Showing papers by "Luca Perregrini published in 2020"

3-D Printed Microfluidic Sensor in SIW Technology for Liquids’ Characterization

Abstract: This article presents the implementation of a novel microfluidic sensor based on a resonant cavity. The cavity is based on the substrate integrated waveguide (SIW) technology and is fabricated by using stereolithographic 3-D printing, which guarantees fast prototyping and allows arbitrary geometry. The proposed sensor consists of a square cavity and an inner meander pipe provided with two openings, where the liquid under test is injected and extracted, and is fed by a coaxial probe, which represents the microwave port of the circuit. S-parameter measurement allows retrieving the electromagnetic properties of the liquid injected in the pipe. In particular, the loss tangent of the liquid is extracted from the variation of the cavity quality factor compared to air-filled pipe, after removing the actual losses of the structure. The dielectric permittivity of the liquid is retrieved from the shift of the cavity resonance frequency relative to the case of air-filled pipe, without any hypothesis of small losses. The performance of the sensor is discussed through the electromagnetic characterization of several fluids.

Voltage-Controlled and Input-Matched Tunable Microstrip Attenuators Based on Few-Layer Graphene

Abstract: This article presents novel tunable microstrip attenuators based on few-layer graphene. The proposed topology consists of a microstrip line sided by pairs of grounded metal vias, with graphene pads located between the microstrip line and the vias. The possibility to control the graphene resistance through an applied bias voltage is exploited with the aim to modify the insertion loss of the attenuators. Several pairs of metal vias are adopted to achieve large tuning range, good input matching, and broadband operation. A systematic investigation of the structure with two, three, and four pairs of vias is presented, along with the experimental validation. Prototypes operating in the frequency range from 1 to 10 GHz and with maximum insertion loss exceeding 60 dB are fabricated and tested.

3-D Printed Bandpass Filter Using Conical Posts Interlaced Vertically

Abstract: A new class of filters using conical post resonators is presented. The proposed structure consists of stacked rectangular cavities where each cavity has a capacitive conical resonating post positioned in its center. The resonator is very similar to that used in combline filters, but in this case, taking advantage of the stacked arrangement and of the conical shape, each post has its upper part partially inserted in the hollow base of the post above it. The resulting structure is more compact than the classical combline filter, whereas the Q-factor is very similar. In order to validate the proposed structure, a doublet filter prototype has been designed, manufactured using additive manufacturing techniques and tested.

Accurate Modeling of Stubs Used as Resonant Coupling Elements in SIW Filters

Abstract: This letter presents an accurate model for the stubs used as frequency-dependent coupling elements in substrate integrated waveguide (SIW) filters, with the aim to generate transmission zeros (TZs) in the frequency response. The model is based on the actual modes excited in the stub, differently from the single-mode (equivalent circuit) representation used in previous works. A procedure to determine the geometrical dimensions of the stub, depending on the synthesized filters parameters, is also presented, based on the full-wave characterization of the structure. The proposed model is validated by the design and the fabrication of an SIW filter.

Slow-Wave Effect Enhanced Substrate Integrated Waveguide with Multi-Antipodal Blind Via-Holes and Distributed Metal Strips

Abstract: A slow-wave (SW) effect enhancement method based on substrate integrated waveguide (SIW) is presented, theoretically studied, and experimentally validated. The SW effect is achieved by incorporating multi-antipodal metalized blind via-holes and distributed metal strips longitudinally connecting the bottom of upper posts. This improved SIW-based topology achieves a dramatic cutoff frequency reduction of 55.5% with reference to the conventional SIW with the same lateral size. Meanwhile, the phase velocity is reduced remarkably, realizing a more compact longitudinal dimension. The two effects give rise to a planar size reduction of 80% compared to the conventional SIW, which presents a significant advance in SIW miniaturization technology. A prototype is fabricated for a proof-of-concept, and the measured results are in good agreement with simulations, demonstrating its promising application potential and prospect in the microwave and millimeter-wave components.

A Simple and Accurate Method for Circularly Polarised Monopulse TM 01 Tracking System Testing

Abstract: The use of the calibration tower to test a monopulse tracking system is expensive and requires the antenna downtime. Alternative ways to test in-lab the tracking system are highly-desirable. This work proposes a simple yet effective structure achieving this objective through the controlled excitation of high-order modes in a circular waveguide that mimic those generated by the signal received from the calibration tower. The theoretical fundamentals are discussed and the design of the waveguide mode exciter at K band is reported, along with results showing its validation.

An Effective Mixed Extracting Method for Electromagnetic Parameters of Periodically Loaded Substrate Integrated Waveguide Units and Its Applications

Abstract: In this article, we propose an effective mixed extracting method for anisotropic constitutive parameters of periodically loaded substrate integrated waveguide (SIW). This method takes the advantage of both scattering parameters retrieval theory and the equivalent homogeneous medium dispersion analysis, which could accurately and effectively extract the equivalent constitutive parameters of the periodically loaded SIW. With this method, the corresponding constitutive parameters of the six typical patterns of periodically loaded SIW schemes are accurately extracted, verified, explained, and compared for their performance. It can be used to quantitatively predict the miniaturization potential of each unit cell and sequentially evaluate the performance as an integrated component. In addition, in terms of application, with the aid of equivalent parameters extracted by the proposed method, a slow-wave SIW evanescent mode filter centered at 12.64 GHz with a frequency bandwidth of 300 MHz is synthesized, fabricated, and measured. In the meanwhile, the theory of slow-wave evanescent mode filter is further consummated, by introducing the dual factors of enhanced permittivity and permeability, as well as analyzing respective advantages in filter synthesis. Measurements and simulation results show good agreement, which embodies the role of the method in guiding the design of actual microwave devices.

Controlled High Order Mode Generation for Tracking Coupler Bench Test

Abstract: The calibration of a monopulse tracking system is typically performed using a calibration tower or a known satellite. This work proposes a simple yet effective technique to excite in a controlled way all the modes generated by the antenna and used to obtain the Σand Δ signals. This allows to test in lab the tracking system, thus reducing both costs and antenna downtime. The theoretical fundamentals are discussed and the design of the waveguide mode exciter at Ku band is reported along with experimental validation.

Upgrade to the K-band uplink channel for the ESA Deep Space Antennas: Analysis of the optics and preliminary dichroic mirror design

Abstract: The incoming planned missions to the Moon and beyond would require an uplink channel significantly larger in frequency than the ones normally used in S and X band. This paper presents a preliminary study for the upgrade of the European Space Agency (ESA) Deep Space Antennas (DSAs) optical configuration in order to implement the new K band uplink channel (22.55–23.15 GHz). Among the different possible Beam Waveguide (BWG) layouts, one of the many aspect to be investigated is the design of new Frequency Selective Surfaces (FSSs), which are employed to merge/separate the different frequency bands. Preliminary designs and results, for both the BWG optics and the dichroic mirrors, are presented, with a particular focus on the advantages and disadvantages of the different solutions.

Exploiting Symmetries in the Variational Meshless Method for 3-D Inhomogeneous Cavities

Abstract: The variational meshless method (VMM) is a novel numerical algorithm that combines the intrinsic advantages of the meshless method based on the use of radial basis functions (RBFs) with the reliability of the variational formulation of electromagnetic boundary problems. It has been originally proposed and demonstrated in the analysis of 2-D structures, both homogeneous and inhomogeneous, aiming at the determination of the mode spectrum and the dispersion diagram. In this article, the VMM is extended to the calculation of the resonant modes of 3-D inhomogeneous cavities. The full theory is presented with implementation details. Moreover, the exploitation of symmetries is also discussed, which significantly speedup the method. Some examples are reported, and the results of the VMM are compared against either analytical values (when available) or commercial numerical codes based on the finite element method (FEM). In all cases, the VMM provides a large number of resonant modes with a limited number of unknowns, exhibiting high accuracy in short computing time.