A co-aperture dual-band linearly polarized slot array based on ridge gap waveguide (RGW), operating at the 74-78- and 102-106-GHz bands, is designed. In each subarray, two groups of longitudinal slots for two frequency bands are excited by a single RGW channel to achieve dual-band unidirectional radiation. Additionally, grooves and notches are implemented inside the RGW structure to improve dual-band matching, and two bandpass filters (BPFs) are incorporated at each side of the subarray to realize independent dual-band feeding while also providing filtering characteristics. The proposed subarray operates as a single channel. It can expand into a multichannel array, enabling multiple-input multiple-output (MIMO) when each subarray is individually excited or broadside radiation when all subarrays are simultaneously excited. A planar array of four subarray columns was fabricated to validate the dual-band concept and its broadside radiation performance. The simulated and measured results show good agreement.

To support high data rates and low-latency E-band wireless backhaul for future 6G and dense network deployments, this paper presents an ultra-high-gain (UHG), dual-polarized parabolic reflector antenna system with automatic beam steering by employing a two-dimensional (2D) movable feed based on gap waveguide technology to stabilize the beam direction when the reflector experiences sway due to strong winds or vibrations. UHG parabolic reflectors offer excellent gain. However, their extremely narrow beamwidth makes them highly sensitive to misalignment of the beam caused by wind and vibrations. To address this issue, this paper proposes a mechanically movable feed architecture that enables automatic dynamic beam alignment within ±2.5° while avoiding the need for a costly high-frequency motor-servo–based beam-steering system. Mechanical analysis and measurements confirm smooth, low-friction motion of the feed on a 2D platform, while electromagnetic evaluations verify stable dual-polarization performance, demonstrating the feasibility and reliability of the proposed system for E-band backhaul applications. A gravity-driven passive beam-stabilization mechanism is introduced. By leveraging mass displacement and spring coupling, the feed position automatically adjusts in real-time response to mast tilt, thereby maintaining real-time beam alignment. Theoretical analysis and prototype validation demonstrate that the system provides a compact, energy-free beam-alignment solution with high mechanical robustness, making it particularly well suited for communication and sensing applications on dynamic platforms.

This paper provides an overview of research activities of Prof. Per-Simon Kildal and his collaborators in developing a systematic analysis approach and corresponding algorithms for determining Green's functions of canonical multilayer structures. The formulation applied in these algorithms is based on the use of symmetries present in the considered structures and on the division of a complex electromagnetic problem into simpler sub-problems by applying the equivalence principle. In this way, a new creative approach was established for teaching electromagnetic field theory, as well as for structuring numerical algorithms. The considered algorithms are very flexible and are continuously being developed to include new classes of electromagnetic structures, such as planar and curved structures containing metasurface layers.

A compact, ultra-thin, low-loss and low-cost slot array antenna is presented for 77-GHz automotive radar, offering high polarization purity. Using strip-on-substrate coaxial multi-layer waveguide (SCMLW) technology, the design features a linear dogbone-shaped non-tilted centrally aligned slot array fed by a meandered metallic strip of the SCMLW. The proposed coaxial line-fed slotted antenna eliminates the angular and positional offset of slot employed in earlier designs, which are known to increase cross-polarization. Four prototypes, two 1×6 and two 2×6 slot arrays, were fabricated by chemical etching on a single platform with an overall thickness of only 0.9 mm, where long slits are introduced to improve radiation patterns. Measurements over 76–81 GHz show reflection coefficients better than $-10$ dB and relative cross-polarization levels below -29 dB for all prototypes, confirming their suitability for millimeter-wave automotive radar applications.

This letter presents a half-mode groove gap waveguide (HM-GGW) employing a high-density mushroom-type artificial magnetic conductor (AMC) to achieve robust millimeter-wave transmission with low-phase sensitivity to assembly misalignment. Conventional HM-GGW structure using low-density pin suffer from pronounced phase variations due to the imperfect approximation of a perfect magnetic conductor. By reducing the unit-cell period, the proposed high-density mushroom-type AMC effectively suppressing misalignment-induced phase perturbations. A W-band 1-to-2 power divider prototype is fabricated for validation. Measurements demonstrate a reflection coefficient better than -10 dB and an insertion loss below 0.8 dB over 85.0 GHz to 96.9 GHz. Under multiple random assembly conditions, the phase imbalance between the two output ports remains within $\pm$1 degrees, confirming the excellent phase robustness and assembly tolerance of the proposed structure.

A compact, efficiency-enhanced feed architecture is proposed for 140-150 GHz for continuous-transverse-stub (CTS) arrays. The design cascades four hard-wall feed channels, each realized with artificial magnetic conductor (AMC) boundaries to produce a uniform aperture distribution (magnitude and phase) across a center-fed aperture, thereby eliminating the need for a large corporate divider network. This architecture can reduce the number of power dividers in the feeding network resulting in a reduction of the insertion loss and gain improvement. The proposed feed has amplitude and phase balance of $\boldsymbol{\pm} \mathbf{1. 5 ~ d B}$ and $\boldsymbol{\pm} \mathbf{1 2}^{\boldsymbol{\circ}}$. When the proposed feeding is used to excite the CTS subarray, a realized gain of 27.8 dBi with radiation efficiency above 82% is achieved for gold plated structure with surface roughness of $\mathbf{0. 9} \boldsymbol{\mu} \mathbf{m}$. The fully metallic AMC structure ensures low ohmic loss and simple fabrication without dielectric loading or precision alignment. The proposed compact, low-loss feed is scalable to realize high-gain antennas for sub-THz band.

This letter presents strip-on-substrate coaxial gap waveguide (SCGW) technology, a novel transmission line for millimeter-wave (mmWave) applications. Its key distinction is an open coaxial structure requiring no electrical contact for the outer conductor. To suppress wave leakage, an electromagnetic bandgap structure-formed by vertically stacked metal pin-bed sheets and a substrate sheet-serves as the outer conductor, encapsulating the strip-type inner conductor. Several fabricated prototypes show that in the 76 GHz to 81 GHz range, reflection coefficients are better than-10 dB, with transmission losses of 0.25 dB/cm to 0.32 dB/cm for single-sided-strip SCGW and 0.18 dB/cm to 0.26 dB/cm for double-sided-strip SCGW, confirming the potential of the design for mmWave applications.

For large planar array antennas, one key performance metric is the active reflection coefficient of each radiating element. However, verifying this coefficient through measurement typically requires extensive S-parameter data, as all mutual couplings between ports must be accounted for. This process is not only time-consuming but also increases the risk of wear and tear on coaxial connectors-such as SMA-due to frequent connecting and disconnecting. In this paper, we propose a simplified method to estimate the active reflection coefficient using measurements of the embedded element radiation patterns, significantly reducing human effort and minimizing connector handling during network analyzer measurements.

This paper presents two innovative packaging techniques for Monolithic Microwave Integrated Circuits (MMICs) designed for multilayer waveguide-based antennas operating near 100 GHz. The first technique involves a transition from a high-permittivity Gallium Arsenide (GaAs) MMIC to a rectangular waveguide using conventional bondwires as the coupling structure within the W-band. This approach enables seamless integration of any off-the-shelf RF chip into waveguide antenna modules without modifying the ground-signal-ground (GSG) pads or adding passive transition substrates. An electromagnetic bandgap (EBG) structure, implemented using metallic pins, effectively suppresses unwanted field propagation. Measurements of a back-to-back (B2B) prototype indicate a reflection coefficient below -10 dB and an average insertion loss of 0.12 dB for a single transition across a bandwidth from 90 to 97 GHz (10.5% relative bandwidth). The second technique introduces a contactless vertical transition from a high-permittivity Alumina (Al2O3) based microstrip line to a waveguide, targeting F-band applications. This proposed concept employs a patch-shaped probe placed on the substrate to couple electromagnetic waves to an H-shaped waveguide aperture positioned above the probe. Experimental results demonstrate a reflection coefficient below -10 dB and an average insertion loss of 0.17 dB over a frequency range of 102 to 120 GHz (15.3% relative bandwidth). In addition, the impact of manufacturing and assembly tolerances on the performance of both transitions is analyzed.

This paper presents an innovative microstrip-to-waveguide transition specifically designed for beam steering antenna applications, ensuring efficient signal transmission in the K-band frequency range. Smooth transitions between microstrip and waveguide technologies are essential for optimizing signal integrity in high-frequency systems, where minimizing loss and maintaining impedance matching are critical for overall performance. By using gap waveguide technology, the proposed design achieves seamless integration between the substrate and the metallic waveguide, enhancing the efficiency of the system while reducing complexity. A bone-shaped coupling slot enables effective energy coupling between the microstrip section and groove gap waveguide section, minimizing reflection loss between the substrate and waveguide sections. Additionally, a “bed-of-nails” structure is employed behind the microstrip to suppress unwanted radiation, ensuring system stability and reduction in cross-talk among neighbouring channels. This design meets the demand for compact, high-efficiency transitions in modern communication systems, providing a robust platform for future beam steering technologies. Simulation results demonstrate excellent performance, with S11below -10 dB and insertion loss less than 0.45 dB over the 17.4 to 19.75 GHz range.

This paper presents a novel 1 to 4 power divider design, implemented using gap waveguide technology for equal power splitting with half out-of-phase outputs and half in-phase outputs. The design incorporates E-plane and H-plane Tees for power division. A coupling ridge and inductive iris formed by gap waveguide pins ensure efficient coupling and impedance matching, eliminating the need for traditional multi-section impedance transformers. The device operates across the 135-155 GHz band with a reflection coefficient below -15 dB, and low insertion loss of 0.05 dB. The phase imbalance is negligible (0.0005 degrees) with equal power division of -6 dB on each of 4-ports. The simulated power divider will be incorporated and tested within high gain array's feeding network in the 140-150 GHz range. The approach to use pins for tuning and inductive iris, for matching and power splitting, ensures precise phase control, low insertion loss, and optimal impedance matching with compact size. Moreover, gap waveguide structure prevents electromagnetic leakage and simplifies manufacturing, making it highly suitable for millimeter-wave and THz systems.

This paper presents a low-profile, high-gain cavitybacked slot array antenna, based on Ridge Gap Waveguide (RGW) technology, to operate within the Ka frequency band. The antenna array consists of two layers. The upper layer incorporates an array of U-shaped slots, positioned over a cavity loaded with a metal ridge section, while the lower layer is a ridge gap waveguide corporate distribution network, feeding each of the cavity-backed slots separately with equal phase and amplitude. The proposed array antenna radiates circularly polarized waves (axial ratio below 3 dB) over a bandwidth of 8.6% ranging from 27.5 to 30 GHz. At the centre frequency of 28.75 GHz, the peak gain at the broadside direction is 27 dBi and the first relative sidelobe level is below -13 dB. The total size of the proposed 8x8-element array antenna is 6.7 lambda(0)x6.5 lambda(0)x1.4 lambda(0)

A novel dual-band dual-circularly polarized (CP) array antenna is presented, capable of achieving right-hand circular polarization (RHCP) in the K band and left-hand circular polarization (LHCP) in the Ka band, making it an excellent candidate for satellite communication and other diplexing communication systems. The antenna's radiating element features a double-C-shaped strip design fed through a metallic via. S-shaped slits are precisely etched onto the strips to ensure isolation between segments operating at different frequency bands. The whole array design incorporates a microstrip line feeding network, resulting in a compact and efficient structure. An 8 x 8 array based on the proposed radiating elements and feeding network was designed, fabricated, and measured. The measurement results indicate the impedance bandwidths (|S-11| < -10 dB) of 17-24.7 GHz (36.9%) and 28.5-33.4 GHz (15.8%), as well as the 3-dB axial ratio (AR) bandwidths of 18.5-24.0 GHz (25.9%) and 28.8-34.3 GHz (17.4%), over K and Ka bands, respectively. Therefore, the array achieves the impedance-AR combined bandwidths of 18.5-24 GHz (25.9%) in the K band and 28.8-33.4 GHz (14.8%) in the Ka band, with peak gains of 17.9 and 19.3 dBic, respectively. The relative sidelobe levels remain below-13 dB for both bands, with the antenna efficiency exceeding 62% and 40% within the combined bandwidths of K and Ka bands, respectively. The proposed dual-CP antenna successfully combines wideband performance across K and Ka bands with a low-profile and structurally simple design, offering a practical and cost-efficient solution.

In this paper, contactless capacitively coupled PCB-to-PCB couplers, referred to as MetaCoax, are used to design a feeding layer with beamforming electronics for an 8x8 element circularly polarized antenna array. The simulated performance of the antenna array, both with and without the feeding layer, shows nearly identical results. The antenna with the feeding layer achieves a 15% bandwidth, with active reflection coefficients of <= -10 dB and axial ratios of <= 3 when scanning within a +/- 60 degrees scan volume. This is accompanied by a gain reduction of <= 0.4 dB compared to a directly fed antenna (i.e., without the feeding layer).

This letter presents an E-band monopulse feed with broadband gap-waveguide adaptive phase shifters for Gregorian reflector antennas tailored for 5G backhaul communications. The monopulse functionality is achieved using a gap-waveguide-based 2x2 step-horn-array feed with a feeding network comprising 3 dB couplers and adaptive phase shifters. The antenna achieves an ultrahigh-gain of 50 dBi through integration of the feed with a Gregorian reflector antenna and employs beamsteering by offsetting the feed from the subreflector focus. However, the feed offsetting degrades the null depth in difference (Delta) patterns. Therefore, a new phase compensation strategy is proposed, involving a codesign of adaptive phase shifters with the offset by using a numerical phase compensation function quantified in this work based on simulation data through GRASP and CST. The fabricated antenna demonstrates reflection coefficients below -10 dB for both polarizations over 71 GHz to 86 GHz. The measured radiation patterns and gains align closely with the simulated results. The system achieves a maximum gain of 50.48 dBi, with beamsteering within +/- 2( degrees) from boresight and a maximum steering loss of 0.96 dB. The null depth of all Delta-beams is maintained above 20 dB. These results highlight the significant potential of this antenna for 5G backhaul communications.

The paper proposes a method to control the aperture distribution of a horn-array antenna and reduce sidelobe levels by setting up soft and hard surfaces. Due to the metal walls between elements, the array suffers from poor aperture distribution for certain polarization. By appropriately configuring the four walls of the square horn as soft or hard surfaces, the aperture distribution can be modified, resulting in a reduction of 3 dB in the first sidelobe levels of both polarizations under ideal conditions. Finally, employing longitudinal corrugations formed by alternating metal strips and dielectric strips achieves soft surfaces, while transverse corrugations achieve hard surfaces, leading to an average improvement of 2 dB in sidelobe levels.

This paper presents a rigorous new analytical derivation of the theorem on the embedded element radiation function of ideally infinite planar array antennas, along with a formula for accurately calculating the main beam direction of finite-sized array antennas based on the theorem. It validates the previously established formula of the embedded element radiation function, where the amplitude is proportional to √cosθ, based on the intuitive reasoning that the effective area of an element should be proportional to its projected area in the direction of interest angle θ, provided that the array antenna has no grating lobes for the full scan, no surface waves, no losses, and active impedance matched. More importantly, the new analytical derivation can accurately predict the embedded element radiation function in cases where there are grating lobes for the array antenna with the full scan, which the intuitive area projection reasoning cannot provide. The theorem concludes that the array’s active element reflection coefficient and inter-element spacing fully determine the embedded element radiation function in all cases. Utilizing this theorem, a new formula for the element phase progression is derived to accurately steer the main beam in the desired direction of the array with a finite number of elements. Several verification cases of wide-scanning array antennas are presented, and the comparisons between numerical simulations, measurements, theoretical results, and some interesting conclusions are discussed in the paper.

A novel method for minimizing the structure and enhancing the beamwidth of linearly tapered slot antenna (LTSA) is presented. In the proposed design, the basic microstrip-fed LTSA is loaded with a joint action structure (JAS) including dual L-shaped gaps and ABS-metal bonding cavity. Compared to the basic unloaded version, the proposed antenna exhibits improved impedance characteristic in the lower band. Additionally, broad beams in principal planes, high front-to-back (F/B) ratio, and improved gain are also obtained. Simulation results reveal that the proposed antenna with 23.5x23.5mm, provides an impedance bandwidth from 4.15 similar to 11.25GHz, while a pattern bandwidth of 62%, more than 116 degrees E- and H-plane 3-dB beamwidths and over 18.0dB F/B ratio are also achieved.

This article presents a 1-D wide scanning slot array antenna based on a ridge gap waveguide (RGW), operating at a 100-GHz band. A novel half-wall decoupling structure is proposed to reduce the mutual coupling and the reflection coefficient simultaneously, thus achieving a more stable active reflection coefficient (ARC) within the +/- 60 degrees scanning range. At the same time, special attention has been given to retaining the embedded pattern suitable for wide scanning performance. An eight-element slot array antenna (8 x 8 slots) with two different feeding networks is fabricated and measured to verify the scanning performance. The prototype achieves 91% total efficiency while scanned up to 60 degrees with 3-dB scanning loss. The measured results show good agreement with the simulations both for the reflection coefficient and radiation performance.

The current development trend of electronic and electrical systems in the industrial field employs digitized and intelligent techniques. With the rise of data-driven fault diagnosis and health management methods, the value of historical system runtime data is increasingly drawing the attention of researchers. Digital communication methods, such as various industrial field buses, are commonly used between the subsystems or devices of a complex industrial system so that the field bus data could contain important information about the whole system. To address these requirements, this paper proposes a data recorder capable of real-time recording the field bus data, CAN data, and Modbus TCP/IP data in particular, in an industrial environment. Utilizing general EMC design, it can accurately and reliably record bus data in the complex electromagnetic environments of industrial sites, providing essential data support for subsequent fault diagnosis and health management.