Empty Substrate Integrated Waveguide Research Articles

Simple and Easily Connectable Transition from Empty Substrate-Integrated Waveguide to a 3D Printed Rectangular Waveguide

3D printing is one of the most promising manufacturing methods in the most developed technological fields, including microwave hardware fabrication. On the other hand, the well-known manufacturing methods of planar substrate integrated circuits allow high-quality prototypes to be made at low cost and with mass production capabilities. The combination of both manufacturing methods, 2D or 2.5D (substrate integrated circuits) and 3D (3D printed structures), will allow us to take advantage of the main strengths of each technology and minimise disadvantages. In this article, for the first time, a transition structure between the Empty Substrate-Integrated Waveguide (ESIW) technology—a planar waveguide integrated on a printed circuit board—and a standard rectangular waveguide manufactured by 3D printing is proposed. This transition will make it possible to combine planar circuits with 3D structures, thus taking advantage of the benefits of both types of technologies. The fabricated prototype presents low losses (0.6 dB for the transmission coefficient and 15 dB for reflection coefficient), good electrical response (very flat), and simultaneously good mechanical stability and robustness to manufacturing and assembly errors. The proposed design for this transition piece is easily realisable for a wide range of affordable 3D printers. Repeatability is guaranteed and the proposed transition allows us to combine different SIC structures to 3D printed circuits. Hence, this transition will enable advancements in the fabrication of microwave devices, particularly with regard to satellite communications.

Through-Wire Microstrip-to-Empty-Substrate-Integrated-Waveguide Transition at Ka-Band

The advantages of the Substrate-Integrated Waveguide (SIW) in terms of low profile, integration with Printed Circuit Board (PCB) and low cost are maintained by the Empty Substrate-Integrated Waveguide (ESIW). Moreover, as the dielectric fill is avoided, other advantages are also added: resonators with higher quality factor and lower insertion losses. Since 2014, when it was proposed, several devices for X-band to Ka-band applications have been accurately designed and manufactured. In this way, transitions are one of the most important components, as they allow the connection between the ESIW and other planar transmision lines such as microstrip. To accomplish this aim, different transitions have been proposed in the literature: based on sharp dielectric tapers combining metallized and non-metallized parts, which increases the manufacture complexity; with a broadened ESIW section, that is less complex at the cost of increasing reflection and radiation losses due to the abrupt discontinuity; based on tapered artificial dielectric slab matrix, more difficult to mechanize; using a tapered microstrip transition, with high radiation losses; and even transitions for multilayer devices. Among all the transitions, the most versatile one is the through-wire transition, as microstrip and ESIW can be implemented in different layers and allows any feeding angle between the microstrip line and the ESIW. In this paper the through-wire transition has been properly validated at Ku- and Ka-bands. Moreover, a back-to-back transition has been accurately manufactured in Ka-band with measured insertion losses lower than 3.7 dB and return losses higher that 11.7 dB, concluding that the transition is not frequency dependent.

Wideband H-Plane T-Junction Power Divider With Compensation Elements Using Double Ridged Empty Substrate Integrated Waveguide

The empty substrate integrated waveguide (ESIW) presents the same advantages as the substrate integrated waveguide (SIW): low cost, low profile, and easy integration, but with lower insertion losses because the dielectric is removed. In order to increase the operational usable bandwidth, one or two ridge layers can be added to the ESIW, leading to the single ridge ESIW (RESIW) or the double ridge ESIW (DRESIW). A transition from microstrip to DRESIW has already been presented, but no other passive components have been implemented in this technology yet. This letter presents a broadband 3-dB DRESIW power divider based on an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$ </tex-math></inline-formula> -plane T-junction with compensation elements, which can be easily manufactured using standard planar circuit manufacturing techniques. The manufactured prototype presents measured return losses greater than 12 dB from 6.9 to 20.4 GHz, representing a 99% fractional bandwidth (FBW), whereas the power division is rather symmetric since the maximum <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{21}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{31}$ </tex-math></inline-formula> parameters are −3.98 and −3.78 dB, respectively.

A high‐performance empty substrate integrated waveguide filter with mixed electric and magnetic coupling

AbstractAn empty substrate integrated waveguide (ESIW) bandpass filter with enhanced electric and magnetic coupling is proposed in this letter. ESIW uses the air as dielectric in order to reduce the dielectric loss caused by usual medium materials. However, the existence of air cavities requires at least three layers of structure, which greatly increases the difficulty of designing complex circuits with high‐performance and multiple requirements. The proposed mixed coupling structure creates the finite transmission zeros based on ESIW technology for the first time, which makes it possible to realize complex high‐performance circuits with ESIW technology. Taking advantage of the multilayer structure of the ESIW, the proposed cross‐coupling is conveniently realized with higher frequency selectivity and lower insertion loss while maintaining the substrate of three layers and the self‐encapsulation characteristics of ESIW. A fourth‐order filter with an H‐shaped slot line on the top metal plane of two adjacent air cavities is produced. A good agreement between the measurements and simulations indicates that the proposed filter achieves an insertion loss as low as 0.7 dB and the 6.1% bandwidth at 9.85‐GHz X band. It demonstrates the improvement of insertion loss and frequency selectivity, which lays a foundation for the design of complex microwave devices.

High‐gain and low‐cost circularly polarized antenna array for 5G MMW applications

A high-gain, low-cost empty substrate integrated waveguide (ESIW)-fed circularly polarized (CP) antenna array is demonstrated for millimetre-wave 5G applications in this letter. The ESIW is formed by metallized FR4 printed circuit boards. By stacking the metallic aluminium z-shaped radiating slots atop the ESIW feeding network, CP radiation is achieved. The proposed 1 × 8 antenna array offers a high measured gain of 17.8 dBic and high measured radiation efficiency of 89.1%. The measured impedance bandwidth for |S11| ≤ −10 dB and measured axial ratio (AR) bandwidth for AR ≤ 3 of the proposed 1 × 8 array are 11.4% (36.5–40.9 GHz) and 7.8% (37–40 GHz), respectively.

Improved Microstrip-to-ESIW Transition With Elliptical Dielectric Taper in Ku- and Ka-Bands

Empty Substrate Integrated Waveguide (ESIW) technology preserves the many advantages of the Substrate IntegratedWaveguide (SIW) such as low cost, low profile, and easy integration with Printed Circuit Boards (PCBs). Moreover, it has additional advantages due to the avoidance of dielectric filling: lower insertion losses and resonators with higher quality factor. In order to connect the ESIW line to classical planar lines, the design of transitions becomes specially important. Due to this, some microstrip-to-ESIW transitions have been published in recent years. Problems of these transitions are usually the complexity of the manufacturing process or increased radiation losses. Knowing the aforementioned disadvantages of the published solutions, in this paper, the transition with an expanded ESIW section has been improved, by adding an easy-to-manufacture dielectric taper that minimizes the undesired radiation losses. Additionally, the new proposed transition can be mechanized easier than previous solutions based on sharp tapers. Moreover, the slight overlap between the microstrip line and the upper ESIW metal cover has been avoided, thus enhancing the return losses of the proposed transition. To validate the proposed transition, two back-to- back prototypes have been manufactured both in Ku- and Ka-band, obtaining insertion losses lower than 0.31 dB and return losses higher than 20.8 dB in Ku-band, and insertion losses lower than 1.36 dB and return losses higher than 14.75 dB in Ka-band.

Enhanced Performance of Multilayer Bandpass Filter Using Slow-Wave Empty Substrate- Integrated Waveguide (SW-ESIW)

In this letter, two compact and high-performance filters based on multilayer slow-wave empty substrate-integrated waveguide (SW-ESIW) are presented. SW-ESIW, which contains the air cavity and a bottom layer including several rows of internal metallized via holes, provides a compromise between insertion loss and footprint. It is the first time that SW-ESIW is used to implement compact filters with multilayer air cavity. The proposed filters are simulated, fabricated, and measured. The measurements are consistent with simulations, indicating that the proposed filters can be reduced more than 35% in dimension compared to the same filters in ESIW. Based on the SW-ESIW technology, the proposed multilayer filters realize the advantages of low insertion loss and miniaturization, and express the tremendous potential on applications to complex and high-performance microwave circuits and systems.

Easy-to-assemble and high quality-factor ESIW filter with post-based soldered inverters in X-band

Empty Substrate Integrated Waveguide (ESIW) devices maintain a compromise between the advantages of classical waveguide technologies, such as high quality factor and low losses, and the advantages of planar ones, like low cost and easy compact integration. Compared with SIW, since ESIW is not dielectric filled, additional advantages are achieved, such as lower insertion losses and resonators with higher quality factor. In recent years several filters and folded filters have been designed in ESIW, using all of them resonators based on irises. An alternative to the use of irises is H-plane cylindrical posts. Although cylindrical posts have been widely used in other technologies like Rectangular Waveguide, SIW or AFSIW, it is the first time that this kind of inverters has been used in ESIW. In this paper, the use of posts in ESIW is proposed and validated through the design and manufacture of a bandpass filter in X-band. Posts are soldered to top and bottom layers after ESIW is assembled, being this kind of filters easier to manufacture and more robust than those based on irises. The designed filter achieves return losses higher than 12 dB and insertion losses lower than 1.6 dB (considering microstrip-to-ESIW transitions) and a quality factor of 918.74.

Broadband High-Gain Empty SIW Cavity-Backed Slot Antenna

To broaden the bandwidth of high-gain substrate-integrated waveguide (SIW) cavity-backed slot antennas, an empty SIW (ESIW) cavity-backed antenna with multiple high-order hybrid modes is proposed. Due to the ESIW configuration, the proposed antenna is independent on substrates and a high efficiency more than 90% in the operational band can be realized even the typical low-cost high-loss FR4 substrate is used. The proposed antenna has a wide measured bandwidth of 40.8% and the maximum measured realized gain can reach 11.1 dBi. The proposed broadband high-gain antenna can be used in radar and communication systems.

Narrowband and Wideband Bandpass Filters Based on Empty Substrate Integrated Waveguide Loaded With Dielectric Elements

Although several bandpass filters have been designed in the recently proposed empty substrate integrated waveguide (ESIW) technology to improve the quality factor and reduce losses with respect to those in SIW and planar technologies, all structures exhibit narrowband properties and none uses the design concept applied in this paper. The idea has been to insert a dielectric element in an ESIW section (DE-ESIW), which can work as a dielectric resonator or impedance inverter depending on the propagation nature of the fundamental mode. Thus, two novel Chebyshev bandpass filters for narrow and wide bandwidths based on this design concept have been designed in this paper in ESIW technology. The narrow bandpass filter has been realized by inserting four dielectric resonators in an evanescent ESIW section and using a coupling matrix synthesis method, whereas the wideband bandpass filter has been implemented by including six dielectric line sections in an ESIW line propagating the fundamental mode and applying a stepped impedance synthesis approach. A novel wideband microstrip to ESIW transition using cubic Bezier curves has also been designed for the successful integration of both narrow and wideband filters with other microstrip components. EM simulation and measurement frequency responses on manufactured prototypes have shown the versatility of the dielectric elements to efficiently implement narrowband and wideband ESIW bandpass filters, using the proposed design techniques based on coupling matrix and stepped impedances, respectively.

Folded Empty Substrate Integrated Waveguide With a Robust Transition to Grounded Coplanar Waveguide in the Ku Band

The benefits of empty substrate integrated waveguide (ESIW) are already well-known and contrasted in the literature. Different variations of transitions are available to maximize the power injection in that structure. Besides, several topological variations of the ESIW have also been proposed, such as the ridge ESIW, which enlarges the monomode bandwidth at the cost of higher losses and larger cross-section area. This paper presents a new variation of topology: the folded-ESIW, that halves the width of the original ESIW waveguide and maintains the cross-section area with good performance indexes and a similar bandwidth. A discussion is made about the feasibility of this novel topology and a new transition is presented with a high degree of robustness and a minimum electrical length. To validate and prove this new proposal, a back-to-back prototype has been designed, manufactured and measured, with results so promising that give access to new design strategies in the ESIW field.

Transition from Microstrip Line to Ridge Empty Substrate Integrated Waveguide Based on the Equations of the Superellipse

In recent years, multiple technologies have been proposed with the aim of combining the characteristics of traditional planar and non-planar transmission lines. The first and most popular of these technologies is the Substrate Integrated Waveguide (SIW), where rows of metallic vias are mechanized in a printed circuit board (PCB). These vias, together with the top and bottom metal layers of the PCB, form a channel for the propagation of the electromagnetic fields, similar to that of a rectangular waveguide, but through a dielectric body, which increases the losses. To reduce these losses, the empty substrate integrated waveguide (ESIW) was recently proposed. In the ESIW, the dielectric is removed from the substrate, and this results in better performance (low profile and easy manufacturing as in SIW, but lower losses and better quality factor for resonators). Recently, to increase the operational bandwidth (monomode propagation) of the ESIW, the ridge ESIW (RESIW) and a transition from RESIW to microstrip line was proposed. In this work, a new and improved wideband transition from microstrip line (MS) to RESIW, with a dielectric taper based on the equations of the superellipse, is proposed. The new wideband transition presents simulated return losses in a back-to-back transition greater than 20 dB in an 87% fractional bandwidth, while in the previous transition the fractional bandwidth was 82%. This is an increment of 5%. In addition, the transition presents simulated return losses greater than 26 dB in an 84% fractional bandwidth. For validation purposes, a back-to-back configuration of the new transition was successfully manufactured and measured. The measured return loss is better than 14 dB with an insertion loss lower than 1 dB over the whole band.

Robust Microstrip to Empty Substrate-Integrated Waveguide Transition Using Tapered Artificial Dielectric Slab Matrix

In this letter, a novel transition from microstrip (MS) line to empty substrate-integrated waveguide (ESIW) with tapered artificial dielectric slab matrix in compact size is proposed. ESIW exhibits effective characteristics for energy transmission, especially in the millimeter waveband, due to the loss of dielectric. Recently, an MS to ESIW transition without sharp dielectric taper is achieved through an expanded ESIW width. Manufacturing and assembling difficulties can be overcome in this kind of transition, especially for a small thickness. In this letter, in order to apply in thin substrate with a compact size, especially in millimeter waveband, a novel robust transition from MS line to ESIW (with the tapered artificial dielectric slab matrix) is designed, fabricated, and measured in back-to-back configuration. In Ka-band, the return loss and insertion loss for one transition are better than 14.7 and - 0.46 ± 0.17 dB, respectively.

Versatile, Error-Tolerant, and Easy to Manufacture Through-Wire Microstrip-to-ESIW Transition

Empty substrate integrated waveguide (ESIW) technology preserves the many advantages of the SIW, such as low cost, low profile, or integration in a printed circuit board. But, since the fields propagate through the air in the ESIW instead of propagating through a lossy dielectric as in the SIW, the ESIW presents lower losses and higher quality factors in resonators. Several transitions have been recently proposed in the literature that connect the ESIW to a classical planar line such as the microstrip. In all these transitions, both the feeding planar lines and the ESIW are built in the same substrate layer (the height of the ESIW cannot be selected independently), and they are based on tapered structures in the planar line and/or in the ESIW that reduce the compactness of the transition. These transitions also combine metallized and nonmetallized parts, which increases the complexity of the manufacturing process. In this article, a new through-wire microstrip-to-ESIW transition is proposed. The feeding lines and the ESIW are implemented in different layers so that the height of the ESIW can be independently chosen, and higher quality factor ESIW filters can be excited. Besides, this novel transition can be manufactured with simple cuts and with uniform metallization so that the manufacturing complexity is reduced. Finally, it is a very compact transition that can be freely rotated; that is, the angle between the feeding lines and the ESIW does not affect the performance of the transition. This provides a high degree of versatility in the design phase.

Empty substrate‐integrated waveguide phase inverter in millimetre‐wave band application

In this Letter, a novel empty substrate-integrated waveguide (ESIW) phase inverter (PI) applied in millimetre-wave has been proposed. ESIW PI, based on the structural symmetry design, is made of four parts: top cover, middle layer, ESIW PCB, and bottom layer. Owing to the reversed-phase transmission channel, the phase difference between the two outputs is absolutely equal to 180°. The simulation and measurement results are in a good agreement. In the entire Ka band, the return losses, insertion losses and amplitude imbalance of ESIW PI are better than 12.7, 2.66, and 0.64 dB ± 0.6 dB, respectively. Besides, the phase difference is within 180.5° ± 2.9° in the same frequency band. In addition, the input and output ports are located in the identical circuit plane, which is easy to integrate with other devices and components.

Empty Substrate-Integrated Waveguide-Fed Patch Antenna Array for 5G Millimeter-Wave Communication Systems

This letter presents a microstrip patch antenna array fed with a low-loss and highly efficient feeding structure called empty substrate-integrated waveguide (ESIW). The proposed antenna array targets 5G wireless communication systems operating at 28 GHz. The antenna array consists of 4 × 4 radiating patches, where every four radiating elements are grouped together forming a 2 × 2 subarray and each of the subarrays is fed by ESIW feeding network by aperture coupling. The experimental results demonstrate good agreement with the simulated results, offering a wide | S 11| < −10 dB bandwidth of 12.4%, i.e., 26.5–30 GHz. A peak gain of 18.2 dBi and a high efficiency of about 91% are achieved using the proposed structure. Furthermore, the low-profile substrate of the ESIW feeding structure makes seamless integration of the proposed antenna array with the millimeter-wave front end. The advantages, such as low fabrication cost and high efficiency, make the proposed antenna array a suitable solution for millimeter-wave 5G wireless communication systems.

Microstrip to Ridge Empty Substrate-Integrated Waveguide Transition for Broadband Microwave Applications

The empty substrate-integrated waveguide (SIW) (ESIW) is an evolution of the SIW. Just as the SIW, the ESIW is of low cost and low profile, and can be integrated into a printed circuit board, but the losses in the ESIW are lower than in those in the SIW thanks to the removal of the dielectric material, which results in ESIW devices with performances close to those implemented with standard rectangular waveguides. In order to increase the operational (monomode) bandwidth of the rectangular waveguides, a metal ridge can be inserted (leading to the ridge waveguide). Extrapolating this idea to the ESIW, in this letter, a study of possible ridge ESIW (RESIW) geometries has been performed, and a novel transition from microstrip line to RESIW is proposed. In order to validate the performance of transition, a back-to-back prototype has been manufactured and measured.

Highly Reliable and Repeatable Soldering Technique for Assembling Empty Substrate Integrated Waveguide Devices

In this paper, a novel mymargin soldering technique that improves the fabrication process of empty substrate integrated waveguide (ESIW) devices is presented. Up until now, in order to fabricate an ESIW device, the tin solder paste was distributed, before assembling, on the contact surface between layers, in order to ensure a good electrical contact. This process has a low degree of repeatability (random soldering thickness and distribution of tin) and reliability (a significant number of nonworking prototypes due to tin overflow). In this paper, we propose the mechanization of a set of plated vias just next to the metalized walls of the ESIW in the central layer. Next, in the top and bottom covers that close this ESIW, additional plated vias are drilled in the same position so that, when the device is assembled (using screws or rivets), metalized holes can be seen passing through the whole structure from top to bottom. These holes are then used as soldering vias that can guide the tin paste straight to the point where it is needed. When the paste is dried, soldered vias ensure a very good electrical contact between layers. In addition, the fluid tin fills any small gap that appears between layers, thus providing a very good electrical contact and mechanical union. This novel soldering technique has been validated with experimental results. Several prototypes of filters centered at 13 and 35 GHz have been fabricated, proving the repeatability and reliability of the proposed soldering technique.

Gain and Bandwidth Improvement of Empty Substrate Integrated Waveguide H-plane Horn Antenna at W-band

A high-gain broadband empty substrate integrated waveguide (ESIW) H-plane horn antenna constructed by four low-cost printed circuit board (PCB) layers is proposed in this paper. The empty structure is fabricated by using high-precision laser engraving technology. A slotted rectangular dielectric load (SRDL) is introduced by simply extending the substrates, resulting a 4-dB gain enhancement and a 31% bandwidth improvement. The proposed antenna gives a measured realized gain at 14.5-dBi level with a relative impedance bandwidth larger than 19.6% (|S11| ≤ − 10 dB). The proposed antenna features the merits of low cost, high gain, and broad bandwidth.

Transition from rectangular waveguide to empty substrate integrated gap waveguide

Empty substrate integrated waveguide (ESIW) is a hollow SIW with its inner dielectric removed to achieve a reduced insertion loss. One of the drawbacks is the top and bottom covers need to be soldered to the middle substrate. Gap waveguide (GW) technology solves the contact issue utilising contactless electromagnetic band-gap (EBG) structures. Therefore, empty substrate integrated GW (ESIGW) is a transmission line having both advantages of ESIW and GW. In this Letter, a wideband transition from rectangular waveguide (RW) to ESIGW is presented. RW is firstly matched to reduced-height RW using E -plane stepped waveguides. Then, a short substrate integrated GW (SIGW) section is introduced between the reduced-height RW and the ESIGW. This section not only serves as an impedance matching component, it also connects the two sides of the ESIGW and maintains the integrity of the substrate. To broaden the bandwidth of the transition, a triangular dielectric is added at the end of the ESIGW. A Ka-band back-to-back prototype of the transition is designed and fabricated. In addition, TRL calibration is used to measure the transmission performance of the ESIGW. The measured results show that the transition works well over the entire Ka-band.