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.

This paper presents a feasibility study for designing a floating patch antenna structure fed with a probe from a microstrip. The main premise is to eliminate the dielectric in the patch design, which is equivalent to having an air dielectric and leads to the necessity of proper support to fasten the patch in the air. The novelty of this paper is that this new device, apart from being fed with the though-wire technique directly from the microstrip line, has to be, by design, robust and easy to manufacture, and, at the same time, it has to present, simultaneously, good values in all of the performance indexes. A prototype has been designed, manufactured, and measured with good performance results: a bandwidth higher than 10% around 2.4 GHz, a radiation efficiency higher than 96%, a 9.63 dBi gain, and a wide beamwidth. The main advantages of this prototype, together with its good performance indexes, include its low fabrication cost, low losses, light weight, robustness, high integration capability, the complete removal of the dielectric material, and the use of a single post for feeding the patch while simultaneously fixing its floating position.

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 $H$ -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 $S_{21}$ and $S_{31}$ parameters are $-$ 3.98 and $-$ 3.78 dB, respectively.

This paper presents a novel dielectricless floating patch antenna structure fed with an empty substrate integrated waveguide (ESIW). The main premise is to eliminate the dielectric from the patch design, which is equivalent to have an air-dielectric and leads to the necessity of a proper 3D printed plastic support to fasten the patch in the air above the ESIW, which is used as the feeding waveguide through a slot under the aperture-coupled approximation. A single-element antenna prototype has been studied, designed, optimized and manufactured in order to achieve excellent bandwidth, directivity, gain and beamwidth performance at 28 GHz. The main advantages of this prototype are a low fabrication cost, low losses, a low profile, high integration capability and removal of bulky dielectric material. On the whole, this prototype is a new suitable solution to be used in millimeter-wave 5G applications and beyond compared to the state-of-the-art.

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.

High-directivity and low-loss directional couplers, based on Empty Substrate Integrated Coaxial Line (ESICL) technology, are presented in this article. The proposed coupled line direcional couplers, are based on combination of a high-isolation section, a tapering transition based on splines between the access lines and high-isolation sections, reduced-width coupled lines, and inclined arms. The design evolution has justified the combination and precise adjustment of these elements, proving to be a solution for enhancing directivity, reducing return losses, and attaining a more stable coupling coefficient. The use of the ESICL technology exhibits significant promise in terms of electrical performance, bandwidth, seamless integration with other planar circuits, and manufacturing simplicity. For comparison purposes, two directional couplers, with the same coupling coefficient but different operation frequencies, have been designed and manufactured. Additionally, a microstrip coupler has been designed and manufactured for comparison. The simulated and measured results clearly indicate that ESICL directional couplers outperform their microstrip counterparts in terms of losses and directivity, without the need for additional lumped elements or complex geometries.