Dual and broadband power dividers at microwave frequencies based on composite right/left handed (CRLH) lattice networks

CIMITECThis paper proposes a dual-band power divider operating at GHz frequencies and implemented by means of impedance transformers (also called inverters) based on lattice networks and transmission line sections. The dual-band functionality of the proposed device is achieved thanks to the composite right/left handed (CRLH) behavior of the impedance transformers, able to provide −90° and +90° phase shift at the first and second design frequencies, respectively, of the divider. By using such combination of transmission line sections and lattice networks, the characteristic impedance of the impedance transformers is roughly constant over wide bandwidths, with the results of broad operating bands. To demonstrate the possibilities of the approach, a prototype device is designed, fabricated and characterized

Signal balancing in unbalanced transmission lines

Balanced lines operating as transmission line interconnects are subjected to differential-mode to common-mode conversion (and vice versa) in situations where symmetry imbalances (e.g., caused by line bends) are unavoidable. In this paper, a technique to compensate for such symmetry imbalances, providing pure differential-mode signals at the differential output port of the line, is presented. Such technique uses a rat-race balun (to generate the differential-mode signal) with the isolated port conveniently loaded, and it is based on the modification of the characteristic impedance of one of the unbalanced lines. A detailed analysis that justifies this compensation technique (valid for any arbitrary four-port network) and provides the design equations is presented. The approach is validated through simulation and experiment, by demonstrating that common-mode signals are not transmitted to the differential output port of a bended (i.e., unbalanced) line pai

Differential microstrip lines with common-mode suppression based on electromagnetic band-gaps (EBGs)

CIMITECA technique for the suppression of the common mode in differential (balanced) microstrip lines, based on electromagnetic band-gaps (EBGs), is presented in this letter. It is demonstrated that by periodically modulating the common-mode characteristic impedance of the line and simultaneously forcing the differential-mode impedance to be uniform (and equal to the reference impedance of the differential ports), the common mode can be efficiently suppressed over a certain frequency band, while the line is transparent for the differential-mode. The main advantage of EBGs, as compared to other approaches for common-mode suppression in differential microstrip lines, is the fact that the ground plane is kept unaltered. Moreover, the design of the differential line is straightforward since the required level of common-mode suppression and bandwidth are given by simple approximate analytical expressions. As a design example, we report a four-stage common-mode suppressed differential line with 68% fractional bandwidth for the common-mode stopband centered at 2.4 GHz, and maximum common-mode rejection ratio (CMRR) of 19 dB at that frequency. Furthermore, we have designed and fabricated a six-stage double-tuned common-mode suppressed differential line in order to enhance the stopband bandwidth for the common mode around 2.4 GHz

Microwave sensors based on resonant elements

This paper highlights interest in the implementation of microwave sensors based on resonant elements, the subject of a special issue in the journal. A classification of these sensors on the basis of the operating principle is presented, and the advantages and limitations of the different sensor types are pointed out. Finally, the paper summarizes the different contributions to the special issue

Dual-band balanced bandpass filter with common-mode suppression based on electrically small planar resonators

The design of fully planar dual-band balanced bandpass filters with common-mode noise suppression is reported. The proposed filters are based on electrically small resonators coupled through admittance inverters. For design purposes, the circuit models of the considered resonators are reported. The key aspect for selective mode suppression (i.e., common-mode rejection in the differential-mode pass bands) is related to symmetry properties. Thus, for the differential-mode the symmetry plane is an electric wall, and the equivalent circuit for that mode provides dual-band functionality. Conversely, for the common-mode the symmetry plane is a magnetic wall, and the equivalent circuit exhibits a rejection band. As a proof of concept, the design of an order-2 Chebyshev dual-band balanced bandpass filter with center frequencies f₁= 1.8 GHz (GSM band) and f₂=2.4 GHz (Wi-Fi band), fractional bandwidth FBW= 7%, and ripple level LA1= 0.01 dB is reported. Index Terms-Balanced filters, common-mod

Branch line couplers with small size and harmonic suppression based on non-periodic step impedance shunt stub (SISS) loaded lines

Altres ajuts: ICREAThis paper presents branch line couplers with compact size and harmonic suppression based on non-periodic reactively loaded artificial lines. The reactive loading elements of the lines are step impedance shunt stubs (SISSs). Such elements provide transmission zeros, which are useful to efficiently suppressing the harmonic content of the device. Moreover, by virtue of reactive loading, the reported artificial lines exhibit a slow wave effect of interest for device miniaturization. The combination of size, harmonic suppression efficiency, and design simplicity (with a clear design methodology) is of interest within the framework of artificial transmission lines and their application to the optimization of microwave passive components

Planar microwave resonant sensors : a review and recent developments

Microwave sensors based on electrically small planar resonant elements are reviewed in this paper. By virtue of the high sensitivity of such resonators to the properties of their surrounding medium, particularly the dielectric constant and the loss factor, these sensors are of special interest (although not exclusive) for dielectric characterization of solids and liquids, and for the measurement of material composition. Several sensing strategies are presented, with special emphasis on differential-mode sensors. The main advantages and limitations of such techniques are discussed, and several prototype examples are reported, mainly including sensors for measuring the dielectric properties of solids, and sensors based on microfluidics (useful for liquid characterization and liquid composition). The proposed sensors have high potential for application in real scenarios (including industrial processes and characterization of biosamples)

Splitter/combiner microstrip sections loaded with pairs of complementary split ring resonators (CSRRs) : modeling and optimization for differential sensing applications

This paper focuses on the analysis of splitter/ combiner microstrip sections where each branch is loaded with a complementary split ring resonator (CSRR). The distance between CSRRs is high, and hence, their coupling can be neglected. If the structure exhibits perfect symmetry with regard to the axial plane, a single transmission zero (notch) at the fundamental resonance of the CSRR, arises. Conversely, two notches (i.e., frequency splitting) appear if symmetry is disrupted, and their positions are determined not only by the characteristics of the CSRRs but also by the length of the splitter/combiner sections. A model that includes lumped elements (accounting for the CSRR-loaded line sections) and distributed components (corresponding to the transmission lines) is proposed and used to infer the position of the transmission zeros. Frequency splitting is useful for the implementation of differential sensors and comparators based on symmetry disruption. Using the model, the length of the splitter/combiner sections necessary to optimize the sensitivity of the structures as sensing elements is determined. Parameter extraction and comparison with electromagnetic simulations and measurements in several symmetric and asymmetric structures is used to validate the model. Finally, a prototype device sensor/comparator based on the proposed CSRR-loaded splitter/combiner microstrip sections is presented

An analytical method to implement high-sensitivity transmission line differential sensors for dielectric constant measurements

A simple analytical method useful to optimize the sensitivity in differential sensors based on a pair of meandered microstrip lines is presented in this paper. Sensing is based on the phase difference of the transmission coefficients of both lines, when such lines are asymmetrically loaded. The analysis provides the combination of operating frequency and line length (the main design parameters) that are necessary to obtain the maximum possible differential phase (±180°) for a given level of the differential dielectric constant (input dynamic range). The proposed sensor is useful to detect tiny defects of a sample under test (SUT) as compared to a reference (REF) sample. It can also be applied to the measurement of the complex dielectric constant of the SUT, where the real part is inferred from the differential phase, whereas the imaginary part, or the loss tangent, is derived from the modulus of the transmission coefficient of the line loaded with the SUT. It is experimentally demonstrated that the proposed device is able to detect the presence of few and small (purposely generated) defects in a commercial microwave substrate, as well as subtle variations in their density, pointing out the high achieved sensor sensitivity. Sensor validation is also carried out by determining the dielectric constant and loss tangent of commercial microwave substrate

Compact coplanar waveguide power splitter with filtering capability based on slow-wave structures

A compact coplanar waveguide (CPW) power splitter with filtering capability is presented in this paper. The splitter consists of a pair of 70.71 Ω impedance inverters implemented by means of inductively and capacitively loaded slow-wave structures. Such slow-wave structures efficiently shorten the length of the inverters, thereby providing substantial size reduction to the power splitter. The filtering functionality is due to the Bragg effect, related to periodicity. The proposed splitter, designed to be functional at 1 GHz, exhibits good performance at that frequency, with measured return loss of 20.6 dB and insertion loss of 3.15 dB and 3.23 dB at the output ports. Moreover, the suppression level at the first, second and third harmonic frequency is better than 12.4 dB, 34.6 dB and 24.7 dB, respectively. As compared to the length of the ordinary inverters, the length of the constitutive slow-wave impedance is reduced by a factor of tw