This work investigates the additive manufacturing process for D-band horn antenna lenses. Two distinct lens designs are fabricated using fused deposition modeling with readily available polypropylene filament. This approach enables the rapid and cost-efficient production of more complex lens surfaces than traditional milling techniques, while maintaining a very low loss tangent and comparable permittivity to Teflon. The performance of these two complex 3D-printed lenses is then measured and compared against a conventionally milled Teflon lens with a simpler, traditional surface geometry at these frequencies. Key metrics such as the radiation pattern, antenna matching, and overall gain are evaluated.

This paper describes an approach to increase the operating frequency of groove gap waveguide (GGW) components while maintaining the CNC milling manufacturing requirements with respect to the cutter diameter. The approach is demonstrated by a fourth order filter. The proposed filter is implemented using the interdigital-pin approach, with a double layer structure for the upper as well as the lower part. This combination is denoted as double layer interdigital-pin and allows for smaller distances between the pins compared to single-layer interdigital pins without requiring a smaller cutter diameter. The overall approach as well as the filter design strategy are discussed. Furthermore, the manufacturing technique is described and the measurement results of a GGW filter in the D-band are presented.

This paper presents the design, manufacturing, and electrical characterization of a dielectric triple-mode bandpass filter. The filter utilizes a triple-mode resonator based on the combination of a ring-shaped TE single-mode and a Y-shaped dual-mode dielectric resonator. For the realization of the resonator consisting of zircona, the cost-efficient Direct Ink Wrinting (DIW) approach is used. Simulations and practical measurements validate the design, showcasing the suitability of the approach to combine different basic resonator types for the realization of multi-mode structures.

This letter presents the design and electrical measurement results of a novel compact diplexer design in Ku-band. The proposed diplexer is based on TM01 delta mode dielectric resonators (DRs). A fourth-order filter with one triplet section for each channel is used. An additively manufactured inset is used for each filter, which contains the resonators and the required support structure and is printed from two materials in one piece. The chosen arrangement enables a compact design and simple assembly. To validate the concept, the design, fabrication, and measurement of the fourth-order dielectric diplexer are presented.

In this paper, three groove gap waveguide (GGW) filters are presented, which utilize different techniques to create transmission zeros (TZs) in the W-band. First, a fourth-order filter with cross-coupling of non-adjacent cavities realizes five TZs. The filter is implemented using a stacked cavity approach, which simplifies the realization of cross-couplings with positive and negative signs. The source to load cross-coupling realizes one TZ more than predicted from theory. In the second filter, two off-centered posts with partial height are used to realize two TZs. These posts act as strongly frequency-dependent coupling elements and enable the realization of TZs in an inline filter topology. An interdigital-pin implementation has been used since otherwise, the distance between the posts and the sidewalls is too small to allow manufacturing using the Computerized Numerical Control (CNC) milling approach. The third filter is of fourth order and implements two TZs by using a stub-loaded cavity approach. All filters are designed as a proof of concept in the W-band (75–110 GHz) to verify the manufacturability at high-frequency bands. The manufactured components are realized by high-precision CNC milling and measurement results show good agreement with the simulation for all proposed filters.

This paper compares the performance of two eighth-order waveguide filters in D-band. Both filters have a complex pair of transmission zeros, which is used for phase equalization, as well as an imaginary transmission zero pair for blocking improvement in the near passband region. The filters are designed in order to be manufactured in E-plane cut, which reduces the insertion loss compared to H-plane-cut manufacturing. Both filters are designed in a way that a quadruplet section implements the complex transmission zero pair. However, they distinguish each other by the realization of the imaginary transmission zeros. While one filter consists of a second quadruplet section, the other filter has two stub-loaded cavities. The flexibility of both approaches is discussed and a performance comparison of manufactured prototypes takes place.

This paper describes the realization of a fourth order waveguide filter, which is designed in the WR-3 frequency band (220 GHz - 330 GHz). The filter implements a classical quadruplet topology. A cross-coupling between the first and fourth resonator realizes a pair of transmission zeros (TZs) to improve the near passband rejection properties. A source to load (SL) cross-coupling is added to the topology for the realization of further TZs. In comparison to former investigations, the SL cross-coupling proposed here consists of two individual coupling slots. An SL cross-coupling in waveguide technique can be designed to show a dispersive behaviour, wherefore additional TZs can be introduced to the filter response. A double slot coupling aperture increases the degrees of freedom with respect to placing these additional TZs. As a result, in total seven TZs in the WR-3 frequency band are generated. Six of these TZs can be placed nearly symmetrically above and below the passband. An adapted coupling matrix description as well as a discrete equivalent circuit are proposed as well. Furthermore, parameter studies are carried out and measurement results are compared to simulation.

In this letter, the design and additive manufacturing (AM) of a groove gap waveguide (GGW) filter in the $D$ -band is presented. For this kind of filter, the manufacturing of very small periodic pin structures is necessary. The conventional manufacturing of these structures by CNC milling is time-consuming, and high-precision milling machines are extremely expensive. Other manufacturing processes such as screen printing are, therefore, required for the cost-effective and efficient production of large quantities. The screen printing process is presented, and its suitability for the production of GGW components in the millimeter-wave area is validated by a third-order bandpass filter prototype in $D$ -band, which was manufactured and electrically characterized.

Within this paper, a corrugated horn antenna in the sub-terahertz regime is manufactured using a novel printing technique and the results are presented. The antenna aperture utilizes an elliptical shape which leads to symmetric radiation. Furthermore, the implemented antenna design leads to low side lobes, also the overall length and weight is comparably small. In addition to the antenna characteristics, the surface of the printed antenna is examined to investigate the roughness and accuracy. A symmetric radiation pattern as well as low losses are reached, which indicates a smooth surface and high accuracy.

In this paper, a lithography based additive manufacturing (AM) technique is used for the realization of a ceramic X-shaped dual-mode filter. The fourth order filter consists of two identical ceramics which are mounted in a copper housing and which are coupled by an aperture. Due to the arrangement of the ceramics and the associated coupling scheme, a negative cross-coupling between the first and fourth resonance is realized, leading to two transmission zeros (TZs), one above and one below the passband. The digital light processing process used for fabrication of the ceramics is described and compared to the stereolithography approach. Subsequently, the filter design process is addressed. The measurement results are compared to the simulation and reveal good agreement.

This paper addresses the optimization of the manufacturing process for the additive manufacturing of groove gap waveguide filters in the D-band. The focus is on the optimization of the 3D screen printing process with regard to the reduction of manufacturing tolerances. The critical parameters here are the consideration of the shrink factor, bending effects due to thermal post-treatment and the selection of a suitable material composition. A third-order filter is intended to show that 3D screen printing can achieve manufacturing accuracies comparable with CNC milling. At the same time, structure sizes can be realized that can no longer be milled.

This paper presents a fully reconfigurable bandpass filter in the W-band. The third-order filter utilizes contactless tuning plungers, which are under the control of piezoelectric motors, to tune its transmission characteristic. This arrangement allows exceptionally precise adjustments, enabling highly accurate tuning options. The tuning element incorporates coupling resonators to change coupling strength between resonators. Notably, both the main resonators and the coupling resonators use identical contactless plungers, simplifying the overall design. The filters' center frequency can be adjusted between 78 GHz and 82 GHz while the bandwidth can be changed independently between 300 MHz and 600 MHz. For most tuning states, an unloaded Q-factor $Q^{0}$ above 1000 can be measured and the filter is able to realize a return loss of better than 20 dB.

This paper discusses dielectric TM-mode filters based on high permittivity Y-shaped ceramics.It is shown that this type of ceramic operates as a dual-mode resonator and therefore contributes two reflection zeros as well as one transmission zero (TZ) to the filter response.Hence, it can be interpreted as a doublet structure and used for the realization of quasi-elliptical filter responses of different order.The dual-mode resonator can be used in multiple different filter set-ups: On the one hand, a combination with classical TM 010 -mode resonators is possible to allow the realization of TZs in an in-line filter configuration without using cross-coupling apertures.Therefore, negative or diagonal cross-couplings, which are often difficult to realize and handle, can be avoided.On the other hand, several Y-shaped ceramics can be coupled directly with each other to increase the number of TZs to n f z = n/2, where n is the order of the filter.Finally, it is shown that even a combination with extracted pole elements is realizable.Prototypes based on modular segments are manufactured as proof of concept.

In this paper, the design and realization of X-band monolithic 3-D printed waveguide filters is discussed. All proposed filters are manufactured with the low-cost fused deposition modeling (FDM) additive manufacturing technique, due to the wide distribution of this printing technology in laboratories and industry. Two combined waveguide components are proposed: The first component is a combination of a twist and a third order filter while the second one combines a fourth order filter with two frequency dependent couplings, a twist and a corner. All components are manufactured with the FDM printing technique and the results are compared with the simulation. Additionally, the metal plating procedure is shortly addressed.

In this paper, a tunable microwave bandpass filter is presented which allows for different center frequency combinations while maintaining a constant bandwidth over a wide frequency range. The special T-shaped form of the coaxial resonator posts allows for adjustment of the center frequency and coupling factor while minimizing the amount of tuning screws. In total, only three tuning elements are used to control the input and inter-resonator coupling as well as the center frequency of the bandpass filter. The filter offers a 57MHz±3MHz bandwidth over a 400MHz frequency range. A demonstrator has been build to verify the concept and exemplary measurements have been taken at 1.73GHz, 1.93GHz and 2.10GHz. The simulations have been compared to the measurements, which validates the 57MHz bandwidth at the 20 dB return loss level for all tuning states.

In this paper, a novel resonator structure combining TM and TE mode operation is presented. By connecting dielectric rods with a ring and appropriate dimensioning, triple-mode operation can be achieved. Based on the eigenmodes used, design strategies are shown for individual adjustment of each mode, which demonstrates the flexibility of the structure for filter design. To validate the approach the triple-mode structure was additively manufactured from a high permittivity ceramic material with ε r ≈ 43.3 using the Lithography-based Ceramic Manufacturing (LCM) process. A third-order bandpass filter operating at 4.5 GHz was fabricated and measured. The measurement results are in good agreement with the simulation and an unloaded quality factor of 2700 is extracted.

In this paper, the design and realization of quasi-elliptical waveguide filters with reduced manufacturing complexity are discussed. The filters are based on TE mode cavities, which are loaded with TM mode stubs. It is shown that dual-, triple- and quadruple-resonance segments are obtained by using up to three stubs loaded on the broad side of a TE mode cavity. The structures obtained can either be used as a stand-alone filter or even as a building block suitable for the realization of higher order filters. The multi-resonance blocks reveal several advantages in the mm-wave area: The manufacturing complexity is easy to handle and comparable to simple all-pole filters, which is especially important at high frequencies. Therefore, three prototypes are manufactured as proof of concept in the D-band (110 GHz-170 GHz). Moreover, the building blocks are able to produce n - 1 transmission zeros (TZs) with n being the number of resonances. Therefore, the blocks generate between one (dual-resonance) and up to three (quadruple-resonance) TZs. Advantageously, the filters can be cut in the E-plane in order to reduce the insertion loss and hence consist of only two components. Three examples are manufactured by high precision CNC milling and reveal good agreement to the simulation by obtaining unloaded Q-factors of up to 1000.

AbstractIn this paper, the influence of the cutting plane as well as the orientation of the cavities in cross-coupled W-band waveguide filters are investigated. When waveguide filters are manufactured with the commonly known CNC (computer numerical control) milling technique, at least one cutting plane is required. The position of this cutting plane has an impact on the composition of the cavities, the manufacturing accuracy, and on the maximal number of transmission zeros (TZs) introduced by a direct source to load (SL) cross-coupling. Similar filter set-ups therefore may show different performances depending on the position of this cutting plane. To examine all these effects, three similar fourth-order W-band filter set-ups are realized with distinct cutting planes and different oriented cavities. The filters are compared in terms of the sensitivity to manufacturing tolerances, the maximal number of TZs introduced by a direct SL cross-coupling as well as their spurious mode performance.

Abstract In this paper, a modular waveguide filter platform suitable for educational and prototyping purposes is presented. The waveguide filter platform is dimensioned to work in the F-band (4.9–7.05 GHz). The design of the platform is discussed and versatile application possibilities are shown in many examples. The platform can be used to realize generalized Chebyshev filters with or without cross-couplings by exploiting TE101 and TE102 mode cavities. Transmission zeros can be introduced by the utilization of wires or aperture couplings. Filter topologies based on the extracted pole technique can be examined as well. Small changes in the set-up also allow the realization of a gap waveguide filter, a diplexer set-up as well as filters with frequency-dependent coupling apertures. Most required components can either be purchased cheaply or be manufactured with a three-dimensional printer.

In this paper, a novel realization of a triple-band filter offering a large spurious free range is presented. Three different resonator types (dielectric TM-mode, dielectric quasi-TM-mode and coaxial resonators) are implemented in order to increase the out of band rejection of the filter. Each of the chosen resonator types are used to implement one of the passbands in the filter response. The proposed topology leads to three real frequency axis transmission zeros between adjacent bands without the need for any complex cross coupling or coupling with a negative sign. Additionally, the topology reveals possibilities for an adaption of the bandwidth and distance between the individual passbands. The presented filter design leads to a large spurious free range up to 3.5 times the center frequency of the center band.