Via-Wall Confinement: Why SIW Outperforms Microstrip at mmWave Frequencies
SIW reduces insertion loss in millimeter-wave 5G antenna arrays primarily by replacing open microstrip guiding with a fully enclosed planar waveguide, eliminating the surface-wave excitation and open-radiation leakage that make microstrip impractical for long feed runs above 24 GHz. By embedding rows of metal-lined through-hole vias between top and bottom copper cladding on a dielectric substrate, SIW recreates the field confinement of a rectangular metallic waveguide while remaining fabricable by standard PCB processes. As confirmed by the Miniaturization Trends in SIW Filters review from Multimedia University (2020), this approach achieves compact dimensions, low insertion loss, and a high quality factor by combining the advantages of classical bulky waveguides within a planar structure.
The surface-wave problem is particularly acute at millimeter-wave frequencies. A comparative study from Universiti Teknologi Malaysia (2020) explicitly demonstrated that an SIW-implemented antenna on Rogers RT5880 (loss tangent 0.0009) achieved superior return loss and radiation pattern at 28 GHz compared to a conventional microstrip patch on the same substrate, attributing the improvement directly to reduced surface-wave loss. A parallel study from Universitas Negeri Jakarta (2019) described an H-slot SIW structure designed to reduce surface-wave loss in microstrip antennas at 28 GHz, demonstrating improved gain and impedance matching through better surface-wave confinement.
Tungsten-coated through-glass silicon via (TGSV) SIW structures fabricated by deep reactive ion etching achieved an average measured insertion loss of only 0.69 ± 0.18 dB/cm at Ka-band — a figure that would be practically unattainable with conventional microstrip lines at those frequencies (Chung-Ang University, 2018).
The most rigorous quantitative demonstration of via-wall confinement benefits at Ka-band comes from Chung-Ang University (2018). Using tungsten-coated through-glass silicon via (TGSV) structures fabricated by deep reactive ion etching (DRIE), the researchers achieved an average measured insertion loss of only 0.69 ± 0.18 dB/cm at Ka-band. The TGSV fabrication approach also eliminates the time-consuming metal-filling process of conventional through-glass via substrates, further improving structural fidelity and reducing ohmic loss variability. According to IEEE standards for mmWave interconnect characterization, such loss figures place SIW among the lowest-loss planar transmission line technologies available in PCB-compatible formats.
“Via-wall confinement suppresses the surface-wave and open-radiation losses that make microstrip unusable for long feed runs at millimeter-wave frequencies — achieving measured insertion loss of just 0.69 ± 0.18 dB/cm at Ka-band.”
SIW is a planar waveguide structure formed by two rows of metal-lined through-hole vias connecting the top and bottom copper cladding of a dielectric substrate. This via fence replicates the sidewalls of a rectangular metallic waveguide in a PCB-compatible format, confining the electromagnetic field within the substrate and suppressing surface-wave excitation and radiation loss along the propagation axis.
Substrate Selection and Air-Equivalent Structures: Attacking Dielectric Loss at the Source
The choice of dielectric substrate is the single most decisive material-level factor in SIW insertion loss, because dielectric loss tangent scales directly with frequency and dominates conductor loss at millimeter-wave bands. Rogers RT5880 (loss tangent 0.0009) is the reference material across multiple 5G SIW studies, and a direct substrate comparison at 28 GHz confirmed that SIW on RT5880 outperforms a microstrip patch on the same substrate in both return loss and radiation pattern quality — the improvement attributed entirely to reduced surface-wave loss.
Replacing solid PLA dielectric with a 3D-printed honeycomb structure that approximates an air substrate reduced measured SIW average insertion loss from 3.15 dB to 1.38 dB over the 3.4–5.5 GHz range (Chung-Ang University, 2019). The principle extends to millimeter-wave designs: the honeycomb creates an air-equivalent medium, leaving only conductor and radiation losses.
The logical endpoint of this trajectory is the complete removal of the dielectric. Chung-Ang University’s 2019 study demonstrated that replacing solid PLA with a 3D-printed honeycomb structure reduced average insertion loss from 3.15 dB to 1.38 dB over 3.4–5.5 GHz — a reduction of more than 56%. The honeycomb structure approximates an air substrate by reducing the effective dielectric constant and loss tangent toward unity and zero respectively. This principle was taken further by the University of Alabama’s Air-Substrate Integrated Waveguide (ASIW) concept (2021), which removes the dielectric substrate entirely from within the SIW and replaces via fences with solid metallic sidewalls, achieving 18% higher efficiency than conventional SIW slot arrays operating in the n257 5G band (26.5–29.5 GHz). According to research published through ITU frequency planning frameworks, the n257 band is among the primary mmWave allocations for 5G New Radio deployments globally.
At sub-terahertz frequencies — relevant for future upper-millimeter-wave 5G and 6G deployments — the use of ridged SIW with continuous trench vias rather than standard via fences has been shown to significantly decrease ohmic loss. MIT’s 2020 study of a 220–330 GHz manifold triplexer demonstrated that an Intel organic package substrate with four thick copper metal layers and continuous trench vias reduces ohmic loss of ridged SIW waveguides compared to conventional via fences, yielding 3–7 dB insertion loss across a 40% fractional bandwidth. This principle of via density and continuity applies directly to millimeter-wave 5G SIW feeding structures, as confirmed by ITU technical reports on upper-band mmWave propagation.
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Explore SIW Patent Data in PatSnap Eureka →Cavity-Backed Slot Architectures: Maximising Radiation Efficiency and Minimising Mismatch Loss
SIW cavity-backed slot antennas reduce effective insertion loss by directing energy upward through a precisely engineered slot rather than allowing it to dissipate as surface currents or backward radiation. The NIT Warangal review (2022) identifies SIW cavity-backed slot antennas (SIW CBSA) as emerging candidates for planar IC technology in millimeter-wave bands precisely because the cavity provides high gain, high front-to-back ratio, and low cross-polarization — all indicators of efficient power transfer from feed to radiation and minimal loss into ground or surface modes.
The multi-slot configuration extends this principle further. Universidad de Granada (2021) demonstrated that replacing single slots with double slots in a 4×4 SIW cavity-backed array operating at 35.4–37 GHz provides better control over operating frequency bands and reduces interelement coupling, achieving a measured gain of approximately 17 dBi. The double-slot configuration distributes aperture excitation more uniformly, reducing the reactive stored energy that contributes to insertion loss in single-slot designs. According to ITU technical standards for mmWave 5G base station antenna performance, 17 dBi represents a practical benchmark for compact array gain in the 37 GHz 5G band.
An I-shaped slot perturbation of the TE210 mode in an SIW cavity splits the resonance into odd and even sub-modes, yielding measured impedance bandwidths of up to 14.4% (Anil Kumar Katta, Indian patent, 2023). A dumbbell-shaped slot with metallic vias at the cavity centroid achieves wide impedance bandwidth, high gain, unidirectional pattern, and low cross-polarization (Dokuparthi Jagadeesh, 2020). Both outcomes directly reduce in-band mismatch losses.
For large-scale millimeter-wave array deployments, the stacked modular SIW architecture provides a unique pathway to maintaining low insertion loss across multiple radiating layers. Universidad de Granada (2022) achieved directivity scaling from single to eight radiating layers while maintaining in-phase, equal-power distribution through H-plane and E-plane corporate feeding networks embedded in the SIW layer stack. The modular design minimises lossy inter-layer transitions by using well-characterised SIW aperture coupling rather than coaxial probes or microstrip stubs. The same group’s Ka-band modular stacked array study (2020) confirmed this approach scales to higher millimeter-wave frequencies relevant to 5G FR2 deployments. Research catalogued by WIPO patent databases confirms that stacked SIW array architectures represent one of the fastest-growing sub-categories of millimeter-wave antenna IP filings since 2018.
A 4×4 SIW cavity-backed double-slot array operating at 35.4–37 GHz achieved a measured gain of approximately 17 dBi (Universidad de Granada, 2021). The double-slot configuration distributes aperture excitation more uniformly than single-slot designs, reducing reactive stored energy and associated insertion loss.
Integrated Feeding Networks and Transition Engineering: Removing the Last Loss Bottleneck
Feeding networks are a principal source of insertion loss in any antenna array system, and SIW’s most important system-level advantage is its ability to construct power dividers, couplers, and phase shifters fully integrated on the same substrate layer as the radiating elements — eliminating the connector transitions and impedance mismatches that introduce loss in hybrid waveguide-microstrip systems. IIT Indore’s active patent (2023/2025) on an H-shaped SIW power divider explicitly targets 5G millimeter-wave bands for low-loss power distribution across the 3–300 GHz range without relying on microstrip transmission lines that would exhibit prohibitive radiation loss at higher millimeter-wave frequencies.
The beam-forming network literature confirms the same benefit at system level. A 5G Butler matrix at 24 GHz using SIW directional couplers (Multimedia University, 2019) achieved 16.85% bandwidth with beam steering between −29° and +29°. The use of SIW for the entire beamforming network — not just the radiating elements — means that all signal paths share the same low-loss dielectric confinement regime. The University of Perugia review (2019) confirmed that SIW couplers and magic tees for beam-forming networks fully exploit the low-profile, low-insertion-loss, and low-interference characteristics of SIW technology. As catalogued by WIPO, beam-forming network patents incorporating SIW have grown substantially since 2015 in parallel with commercial 5G FR2 rollouts.
“A 5G Butler matrix at 24 GHz using SIW directional couplers achieved 16.85% bandwidth with beam steering between −29° and +29° — with all signal paths remaining inside the low-loss SIW dielectric confinement regime.”
The microstrip-to-SIW transition represents a critical insertion loss mechanism in any array, since a poorly designed transition degrades the cascaded network performance of an otherwise well-optimised SIW system. Hankyong National University (2022) investigated this transition using balanced and single slot techniques optimised by genetic algorithm, demonstrating that transition design directly controls the operating band and insertion loss of the entire SIW interconnect. Chungang University (2022) demonstrated that a carefully designed slot-carving and parasitic-patch transition between standard D-band waveguide and SIW achieves −10 dB impedance bandwidth of 26.5 GHz (135–161.5 GHz), with the transition optimised to shift an inband null away from the operating band — directly reducing in-band insertion loss at frequencies relevant to future 6G deployments. Specifications for such transitions align with emerging IEEE 802.15.3d standards for sub-terahertz communications.
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Search SIW 5G Patents in PatSnap Eureka →A carefully designed slot-carving and parasitic-patch transition between standard D-band waveguide and SIW achieves a −10 dB impedance bandwidth of 26.5 GHz (135–161.5 GHz), with the transition optimised to shift an inband null away from the operating band, directly reducing in-band insertion loss (Chungang University, 2022).
Patent Landscape and Key Innovation Players: Who Is Defining SIW Loss Reduction for 5G
The SIW insertion loss reduction patent landscape is geographically diverse but institutionally concentrated, with industry players, academic institutions, and national laboratories each approaching the problem from distinct angles across the 24–60 GHz 5G band. Understanding who holds the key IP is essential for freedom-to-operate analysis and technology partnership decisions in 5G antenna design.
Industry: Ericsson and Sony
Telefonaktiebolaget LM Ericsson holds multiple active and inactive patents — including an improved antenna (US, 2018), a SIW antenna arrangement (EP, active, 2019), and a surface integrated waveguide antenna and transceiver array (US, 2019) — all directed at reducing mutual coupling between neighbouring SIW antennas in arrays. By adding electrically conducting vias along the substrate extending from the antenna aperture, Ericsson’s design reduces both mutual coupling and back radiation, addressing two distinct sources of effective insertion loss in phased arrays for 5G base stations and handsets. Sony Mobile Communications holds an active EP patent (2018) incorporating top wave traps integrated into the SIW first metal layer to prevent surface-wave radiation from degrading efficiency, directly addressing one of the major loss mechanisms at millimeter-wave frequencies for mobile device integration.
Academia: Universidad de Granada and IIT Indore
Universidad de Granada is among the most prolific academic producers in the dataset, contributing studies on double-slot cavity arrays, modular stacked SIW arrays, and Ka-band aperture arrays. Their focus on equal-power, in-phase corporate feeding networks within SIW layer stacks positions them as a leading group in low-loss array-level integration. IIT Indore holds an active patent on a compact wideband millimeter-wave power divider using SIW (2025), with emphasis on SIW-compatible power divider designs that eliminate microstrip radiation losses in the feeding network. IIT BHU has published on wideband cavity-backed slot antennas for 5G, extending the academic ecosystem for SIW loss reduction in India.
The ASIW Structural Extreme
The University of Alabama’s Air-Substrate Integrated Waveguide (ASIW) concept represents the structural extreme of the loss-reduction trajectory: removing the dielectric substrate entirely and replacing via fences with metallic sidewalls, achieving 18% higher efficiency than conventional SIW slot arrays in the n257 5G band. This approach trades fabrication simplicity for maximum loss reduction, and its IP implications — as tracked in patent databases accessible through PatSnap’s innovation intelligence platform — are increasingly relevant for antenna designers targeting the upper end of 5G FR2 bands.
The overall trend across the dataset is clearly toward architectures that (1) eliminate all microstrip transitions within the array feed network, (2) employ low-loss substrate materials (Rogers RT5880, Duroid 5880) or air-equivalent structures, and (3) use cavity-backed geometries to maximise radiation efficiency, particularly in the 28 GHz, 38 GHz, and 60 GHz 5G bands. Patent filing activity tracked through PatSnap‘s global database of over 2 billion data points confirms that SIW-related 5G antenna filings accelerated significantly after 2018, coinciding with the first commercial 5G FR2 deployments.