Air-filled Substrate Integrated Waveguide Research Articles

Contactless AF-SIW phase shifters based on periodic structures at mmWaves

This document presents different phase shifter designs implemented in contactless air-filled substrate-integrated waveguide (CLAF-SIW) technology. The phase shifters are based on unit cells that avoid leakage losses in the assembled layers and produce the desired phase shift along the waveguide. The unit cells are represented by waveguides whose lateral walls have double-mushroom structures, and phase-shifting elements are in their propagation zone. The proposed phase-shifting elements are integrated cavities, integrated cavities with patches, and integrated cavities with mushroom-like patches. Transitions are needed to match impedances between the waveguides loaded with phase-shifting elements and a reference CLAF-SIW. Other transitions are designed to measure the prototypes, from coplanar waveguide to SIW and SIW to CLAF-SIW. Finally, some prototypes are manufactured to provide an experimental validation of the proposed phase-shifting elements. Good agreement is obtained between the simulated and measured results for all the CLAF-SIW phase shifters in the frequency range between 30 and 50 GHz.

Self-Packaged mm-Wave Broadband Air-Filled SIW Filtering Power Divider With Sharp Roll-Off Skirt and High In-Band Isolation

Self-Packaged mm-Wave Broadband Air-Filled SIW Filtering Power Divider With Sharp Roll-Off Skirt and High In-Band Isolation

Air-filled SIW technology for mass-manufacturable and energy-efficient terahertz systems

To accommodate the ever-growing data requirements in densely populated areas and address the need for high-resolution sensing in diverse next-generation applications, there is a noticeable trend towards utilizing large unallocated frequency bands above 100 GHz. To overcome the harsh propagation conditions, large-scale antenna arrays are crucial and urge the need for cost-effective, mass-manufacturable technologies. A dedicated Any-Layer High Density Interconnect PCB technology for highly efficient wireless D-band (110–170 GHz) systems is proposed. Specifically, the adapted stack accommodates broadband air-filled substrate-integrated-waveguide components for efficient long-range signal distribution and low-loss passives. The viability of the suggested technology platform is demonstrated by designing, fabricating and measuring several essential low-loss air-filled substrate-integrated-waveguide components, such as a dual rectangular filter, with a minimal insertion loss of 0.87 dB and 10 dB-matching within the (132.8–139.2 GHz) frequency band, and an air-filled waveguide with a routing loss of only 0.08 dB/mm and a flat amplitude variation within 0.01 dB/mm over the (115–155 GHz) frequency range. A broadband transition towards stripline, with a limited loss of 1.1 dB, is described to interface these waveguides with compactly integrated chips. A tolerance analysis is included as well as a comparison to the state of the art.

Compact millimeter-wave air-filled substrate-integrated waveguide crossover employing homogeneous cylindrical lens

Compact millimeter-wave air-filled substrate-integrated waveguide crossover employing homogeneous cylindrical lens

Advanced Modeling of SIW Structures by 2-D Finite Element Method

This article presents an advanced modeling of substrate-integrated waveguide (SIW) structures by the 2-D vector finite element method (FEM). All types of losses are considered, together with input/output coupling by the rectangular waveguide and coaxial cable. Multiple dielectric regions can be defined, allowing the modeling of partially air-filled SIW structures with excellent accuracy and efficiency.

D-Band Air-Filled Substrate Integrated Waveguide (AFSIW) and Broadband Stripline to AFSIW Launcher Embedded in Multi-Layer PCBs

We report <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 air-filled substrate integrated waveguides (AFSIWs) with solid copper sidewalls fabricated inside a multi-layer printed circuit board (PCB) with broad wall width of 1.6 mm and cavity height of 300 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m. Measurements show a loss of 0.07–0.08 dB/mm across 115–155 GHz. This result is the first demonstration of an AFSIW above 100 GHz in a low-cost mass manufacturable PCB and has the lowest loss compared to reported planar PCB lines or substrate integrated waveguides (SIWs) in PCBs and Interposers. We also introduce a broadband stripline to the AFSIW launcher using a broad wall transverse slot which offers ease of manufacturability over existing transitions having a measured insertion loss of 1.1 dB and 27% bandwidth. The combination of a low-loss AFSIW and wideband launcher allows both striplines and AFSIWs to coexist in the same multi-layer PCB.

Air-Filled SIW Remote Antenna Unit With True Time Delay Optical Beamforming for mmWave-Over-Fiber Systems

A low-complexity and efficient mmWave-over-fiber remote antenna unit (RAU) is proposed for broadband transmission and wide-angle squint-free beam steering in the full [26.5–29.5] GHz n257 5G band. It leverages an optical beamforming network (OBFN), implemented on a silicon photonics integrated circuit, and a broadband optically enabled 1x4 uniform linear array (ULA). The antenna elements (AEs) of the ULA are implemented in air-filled substrate-integrated-waveguide technology. They adopt an improved aperture-coupled feeding scheme to achieve high efficiency, high isolation and minimal back radiation over a broad frequency band. Each AE is compactly integrated and co-optimized with a dedicated opto-electrical transmit chain, maximizing the RAU’s performance, including beamforming flexibility and energy efficiency, while minimizing its size. The separately packaged OBFN implements true-time-delay beamforming by means of four switchable optical delay lines that are capable of discretely tuning the delay difference between AEs with a resolution of 1.6 ps, up to a maximum delay of 49.6 ps to fully exploit the ULA’s full grating-lobe-free scan range. The measured AEs are excellently matched in the [25.1–30.75] GHz band, exhibit high isolation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ &gt;$</tex-math></inline-formula> 15 dB) in the operating band, and feature a stable peak gain of 6.8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 0.72 dBi with a beamwidth of at least 95 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> . Additionally, optical beamforming was successfully demonstrated by steering the RAU’s beam towards angles up to 51.8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> without grating lobes. The optically enabled 1 × 4 ULA successfully establishes a 64-QAM wireless communication link at 2.2 Gbaud (13.2 Gbps) while beam steering up to 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ ^\circ$</tex-math></inline-formula> with an error vector magnitude below 7.6%.

High‐performance filtering power divider based on air‐filled substrate integrated waveguide technology

AbstractA filtering power divider based on air‐filled substrate‐integrated waveguide (AFSIW) technology is proposed in this study. The AFSIW structure is used in the proposed filtering power divider for substantially reducing the transmission losses. This structure occupies a large area because of the use of air as a dielectric instead of typical dielectric materials. A filtering power divider provides power division and frequency selectivity simultaneously in a single device. The proposed filtering power divider comprises three AFSIW cavities. The filtering function is achieved using symmetrical inductive posts. The input and output ports of the proposed circuit are realized by directly connecting coaxial lines to the AFSIW cavities. This transition from the coaxial line to the AFSIW cavity eliminates the additional transitions, such as AFSIW‐SIW and SIW‐conductor‐backed coplanar waveguide, applied in existing AFSIW circuits. The proposed power divider with a second‐order bandpass filtering response is fabricated and measured at 5.5 GHz. The measurement results show that this circuit has a minimum insertion loss of 1 dB, 3‐dB fractional bandwidth of 11.2%, and return loss exceeding 11 dB.

Contactless Air-Filled Substrate-Integrated Waveguide (CLAF-SIW) Resonator for Wireless Passive Temperature Sensing

In this article a wireless passive temperature sensor is designed, fabricated, and tested. The sensor uses a contactless air-filled substrate-integrated waveguide (CLAF-SIW) resonator that consists of an air cavity surrounded by a low-impedance electromagnetic band gap (EBG) structure. The contactless feature of the sensor mitigates the fabrication complexity issue of air-filled SIW (AF-SIW) while it benefits from the high-quality factor of an air-filled resonator. The resonant frequency of the CLAF-SIW resonator is dependent on the permittivity of the substrate and the dimensions of the structure which are both temperature-dependent. Change in temperature results in a variation in the resonant frequency of the sensor. As such, we measure temperature by measuring the resonant frequency of the sensor. The developed CLAF-SIW sensor has a measured unloaded quality factor of 1340 that allows for long-range wireless measurements. The resonant frequency of the sensor is measured using a ringback-based wireless interrogation system. The interrogation system energizes the sensor using radio frequency (RF) pulses and determines the frequency of the ringback signals radiated by the sensor using frequency domain analysis. The sensor has a sensitivity of 300 kHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^\circ \text{C}$ </tex-math></inline-formula> and an interrogation-to-sensor distance of 80cm.

Multilayer GCPW-to-AFSIW Transition for High-Performance Systems on Substrate

This letter presents a transition from a top layer grounded coplanar waveguide (GCPW) to an inner layer air-filled substrate-integrated waveguide (AFSIW). Such type of transition is crucial for the interconnection of top layer surface-mounted radio-frequency integrated circuits (RFICs), toward the integration of complete microwave and millimeter-wave systems taking advantage of the low-cost and high-performance AFSIW technological platform. To fulfill the new space application needs, the proposed transition has been developed in the satellite downlink Ka-band ranging from 27.5 to 31 GHz. The structure is detailed with design guidance. For experimental evaluation, a back-to-back prototype has been fabricated and measured. In the operating frequency range, the proposed transition achieves a simulated and measured insertion loss (IL) as low as 0.135 ± 0.015 dB and 0.3 ± 0.18 dB, respectively.

Self-Temperature-Compensated Air-Filled Substrate Integrated Waveguide (AFSIW) Quasi-Elliptic Filters

Patented single-slab self-temperature-compensated air-filled substrate integrated waveguide (AFSIW) cavities and quasi-elliptic filters are proposed and demonstrated in this article. Such components are of high interest for the design of thermally stable circuits and systems on substrate meeting the size, weight, power, and cost (SWaP-C) reduction expected for future systems, especially for space applications. First, a theoretical multiphysics model is presented for the synthesis of single-slab self-temperature-compensated AFSIW cavities. It is demonstrated from theory that by properly choosing the dielectric slab material and dimensions, perfect temperature compensation can be achieved. This extended technique allows the implementation of temperature compensation in any type of cavity, filter, and multiplexer configuration. For demonstration purposes, a single-slab self-temperature-compensated in-line folded seventh-order quasi-elliptic AFSIW filter operating at 12 GHz with a 250-MHz (2.27%) −3-dB bandwidth is designed and fabricated. It achieves a measured unload <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor of 992 at ambient temperature (23 °C) and a measured resonance frequency thermal stability as low as 0.58 ppm/°C at −20 °C and 0.89 ppm/°C at 70 °C compared with its temperature-uncompensated counterpart achieving a thermal stability of −15.5 ppm/°C at −20 °C and −17.73 ppm/°C at 70 °C. Furthermore, it is demonstrated in this article that transmission zeros (TZs) created by cross-couplings in the in-line folded configuration of the self-temperature-compensated quasi-elliptic filter achieve a thermal stability of 2.55 ppm/°C and 2.3 ppm/°C (2.34 ppm/°C and 4.37 ppm/°C) at −20 °C (70 °C), in the lower and upper bands, respectively.

Wideband and Low-Loss Beam-Scanning Circularly Polarized Antenna Based on Air-Filled SIW

In this letter, a wideband beam-scanning antenna with circular polarization (CP) characteristics is proposed. The antenna is designed based on an air-filled substrate-integrated waveguide (SIW), which is composed of three layers of printed circuit board. Since the medium is dug out, the transmission structure has low-loss characteristics. An array of slots is etched on the top layer as radiating elements. Due to the fast-wave characteristic of the air-filled SIW, the antenna can radiate over a wide bandwidth. The proposed antenna is designed, fabricated, and tested. Within the frequency band of 12-18 GHz (40% relative bandwidth), the measured scanning angle is from 28° to -13°. The antenna axial ratio is below 3 dB at the corresponding maximal beam direction, and the gain is above 10.30 dBic over the whole band. This antenna has potential applications in the satellite and wireless communication systems for its advantages of wideband, low loss, CP properties, low cost in fabrication, and simplicity in design.

Multipolarization-Reconfigurable Air-Filled Substrate Integrated Waveguide Cavity-Backed Slot Antenna

A novel single-feed ultrawideband cavity-backed slotantenna with a reconfigurable polarization capability is demon-strated in substrate-independent air-filled substrate integratedwaveguide (AFSIW) technology for Internet-of-Things applica-tions in the [5.15-5.85] GHz frequency band of the unlicensednational information infrastructure. The antenna achieves an ul-trawide impedance bandwidth by exploiting a double ring of slotsand supports four switchable linear polarization states (±45°,0°,+45°,and 90°) by leveraging four quartets of p-i-n diodes. Byelectrically shorting the slots at well-defined positions by these p-i-ndiodes, dynamic polarization reconfiguration is achieved by switch-ing their dc bias current, supplied at the antenna feed through anexternal bias tee and routed from the antenna's back to front cavityplane via the AFSIW sidewalls. This new simple, yet effective, biasnetwork enables the integration of all polarization control electron-ics inside the antenna cavity to protect them from environmentaleffects. Finally, measurements prove that the prototype exhibits anoverlapping impedance bandwidth of 29%, from 4.85 to 6.45 GHz,and a stable conically shaped radiation pattern across the operating band width with a 3 dB beamwidth of 45°and a peak gain of 6.5 dBi for all four states.

Wideband air‐filled ridge substrate‐integrated waveguide

A wideband air-filled ridge substrate integrated waveguide (AFRSIW) and its transition to microstrip are proposed first in this paper. The AFRSIW combines the broadband advantage of the ridge substrate integrated waveguide (RSIW) and the low loss of the air-filled SIW (AFSIW). Therefore, the AFRSIW allows for lower cut-off frequency and broader mono-modal bandwidth compared with AFSIW with same width and height, because of the involvement of the ridge made of an additional layer of dielectric substrate. Moreover, the AFRSIW has lower loss compared with RSIW due to the removal of the dielectric. The transition from AFRSIW to microstrip consists of a tapered microstrip line and two suppressing stubs. The tapered microstrip line is used to ensure impedance matching, and two suppressing stubs preventing the undesired radiation are introduced to improve the impedance match broadening the operating bandwidth of the transition. The AFRSIW together with the transition is simulated and optimized with HFSS. For demonstration, a back-to-back transition prototype is fabricated and measured. A mono-modal bandwidth of 77.6% with 15 dB return loss is obtained from 8.6 to 19.5 GHz.

Cost-Effective High-Performance Air-Filled SIW Antenna Array for the Global 5G 26 GHz and 28 GHz Bands

A cost-effective, compact, and high-performance antenna element for beamforming applications in all fifth-generation (5G) New Radio bands in the [24.25–29.5] <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \,$</tex-math></inline-formula> GHz spectrum is proposed in this letter. The novel antenna topology adopts a square patch, an edge-plated air-filled cavity, and an hourglass-shaped aperture-coupled feed to achieve a very high efficiency over a wide frequency band in a compact footprint ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{{0.48} \lambda _0 \times \text{0.48}\lambda _0}$</tex-math></inline-formula> ). Its compliance with standard printed circuit board (PCB) fabrication technology, without complex multilayer PCB stack, ensures low-cost fabrication. The antenna feedplane offers a platform for compact integration of active electronic circuitry. Two different modular 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \boldsymbol{\times }$</tex-math></inline-formula> 4 antenna arrays were realized to demonstrate its suitability for broadband multiantenna systems. Measurements of the fabricated antenna element and the antenna array prototypes revealed a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 10 dB impedance bandwidth of 7.15 GHz (26.8%) and 8.2 GHz (30.83%), respectively. The stand-alone antenna features a stable peak gain of 7.4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \,\pm \,$</tex-math></inline-formula> 0.6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \,$</tex-math></inline-formula> dBi in the [24.25–29.5] <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \,$</tex-math></inline-formula> GHz band and a measured total efficiency of at least 85%. The 1 × 4 array provides a peak gain of 10.1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \,\pm \,$</tex-math></inline-formula> 0.7 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \,$</tex-math></inline-formula> dBi and enables grating-lobe-free beamsteering from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${-}\text{50}^\circ$</tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \text{50}^\circ$</tex-math></inline-formula> .

Partially Filled Half-Mode Substrate Integrated Waveguide Leaky-Wave Antenna for 24 GHz Automotive Radar

A novel highly efficient leaky-wave antenna (LWA), based on a periodic set of holes created in a half-mode substrate integrated waveguide (SIW), is conceived for automotive radar. The computer-aided design of this partially filled SIW (PFSIW) LWA is carried out using a full-wave electromagnetic simulator. As a proof-of-concept, an LWA prototype having a plate size of 15 × 126 mm $^2$ is fabricated through a standard low-cost printed circuit board (PCB) manufacturing process. Our manufactured prototype yields more than 25% impedance bandwidth, targeting the 24 GHz automotive short-range-radar band. Moreover, the measured peak gain and total antenna efficiency reach up to 15.5 dBi and 85% at 24 GHz. Furthermore, the main radiating direction steers continuously from 38 $^\circ$ to 58 $^\circ$ with an average half-power beamwidth of 12 $^\circ$ when the operating frequency changes from 22 to 26 GHz. In comparison, a 160 mm long dielectric-filled SIW (DFSIW) LWA yields a measured scanning range of 49 $^\circ$ and a total antenna efficiency of 43.8%, whereas an 80.3 mm long air-filled SIW (AFSIW) LWA exhibits a measured scanning range of 9 $^\circ$ and a total antenna efficiency of 80%. Therefore, PFSIW technology provides an optimal tradeoff between DFSIW and AFSIW for the envisaged short-range automotive radar application.

Fabrication-Tolerant Broadband Air-Filled SIW Isolated Power Dividers/Combiners

This article introduces two-way broadband air-filled substrate integrated waveguide (AFSIW) isolated power dividers/combiners based on surface mounted absorbing materials. The proposed structures take advantage of the AFSIW multilayer feature. The absorber implementation is found highly tolerant of variations in dimensions and positioning. Three different power dividers/combiners topologies are analyzed theoretically, simulatively, and experimentally. The measurement results validate the broadband responses of the fabricated Ka-band demonstrators. The proposed power dividers/combiners are intended to exploit high-power AFSIW system on substrate (up to few hundred watts).

Air-Filled Substrate Integrated Waveguide Leaky-Wave Antenna With Wideband and Fixed-Beam Characteristics

In this communication, a novel wideband fixed-beam leaky-wave antenna (LWA) is proposed. The antenna is designed based on air-filled substrate integrated waveguide (SIW), which is composed of one layer of printed circuit board (PCB) in the middle and two layers of thin copper plates on the top and bottom. The different layers are aligned and fixed by screws. A long slot is etched on the top surface of air-filled SIW as a radiator. Due to the dispersive characteristic of the air-filled SIW, the antenna can radiate at a fixed direction over a wideband. To the best of our knowledge, this is the first time that the air-filled SIW is adopted for LWA design. The proposed antenna is designed, fabricated, and tested. The measured results show that its wide operating bandwidth reaches up to 37.0%, ranging from 11 to 16 GHz. The excellent fixed-beam radiation performance is obtained over the operating bandwidth. The radiation direction is fixed at 59° with only ±3° variation, and the peak gain is within 14.0-15.3 dBi. Although the beam angle can only be fixed nearly the endfire, this method offers a simple way to realize wideband fixed-beam feature.

Genetic Algorithm-Based Approach for Minimising Losses in Substrate-Integrated Waveguide

The transitions in air-filled substrate-integrated waveguide (SIW) are studied here for millimetre-wave applications. A good design of an air-filled SIW (AFSIW) must allow for minimum losses in its interconnects between the air-filled and dielectric-filled regions of the SIW. This paper assesses the influence of the geometry of transition taper in an AFSIW on the return and insertion losses using full-wave analysis of a complete AFSIW structure. The data from the return and transmission losses provide a basis in the optimisation of the design of the transition tapers. The optimisation approach uses the multi-objective genetic algorithm (GA) with full-wave analysis to find an optimum profile of the transition. Defining the profile of the transition taper with a clamped cubic spline as a phenotype, the developed procedure shows that further losses are possible within the prescribed frequency bands. Furthermore, the length of the transition taper can be significantly reduced while maintaining an optimal quality of signal transmission in the transition. The simulation results show the efficacy of the proposed strategy where the optimal taper geometry is shown to provide a wider band of operating frequencies with lower return loss compared to a more established taper geometry.

Dielectric Slab Air-Filled Substrate Integrated Waveguide (SAFSIW) Bandpass Filters

This letter introduces stepped-impedance bandpass filters based on the slab air-filled substrate integrated waveguide (SAFSIW), which provides a compromise in terms of loss and footprint between substrate integrated waveguide (SIW) and air-filled SIW (AFSIW). First, the theoretical unloaded quality factor of the SAFSIW guided-wave structure is presented. Then, a design procedure of SAFSIW stepped-impedance bandpass filters is introduced. Finally, for demonstration purposes, a third-order Chebyshev filter, centered at 30 GHz, is synthesized, optimized, fabricated, and measured. With a low-cost FR-4 to enclose the structure, a return loss better than 15 dB with a minimum insertion loss of 0.99 dB in the passband is obtained in experiments.