimental results are in excellent agreement with simulated predictions, confirming thus the advantages of the new proposed compact inverter design. The total length of the filter structure can be reduced by 17.75 % if the compact impedance inverted is employed.

This paper describes a multi-functional microwave device that can be reconfigured to behave either as a filter or an antenna. The device is based around a single resonant element, referred to as a building block element that is connected to 4 ports. The resonant element is a microstrip square patch working in the 2.45 GHz unlicensed Industrial Scientific and Medical (ISM) band used for IEEE 802.11 WiFi. The proposed building block is simple in its design and construction. The paper also presents devices composed of three building blocks, which can realize more complex filtering and antenna mode performance. In addition, PIN diodes have also been incorporated into the devices in order to facilitate electronic control. Measured results, pertaining to fabricated rototypes, show that filter and antenna operation can be achieved, in the same device at a frequency of around 2.45 GHz with acceptable insertion loss and efficiency. In the future, it is anticipated that this could lead to a new paradigm, namely a device that is analogous to a field programmable gate array (FPGA) operating in the microwave frequency regime.

[EN] This paper describes a coplanar waveguide coupled to two split-ring resonators that, in turn, are loaded with two different reactive elements. By these means, balanced composite right/left-handed-like (CRLH-like) and also dual balanced CRLH-like (D-CRLH-like) responses can be obtained with the same structure showing opposite propagation characteristics. This behavior is achieved by simply varying one of the reactive elements, i.e., the capacitive or inductive load. The physical behavior of these transmission lines has been successfully explained by means of a single equivalent circuit. Besides, the proposed transmission lines have an extended bandwidth due to the balanced nature of the structure. The bandwidth of these lines can be electronically controlled using varactor diodes reverse-biased by an external dc voltage. Thus, a reconfigurable cell with CRLH-like and D-CRLH-like propagation has been designed and manufactured. The simulated and measured results show fractional bandwidths from 0% (no transmission) to 9.3% for simulations and from 0% (no transmission) to 8.7% for measurements. Undoubtedly, these new proposed transmission lines will be useful for designing reconfigurable devices that can be used in future communication systems such as radar, wireless applications, global positioning systems, or radio-frequency identification systems, among others., This work was supported by the Ministerio de Economia y Competitividad, Spanish Government, under Research Project TEC2013-47037-C05-3-R and Research Project TEC2013-47037-C05-1-R and by the Ministerio de Educacion, Cultura y Deporte under the Fellowship Program for Training University Professors.

[EN] This letter presents the design and performance of a planar narrow bandwidth bandpass filter with high quality factor. The structure is composed of an empty substrate integrated coaxial line with the center conductor suspended in air. The component dimensions have been calculated by means of classical microwave filter design theory. The filter has been manufactured using standard printed circuit board fabrication processes. A measured insertion loss of 1.59 dB, 2.93% fractional bandwidth, and a Q-factor of 1505 have been obtained at 15 GHz. A Q-factor comparison with other substrate and empty substrate integrated technologies shows the advantages of the solution considered in this letter. The proposed filter proves to be suitable for the implementation of integrated microwave or millimeterwave subsystems with severe restrictions, i.e., low in-band losses, very narrow bandpass responses, low frequency dispersion, high out-of-band rejection, and low manufacturing cost., This work was supported by the Ministerio de Ciencia e Innovacion, Spanish Goverment, under Project TEC2016-75934-C4-X-R and Project TEC2016-75934-C4-1-R.

In this paper, a novel technique for cascading generalized scattering matrices based on a Krylov's iterative solver is presented. This new technique is fully general, since it can be applied to solve the connection of an arbitrary number of networks, each one with an arbitrary number of ports, and it is easy to implement. This technique is able to compute, not only the modal spectra at the free ports of the global network, but also the modal spectra at the connected ports, so that the field inside the full network can be computed for an arbitrary incidence. In addition, this technique can also be used to evaluate the scattering parameters of the global network.

In the future, mobile handsets might incorporate more than 20 separate radios, creating a di-cult antenna design problem due to the sever space restrictions. This paper proposes a reconflgurable wideband antenna, for use within clamshell mobile handsets. The impedance bandwidth of the new antenna was selected in order to meet current and future demands within the industry. It has been suggested that a portable Cognitive Radio must be capable of simultaneous communication (via a narrowband antenna) and spectrum sensing (via a wideband antenna). For this reason a narrowband slot antenna has also been integrated within the wideband radiator.

A study of the efficiency of small dipole antennas loaded with a left-handed transmission line is described. The antenna is composed of a ladder network periodic structure of a number of unit cells. Left-handed performance can be obtained in straight or meandered capacitive-inductive (CL) lumped loading. Its performance is compared to a right-handed dipole with inductive (L) lumped loading. Differently loaded dipoles with four unit cells with the same size reduction have been compared. Right-handed loading gives the best efficiency as expected, but left-handed loading shows the greater degree of freedom to achieve a desired impedance at the terminals. The efficiency is also increased when the CL-loaded dipole is meandered, because of the higher radiation resistance. Moreover, different numbers of unit cell have been compared in order to clarify the number for the best efficiency with size reduction. In a low-order mode, an inductively loaded dipole has highest efficiency for two unit cells, with reduced efficiency with the number of loading elements. However, the reverse is true for the CL-loading. The efficiency of a meandered CL-loaded dipole becomes comparable to the conventional L-loading for higher than four cells. CL-loading with higher mode number gives higher efficiency than a conventional dipole with multiple inductive loads.

International audience; Three types of coplanar transmission lines loaded with split-ring resonators (SRRs) and including series gaps and/or shunt wires are analyzed in this letter. The phase advance originally predicted for these microstructures can be modified and their frequency selectivity can be enhanced while maintaining the advantage of miniaturization. Full-wave electromagnetic simulations and measurement of different prototypes operating in S- and C-frequency bands are performed for retrieving the effective permittivity and permeability. It is shown that right-handed transmission bands can be obtained slightly below the resonance frequency of the SRRs, giving an effective control of the propagation characteristics in magnitude and phase of these planar transmission lines.

In this letter, an empty substrate integrated waveguide H-plane sectorial horn antenna is presented. The antenna is integrated within a planar substrate and is fed by means of a microstrip transmission line. It is composed of a partially empty substrate layer stacked between two cover metallic plates. Results obtained for a prototipe designed and fabricated at Ku-band show a measured efficiency close to 90% and matched responses. No extra loading elements are needed in order to reduce reflection at the end of the aperture conversely to previous designs. Moreover, the structure is quite simple, cheap and does not depend on substrate characteristics i.e. dielectric permitivity or loss tangent. This new methodology for manufacturing substrate integrated antennas without dielectric considerably improves the performance of conventional substrate integrated horn antennas.

This letter presents an omnidirectional horizontally polarized planar printed loop-antenna using left-handed CL loading with 50-Omega input impedance. The antenna has a one wavelength circumference and gives an omnidirectional pattern in the plane of the loop, whilst working in an n = 0 mode. In contrast, a conventional right-handed loop, with the same dimensions, has a figure of eight pattern in the plane of the loop. The antenna is compared with other right-handed periodically loading loop antennas and shown to have the best efficiency and is much easier to match. Design details and simulated results are presented. The concept significantly extends the design degrees of freedom for loop antennas.

The ultimate aim of the research, presented in this paper, is to create a block of hardware which can be reconfigured to assume any given circuit function (e.g. filter, coupler, antenna, etc). Ultimately the hardware should be capable of performing those functions over any given bandwidth and at any required frequency. In essence what we have described is the microwave equivalent of a Field Programmable Gate Array (FPGA). This paper presents an early step toward the development of this technology. Specifically the paper describes a 3 port device, based around a single resonant element; namely a triangular microstrip patch. The device incorporates 7 microwave switches. These switches enable the device to be reconfigured between two different modes, namely narrowband antenna and 2-pole bandpass filter. Filter mode performance is obtained between ports 1 and 2. Antenna mode performance is obtained on port 3.

The ultimate aim of the research presented in this paper is to create a block of hardware which can be reconfigured to assume any given circuit function (e.g. filter, coupler, antenna, etc.) and ultimately to perform those functions over any given bandwidth and at any required frequency. In essence what we have described is the microwave equivalent of a Field Programmable Gate Array (FPGA). This paper presents an early step toward the development of this technology. Specifically the paper describes a device which comprises three triangular microstrip patches. This circuit can operate as a 3-pole bandpass filter or a narrowband antenna. Different functionality is available on different ports of the device and there is no requirement for any microwave switches. In comparison with a device incorporating switches this would reduce losses and simplify the structure.

The traditional cascading of generalised scattering matrices (GSMs) assumes that the modal sets at the connected ports of a cascaded network are strictly equal. This implies a careful selection of the modal polarities, or the reference systems, of every port. Usually, the connection scheme of every device is known a priori. Then, the individual GSMs are pre-processed, or auxiliary devices, which correct possible modal mismatches at the ports, are included in appropriate positions among the cascade, so that the traditional cascading-by-pairs approach can be directly applied. This scheme clearly complicates the reutilisation of previously calculated GSMs, and mixes the cascading with the solution of the individual building blocks. In this study, a systematic procedure is proposed to define the polarity of the modes at the ports of a device fed with transmission lines or waveguides showing a single or double symmetry. The modified expressions to calculate the scattering parameters of the cascade of two multiport devices, incorporating the regular modal corrections to apply when this criterion is used to define the modal polarity at the ports, is also presented in this study. This strategy is more convenient from the point of view of programming, less error-prone and easier to implement., This work was supported by the Ministry of Science and Innovation, Spanish Government, under Research Projects TEC2013-47037-C05-3-R and TEC2013-47037-C05-1-R.

Recently, a new empty coaxial structure, entirely built with printed circuit boards, has been proposed. The resulting coaxial line has low radiation, low losses, high-quality factor, and is nondispersive. Up to now, this coaxial line has not been completely integrated in a planar substrate, since a working transition to a traditional planar line has not been defined yet. Therefore, in this paper, a high-quality transition from coplanar waveguide to this new empty coaxial line is proposed. With this transition, the coaxial line is completely integrated in a planar circuit board, so that it truly becomes an empty substrate-integrated coaxial line. The proposed transition has been fabricated. Both full-wave simulated and measured results show an excellent agreement. Therefore, the proposed transition is suitable to develop completely substrate-integrated components for applications in wideband communication systems that require very high quality responses and protection from external interferences. To show this fact, this new transition has been applied to integrate a high-performance empty coaxial filter in a planar substrate. The measured response of this filter is excellent, and proves the goodness of the proposed transition that has enabled, for the first time, the complete integration of an empty coaxial line in a planar substrate., This work was supported by the Ministerio de Economia y Competitividad, Spanish Goverment under Research Projects TEC2013-47037-C5-3-R and TEC2013-47037-C5-1-R.

A new small antenna consisting of a dipole with left-handed loading is proposed. The antenna is composed of a ladder network periodic structure of unit cells having series capacitors and shunt inductors. Placing capacitors into one side of the network leads to out of phase currents with different amplitudes that allow strong radiation. The numerical analysis show that the antenna has a length of 0.15 wavelengths in free space, input impedance close to 50 Omega and well-behaved radiation patterns, but that losses in the loading components reduce efficiency to 16%. The antenna is compared with other right-handed periodically loading dipoles and shown to less efficient than inductive loading, but much easier to match

This letter presents a dual composite right/left-handed microstrip line loaded with modified complementary split-ring resonators. In this particular case, the well-known resonant particle employed has been capacitively loaded in order to obtain a balanced frequency response. The inclusion of this capacitive element has two main effects. On the one hand, the right-and left-handed bands are interchanged; on the other hand, the possibility to control the position of the right-handed band, while maintaining the left-handed one unaltered. Consequently, it is relatively simple to design balanced transmission lines with improved bandwidth and reconfigurable properties. In addition, the equivalent circuit that describes the electromagnetic behavior of the structure has been obtained. Finally, a prototype has been fabricated and measured to confirm experimentally the validity of the proposed design., This work was supported by the Ministerio de Ciencia e Innovacion, Spanish Goverment, under Research ProjectsTEC2010-21520-C04-03 and -01 and the Autonomous Government of Castilla-La Mancha under Research Projects PPII10-0047-0220 and PPII10-0027-1277.

During the last years, the metamaterials field has grown rapidly due to the possibility of accomplishing a methodology to achieve negative effective parameters ee f f Pendry et al. (1996) and μe f f Pendry et al. (1999), and their experimental verification Smith et al. (2000) Shelby, Smith & Schultz (2001). The main research work has been concentrated on the theoretical consequences of negative parameters, as well as techniques for practically realizing left-handed media for various optical/microwave concepts and applications. Among recent concepts, properties, and devices based on engineered metamaterials, we can mention frequency selective structures, which have opened the path to a new range of passive devices for guided applications. In this context, split ring resonator (SRR) loaded transmission lines represent the cutting edge of research in the field of one-dimensional (1D) planar left-handed structures. These structures were firstly proposed by Martin et al. in 2003 Martin et al. (2003) by magnetically coupling a shunted coplanar waveguide (CPW) and pairs of SRRs. These planar devices exhibit backward propagation in a narrow frequency band above the resonant frequency of the rings, with the necessary degree of flexibility to design compact low insertion losses filters. Thus, based on this former configuration different approaches have been proposed with the aim of improving performances and overcome possible drawbacks such as asymmetrical response shape or transmission bands with smooth edges. For instance, a combined right/left-handed CPW structure was implemented by cascading SRRs-wire and SRRs-gap stages Bonache et al. (2005), satisfactorily achieving a transmission upper band with a sharp cut-off. Furthermore, new CPW lines with extra loading elements have shown interesting properties in terms of improved out-of-band behavior and response selectivity Borja, Carbonell, Boria, Cascon & Lippens (2010) Borja, Carbonell, Boria & Compact Coplanar Waveguide Metamaterial-Inspired Lines and Its Use in Highly Selective and Tunable Bandpass Filters

In this paper, a simple geometrical modification of the well-known split-ring resonator (SRR) topology is proposed. This modification consists of joining the opposite sides of the rings by means of an inductive connection. Due to this modification, it is possible to synthesize a dual composite right-/left-handed artificial transmission line from a host coplanar waveguide (CPW). In addition, it is quite straightforward to synthesize a dual balanced line showing a wider transmission bandwidth (around 13% for 3 GHz and 8% for 6 GHz) with this new SRR geometry. In fact, in order to design a balanced line, one must just modify the inductance of the direct connection between the rings, which can be derived from the equivalent circuit of this new ring, which is also presented in this paper. The final result is a balanced artificial CPW transmission line with a dual composite right-/left-handed behavior. In this case, the right-handed transmission band is placed below the left-handed one, and there is no frequency separation between both transmission bands. © 1963-2012 IEEE., This work was supported in part by the Ministerio de Ciencia e Innovacion, Spanish Goverment, under Research Projects TEC2010-21520-C04-03 and TEC2010-21520-C04-01 and by the Autonomous Government of Castilla-La Mancha under Research Projects PPII10-0047-0220 and PPII10-0027-1277.

This letter presents a passive UHF printed loop antenna with left-handed loading. The RFID reader antenna can work at near- and far-field operation within the European UHF (865-868 MHz) band. The operation frequency and radiation properties can be modified by employing varactor diodes. Also, the antenna can work in the near-field region having a flat magnetic distribution in the interrogation zone. A comparative study with other passive RFID reader conventional antennas shows that the left-handed loop achieves stronger near H-field with good impedance matching. Design details, simulated results, and a fabricated prototype are presented. The concept significantly extends the design degrees of freedom for RFID antennas.

A new fully modal characterisation procedure is proposed to reduce the number of unknowns needed to characterise the ports of an arbitrary H-plane device in rectangular waveguide, so that no equivalent currents will be involved in the characterisation of the ports. Moreover, since no currents are needed to characterise the ports, the weights of the scattered modes can be unknowns of the resulting system of equations. This is an important fact, since, to find the wanted modal weights, a subsequent projection step is not necessary anymore. The new method is then advantageous when compared to other hybrid alternatives in the literature, not only because the ports are solved using fewer unknowns, which is the main advantage of the proposal, but also because the scattering parameters can be computed directly, once the system of equations is posed., This work was supported by Ministerio de Ciencia e Innovacion, Spanish Government, under Research Project TEC2007-67630-C03-01 and by the Autonomous Government of Castilla-La Mancha under Research Project PPII10-0047-0220.

This letter presents a tunable bandwidth bandpass filter based on varactor-loaded metamaterial coplanar waveguide (CPW) lines. The CPW lines are based on series gaps and split-ring resonators. The varactors are reverse-biased semiconductor diodes connected between both sides of each series gap. This configuration, directly inspired from the so-called metamaterial technology, takes advantage of the high dispersion of the loaded transmission line. Therefore, strong permittivity and permeability responses induced by means of the resonators are obtained. A single varactor-loaded transmission line is first analyzed. Then, a third-order tunable filter with fractional bandwidth tuning range from 5.8% to 21.5% is experimentally assessed. The proposed filters can be used in several practical applications such as multichannel wireless and satellite communication systems, where reconfigurable devices are often required., This work was supported in part by the Centre National d'Etudes Spatiales (CNES), the Ministerio de Ciencia e Innovacion, Spanish Government under Research Project TEC2010-21520-C04, and the Autonomous Government of Castilla-La Mancha under Research Projects PPII10-0027-1277 and TC20112325.

In this letter, a balanced metamaterial-inspired coplanar waveguide transmission line with enhanced bandwidth is presented. The coplanar waveguide line is composed of a basic cell with two split-ring resonators, two series capacitances (interdigital capacitors), two wide shunt inductances (metallic strips), and four shunt capacitances (implemented through open-ended stubs). The use of split-ring resonators together with metallic shunt strips provides negative permeability and permittivity, respectively. Likewise, the employment of additional series and shunt capacitances permits to control both the left-and right-handed bands, thus achieving a balanced composite transmission line. The configuration exhibits a wide bandpass response as a result of this balance between advance and delay phase offsets. The interpretation is based on an equivalent circuit model, full-wave electromagnetic analysis, and measured responses of a prototype designed for microwave (C-band) frequency operation. Due to the small dimensions of the resonators employed, the resulting line is very compact. Potential use of these transmission lines can be foreseen in many applications concerning planar microwave devices with severe size restrictions and wide frequency bandpass responses., Manuscript received November 05, 2011; accepted November 27, 2011. Date of publication December 07, 2011; date of current version December 22, 2011. This work was supported by the Ministerio de Ciencia e Innovacion, Spanish Government under Research Project TEC2010-21520-C04 and the Autonomous Government of Castilla-La Mancha under Research Project PPII10-0027-1277.

Ultimately, the research presented will lead to the development of a microwave integrated circuit that is analogous to a field programmable gate array. An early step towards the development of this technology is presented. Specifically, a 3-port device, based on a single resonant element, namely a microstrip square patch, is described. The device operates simultaneously as a filter and an antenna. Filter performance is obtained between ports 1 and 2. Antenna performance is obtained on port 3.