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This contribution presents miniaturization techniques for folded circular substrate integrated waveguide (FCSIW) cavity filters. The cavities support dual-mode operation. Two of these cavities are combined to form a fourth-order filter. Two filter designs are implemented. The first one serves as a reference and exhibits good manufacturability. For the second one, the cavity is modified, which leads to $50\%$ more compactness. The designs are experimentally verified with 10 GHz bandpass filters. Even though the achieved level of compactness requires higher technological effort, the measurements validate the miniaturization concept. The out-of-band rejection exceeds 40 dB between 11.2 and 30 GHz for the reference filter and between 11.3 and 33 GHz for the miniaturized one. The implemented components are compared with state-of-the-art filters.

This contribution presents a vertical transition between a WR34 rectangular waveguide (RWG) and two grounded coplanar waveguides (GCPW). It is intended for dual-band phased array applications and thus includes a diplexer. The RWG is the common port and the GCPWs are the diplexed 20- and 30-GHz ports. This yields a very compact design compared to conventional cascaded circuit topologies. The realized component exhibits a port matching and isolation exceeding 10 and 30 dB, respectively, over more than 500 MHz in both bands.

This work presents diplexers realized with folded circular substrate integrated waveguide (FCSIW) cavity filters. The properties of such cavities are analyzed, and empirical equations for calculating the resonant frequencies are given. The analysis relies on an even-/odd-mode decomposition. A 10-GHz filter is designed based on this approach. In the second step, its size is reduced, still maintaining the passband behavior. An asymmetric taper is used to connect two such filters to realize a diplexer. Two diplexers with center frequencies of 10/15 and 12/13.5 GHz are presented. The diplexers are several times more compact than comparable devices reported in the literature. The components are manufactured, and the functionality is demonstrated by simulation and measurements.

Drive-induced oscillations (DIOs) in helix traveling-wave tubes (TWTs) may occur during large-signal amplifier operation. As the kinetic beam energy is reduced, the beam–wave synchronism possibly shifts into the $\pi $ -point, thus enabling simultaneous interaction with the forward and the backward circuit mode. There, asymmetries in the beam–wave interaction region introduce an additional coupling mechanism and lower the oscillation threshold compared with backward-wave oscillations (BWOs). Consequently, DIOs are likely to arise. In addition even without asymmetries, drive-induced BWOs are observed. A hybrid time- and frequency-domain simulation approach is presented and applied to analyze this phenomenon in a helix TWT. In addition, an effective suppression technique is proposed.

This article reports a solid-state power amplifier module in low-temperature cofired ceramic (LTCC) technology. For compactness and low loss, the package utilizes substrate-integrated waveguides (SIWs). To meet the thermal requirements, the amplifiers are mounted on a metallic plate that is integrated into the LTCC multilayer and transfers the heat to a spreader. Both RF and thermal measurement results for a package with two integrated 10-W gallium nitride (GaN) power amplifiers at the K-band are presented. They demonstrate the suitability of the module for highly integrated transmitters as needed for phased arrays or multiple-feed-per-beam satellite antennas.

A broadband permittivity extraction method for fluids by means of electrically small impedance sensors is reported. It relies on an equivalent circuit model of the sensors, which takes into account the most significant parasitic effects. It assumes the sensor’s intrinsic susceptance and conductance to depend linearly on the real and the imaginary part of the permittivity, respectively. The simplicity of the approach eases calibration. Besides conventional thru-reflect-line standards, which define the reference plane, only air and a single reference liquid are needed. The method is applied to three different devices, namely, a common open-ended coaxial line, a compact printed circuit board design, and an integrated microchip sensor for (milli-)liter, microliter, and picoliter sample volumes, respectively. It is shown how the frequency limits can be determined, and how the sensitivity can be maximized in terms of the model parameters. The method is shown to be robust against production tolerances.

This article presents a novel broadband septum polarizer with a relative bandwidth (BW) of 37.8%. This is significantly more than the approximate 25% BW of square and circular waveguide polarizers. It is enabled by using an equilateral triangular common port waveguide, which guarantees the largest possible frequency range between fundamental and next higher order mode cutoff. The transition between the triangular section and the rectangular input waveguides, which includes the septum, is designed to accommodate this large BW. The simulation is validated using a polarizer designed for 75–110 GHz and fabricated by conventional precision milling. A second polarizer is realized for the 18-to-26 GHz range by employing additive manufacturing to demonstrate the advantages of this technology in this context. In both cases, the axial ratio remains below 1.3 dB, whereas the input port isolation and the input return loss exceed 17 and 15 dB, respectively.

Sc3+ substituted M-type ferrites are effective microwave magnetic materials with a ferromagnetic resonance frequency in the range of 20 GHz–50 GHz. We report on the fabrication of oriented ferrite thick films as microwave components for application in the Ka-band at 30 GHz. Films of BaFe11.5.Sc0.5O19 were prepared by screen-printing on alumina substrates, drying in an external magnetic field, and sintering at 900 °C. Low-temperature sintering is achieved through use of a mixed BBSZ/CuO sintering aid. A strong anisotropy of the sintered ferrite films is revealed by XRD analysis. Microwave properties of the films were determined in a coplanar waveguide setup. The ferromagnetic resonance frequency of the films is at 30 GHz and the textured films possess good nonreciprocal properties which scale with film thickness. The films were tested in a Y-junction circulator, and represent promising materials for self-biased microwave components fabricated in thick film technology.

A compact 20/30 GHz diplexer based on substrate integrated waveguide (SIW) cavities and grounded coplanar waveguide (GCPW) feed lines is proposed. It features additional in-phase reactive power splitting in both passbands by exploiting symmetries. The component is realized in a vertically cascaded configuration using multilayer printed circuit board (PCB) technology, achieving a footprint of only 6×8 mm2. The compactness of the diplexer enables utilization in highly integrated applications such as shared aperture transmit/receive (Tx/Rx) phased arrays.

We present a design approach for a self-biased Ka-band isolator. A pre-sintered barium hexaferrite is integrated in a RO4003C laminate. In combination with a microstrip design this yields a compact and cost-effective component. The operating principle of the isolator and a concrete design example are presented. The experimental work confirms the theoretical expectations and reveals the optimization potential.

Parallel plate capacitor configurations are common for permittivity measurements. Depending on the exact geometry of the plates, the contribution of the usually unwanted fringing fields can be significant. At low frequencies, this effect can be simply avoided by means of properly driven guard electrodes. This way, only the approximately homogeneous field beneath the main electrode is measured. This paper proposes a microwave implementation of such a sensor and a simple method based on scattering parameter measurements for permittivity extraction. The intended application is the size independent assessment of biological cell properties in a microfluidic setup. The paper presents simulation results for a parallel plate cell sensor without and with a guard electrode. Experimental verification is provided with a scaled version realized in printed circuit board technology. The measurements are performed on a dielectric slab at different positions.

This paper reports the realization and measurements of two power amplifier MMICs at Ka-band. Both MMICs were manufactured using an industrial 0.15 $\mu$ m AlGaN/GaN HEMT technology. The power amplifiers MMIC1 and MMIC2 are three-stage designs utilizing a total gate width (TGW) of 5.12 mm and 10.24 mm, respectively. In order to maximize the efficiency, the MMICs exhibit a staging ratio of 1: 2: 6.4. The measurements demonstrate for MMIC18-10.5 W of output power with 28-32% of power-added efficiency (PAE) between 25 and 29 GHz, i.e., over a fractional bandwidth of 15%. In the same frequency band, MMIC2 exhibits more than 15 W of output power and 25% of PAE. The best performance for MMIC2 was measured at 27 GHz and reaches 20 W associated with a PAE of 27%.

The paper investigates experimentally the effect of harmonic terminations on AlGaN/GaN power amplifiers (PA) performance at K-/Ka-band. Two technologies are compared, a 0.25 µm and 0.1 µm process. In both cases, a harmonic termination increases the achievable output power by about 10 % at the expense of bandwidth, whereas the efficiency is improved only in the first one.

This paper studies an integration concept for a self-biased Ka-band circulator. Non-reciprocity is achieved by means of a pre-sintered scandium substituted barium hexaferrite which, as a hard-magnetic material, does not require external magnetic biasing. The ferrite is integrated into a microstrip circuit on a RO4000 laminate. This yields a compact and potentially low-cost circulator. The basic functionality is demonstrated in a first experiment. The results are still quite preliminary, though. Yet, some important conclusions can be drawn regarding the required design optimization measures.

An alternative to wire-bonding and flip-chip interconnects of integrated circuits and printed circuit boards (PCB) is presented. The flip-line interconnect combines the advantages of wire-bonding and flip-chip technology while avoiding their disadvantages. It is especially useful for prototype setups where device inspection and repairability are crucial. The proposed structure is analyzed using full-wave simulation software. It is shown, that in contrast to wire-bonding, the transition length is not critical. A transition from a CMOS chip with a pad pitch of 100 µm to a regular PCB is manufactured. Measurements at W-band (75–110 GHz) reveal a return loss better than 12 dB and transmission above -3.4 dB.

This contribution deals with a 20/30 GHz diplexer intended to feed substrate integrated waveguide (SIW) antennas. As these feature circular polarization, they have a square cross section which is implemented in a thick multilayer. The transition between the thick antenna and the thin front end is part of the proposed diplexer. Realizing it as a step yields a low-loss and very compact component occupying approximately 5 × 8 mm2. The paper describes the structure and reports its design and realization. The functionality is demonstrated in simulation and verified experimentally. The measured insertion loss is 1 dB in the 20 GHz receive (Rx) path and 1.6 dB in the 30 GHz transmit (Tx) one. The port isolation exceeds 30 dB at 30GHz.

Doped barium hexaferrite films prepared on alumina substrates by means of the sol-gel method, intended for utilization in self-biased nonreciprocal components, are presented in this letter. To cover a broad range of potential applications, the ferromagnetic resonant frequency (FMRF) of the material is controlled by substituting iron for scandium and aluminum. The films are deposited on coplanar waveguides to permit broadband measurements of the FMRF. As shown from measurements, the resonance can be shifted from $\text {43.2}$ GHz for the undoped sample to $\text {27.1}$ GHz and $\text{65.1}$ GHz for the films with the highest tested scandium and aluminum doping, respectively. X-ray diffraction analysis is used to evaluate the formation of secondary phases in the film. Measurement results for the hysteresis curves are obtained by vibrating sample magnetometer measurements. The results for doped and undoped samples are discussed in this letter.

Two magnetic field tapering concepts for the suppression of backward-wave oscillations in helix traveling-wave tubes (TWTs) are presented. Therefore, the beam-wave interaction in a homogeneous helix section is modified. Increasing the field strength reduces the beam diameter and consequently the beam-wave coupling, while an additional offset in the focusing field alters the synchronism between both. The theoretical background is introduced and results from a 1-D small-signal and a 3-D particle-in-cell code are presented and compared. Furthermore, a concept to apply the suppression techniques to a complete TWT is presented, and the influence on the amplifier output characteristics is analyzed.

Commercial Ku-band tapered helix traveling-wave tubes (TWTs) and a folded-waveguide ${Q}$ -band TWT are modeled and simulated in CST Particle Studio (PS) on a desktop computer. Efficient models for the electron beam, the severs, and the delay line are investigated to enable accurate and automatable model generation, simulation, as well as pre- and postprocessing. The results of particle-in-cell simulation in CST PS are presented and compared to those of the specialized steady-state simulation codes MVTRAD and KlysTOP, as well as to measurements.

A selection of hybrid frequency- and time-domain approaches is evaluated with respect to their suitability for predicting the multi-tone behavior of a reference Ku-band helix traveling-wave tube. For this, a frequency-domain code is extended by a selection of frequency-dependent and frequency-independent envelope models and compared to a number of simulated and measured responses to two-tone signal excitation with varying frequency spacing. The selected envelope methods are investigated both in the hybrid approach and based on measured TWT characteristics. Output levels and classical multi-tone metrics, such as intermodulation products and phase transfer factors, are considered. By reducing a modulation scenario to a number of significant sequences, a comparison to full physics-based frequency-domain simulation is presented to show the potential of the proposed approach.

The nondestructive characterization of small liquid volumes, as well as the detection of single biological cells, can lead to new insights for biomedical and biotechnological applications. The dielectric permittivity of the sample, which depends on the chemical composition, is detected using electromagnetic sensors in the microwave frequency range. The sensing system proposed here is based on resonant near-field sensors, which are combined with a microfluidic chip. The sample volume of a few picoliters enables single-cell measurements. A novel process featuring a biocompatible polymer material is used for fabricating the microfluidic channel for liquid samples. Two opposed sensing tips are integrated at the bottom of the channel to improve the sensitivity to small dielectric contrasts. They are connected to two resonators, which allows to simultaneously characterize the sample permittivity at two different frequencies. In a proof-of-principle experiment, single cells of the Chinese hamster ovary cell line are detected. This shows that the proposed sensing system is suitable for single-cell characterization due to its high sensitivity and spatial resolution. A potential biomedical application is the systematic investigation of various cell types and states to elucidate potential distinguishing characteristics.

This paper presents requirements and front-end solutions for low-cost communication systems with data rates of 100 Gbit/s. Link budget analyses in different mass-market applications are conducted for that purpose. It proposes an implementation of the front-end as an active antenna array with support for beam steering and polarization multiplexing over the full W-band. The critical system components are investigated and presented. This applies to a transformer coupled power amplifier (PA) in 40 nm bulk CMOS. It shows saturated output power of more than 10 dBm and power-added-efficiency of more than 10 % over the full W-band. Furthermore, the performance of microstrip-to-waveguide transitions is shown exemplarily as an important part of the active antenna as it interfaces active circuitry and antenna in a polymer-and-metal process. The transition test design shows less than 0.9 dB insertion loss and more than 12 dB return loss for the differential transition over the full W-band.

This contribution presents the system design procedure and performance of an array fed reflector antenna. Combining the inherent benefits of a reflector antenna—high gain, low-cost, and simplicity—with the agility provided by a scannable active array feed, enables a new range of applications, for instance in commercial mobile antenna terminals. The whole arrangement features a restricted field of view for either scanning or multibeam applications. To minimize system cost, a planar patch antenna array in printed circuit board technology is used for the feed and the reflector diameter is restricted to 60 cm. To obtain optimal performance, both the reflector and the feed are specifically designed for the desired application, i.e., mobile satellite communication at Ka -band. A comprehensive study of various rotationally symmetric reflectors is carried out to determine arrangements maximizing the field of view and still complying with the respective regulations. For the feed, a 30 GHz transmit array with 49 elements is developed, enabling 2-D scanning in a ±6° conical sector. It includes a wideband signal distribution network and frontend electronics.

Several different microwave circuits, including beamforming networks and balanced amplifiers, make use of 3-dB power dividers and combiners. A well-known architecture able to work over large bandwidths, a critical request for many applications, is based on E-plane three-port waveguide structures, where a lossy element is added to overcome the inherently poor isolation given by lossless three-port junctions. While a standard implementation based on normal rectangular waveguides often results in large and heavy structures, an implementation based on substrate-integrated-waveguide (SIW) technology offers advantages in terms of compactness, weight reduction, cost minimization, and integration possibilities with active stages. This paper presents the design, fabrication, and characterization of two SIW E-plane 3-dB power divider/combiners where the lossy element is realized using a resistive layer. The prototypes cover the entire $X$ -band from 8 to 12 GHz, and the resistive layers are realized according to two different manufacturing techniques to investigate the potentials of both approaches. The optimization of the resistive layer geometry and resistivity, a critical aspect for low-profile SIW circuits, is discussed in detail. In particular, an analytical formula is derived, which allows to determine the optimum values for the resistive layers’ principal parameters, namely the length and resistivity, without the use of full-wave numerical solvers.

A fully differential power divider with ultra-broadband performance is presented. It consists of multi-section Wilkinson power combiners vertically aligned in a multilayer circuit board, which are fed by differential via transitions. The carbon paste decoupling resistors are integrated in the stack. The measured differential-mode output isolation exceeds 10 dB above 2.9 GHz. The excess insertion loss remains below 1.0 dB up to 21 GHz and reaches 2.0 dB at 36.5 GHz. The structure, which is designed for compactness, occupies only 50 mm2.

A vertical transition from differential microstrip line to WR10 rectangular waveguide is presented. In contrast to other approaches, it does not necessitate a backside cavity. This simplifies the integration into multilayer circuits. The measured response which agrees well with the simulated one demonstrates a good performance over the entire W-Band. The insertion loss ranges from 0.5dB to 1.1dB whereas the return loss is better than 13dB over the whole bandwidth of 37.8%.

This contribution deals with a compact substrate integrated waveguide (SIW) diplexer for terminal array antennas at K-/Ka-band. The diplexer connects the transmit (Tx) and the receive (Rx) frontend with an antenna element. It is comprised of a bifurcation and two second order bandpass filters with low insertion loss. The Rx-filter has additionally two transmission zeros in the Tx-band. The structure is implemented in multilayer printed circuit board (PCB) technology. This yields a compact design which can be integrated in an array with half-wave element spacing. The simulated diplexer performance is validated by measurements. The insertion loss in the Rx-band remains below 0.7 dB, while the Tx-/Rx-isolation exceeds 40 dB in a 1.2 GHz band at Tx.

Partial substitution of Fe 3+ by Sc 3+ or In 3+ in M-type ferrite is an effective method to tailor their anisotropy field and resonance frequency. BaMe x Fe 12- x O 19 with Me = Sc and In (0 ≤ x ≤ 2) was synthesized by the mixed-oxide route. XRD revealed a continuous increase of the hexagonal lattice parameters with substitution rate x. Both, the saturation magnetization and coercivity at room temperature are reduced with x. The ferromagnetic resonance frequency decreases from 48 GHz at x = 0 to 30 GHz at x = 0.5 for Sc-substituted ferrites. For In-substitution, a smaller reduction of the resonance frequency with x is observed, e.g. to 37 GHz at x = 0.5. Addition of BBSZ glass allows sintering at 900 °C. Low-temperature fired samples exhibit ferromagnetic resonance at the same frequencies and represent promising materials for self-biased microwave components for integration into LTCC multilayer modules.

An ultrawideband K-/Ka-band lens antenna for future satellite communication systems is presented. It consists of an extended hemispherical dielectric lens that is fed by a square substrate-integrated waveguide (SIW) and therefore offers a low-cost alternative to horn antennas. The design procedure is explained, and the antenna performance is presented. A sophisticated test fixture is developed to excite the square SIW. The measured ${S}$ -parameters and far-field patterns validate the concept and exhibit more than 13 GHz bandwidth.

A large-signal beam-wave interaction code for folded-waveguide traveling-wave tubes is presented. Formulation in frequency domain yields fast results of the steady state. The slow-wave structure is described by an equivalent circuit, while the electrons of the beam are modeled by means of a particle-in-cell approach. The latter exploits the periodicity of the electromagnetic fields in the beam tunnel region, thus allowing to work with a relatively low number of injected particles compared to conventional implementations. Physically consistent solutions are then obtained iteratively by incorporating the well-established Broyden’s method. Further improvement in terms of computation time is achieved by initializing the iterative algorithm with results from previous simulations. The approach is verified by a comparison with published interaction simulation results. Single-frequency responses are obtained within a few minutes, which compares favorably with other specialized simulation packages and enables device optimization with acceptable effort.

A design approach for substrate-integrated waveguide (SIW) to rectangular waveguide (RWG) transitions based on the synthesis of antipodal finline tapers is proposed. The taper is designed using a reflection-based impedance definition as no suitable model is available for antipodal finlines. The characteristics of the finline are determined from full-wave simulation. To demonstrate the proposed method, two SIW-to-RWG transitions are designed and characterized at the $K$ -band. The measured back-to-back transitions exhibit a return loss above 15 dB and an insertion loss below 1 dB between 16.7 and 20.5 GHz and between 21.1 and more than 31 GHz, respectively. A good agreement between the synthesis model and full-wave simulation of the taper on one hand and between simulation and measurements of back-to-back transitions on the other hand is demonstrated.

In this contribution a dual-band, dual-polarized microstrip antenna element for array applications is presented. The patch antenna is designed to operate simultaneously at around 30 and 20 GHz, the up- and downlink frequencies of modern Ka-band satellite communication systems. The antenna is smaller than half the freespace wavelength at 30 GHz to enable its utilization as array element of dual-band ground terminals. Integrating transmitter and receiver circuits allows, in turn, for a very compact active terminal solution. To minimize production cost, the design is carried out in standard multilayer printed circuit board technology. The antenna features two distinct polarization ports suitable for either dual linear or dual circular polarization if both ports are excited in quadrature. The single antenna design process is described in detail and simulation and measurement results are presented. Finally, different arrays based on this patch antenna are evaluated by simulation and measurements.

In this study, a sparse multiple-input multiple-output radar system with difference co-array processing is presented. It consists of two non-uniform transmitter arrays in split configuration and a symmetrical hybrid receiver array. A combination of a periodically thinned array and two non-uniform sub-arrays is used to construct the receiver structure. A low-cost three-step optimization procedure is proposed to synthesize the array arrangement with system constraints. In addition, a combination of fast Fourier transform (FFT) and MUltiple SIgnal Classification (MUSIC) techniques is applied for a range/direction-of-arrival estimation with low computational effort. High angular resolution is achieved in the MUSIC spectrum by implementing a difference co-array concept together with spatial smoothing. A thinning rate in excess of 95% is demonstrated. Lastly, the performance of the proposed system is validated by measurements of point scatterers and extended objects.

This paper reports on recent progress in the field of terminal antennas for Ka-band satellite communications, the focus being on mobility scenarios requiring beam steering agility. Selected European activities are briefly reviewed, before a more in-depth view of ongoing work performed at the Hamburg University of Technology is given. Three different approaches are reported.