This study describes the design and experimental verification of the ridge gap waveguide, appearing in the gap between parallel metal plates. One of the plates has a texture in the form of a wave-guiding metal ridge surrounded by metal posts. The latter posts, referred to as a pin surface or bed of nails, are designed to give a stopband for the normal parallel-plate modes between 10 and 23 GHz. The hardware demonstrator includes two 90 bends and two capacitive coupled coaxial transitions enabling measurements with a vector network analyser (VNA). The measured results verify the large bandwidth and low losses of the quasi-transverse electromagnetic (TEM) mode propagating along the guiding ridge, and that 90 bends can be designed in the same way as for microstrip lines. The demonstrator is designed for use around 15 GHz. Still, the ridge gap waveguide is more advantageous for frequencies above 30 GHz, because it can be realised entirely from metal using milling or moulding, and there are no requirements for conducting joints between the two plates that otherwise is a problem when realising conventional hollow waveguides.

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Design and experimental verification of ridge gap waveguide in bed of nails for parallel-plate mode suppression

Recently it has been shown that so-called gap waveguides can be generated in the gap between parallel metal plates The gap waveguides are formed by metal ridges or strips along which local waves propagate, and parallel plate modes are prohibited from propagating by providing one of the surfaces with a texture that generates an artificial magnetic conductor (AMC) or an electromagnetic bandgap (EBG) surface on both sides of the ridges or strips The bandwidth of the gap waveguide is determined by the cut-off bandwidth of a parallel-plate waveguide where one surface has such a texture (and no ridges or strips) This paper studies the bandwidths (or stop bands) of such parallel-plate cut-offs when the AMC or EBG is realised by a metal pin surface, corrugations or a mushroom surface It is shown that cut-off bandwidths of up to 4:1 are potentially available, and thereby similar bandwidths should be achievable also for gap waveguides

https://publications.lib.chalmers.se/records/fulltext/138299/local_138299.pdf

Numerical studies of bandwidth of parallel-plate cut-off realised by a bed of nails, corrugations and mushroom-type electromagnetic bandgap for use in gap waveguides

This paper presents the basic ideas of how local waveguides and transmission lines can be designed to propagate along desired paths in the air gap between two metal surfaces. The principle of operation is related to the performance of artificial magnetic conductors, EBG surfaces and soft and hard surfaces. Three different major types of gap waveguides are described: ridge gap waveguides, microstrip gap lines and groove gap waveguides. Different realizations of the cut-off structures suppressing normal parallel plate modes are described, as well as expected applications, and possible problem areas preferably seen as research challenges.

Three metamaterial-based gap waveguides between parallel metal plates for mm/submm waves

The suppression of parallel plate and cavity modes in shielded microstrip circuits is presented. To this aim a textured metal lid consisting of periodically located pins known as a bed of nails is employed. The mode suppression has a bandwidth of more than 2:1, and it does not interfere much with the microstrip circuit. Thereby, this mode suppression technique introduces a new advantageous packaging technology for high frequency circuits.

Parallel Plate Cavity Mode Suppression in Microstrip Circuit Packages Using a Lid of Nails

Single-layer, wideband, and low-loss corporate-feed networks for slot antenna arrays are described. The antenna is built using ridge gap waveguide technology, formed between two parallel metal plates without the requirements of electrical contact between these plates. The corporate-feed network is realized by a texture of pins and a guiding ridge in the bottom plate, and the radiating slots are placed in the smooth top plate. The paper describes two test antennas: a 4 $\,\times\,$ 1 linear slot array and a 2 $\,\times\,$ 2 planar slot array. Both have been fabricated and tested at Ku- band. The linear array shows more than 20% bandwidth and the 2 $\,\times\,$ 2 array shows a bandwidth of 21% for 10-dB return loss. There are good agreements between measured and simulated patterns for both antennas. Measured gain for the planar array is found to be at least 12.2 dBi over 12–15 GHz band.

/pdf/wide-band-slot-antenna-arrays-with-single-layer-corporate-405rdmmfz6.pdf

Wide-Band Slot Antenna Arrays With Single-Layer Corporate-Feed Network in Ridge Gap Waveguide Technology

This letter presents a new metamaterial-based waveguide technology referred to as ridge gap waveguides. The main advantages of the ridge gap waveguides compared to hollow waveguides are that they are planar and much cheaper to manufacture, in particular at high frequencies such as for millimeter and sub- millimeter waves. The latter is due to the fact that there are no mechanical joints across which electric currents must float. The gap waveguides have lower losses than microstrip lines, and they are completely shielded by metal so no additional packaging is needed, in contrast to the severe packaging problems associated with microstrip circuits. The gap waveguides are realized in a narrow gap between two parallel metal plates by using a texture or multilayer structure on one of the surfaces. The waves follow metal ridges in the textured surface. All wave propagation in other directions is prohibited (in cutoff) by realizing a high surface impedance (ideally a perfect magnetic conductor) in the textured surface at both sides of all ridges. Thereby, cavity resonances do not appear either within the band of operation. The present letter introduces the gap waveguide and presents some initial simulated results.

E. Alfonso

Papers

Local Metamaterial-Based Waveguides in Gaps Between Parallel Metal Plates