This paper studies the corona discharge power thresholds in microstrip bandpass filters (BPFs) and, in particular, is focused on a solution based on λ/2 cover-ended resonators to enhance their peak power handling capability (PPHC). First, a parametric analysis is carried out to evaluate the variation of the maximum electric field and the unloaded quality factor (Qu) as a function of the cover's geometrical dimensions (i.e. height, length, and width). Next, several microstrip BPFs centered at 1.6 GHz are designed, and their behaviors under moderate-to-high applied RF power signals are simulated to corroborate the previous study. A suitable number and size of covers are selected to enhance PPHC without barely degrading the filters’ electrical performance and, consequently, without hardly increasing the insertion losses. Finally, two third-order filters with covers and without covers (benchmark prototype) are manufactured, by way of illustration, and they are tested in the European High-Power RF Space Laboratory to validate the good performance of the proposed solution, where a PPHC enhancement of 3.1 dB at high pressures is achieved as compared to the benchmark prototype.

This work focuses on the impact of the build orientation on additively manufactured waveguide-based hybrid couplers for D-band frequency range and relates it to other sources of uncertainty within the overall manufacturing process and measurement instrumentation for the D-band frequency range. The designed specimens are first printed from UV curable photopolymer resin and subsequently metal coated by an electroless silver plating process, which in turn is improved by making use of the slotted waveguide approach. Although the requirements toward geometrical precision to achieve phase errors below 10° are in an order of 0.1 mm, a desktop grade DLP printer is utilized in this work in order to point out the prospects and limitations of additive manufacturing. Furthermore, waveguide paths with bends are part of the model and their impact on the measured attenuation is estimated explicitly.

Despite this narrow field of tolerances, one specimen could have been realized, which achieves a measured output magnitude imbalance of 0.7 dB over the frequency range from 120 to 155 GHz while at the same time exhibiting a phase deviation of only <10° from the desired 90°. With these demonstrated results, the proposed approach provides suitability for future applications in the D-band frequency range.

Shape-changing mechanical metamaterials have drawn the attention of researchers toward the development of continuous-range tunable frequency selective surfaces (FSSs). In this paper, a novel tunable FSS utilizing an origami-inspired “eggbox” structure is presented featuring four-degrees of freedom that can change the frequency response of two orthogonal linear polarizations. The centrosymmetric “eggbox” structure can be folded or rotated along two axes that lead to unprecedented reconfigurability compared to traditional Miura-Ori-based structures which have fewer degrees of control. The utilized cross-shaped dipole FSS element shows enhanced bandwidth, support for orthogonal linear polarization, and ease of fabrication. The prototype is fabricated using a low-cost fully additive inkjet printing process with silver nanoparticle conductive ink. The outcome of this study shows a 25% frequency tunable range over two polarization directions. The design can be an ideal spatial filtering candidate for advanced ultra-wideband terrestrial and space applications.

Identification of human individuals within a group of 39 persons using micro-Doppler (μ-D) features has been investigated. Deep convolutional neural networks with two different training procedures have been used to perform classification. Visualization of the inner network layers revealed the sections of the input image most relevant when determining the class label of the target. A convolutional block attention module is added to provide a weighted feature vector in the channel and feature dimension, highlighting the relevant μ-D feature-filled areas in the image and improving classification performance.

The 5th generation new radio (5G NR) standards create both enormous challenges and potential to address the spatio-spectral-temporal agility of wireless transmission. In the framework of a research unit at TU Ilmenau, various concepts were studied, including both approaches toward integrated circuits and distributed receiver front-ends (FEs). We report here on the latter approach, aiming at the proof-of-principle of the constituting FEs suitable for later modular extension. A millimeter-wave agile multi-beam FE with an integrated 4 by 1 antenna array for 5G wireless communications was designed, manufactured, and verified by measurements. The polarization is continuously electronically adjustable and the directions of signal reception are steerable by setting digital phase shifters. On purpose, these functions were realized by analog circuits, and digital signal processing was not applied. The agile polarization is created inside the analog, real-time capable FE in a novel manner and any external circuitry is omitted. The microstrip patch antenna array integrated into this module necessitated elaborate measurements within the scope of FE characterization, as the analog circuit and antenna form a single entity and cannot be assessed separately. Link measurements with broadband signals were successfully performed and analyzed in detail to determine the error vector magnitude contributions of the FE.