Ridge gap waveguide to microstrip line transition with perforated substrate

Summary form only given. The ridge gap waveguides is one of the highly recommended guided structures in high frequency applications. This is due to its ability to carry the signal with low losses. The signal pass through this structure in the form of Quasi TEM mode, which grantee less dispersion compared to other structures working in the same operating band with ridge gap waveguide, like SIW. One of the major drawbacks of the ridge gap waveguide is related to the used excitation technique. It is always difficult in fabrication and in many cases, it is responsible for limiting the possible bandwidth of the structure. One simple and straightforward idea is to connect the ridge gap waveguide to one of the standard 50Ω lines, such as Microstriop lines or Coplaner waveguides. This work is focused on the Microstrip line case. It is required that the ridge waveguide is directly connected with the 50Ω Microstrip line. The direct connection will have a certain level of mismatch and the reflection increases as the dielectric constant of the microstrip line substrate increases. As a first step of the transition design, a low relative permitivity substrate is chosen. This initially reduces the reflection occurs at the transition. The second step of the transition design is to insert two sections of matching between the microstrip line and the ridge gap waveguide with the help of lower dielectric constants substrates than those used in the microstrip line. The substrates with these lower dielectric constants can be achieved by using the same substrate and apply perforation. Controlling the perforation density will adjust the relative permitivity of the substrate at the required value to achieve matching. Using the previously described technique, the ridge gap waveguide can be attached directly to a 50Ω microstrip line. Connecting the microsrtip line to one of the standard coaxial connectors, like (SMA, 2.4mm, 3.5mm or 1.85mm), is a well-established connection. This provides a very easy procedure for ridge gap waveguide measurements. It is worth to mention that the fabrication process for such a transition is very simple as it is a two dimensions printed structure. To eliminate the radiation of this transition, an extension of the periodic cells is placed in the microstrip line side. Within the microstrip line part, the periodic cells will introduce some sort of packaging to get rid of leakage due to radiation. This extension also provides more smooth transition between the ridge gap waveguide and the microstrip line packaged with similar periodic structure. One important point that should be taken into consideration is that the substrate thickness of the microstrip line must be exactly the same as the gap height in the ridge gap structure.

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