Design of an Additively-Manufactured Self-Supported All-Metal Coaxial-Line X-Band Bandpass Filter

• Published in: IEEE access Vol. 12; pp. 68171 - 68183
• Main Authors: Pons-Abenza, Alejandro, Arregui, Ivan, Angel Gomez Laso, Miguel, Lopetegi, Txema, Martin-Iglesias, Petronilo
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 2024; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Band-pass filters; Bandpass filter; Bandpass filters; Coaxial components; coaxial-line filter; Conductors; Connectors; Design; Electrostatic discharges; Electrostatic shielding; Filter design (mathematics); Frequency measurement; Intermodulation; Laser beam melting; Low pass filters; Manufacturing; metal 3D-printing; Microwave filters; Radio frequency; Radio frequency shielding; Rejection; Resonator filters; RF discharge-pumped lasers; Risk management; stepped-impedance filter; Superhigh frequencies; Three-dimensional printing
• ISSN: 2169-3536; 2169-3536
• DOI: 10.1109/ACCESS.2024.3399745

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 <inline-formula> <tex-math notation="LaTeX">\lambda /4 </tex-math></inline-formula> 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.