Millimeter-wave Components Research Articles

3-D Printing and Gallium-Based Liquid Metal Technologies for Microwave and Millimeter-Wave Components

3-D Printing and Gallium-Based Liquid Metal Technologies for Microwave and Millimeter-Wave Components

Paper] Study on Single Frequency Downlink with Coupling Loop Interference Canceller for Professional SC-FDE Wireless Camera using Millimeter-wave Band

Professional wireless cameras using the millimeter-wave band can transmit more information than those in the UHF band, making this band especially useful for transmitting high-quality video and audio with low latency. Although such devices have been put into practical use, there is a need to downsize the equipment on the camera side to reduce expensive millimeter-wave band components and improve operability. In this study, we configure the downlink of a professional wireless camera for UHDTV as a single frequency network (SFN) and study the expansion of coverage provided by a booster. A coupling loop interference canceller and multi-path equalizer are installed in the booster. A computer simulation shows that the booster works well. SFN interference, in which the master and booster waves multiply propagate, can be equalized through frequency domain equalization (FDE) of the single-carrier (SC) system at the receiver side.

Design of Stray Radiation Sensor for ITER ECE Diagnostic

The Electron Cyclotron Emission (ECE) diagnostic has a primary role in the measurement of electron temperature profile and electron temperature fluctuations in ITER. This diagnostic shall be exposed to significant power due to unabsorbed Electron Cyclotron Heating (ECH) power in the plasma. The expected stray power loads could be a few tens of watts, and therefore, the protection of millimetre wave components is one of the design challenges of ITER ECE diagnostic. This protection system includes sensors, a band stop notch filter, and a shutter to stop the RF stray radiation from being incident on the sensitive components. The sensors will be positioned along the ECE transmission line, and shall be used for real-time power monitoring of the stray radiation. Here, we describe a novel design of a sensor for monitoring the stray radiation power. This sensor is a Schottky Diode rectenna, known for high-power and high-speed millimetre wave detection capability. It consists of a 2x2 microstrip patch antenna array, a matching circuit, a diode, and a low pass filter. The antenna array is designed analytically and optimized in CST Microwave Studio, for wide reception angle, high gain, and low side lobe levels. Furthermore, the rectifying circuit is optimized using Agilent Advanced Design System (ADS) software to get better rectification and impedance matching of the signal, thereby improving its detection sensitivity. The ADS simulation results show that the detection sensitivity is about 1000V/W for input power of -30 dBm at 170 GHz, thereby achieving the required performance of the sensor.

Gap Waveguide Topology With Reduced Height Pins for Millimeter-Wave Components

Gap Waveguide Topology With Reduced Height Pins for Millimeter-Wave Components

Homotopy Optimization and ANN Modeling of Millimeter-Wave SIW Cruciform Coupler

The development of millimeter-wave and terahertz (THz) passive components such as couplers and filters is an intimidating task because of underlying ultrasensitivity of electrical performances to geometric dimensions and processing tolerances. It is a common practice for us to use an integrated optimizer of commercial electromagnetic (EM) software packages for the design and optimization of such geometric parameters. However, those optimizers may fail to achieve a desired performance if initial variables are not in a range close enough to the optimal solution. In this article, we introduce an homotopy approach to optimizing the geometric parameters of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula> -band cruciform coupler based on substrate integrated waveguide (SIW) technique in conjunction with an artificial neural network (ANN) model. Starting from a set of initial variables, a homotopy optimization is set to search for an optimum solution. The ANN technique is adopted as the surrogate in place of a usual time-consuming EM model to accelerate the homotopy optimization process of the cruciform coupler. We propose a feed-forward computational formulation inspired by the fundamental transmission line impedance equation. Such a transmission line knowledge-based feedforward network results in a faster convergence with better accuracy than its conventional counterpart. To demonstrate the homotopy optimization method based on the ANN model, an example of multiparameterized cruciform coupler design is detailed. This cruciform coupler with optimized geometric dimensions is simulated, fabricated, and measured. Measured and simulated results validate the combined ANN model and homotopy method. An equivalent lumped-element circuit model of the cruciform coupler is also proposed in this work. An ANN model development technique is described how to extract the equivalent circuit parameters for given coupler specifications. Extracted circuit parameters in connection with the desired coupler performance are then compared with published results which verify the ANN model development algorithm.

Experimental Characterization of Millimeter-Wave Substrate-Integrated Waveguide Interconnect with Slot Transition in Flexible Printed Circuit Boards

For high-speed communication services such as 5G technology, the use of millimeter-wave (mmWave) components substantially increases in mobile applications. The interconnect based on a substrate-integrated waveguide (SIW) is an efficient solution for connecting these devices. However, the SIW characteristics in the mmWave frequency range are not sufficiently presented from the practical viewpoint. In this paper, the experimental characterization of mmWave SIWs in flexible printed circuit boards (FPCBs) and their simulation results are presented. A practical method using balanced/single slot transition is proposed for microstrip-to-SIW transition. Using a full-wave simulation and genetic algorithm, the proposed slot technique is optimized. It is experimentally demonstrated that the cutoff frequency affects the operating band of the SIW differently. The per-unit-length losses of the full-mode and half-mode SIWs are obtained as 0.0375 dB/mm and 0.0609 dB/mm, respectively. Using the measurements, the SIW type effect on the transmission loss is quantitatively analyzed, and the loss is increased up to 62.4% at 39 GHz.

Harmonized Rapid Prototyping of Millimeter-Wave Components Using Additive and Subtractive Manufacturing

In this article, a harmonized fabrication and assembly process combining additive and subtractive manufacturing (SM) is introduced for the rapid manufacture of millimeter-wave components, especially those using hollow substrate integrated waveguide (HSIW). HSIW has been shown to have some significant advantages for millimeter-wave communications, radar, and sensing systems, but its fabrication can be challenging. To pattern the metallic layers that form the top and bottom HSIW walls, as well as other structures such as microstrip lines and landing pads for integrated circuits and passive components, a subtractive fabrication process using a water-jet laser cutter was employed. To fabricate the dielectric substrate using low-cost Acrylonitrile Butadiene Styrene (ABS), with cavities for the waveguides, a Stratasys PolyJet 3-D printer (Objet 1000) was used. The HSIW components were then assembled using commercially available through-substrate copper transitions, completely eliminating the process of through-substrate via-hole formation and metallization. The manufacturing techniques conventionally used for these vias are generally expensive and intricate at millimeter-wave frequencies. Therefore, the proposed fabrication and assembly process in this article decreases the overall fabrication cost and complexity, and it is shown that this is achieved without compromising the performance of the millimeter-wave HSIW components. The measurement results show that a propagation loss of 13.55 dB/m (0.01355 dB/mm) is achieved for the first HSIW prototype. Based on HSIW structures, it is believed to be among the lowest propagation losses ever reported at these frequencies. The proposed harmonized fabrication and assembly technique also has a strong potential, by combining the advantages of additive and SM techniques, to realize a new class of millimeter-wave components with the possibility of manufacturing conformal and flexible component shapes, based on the materials used.

A Review on SIW and Its Applications to Microwave Components

Substrate-integrated waveguide (SIW) is a modern day (21st century) transmission line that has recently been developed. This technology has introduced new possibilities to the design of efficient circuits and components operating in the radio frequency (RF) and microwave frequency spectrum. Microstrip components are very good for low frequency applications but are ineffective at extreme frequencies, and involve rigorous fabrication concessions in the implementation of RF, microwave, and millimeter-wave components. This is due to wavelengths being short at higher frequencies. Waveguide devices, on the other hand, are ideal for higher frequency systems, but are very costly, hard to fabricate, and challenging to integrate with planar components in the neighborhood. SIW connects the gap that existed between conventional air-filled rectangular waveguide and planar transmission line technologies including the microstrip. This study explores the current advancements and new opportunities in SIW implementation of RF and microwave devices including filters, multiplexers (diplexers and triplexers), power dividers/combiners, antennas, and sensors for modern communication systems.

Structured-Glass Waveguide Technology for High-Performance Millimetre-Wave Components and Systems

This work presents a novel waveguide medium based on laser-induced structured-glass for the design of high-end millimetre-wave components and systems. The material properties, fabrication process and functional attributes of the structured-glass technology are first described and then applied in order to demonstrate a fourth-order bandpass filter prototype operating within the W-band frequency range, centered around 88 GHz with a narrow fractional bandwidth of 2.3&#x0025;. The basic filter design, dimensional considerations, and assembly process are discussed in order to outline the fabrication process. The prototype filter, along with its associated feed-line transitions and split-block interface are measured and characterized in the laboratory in order to validate the design approach. The measured response is shown to be exceptionally accurate; the insertion loss is found to be approximately 1.43 dB - 1.97 dB throughout the measured passband with a return loss of better than 22 dB and center-frequency offset of approximately 0.117&#x0025;. A comparison to existing technologies is discussed in order to highlight the advantages of the proposed medium and to contrast the differences in both manufacture and achievable results for high-end components.

Bandpass filters based on integrated aperture‐ and gap‐coupled discontinuities

An electromagnetic coupling mechanism is discussed for distributed-element aperture- and gap-coupled discontinuities based on rigorous lumped-element equivalent circuit analysis. The two discontinuities are analysed in terms of their transmission poles and transmission zeros for the selectivity enhancement of microwave and or millimetre-wave components. The integration of these two discontinuities is put forward for bandpass filter design. A frequency-dependent lumped-element equivalent circuit is employed to study the behaviour of the two distributed-element discontinuities in the transverse direction. Bandpass filters are characterised based on the dual aperture- and gap-coupled discontinuities integrated within substrate integrated waveguide structures. It is shown that multiple transmission zeros close to transmission poles are realised due to the magnetic and electric field cancelation in the gap-coupled discontinuity, while the aperture-coupled discontinuity contributes to a resonator with a higher quality factor. The integration of both aperture- and gap-coupled discontinuities shows the priority of this kind of microwave resonator in terms of selectivity, size, and upper stopband in comparison with the conventional aperture-coupled one.

Hand and Body Blockage Measurements With Form-Factor User Equipment at 28 GHz

Blockage by the human hand/body is an important impairment in realizing practical millimeter-wave wireless systems. Prior works on blockage modeling are either based on theoretical studies of double knife-edge diffraction or its modifications, high-frequency simulations of electromagnetic effects, or measurements with experimental millimeter-wave prototypes. While such studies are useful, they do not capture the form-factor constraints of user equipments (UEs), such as moderate array sizes, gains, and beamwidths. In this work, we study the impact of hand/body blockage with a UE at 28 GHz built on commercial millimeter-wave components. We report five controlled studies with different types of hand holdings/grips, antenna types, and directional/narrow beams. For both hard and loose hand grips, we report considerably lower blockage loss estimates than prior works. Critical in estimating the loss is the definition of a “region of interest” (RoI) around the UE where the impact of the hand/body is seen. Toward this goal, we define an RoI that includes the spatial area where significant energy is seen in either the no blockage or blockage modes. Our studies show that significant spatial area coverage improvement can be seen with a loose hand grip due to hand reflections.

A Novel Method for Intrusive Stochastic Estimation of Geometric Tolerance Effects in Finite Element Electromagnetic Analysis

The robust design of microwave, millimeter-wave, or Terahertz components and structures incorporating manufacturing process tolerances would enhance the fabrication yield and thereby reduce the overall production cost. Based on the spectral stochastic finite element method (SSFEM) for material variations, a novel geometrical SSFEM (GSSFEM) is proposed to analyze dimensional uncertainty in 3-D microwave models. The Jacobian for Piola mapping is represented as a function of stochastic variables to capture mesh level uncertainties. Polynomial chaos expansion is used to approximate the electric field as a random process. The technique is validated by applying it to waveguide problems with uncertainty in geometric dimensions. GSSFEM results are compared with analytical formulations of the transmission coefficient for a physical insight and further with the Monte Carlo simulations for quantitative evaluation. The results using the proposed approach are in excellent agreement with conventional methods and are found to be faster than sparse grid stochastic collocation, while the scaling of the computational requirements with the number of degrees of freedom and stochastic dimension is as good as this efficient scheme. Furthermore, this approach has been employed to analyze uncertainty in multiple geometric parameters to compare their sensitivity. The proposed GSSFEM can be employed for analyzing the impact of fabrication tolerance of passive waveguide components at microwave frequencies and beyond.

Dry Film Photoresist-Based Microfabrication: A New Method to Fabricate Millimeter-Wave Waveguide Components.

This paper presents a novel fabrication method based on dry film photoresists to realize waveguides and waveguide-based passive components operating at the millimeter-wave frequency (30–300 GHz). We demonstrate that the proposed fabrication method has a high potential as an alternative to other microfabrication technologies, such as silicon-based and SU8-based micromachining for realizing millimeter-wave waveguide components. Along with the nearly identical transfer of geometrical structures, the dry film photoresist offers other advantages such as fewer processing steps, lower production cost, and shorter prototyping time over the conventional micromachining technologies. To demonstrate the feasibility of the fabrication process, we use SUEX dry film to fabricate a ridge gap waveguide resonator. The resonator is designed to exhibit two resonances at 234.6 and 284 GHz. The measured attenuation at 234 GHz is 0.032 dB/mm and at 283 GHz is 0.033 dB/mm for the fabricated prototype. A comparative study among different existing technologies indicates that the reported method can give a better unloaded Q-value than other conventional processes. The measured unloaded Q-values are in good agreement with the simulated unloaded Q-values. The signal attenuation indicates that SUEX dry film photoresists can be used to fabricate passive devices operating at millimeter-wave frequencies. Moreover, this new fabrication method can offer fast and low-cost prototyping.

Slow-Wave Effect Enhanced Substrate Integrated Waveguide with Multi-Antipodal Blind Via-Holes and Distributed Metal Strips

A slow-wave (SW) effect enhancement method based on substrate integrated waveguide (SIW) is presented, theoretically studied, and experimentally validated. The SW effect is achieved by incorporating multi-antipodal metalized blind via-holes and distributed metal strips longitudinally connecting the bottom of upper posts. This improved SIW-based topology achieves a dramatic cutoff frequency reduction of 55.5% with reference to the conventional SIW with the same lateral size. Meanwhile, the phase velocity is reduced remarkably, realizing a more compact longitudinal dimension. The two effects give rise to a planar size reduction of 80% compared to the conventional SIW, which presents a significant advance in SIW miniaturization technology. A prototype is fabricated for a proof-of-concept, and the measured results are in good agreement with simulations, demonstrating its promising application potential and prospect in the microwave and millimeter-wave components.

Space-Time Modulation: Principles and Applications

The ever-increasing demand for high-datarate wireless systems has led to a crowded electromagnetic (EM) spectrum. This demand has successively spurred the development of versatile microwave and millimeter-wave integrated components possessing high selectivity, multifunctionalities, and enhanced efficiency. These components require a class of nonreciprocal structures endowed with extra functionalities, e.g., frequency generation, wave amplification, and full-duplex communication. Space-time (ST) modulation has been shown to be a perfect candidate for high-data-rate transmission given its extraordinary capability for EM-wave engineering. ST-modulated (STM) media are dynamic, directional EM structures whose constitutive parameters vary in both space and time.

A Wideband 3-dB Directional Coupler in GGW for Use in V-Band Communication Systems

In this article, a broadband 3-dB directional coupler is proposed using groove gap waveguide (GGW) structures. Gap waveguide technology has been introduced to overcome manufacturing and assembling challenges of different millimeter-wave components and devices. The presented coupler has wideband coupling flatness with low return loss in 60-GHz frequency band and can be easily adapted to other frequency ranges. Experimentally, a sample prototype of the proposed 3-dB coupler has been designed and fabricated. The measured return loss and isolation are better than 20 dB and the power-split unbalance within ±0.5 dB is obtained over the frequency range from 57 to 74 GHz (26% BW). The proposed structure has the capability of easily integrating with other millimeter-wave components.

Conductive Polymer Metallized Vias: A New Approach for Substrate Integrated Waveguide Development

Substrate integrated waveguides (SIWs) have huge potential for the development of microwave and millimeter-wave components in modern communication devices. Herein, a novel approach based on the vacuum suction of conductive polymer is introduced to substitute classical Cu electroplating technique for the simple and rapid metallization of conductive vias embedded in the dielectric substrate. Various combinations of vacuum level and vacuum duration are tested on vias with different geometries. Meaningfully, with the proper control of these two parameters, the specific partial height via becomes achievable in a single-layer substrate. As a proof of concept, two bandstop SIW filters based on the partial height via resonator are developed in a self-made flexible substrate and a commercial rigid laminate. Relatively good agreement can be seen between the measured and simulated results of their reflection coefficients and resonant frequencies, which confirm the reliability and robustness of this approach for the future SIW development.

A Simple and Accurate Method for Extracting Super Wideband Electrical Properties of the Printed Circuit Board

In order to accurately design microwave, millimeter-wave components and circuits, a simple and accurate method for extracting extremely wideband characteristics of the printed circuit board (PCB), including relative dielectric constant, dielectric loss tangent, and equivalent copper conductivity, is proposed and validated in this paper. By properly selecting wideband distribution of multiple TMmn0 modes in the designed circular substrate integrated waveguide (CSIW) cavities, extremely broadband properties of PCB can theoretically be extracted with only one pair of CSIW cavities. The proposed method overcomes the limitations of conventional methods that only support narrowband applications, require a large number of cavities, and have relatively large errors. The experiments show that the proposed method is able to extract, accurately and efficiently, 8-110 GHz characteristics of a TLY-5Z substrate-based PCB and the extracted results are verified by designing and measuring the fourth-order Chebyshev filter at X-band.

$Ka$ -Band Fully Metallic TE40 Slot Array Antenna With Glide-Symmetric Gap Waveguide Technology

Gap waveguide has recently been proposed as a low-loss and low-cost technology for millimeter-wave components. The main advantage of the gap waveguide technology is that the microwave components can be manufactured in two metallic pieces that are assembled together without electrical contact. The leakage through a thin air gap between the two pieces is prevented by a 2-D periodic structure offering an electromagnetic bandgap (EBG). This EBG is conventionally implemented with metallic pins. Here, we propose the usage of a holey glide-symmetric EBG structure to design a 4 × 4 slot array antenna that is fed with a TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> mode. The TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> excitation is designed based on a TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> -TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> mode converter whose performance is initially evaluated by radiation pattern measurements. The final antenna, the 4×4 slot array antenna, was manufactured in aluminum by computer numerical control (CNC) milling. The antenna has a rotationally symmetric radiation pattern that could find application as a reference antenna as well as for 5G point-to-point communications.

A Broadband Millimeter-Wave Waveguide Window: A Low-Cost Design for Environmental Protection

In this paper, a full W-band waveguide window for the protection of components from the environment is presented. The window is based on rectangular dielectric block placed inside the rectangular waveguide. Electrical design steps for broadband performance are presented, and a simple cost effective mechanical process flow is employed for the fabrication of windows. Four different dielectric windows are evaluated, and they exhibited less than 0.3-dB insertion loss and better than 20-dB return loss: two windows over full W-band, whereas other two over 3-GHz bandwidth. Temperature testing is carried out for 4 h at −40 °C and +70 °C, and the humidity level is set at 95% at +70 °C. Minimum insertion loss variation of ±0.5 dB over the temperature range is observed. To check the compatibility of the windows with millimeter-wave components, a W-band switch is tested with the windows at its input and output ports. The experimental results show that the windows have low-loss characteristics and are free from ghost modes.