Novel design method for millimeter-wave gap waveguide low-pass filters using advanced manufacturing techniques

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

Gap waveguide topology with reduced height pins for millimeter-wave components

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)

Compact harmonic rejection filter for C-band high-power satellite applications

A compact high-power low-pass filter for C-band broadband satellite applications is presented in this paper. The filter is composed of three different sections. A 9th-order compact high-power multi-ridge structure achieves the fundamental mode stopband and the suppression of all-higher order modes. The required slope between the pass- and the stopband is accomplished by means of two step-shaped bandstop elements separated by very short waveguide sections. The passband of the filter is achieved through two compact matching networks. The filter is only 164-mm long, has less than 0.05 dB of insertion loss, handles 9.6 kW (single-carrier multipactor analysis), and has a very wide stopband (up to Ku-band). A dramatic size reduction has been achieved with respect to other commercially available solutions.This work was supported by the Spanish Ministerio de Ciencia, Innovación y Universidades – Agencia Estatal de Investigación under Project TE2017-85529-C3-2-R (AEI, FEDER-EU)

Filtro paso banda en tecnología groove gap waveguide con altura de pines reducida para facilitar su fabricación

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

Enhancement of the peak power handling capability in microstrip filters by employing smooth-profiled conductor strips

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

Multipactor breakdown analysis of Ku-band meandered low-pass filter

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.7343236This 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

Robust design of 3D-printed W-band bandpass filters using gap waveguide technology

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

Rectangular waveguide filters with meandered topology

In this paper, a new topology for rectangular waveguide bandpass and low-pass filters is presented. A simple, accurate, and robust design technique for these novel meandered waveguide filters is provided. The proposed filters employ a concatenation of ±90° E-plane mitered bends (±90° EMBs) with different heights and lengths, whose dimensions are consecutively and independently calculated. Each ±90° EMB satisfies a local target reflection coefficient along the device so that they can be calculated separately. The novel structures allow drastically reduce the total length of the filters and embed bends if desired, or even to provide routing capabilities. Furthermore, the new meandered topology allows the introduction of transmission zeros above the passband of the low-pass filter, which can be controlled by the free parameters of the ±90° EMBs. A bandpass and a low-pass filter with meandered topology have been designed following the proposed novel technique. Measurements of the manufactured prototypes are also included to validate the novel topology and design technique, achieving excellent agreement with the simulation results.This work was supported by ESA’s Networking/Partnering Initiative (NPI) under Contract 4000114859/15/NL/HK, Gobierno de Navarra under Project 0011-1365-2017-000130, and MINECO (Spain) under Projects TEC2014- 51902-C2-2-R and TEC2017-85529-C3-2-R

General synthesis of tapered matching sections for single mode operation using the coupled-mode theory

In this paper, a novel and general method to synthetize microwave waveguide tapers intended for single mode operation is proposed. The technique is based on the use of an exact series solution of the inverse scattering synthesis problem. An additional strategy necessary for dealing with waveguides where the propagation constant varies with the position is included. The coupled-mode theory is employed to model the electromagnetic behavior of the taper with the inherent mismatch caused by the connection of the waveguides with different cross-sections. The novel method allows us to synthesize the (classical) transmission line taper functions of Klopfenstein and Hecken, making them suitable for general waveguide tapers with single mode operation. Additionally, a new type of taper functions, also suitable for general waveguide tapers, is presented. The novel functions are obtained by partially employing the frequency response of multisection transformers, resulting in fully smooth tapers that can offer shorter lengths than the classical proposals. The taper synthesis procedure is demonstrated in rectangular waveguide technology, by requiring realistic and challenging specifications for different cases with different waveguide cross-sections to be matched: height mismatch, width mismatch, and simultaneous height and width mismatch. Several prototypes of Klopfenstein, Hecken and novel function tapers have been fabricated in an aluminum alloy by means of an Additive Manufacturing technique (Direct Metal Laser Sintering). The simulation and measurement results obtained for the rectangular waveguide taper prototypes confirm the accuracy of the novel synthesis technique proposed.This work was supported by the MINECO (Spain) under project TEC2017-85529-C3-2-R (AEI, FEDER-EU)

Synthesis of one dimensional electromagnetic bandgap structures with fully controlled parameters

In this paper, we propose a novel synthesis strategy for the design of one dimensional electromagnetic bandgap (1- D-EBG) structures where all the performance parameters of these devices can fully be controlled, i.e., the central frequency of the forbidden band, its attenuation level and bandwidth, and the ripple level at the passbands. The novel synthesis strategy employs a new inverse-scattering technique to accurately synthesize the 1-D-EBG structure, targeting a properly interpolated version of a classical periodic filter fulfilling the required frequency specifications. The new inverse-scattering technique follows a continuous layer peeling approach and relies on the coupled-mode theory to precisely model the microwave structures. Telecommunication and radar systems, as well as material characterization devices, will be profited by this proposal with which enhanced filters, sensors, power dividers, couplers, mixers, oscillators, and amplifiers can be designed in many different technologies. As a proof of concept, a 1-D-EBG structure in microstrip technology with a single forbidden band (free of spurious stopband replicas), with attenuation level of 30 dB, fractional bandwidth larger than 100%, and return loss level at the passbands of 20 dB, has been designed and fabricated. The measurements obtained are in very good agreement with the simulations and target specifications, being free of spurious replicas up to the 15th harmonic, showing the robustness and very good performance of the novel design strategy proposed.This work was supported by MINECO (Spain) under Projects TEC2014-51902-C2-2-R and TEC2014-55735-C3-R