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.

Substrate integrated waveguides (SIWs) are a compromise in terms of performance, cost, and volume between classical planar technologies and high quality three-dimensional waveguides. Empty SIWs (ESIW) reduce the losses by removing the dielectric substrate. In order to increase the usable bandwidth of the ESIW, a ridge layer can be added to the ESIW, thus obtaining the so-called ridge ESIW (RESIW). A transition from microstrip to RESIW has already been presented, but no other passive component has yet been implemented in this new technology. In this letter, we present a novel bandpass filter in RESIW, based on a new U-shaped geometry acting as impedance inverter, that can be easily fabricated with planar circuit manufacturing techniques. A design procedure for this filter is presented. A four-pole Chebyshev filter centered at 15 GHz, with a relative bandwidth of 3%, has been manufactured. The measured values for insertion and return losses are, respectively, lower than 1.05 dB and greater than 18 dB in the whole passband.

The Empty Substrate Integrated Waveguides (ESIW) maintain the advantages of the Substrate Integrated waveguide (SIW) (i.e. low-volume, low profile, lightweight, easy manufacturing, and integration in a planar circuit board), and present lower losses and higher quality factors in resonators due to the propagation of the fields through air, instead of through lossy dielectric as in SIW. The operational (monomode) bandwidth of the ESIW can be increased with the Single Ridge ESIW (SRESIW). However, the bandwidth can be further increased with the Double Ridge ESIW (DRESIW). In this paper, a brief study of possible DRESIW geometries has been performed, and two transitions from microstrip line (MS) to DRESIW with a dielectric taper geometry based on different equations are proposed. The new wideband transitions present simulated return losses in back-to-back configurations greater than 20 dB in more than a 95% fractional bandwidth. The transition that presents a better compromise between return losses, bandwidth and ease of fabrication is manufactured. The measured return and insertion losses are better than 19.7 dB and 1.5 dB, respectively, in a 96.4% fractional bandwidth.

The electrical response of low-frequency band-pass filters based on periodic substrate integrated waveguide (SIW) technology typically shows permitted and forbidden frequency bands. Therefore, this type of filters can be designed using a conceptually very simple and efficient procedure based exclusively on the study of the dispersion properties of the periodic structure. In this paper, we go a step further with the design of a periodically air-filled SIW band-pass filter in which part of the dielectric substrate is removed to reduce insertion losses, and whose unit cell parameters, which are directly related to the center frequency ( $f_{c}$ ) and bandwidth (BW) of the first passband, and also to the first stopband or bandgap (BG) of the structure, have been appropriately selected for filtering purposes, thus providing some useful design rules. Furthermore, we apply the concept of glide symmetry for achieving a much larger fractional bandwidth (FBW) than that obtained in conventional air-filled SIW filters found in the technical literature. Finite implementations of both periodic structures with and without glide symmetry have been analyzed, showing their filtering response for validation purposes. Additionally, to overcome the matching level restrictions in the resulting air-filled periodic SIWs, a microstrip-to-SIW transition including a novel coupling iris is proposed. A prototype of the proposed air-filled glide-symmetric periodic SIW filter has been manufactured and experimentally validated, illustrating the potential of this technique to obtain large FBWs that can not be achieved in conventional air-filled SIW filters. The proposed filter proves to be a good candidate for millimeter wave applications.

Manufacture of hybrid 3D-planar circuits, especially those incorporating empty waveguides on substrates, can benefit from most standardized planar fabrication processes, although they are not exactly the same. For this reason, planar circuit manufacturing methods must be adapted to the requirements of these new circuits. Through numerous fabrications and successful designs, several enhancing strategies have been established to improve all the manufacturing phases to achieve better results. They all have been proved in the following substrate-integrated technologies for the manufacturing of microwave devices: ESIW, ESICL, continuous profile, and microstrip. Thanks to these improvements, good-quality prototypes such as transitions, filters, circulators, couplers, antennas, among others, have been fabricated. Throughout the next chapter, these strategies applied along the manufacturing process will be explained: from the first manufacturing phase to the final welding of the whole circuit and taking into account external elements such as wires that may be present in these structures. For this purpose, some devices that have been published will be used as examples.

It is well-known that Empty Substrate Integrated Waveguides allow not only the integration of classic waveguides, such as rectangular waveguides, into a printed circuit board maintaining the quality of traditional waveguide devices, but also keeping in these circuits the advantages of planar devices: low cost, high integration and mass production capabilities. Nevertheless, a critical point to consider in the success of manufacturing these devices is the soldering of metal covers that close the structure and create the waveguide. This paper presents a new soldering process that simplifies the former procedures, making it easier and reducing economic and time costs. To validate this new assembling procedure, two prototypes have been manufactured and measured: a back-to-back from microstrip to ESIW, and a Ku-band filter; repeteability of the fabrication process has been proved and high performance results have been obtained.