BUSCADOR RECOLECTA

In this paper, a W-band 3D-printed bandpass filter is proposed. The use of higherorder TE10n modes in groove gap waveguide (GGW) technology is evaluated in order to alleviate the manufacturing requirements. In addition to the use of higherorder modes, the coupling between them is analyzed in detail to improve the overall fabrication robustness of the component. This allows the implementation of narrowband filters operating at millimeter-wave frequency bands (or above), which usually demand complex manufacturing techniques to provide the high accuracy required for this kind of devices. In order to show the applicability of the proposed method, a narrow-band 5th-order Chebyshev bandpass filter centered at 94 GHz, which can be easily fabricated by state-of-the-art stereolithographic (SLA) 3D-printing techniques followed by silver coating, is shown. Excellent measured performance has been obtained.

To date, there is no straightforward method for monitoring meteorological conditions in real-time through experimental measurements. Consequently, all weather predictions rely on forecasting models, which are unable to adapt to actual weather changes, thereby compromising their accuracy. The project described in this paper seeks to establish a weather measurement system that leverages the relationship between climatic conditions and the phenomena of cosmic ray degradation and muon generation. If this relationship is accurately defined, it could lead to the development of a model that predicts atmospheric conditions based on the flux of muons and cosmic rays and the occurrence of the aforementioned phenomena. This paper provides a theoretical foundation to support the viability of the project, outlines the proposed configuration of the system, and discusses the implementation of its most crucial components. This project was undertaken by students from the Degree in Engineering in Telecommunication Technologies at the Public University of Navarre (UPNA), within the course Projects in Telecommunication Systems, Proyecto PID2020-112545RB-C53 del Ministerio de Ciencia e Innovación - Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033).

A design technique to include multiple and fully-controlled transmission zeros (TZs) in the frequency response of rectangular waveguide commensurate-line stepped-impedance filters is presented in this letter. These bandpass filters (BPFs) are known for having reduced sensitivities against manufacturing inaccuracies and are composed of multiple waveguide sections. In order to improve their selectivity, 3λg/4 and λg/4-stubs are included to create multiple TZs around the passband. The proposed technique allows us to add multiple stubs in a single section and, therefore, only minor adjustments in the affected part of the filter are required, which simplifies the overall design process. The technique has been verified with a design example with four TZs (two on each side) near the passband., This work was supported by the Spanish Ministerio de Ciencia e Innovación –Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033) under Project PID2020-112545RB-C53 and by the European Union’s Horizon 2020 Research and Innovation Program under Grant 811232-TESLA-H2020-MSCA-ITN-2018.

In this work, a novel topology of groove gap
waveguide (GGW) technology is presented to facilitate the
fabrication process by Computer Numerical Control (CNC)
milling. GGW has been proposed as an interesting alternative to
the rectangular waveguide for the design of microwave and
millimeter-wave components. This technology consists of two
parallel metal plates, where one of them has a (lambda)/4-height pin bed
that provides a high impedance condition at the plane over the
pins, avoiding electrical contact requirement with the upper plate
and hence facilitating the fabrication requirements. However, the
manufacture by CNC milling of the pins may be troublesome,
especially for devices operating at high frequency. A way to
facilitate this process is achieved by using pins with reduced
height. Moreover, the proposed configuration allows us to
maintain the standard dimension ports of the equivalent
rectangular waveguide and the operation in its corresponding
bandwidth. A comparison with other GGW topologies has been
presented and a bandpass filter has been fabricated to validate
its usefulness., Este proyecto ha sido financiado por el Ministerio de
Ciencia e Innovación –Agencia Estatal de Investigación
(MCIN/AEI/ 10.13039/501100011033) en el marco del
proyecto PID2020-112545RB-C53.

In this work, a very compact rectangular waveguide low-pass filter with meandered topology based on commensurate lines for Ku-band satellite applications is analysed for high-power handling capabilities. The device consists of rectangular waveguide sections properly cascaded to form a meandered topology to obtain the desired value of the local reflection coefficients. which are essential to achieve the target frequency response and also to keep large mechanical gaps. Hence, this technique allows us not only to design a filter with compact size but a filter geometry which is suitable for high power applications. In the paper, the low-pass filter based on commensurate lines is first designed by cascading E-plane mitered bends (±90° EMBs) in CST Microwave Studio (MWS) and then the values of the electromagnetic fields at the passband frequencies are exported to Spark3D to perform a multipactor analysis. The critical areas inside the device where the multipactor discharge occurs will also be identified in the high-power analysis. https://doi.org/10.5281/zenodo.7343236, This work was supported by the Spanish Ministerio de Ciencia e Innovación –Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033) under Project PID2020-112545RB-C53 and by the European Union’s Horizon 2020 Research and
Innovation Program under Grant 811232-TESLA-H2020-MSCA-ITN-2018.

In this paper, transmission-line theory is applied to implement a physical model for compact one-turn inductors, which simultaneously incorporates the frequency-dependent effects introduced by the conductor skin effect and the loss originated by the coupling with the ground plane. For this purpose, S-parameter measurements are processed to extract the associated parameters, which exhibit scalability with the turn radius. This allows the model to be used for interpolation and extrapolation analyses. In this regard, the device performance is assessed for one-turn inductors in series connection, for different load impedances, and when the turn is narrowed. To validate the proposal, agreement between the model and the experimental transmission line RLGC parameters, the return loss, and the Q-factor is obtained up to 20 GHz., The support received by the Spanish Ministerio de Ciencia e Innovación-Agencia Estatal de Investigación (MCIN/AEI/ 10.13039/501100011033) under Project PID2020-112545RB-C53; Consejo Nacional de Humanidades, Ciencias y Tecnologías; 10.13039/501100017266-Gobierno de Navarra (Grant Number: 0011-3947-2022-000006).

Este trabajo presenta la validación de la tecnología CLAF-SIW para la fabricación de filtros en el rango de frecuencias de ondas milimétricas. El filtro estudiado es un filtro paso banda compuesto por cuatro cavidades apiladas y acopladas mediante iris (se utilizan cinco iris en total). Cada capa está compuesta por una placa de circuito impreso (PCB) de espesor comercial. Las capas de iris se prototipan metalizando los bordes de las ranuras, mientras que las capas de cavidad contienen la estructura CLAF-SIW utilizando setas dobles como estructura EBG. El filtro se obtiene inmediatamente simplemente adaptando el ancho efectivo de la cavidad CLAF-SIW a la cavidad de referencia, para la cual se han estudiado los efectos que afectan a este valor efectivo. Se ha fabricado un prototipo con buena concordancia entre la medición, la simulación y la respuesta ideal del filtro de cavidad para una banda de paso de 36 a 37,5 GHz. Las pequeñas discrepancias se deben a las diferencias en la separación real entre los laminados y las tolerancias de fabricación., Este trabajo ha sido apoyado por la ayuda TED2021-129938B-I00 financiada por MCIN/AEI/10.13039/501100011033 y Unión Europea NextGenerationEU/PRTR. También ha sido apoyado por las ayudas PID2020-112545RB-C54, PID2020-112545RB-C53, PDC2022-133900-I00 y PDC2023-145862-I00 financiadas por MCIN/AEI/10.13039/501100011033 y por la ayuda FPU20/00256 financiada por el Ministerio de Universidades.

This article presents the design and manufacturing of a fully metallic X-band bandpass filter in coaxial-line technology. The device is 3D-printed as a self-supported structure without any dielectric inside. A short-circuit λ/4 parallel stub bandpass filter provides the required mechanical support for the self-supported 3D-printing process. To enhance filter out-of-band performance, a second stage consisting of a stepped-impedance low-pass filter is integrated, also using coaxial-line technology. Both filters are designed separately and then combined to achieve desired frequency specifications. A prototype with a
passband at X-band (between 8 and 12 GHz) is manufactured using Selective Laser Melting, showing excellent agreement between simulations and measurements. This approach promises highly integrated, multifunctional monoblock coaxial filters with additional benefits such as increased RF shielding and protection against electrostatic discharge., Este trabajo ha sido financiado por el Ministerio de Ciencia e Innovación - Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033), Proyecto PID2020-112545RBC53. A. Pons Abenza agradece también la financiación recibida por parte del Ministerio de Universidades del Gobierno de España, bajo el programa Margarita Salas.

A new topology for groove gap waveguide (GGW) technology is proposed to ease its manufacturing process by computer numerical control (CNC) milling. GGW technology consists of two metal plates, where one of them presents a λ/4 height pin bed that avoids contact with the other plate, making it an ideal alternative to other waveguides for millimeterwave applications. However, the manufacture of the pins by CNC milling may be troublesome due to the large pin height required. A GGW with reduced height pins will be proposed, maintaining the standard dimensions of the equivalent rectangular waveguide ports and the operation bandwidth. The performance of this new topology will be compared with other proposals by means of simulations and measurements, and a bandpass filter will be also implemented and manufactured in this technology to validate its usefulness., This work was funded by the Spanish Ministerio de Ciencia e Innovación-Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033 under project PID2020-112545RB-C53).

A novel photonic-assisted 2-D Terahertz beam steering chip using only two tuning
elements is presented. The chip is based on an array of three leaky wave antennas (LWAs) with
a monolithically integrated beamforming network (BFN) on a 50 µm-thick indium phosphide
substrate. The THz beam angle in elevation (E-plane) is controlled via optical frequency tuning
using a tunable dual-wavelength laser. An optical delay line is used for azimuth (H-plane) beam
control. The simulated beam scanning range is 92° in elevation for a frequency sweep from
0.23 THz to 0.33 THz and 69.18° in azimuth for a time delay of 3.6 ps. For the frequency range
from 0.26 THz to 0.32 THz, it is confirmed experimentally that the THz beam scans from −12°
to +33°, which is in good agreement with the numerical simulations. The beam direction in
azimuth scans with a total angle of 39° when applying a delay difference of 1.68 ps. A good
agreement is found between theoretically predicted and experimentally determined THz beam
angles with a maximum angle deviation below 5°. The experimental scanning angles are limited
due to the mechanical constraints of the on-wafer probes, the on-chip integrated transition and
the bandwidth of the THz receiver LNA. The mechanical limitation will be overcome when using
a packaged chip., Deutsche Forschungsgemeinschaft (Project-ID 287022738– CRC/TRR 196(Project C07)); Bundesministerium für Bildung und Forschung (6GEM, grant No. EFRE-0400215, grant No.16KISK017, grant No.16KISK039,
NRW/EFRE Terahertz-Integrationszentrum (THzIZ), Open6GHub); Agencia Estatal de Investigación (/MCIN/AEI/
10.13039/501100011033, PID2019-109984RB-C43/AEI/10.13039/501100011033, PID2020-112545RB-C53); Ministerio de Ciencia e Innovación (FPU Program 00013/2018).

We propose a novel experiment, the Canfranc Axion Detection Experiment (CADEx), to probe dark matter axions with masses in the range 330–460 μeV, within the W-band (80–110 GHz), an unexplored parameter space in the well-motivated dark matter window of Quantum ChromoDynamics (QCD) axions. The experimental design consists of a microwave resonant cavity haloscope in a high static magnetic field coupled to a highly sensitive detecting system based on Kinetic Inductance Detectors via optimized quasi-optics (horns and mirrors). The experiment is in preparation and will be installed in the dilution refrigerator of the Canfranc Underground Laboratory. Sensitivity forecasts for axion detection with CADEx, together with the potential of the experiment to search for dark photons, are presented., SA and JM are supported by
grants PID2019-108122GB-C32 and the Maria de Maeztu grant CEX-2019-000918-M of
ICCUB. The work of UPCT and IFIC is supported by grant PID2019-108122GB-C33, funded
by MCIN/AEI/10.13039/501100011033/ and by “ERDF A way of making Europe”. JMGB
thanks the grant FPI BES-2017-079787, funded by MCIN/AEI/10.13039/501100011033
and by “ESF Investing in your future”. The work of Universidad de Cantabria is supported by the Ministry of Science and Innovation under Grant PID2019-110610RB-C22.
CAB and IMDEA-Nanoscience work is supported by grants PID2019-105552RB-C41 and
PID2019-105552RB-C44 and by Comunidad de Madrid under Grant P2018/NMT-4291.
IMDEA-Nanoscience acknowledges financial support from “Severo Ochoa” Programme for
Centers of Excellence in R&D (MINECO, Grant SEV-2016-0686). D.G. and A.G also
acknowledge Grant DEFROST N62909-19-1-2053 from ONR Global. RBB, FJC, BJK,
EMG, JMS and PV thank the Spanish Agencia Estatal de Investigación (AEI, MICIU)
for the support to the Unidad de Excelencia María de Maeztu Instituto de Física de
Cantabria, ref. MDM-2017-0765. RBB, FJC, EMG and PV thank the Spanish Agencia
Estatal de Investigación (AEI, MCI) for the funds received through the research project,
ref. PID2019-110610RB-C21. RBB, FJC, BJK, EMG, JMS and PV also thank the ‘Dark
Collaboration at IFCA’ working group for useful discussions. The work done by ANTERAL
S.L. is supported by project QON-Space financed by the Navarra Government Project No.
0011-1365-2021-000220. UPNA acknowledges financial support from the Spanish State
Research Agency, Project No. PID2019-109984RB-C43/AEI/10.13039/501100011033 and
Project No. PID2020-112545RB-C53/MCIN/AEI/ 10.13039/501100011033.

This letter proposes a new design approach for filtering antennas. The novel matching reflection coefficient based method allows the integration of filters and antennas without compromising the frequency behavior of either of these components. Moreover, this integration is done avoiding the need of lengthy optimization processes and provides a high degree of flexibility in the types of antennas that can be used. In order to validate it, two examples are provided. In both cases, a 4 th -order Chebyshev bandpass filter at 101.5 GHz implemented in stacked groove gap waveguide (GGW) configuration is used, firstly along with a single aperture antenna and, subsequently, with a slotted ridge gap waveguide (RGW) array. This second example has been manufactured to demonstrate the usefulness of the new design methodology. Excellent measured performance has been obtained for a filtering antenna at W-band for the first time., This work was funded by the Spanish Ministerio de Ciencia e Innovación - Agencia Estatal de Investigación (MCIN/AEI/ 10.13039/501100011033) under Project PID2020-112545RB-C53

In this paper, a design approach for effective low-pass filters (LPF) that use the Rth-passband replica of the stepped-impedance prototype response is presented. Traditional LPF design methods often rely on well-established techniques, but they may not always deliver the desired performance or flexibility. By incorporating the Rth-passband replica of the stepped-impedance prototype, we introduce a new perspective that opens up new possibilities in filter design. This approach has the potential to overcome some of the limitations associated with existing methods, offering improved filter performance, robustness, and novel design possibilities and flexibility. Additionally, we will showcase its practical application by designing, fabricating, and measuring a 5th-order gap waveguide LPF that employs the first replica as per the provided guidelines., This work was supported by the Spanish Ministerio de Ciencia e Innovación Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033) under Project PID2020-112545RB-C53.

In this paper, we introduce an innovative approach for determining the complex permittivity (ε) and permeability (𝜇)) of magnetodielectric composites. Our methodology uses artificial neural network (ANN) modeling to determine these key parameters from S-parameter data collected at 2.45 GHz. These measurements are performed by a novel microstrip split ring resonator (SRR)-based resonant sensor, offering enhanced precision and reliability in the estimation process., Agradecemos el apoyo recibido a través del proyecto PID2020-112545RB-C53 del Ministerio de Ciencia e Innovación - Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033), así como por parte de Samueli School of Engineering, University of California, Irvine, USA. Germán Álvarez-Botero agradece igualmente el apoyo recibido a través del programa ANDIA del Gobierno de Navarra.

Trabajo presentado al International Workshop on Multipactor, Corona and Passive Intermodulation (MULCOPIM), Valencia, Spain, 19-21 October 2022 (Session 08), In this paper, the PPHCs of two filter design techniques, stepped-impedance (SI) and smooth-profile (SP), are presented for four design prototypes. Smooth-profiled filters feature smooth variations in the characteristic impedance profile, avoiding sharp edges, which accumulate electric fields. The absence of sharp edges in SP reduces the voltage magnification factor, which in turn improves the PPHC of the filter. The phenomenon of electric fields accumulation at the sharp corners of the SI filters is presented and compared with smooth transitions in SP filters. Furthermore, 1D graphs of electric field intensity are presented along the strip contour of the microstrip lines. Finally, SPARK3D results clearly demonstrate that SP filters can handle higher peak powers than their SI counterparts between critical pressure and ambient pressure, for all the studied designs., This work was supported by the Spanish Ministerio de Ciencia e Innovación –Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033) under Project PID2020-112545RB-C53 and by the European Union's Horizon 2020 Research and Innovation Program under Grant 811232-TESLA-H2020-MSCA-ITN-2018. Jamil Ahmad also acknowledges the funding received through the PRE2018-085491 grant.

Space Systems have been historically characterised by high performance, high reliability and high cost. Every new generation
of space systems tends to improve performance, keep as much as possible reliability, speeding the lead time and lower the
cost. Aggressive approach is nowadays followed by some of the players of the new space ecosystem where, for instance, reli-
ability can be relaxed thanks for the in-orbit redundancy or robustness to failures by having a constellation with a high number
of satellites. This push towards the technology and system limit requires to investigate new methods for the manufacturing
of RF/Microwave parts. RF devices such as those based on waveguide structures, benefit from an additive manufacturing
approach in terms of radio frequency (RF) performance and compactness. However each manufacturing approach comes with
specific features and limitations which need to be well understood and, in some cases, even taking advantage of them. This
paper provides a short review of some of the RF/Microwave parts already manufactured using this technology. The paper will
focus mainly on metal 3D printing parts since this technology is, at the moment, well accepted by the space community., UPNA thanks the support of the Spanish
Ministerio de Ciencia e Innovación-Agencia Estatal de Investigación (MCIN/AEI/ 10.13039/501100011033) under Project PID2020-112545RB-C53.

In this paper, a novel design method for rectangular waveguide filters intended for fabrication using direct metal additive manufacturing is proposed. The synthesized filters will feature a smooth profile that allows us to fabricate them orienting the filter propagation axis in the vertical building direction, achieving an optimum configuration for direct metal additive manufacturing fabrication. The novel design method is valid for any all-pole transfer function, which is initially implemented with a commensurate-line distributed unit element prototype. The impulse response of that initial prototype is then properly interpolated to obtain the target response for a smooth-profiled filter with similar length and profile excursion. Finally, the target impulse response just generated is implemented in rectangular waveguide technology employing a novel inverse scattering synthesis technique that relies on the coupled-mode theory to model the electromagnetic behavior of the waveguide filter. The novel inverse scattering synthesis technique is general and also valid for the case of filters with very high rejection levels, which is of great relevance in rectangular waveguide technology. A Ku-band low-pass filter with stringent satellite specifications is designed using the proposed method, fabricated by means of a direct metal additive manufacturing technique, and measured with a vector network analyzer. A very good agreement is achieved between the simulated and measured results, fulfilling the required specifications and demonstrating the feasibility and performance of the novel design method., This
work was supported in part by the Spanish Ministerio de Ciencia e
Innovación—Agencia Estatal de Investigación (MCIN/AEI/10.13039/
501100011033) under Project TEC2017-85529-C3-2-R (co-funded by
the Fondo Europeo de Desarrollo Regional (FEDER) “A way to make
Europe”) and Project PID2020-112545RB-C53, and in part by the Advanced
Technologies for future European Satellite Applications (TESLA) Project
(European Union’s Horizon 2020 Research and Innovation Programme
through the Marie Sklodowska-Curie Grant) under Grant 811232.

This paper presents a design methodology that significantly increases the peak power handling capability (PPHC) of microstrip filters. The PPHC is limited in microstrip technology by the corona effect: a physical phenomenon caused by the ionization of the air under the presence of strong electric fields around the planar circuit. Microstrip filters with a low electric field strength in the air increases the corona threshold level, resulting in high PPHC. Conventional stepped impedance (SI) filters, which consist of cascaded step-shaped elements, exhibit sharp discontinuities. These geometric edges amplify the electric field strength in the air, consequently reducing the corona threshold. Our research group has recently reported a new synthesis technique that introduces a smooth-profile (SP) conductor strip. This SP strip eliminates any sharp discontinuities and significantly reduces the strength of the electric field. This paper focuses on the examination of the high power performance of 7th-order SP and SI low-pass filters. The cut-off frequency (fc) for both types of filters is set at 447.45 MHz, while the frequency for maximum stop-band rejection (fo) is 1 GHz. The findings indicate that the SP filter shows a notable enhancement in peak power handling capability (PPHC), with gains of 2.48 dB and 4.80 dB observed at critical pressure and ambient pressure, respectively., This work was supported by the Spanish Ministerio de Ciencia e Innovación — Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033) under Project PID2020-112545RB-C53. Jamil Ahmad also acknowledges the funding received through the PRE2018-085491 grant.

In this paper, a W-band 3D-printed bandpass filter is proposed. The use of higher-order TE10n modes in groove gap waveguide (GGW) technology is evaluated in order to alleviate the manufacturing requirements. In addition to the use of higher-order modes, the coupling between them is analyzed in detail to improve the overall fabrication robustness of the component. This allows the implementation of narrow-band filters operating at millimeter-wave frequency bands (or above), which usually demand complex manufacturing techniques to provide the high accuracy required for this kind of devices. In order to show the applicability of the proposed method, a narrow-band 5th-order Chebyshev bandpass filter centered at 94 GHz, which can be easily fabricated by state-of-the-art stereolithographic (SLA) 3D-printing techniques followed by silver coating, is shown. Excellent measured performance has been obtained., Open Access funding provided by Universidad Pública de Navarra. This work was funded by the Spanish Ministerio de Ciencia e Innovación –Agencia Estatal de Investigación (MCIN/AEI/1010.13039/501100011033) under Projects TEC2017-85529-C3-1-R and TEC2017-85529-C3-2-R (co-funded by FEDER “A way to make Europe”) and Projects PID2020-112545RB-C51 and PID2020-112545RB-C53.

In this contribution, the design and manufacturing of an all-metal coaxial-line X-band bandpass filter is discussed. The device is 3D-printed as a self-supported structure without any dielectric inside the coaxial. The mechanical support between the inner and outer coaxial-line conductors is provided by means of λ/4 short-circuited stubs, which are also used in the bandpass filter design. The real transmission zeros (TZs) produced by the short-circuited stubs are responsible for a high filter selectivity. In order to enhance the filter performance, a second stage consisting in a coaxial-line stepped-impedance low-pass filter is integrated in the design to provide the rejection level required for the out-of-band behaviour. Following our design method, the bandpass and low-pass filters are designed separately, and a final matching step is performed to connect both and to achieve the aimed frequency specifications. In this way, a monoblock coaxial filter with very good in-band and out-of-band performance can by obtained by using an additive manufacturing (AM) procedure. Only the input/output (I/O) coaxial connectors will need to be assembled to the filter to perform the frequency measurements. The filters in this work can be seen as a first proposal towards more complex multi-functional monoblock structures using additively-manufactured coaxial technology, for highly-integrated RF chains. Other expected benefits beyond the compactness or lightweight are an increased RF shielding, electrostatic discharge risk reduction, and Passive Intermodulation (PIM) protection. In the paper, a prototype with a passband between 8 and 12 GHz is designed and manufactured, using a bandpass filter with three stubs and an integrated 15th-order low-pass filter, providing rejection for spurious frequencies up to 30 GHz. The filter is manufactured using Selective Laser Melting (SLM) and measurements show an excellent agreement with the simulations., This work was supported by the Spanish Ministerio de Ciencia e Innovación-Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033) under Project PID2020-112545RB-C53. The work of Alejandro Pons-Abenza was supported by the Spanish Ministerio de Universidades under Margarita Salas Program

In this letter, a novel design for a 3-D-printed, self-supported coaxial-line X-band filter is presented. The filter is intended for Earth observation (EO) data downlink systems, where it must effectively reject signals in a wide frequency range. The filter design incorporates a 15th-order low-pass filter structure with a smooth profile, integrated with a short bandpass section with four $\lambda /4$ short-circuited stubs. The optimization of the low-pass section is attained by means of shape deformation, including the inner and outer coaxial conductors, and leads to a wide rejection band up to around 40 GHz, to suppress the third harmonic and other undesired out-of-band frequencies. A prototype was fabricated in one piece in an aluminum alloy using selective laser melting (SLM) and measured, exhibiting excellent agreement with simulations. In terms of out-of-band performance, the proposed coaxial-line filter is superior to other related state-of-the-art solutions., This work was supported in part by the National Science Centre, Poland, under Agreement 2020/39/O/ST7/02897; and in part by Spanish Ministerio de Ciencia e Innovación-Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033) under Project PID2020-112545RB-C53.

In this paper, a groove gap waveguide (GGW) low-pass filter is proposed for the first time. Gap waveguide technology represents an interesting alternative as a low-loss, cost-effective, high- performance transmission line and packaging solution for microwave and millimeter-wave systems. This technology may exhibit a frequency behavior similar to rectangular waveguide but with some advantages such as the no need of electrical contact between the upper and lower plates of the GGW, making it an attractive alternative in the design of satellite devices at high frequencies. However, all the previous literature focused on band-pass filters, while design methods for GGW low-pass filters have not been reported. Furthermore, in this paper a new manufacturing approach is proposed and its performance has been compared with traditional methods such as Computer Numerical Control (CNC) milling. The new approach relies on the Selective Laser Melting (SLM)-3D printing of the filter followed by a post-processing step, in which it is partially mechanized using CNC milling to improve the surface finish. Measurements of the manufactured prototypes are also included to compare both techniques at millimeter-waves, showing the advantages of the new fabrication method and the excellent agreement with the simulations., This work was supported by the Spanish Ministerio de Ciencia e Innovación–Agencia Estatal de Investigación (MCIN/AEI/
10.13039/501100011033) under Project PID2020-112545RB-C53.

This article presents the design and experimental validation of a W-band waveguide cavity filter operating
around 91 GHz, using a periodic electromagnetic bandgap (EBG)
structure with glide symmetry to implement the filter in a
stack of multiple thin metallic sheets without electric contact
between them. The filter is based on vertically stacked cavities
that use the TE103 mode, which offers increased robustness to
manufacturing and assembly errors due to the large dimensions
of the cavity. The glide-symmetric circular hole EBG structure
is analyzed and integrated to suppress unwanted field leakage
between the metallic layers with a broad stopband. The proposed
filter maintains effective operation in the 88–94-GHz frequency
range, even with gap variations between layers of up to 20 µm.
The filter is fabricated using laser cutting, achieving a low
surface roughness and high dimensional accuracy. Experimental
measurements show excellent agreement with the simulations,
with a return loss greater than 20 dB and an insertion loss
below 0.5 dB. These results demonstrate the possibility to
achieve high performance filters at millimeter-wave frequencies
while maintaining low fabrication complexity and cost using the
multilayer waveguide technology., This work was supported in part by Spanish Government, Ministerio de Ciencia, Innovación y Universidades, through the Projects New Array Antenna Technologies and Digital Processing for
the Future Integrated Terrestrial and Space-Based Millimeter Wave Radio Systems UPM-InTerSpaCE under Grant PID2020-112545RB-C51; in part by the Filters and Passive Components for Future Integrated Terrestrial and Space-based Millimeter Wave Radio Systems UPNA-InTerSpaCE under Grant PID2020-112545RB-C53; and in part by the Sub-Terahertz Antenna
Technologies for Communications In the Road to 6G UPM -STAIRto6G funded by MICIU/AEI/10.13039/501100011033 and FEDER, UE, under Grant PID2023-151385OA-I00. The work of Sergio Garcia-Martinez was supported by the Universidad Politécnica de Madrid, Programa Propio.

This work presents the design of a cavity-stacked bandpass filter (BPF) using contactless air-filled substrate integrated waveguide (CLAF-SIW) technology for millimeter-wave frequencies. This technology is a variant of air-filled SIW technology, incorporating contactless techniques. It enables the reduction of dielectric losses in SIW filters while supporting multilayer structures with robust assembly. The cavity-stacked filter topology allows for very good frequency responses with a reduced footprint and no transitions needed. As an example, a 4th-order Chebyshev bandpass filter composed of four stacked cavities, coupled through irises, is shown. The iris layers are fabricated by metallizing the slot edges of a PCB, while the cavity layers are implemented using CLAF-SIW. The filter has been designed and manufactured to provide a passband response from 36 GHz to 37.5 GHz. A good agreement between measurement and simulation has been achieved. The losses in the proposed CLAF-SIW filter are primarily due to the metal roughness of the low-cost commercial laminates used., This work has been supported by grant TED2021-129938B-I00 funded by MCIN/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR. It has also been supported by Grants PID2020-112545RB-C53, PID2020-112545RB-C54, PDC2022-133900-I00, and PDC2023-145862-I00, funded by MCIN/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR. It has also been supported by Grant FPU20/00256 funded by MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future.