Angel Belenguer

Novel Empty Substrate Integrated Waveguide for High-Performance Microwave Integrated Circuits

Over the last years, a great number of substrate integrated circuits has been developed. These new circuits are a compromise between the advantages of classical waveguide technologies, such as high quality factor and low losses, and the advantages of planar circuits, such as low cost and easy compact integration. Although their quality factor and losses are better than for planar circuits, these characteristics are worse than in the case of waveguides, mainly due to the presence of the dielectric substrate. In order to improve the performance of the integrated circuits, a new methodology for manufacturing empty waveguides, without a dielectric substrate, but at the same time completely integrated in a planar substrate, is proposed in this work. A wideband transition with return losses greater than 20 dB in the whole bandwith of the waveguide allows the integration of the empty waveguide into the planar substrate so that the waveguide can be directly accessed with a microstrip line. Therefore, a microwave circuit integrated in a planar substrate, but at the same time with a very high quality factor (measured quality factor is 4.5 times higher than for the same filter in the substrate integrated waveguide), and very low losses is successfully achieved.

A Reconfigurable Passive UHF Reader Loop Antenna for Near-Field and Far-Field RFID Applications

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.

Efficient Analysis of Substrate Integrated Waveguide Devices Using Hybrid Mode Matching Between Cylindrical and Guided Modes

In this paper, a new method to efficiently analyze substrate integrated waveguide (SIW) based devices with multiple accessing ports is presented. The problem is considered as a 2-D electromagnetic problem assuming no field variation normal to the dielectric substrate. The incident and scattered fields from each circular cylinder are expanded with cylindrical modes, and the fields in the waveguide ports are expanded using progressive and regressive modal summations. The addition theorems of Bessel and Hankel functions are used to analyze the full-wave behavior of the SIW device. In order to extract the circuital parameters, the hybrid mode-matching between guided and cylindrical modes is done by projecting continuity equations in a circular boundary containing the whole SIW structure over the inner modes of each region. Applying this new technique, it is possible to analyze multiple port devices by solving a set of integrals that can be easily approached analytically or by using the inverse fast Fourier transform, avoiding the use of non efficient numerical methods. It is shown that the new method runs faster than commercial software packages and other techniques recently published.

Hybrid Technique Plus Fast Frequency Sweep for the Efficient and Accurate Analysis of Substrate Integrated Waveguide Devices

In this paper, we adapt a novel mode-matching and method-of-moments hybrid technique to efficiently analyze substrate integrated waveguide (SIW) based devices. The hybrid technique is formulated in terms of a single equivalent current. This fact is used to include the emergent modal weights, i.e., the scattering parameters, as unknowns of the method-of-moments system of equations. In this case, it is relatively easy to develop fast frequency sweep schemes that can be used to highly accelerate the solution of an arbitrary device and, as a result, a very efficient technique is obtained. This technique can be applied to the analysis and design of SIW devices, and it is highly competitive when compared to other method-of-moments and mode-matching hybrid formulations or when compared to reference commercial software.

Wideband Passband Transmission Line Based on Metamaterial-Inspired CPW Balanced Cells

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.

Balanced Right/Left-Handed Coplanar Waveguide With Stub-Loaded Split-Ring Resonators

In this letter, a host coplanar waveguide (CPW) loaded with modified split-ring resonators (SRR) is presented. In recent publications, it has been demonstrated that the capacitive interaction between the host CPW line and the SRRs is the cause of a right-handed band, which degrades the selectivity of the response. Consequently, an open-ended microstrip stub connected to the rings is used to modify this interaction, and thus has an effective control of the rejection above the passband. Fortunately, these stubs only affect the frequency position of the right-handed band. As a result, it is quite straightforward to obtain balanced composite right/left-handed (CRLH) transmission lines with increased transmission bandwidth and improved rejection levels, which are the main drawbacks of traditional SRR-loaded CPW lines. Moreover, the response of the modified cell shows a pair of transmission zeros at both sides of the passband. Therefore, this new cell is a very interesting choice for designing balanced CRLH lines and is very attractive for filter applications.

Improvement for the design equations for tapered Microstrip-to-Substrate Integrated Waveguide transitions

This article describes a new design strategy for Microstrip-to-Substrate Integrated Waveguide (SIW) transitions with different geometries. This design strategy focuses in obtaining a good initial point for the length and the width of the transition. Later, these parameters are optimized together in order to calculate a low reflection transition in the desired bandwidth. With this method, different transitions have been designed, in which the impedance variation follows different mathematical expressions, some of them extracted from the classical theory.

Hybrid Mode Matching and Method of Moments Method for the Full-Wave Analysis of Arbitrarily Shaped Structures Fed Through Canonical Waveguides Using Only Electric Currents

A new hybrid mode matching and method of moments formulation based only on electric currents is presented in this paper. The use of only one equivalent current allows the introduction of a new set of unknowns. The chosen new unknowns are the weights related to the scattered modes that emerge from the ports to the waveguides that feed the problem. Applying this new formulation, the matrices that must be inverted are smaller and the generalized scattering matrix can be obtained directly from the solution of the resulting system of equations so that no additional projection is needed to obtain the scattering parameters, as happens with traditional approaches with two equivalent currents. As a result, certain efficiency improvement is obtained, as can be seen when this technique is applied to the solution of H-plane problems in rectangular waveguide.

Efficient CAD tool of direct-coupled-cavities filters with dielectric resonators

This article describes a new CAD tool of directly coupled cavities filters with dielectric resonators based on a very efficient hybrid analysis method. The CAD tool efficiently combines two accurate analysis techniques: a first one, based on the integral equation method, for the analysis of the standard rectangular waveguide filter steps, and a second one, based on mode matching and spectral methods, for solving the dielectric resonators. The suitable combination of these two analysis techniques provides high improvements in the CPU time required in the CAD of these filters. The CAD tool is based in ASM with a hybridization of several optimization algorithms, including a continuous-time genetic algorithm. A band-pass filter with dielectric resonators has been successfully designed making use of this novel CAD tool

Dual Composite Right-/Left-Handed Coplanar Waveguide Transmission Line Using Inductively Connected Split-Ring Resonators

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.