Reduction of the impedance dependence on the Suspended-Strip Gap Waveguide

Summary form only given. Gap waveguides have been recently proposed as an alternative to classical waveguides for the high frequency microwave regime. The use of a periodic bed of nails leads to obtain a guiding structure which do not require contact between metallic walls and do not need the use of dielectrics. Consequently, better results in the manufacturing process and lower losses are obtained. Among gap waveguides, the Suspended-Strip Gap Waveguide (SSGW), shown in Fig. 1a) and 1b), seems to be an interesting option for the prototyping stage, since the same periodic structure can be used for several printed circuits.To the date, designs have been focused to maximize the stopband (SB) of the periodic structure. This implies a period comparable to the strip width. Therefore, the structure will change depending on the strip position and orientation and, hence, the impedance of the transmission line will also have this dependence. As an example, the design presented in (Carlos Gahete Arias et. al, IEEE Microwave and Wirelesss Components Letters, 23, 6, 2013) presents a SB=23GHz-49GHz, Fig. 1c), which covers the operating band (28GHz-40GHz). This structure presents a variation of 7-10 at all frequencies when the strip is horizontally shifted, Fig. 1d), what complicates noticeably the circuit design. In this work, it is proposed the use of a dense periodic structure which results more homogenous. By using optimized p, wp and hp, it is obtained a stopband only slightly lower than previous, SB=25,8GHz-44,5GHz, see Fig. 1e), but now with much lower impedance dependence on position (lower than 2), and also on frequency, Fig. 1f). Moreover, losses remain almost unchanged since the distance ha has been maintained.