Authors: Prof. Per-Simon Kilda
Source: FERMAT, Volume 11, Communications 4, Sep_Oct, 2015
Introductory Text: • I defined “soft and hard surfaces” in 1988. These were a generalization of the corrugated surfaces. Today we represent them ideally as canonical PEC/PMC strip grids, realized as metasurfaces.
• The simple and conceptual generalization made it easier to see new applications, and these came in terms of inventions. The patented hat antenna with a corrugated “soft” brim has been as a feed in a reflector antenna manufactured in more than 1 million copies for use in radio links.
• The soft surface is anisotropic, but has otherwise the same characteristics as an EBG surface. It stops waves from propagating along the surface. Thus, it is a forerunner of the EBG surface.
• I used the hard surface to make struts invisible in 1988 (i.e. to reduce forward scattering, also referred to as superstealth). The journal article was published in 1996, ten years before the first cloaking paper appeared. Thus, the hard struts was really the first cloaking concept, and they worked in practice over 20% bandwidth, for any polarization of an incident wave with given angle of arrival.
• The soft and hard surfaces have been used in many antenna applications and realized in many ways since 1988. • This conceptual thinking resulted in the definition of gap waveguides in 2009. Gap waveguides are waveguides realized in a narrow air gap between parallel plates, by using a texture in one of the plates. The wave propagation is controlled by designing a stopband for normal parallel-plate modes, and allowing the waves to propagate along ridges, grooves or microstrips. This gives ridge, groove and microstrip gap waveguides.
• The stopband appears ideally those places where one of the surfaces is a PEC and the other a PMC. The gap between a PEC and a PMC cannot support any waves when it is narrower than quarter of the wavelength.
• We have since 2009 researched the gap waveguide to a competitive waveguide technology for wideband millimeterwave applications, including low loss transmission lines, high-Q filters, transitions, resonance-free EM packaging of microstrip and co-planar waveguide circuits and MMICs, distribution networks and directive antennas. The industrial applications are approaching.
• The present slides give an introduction to these concepts.
• Some selected references are given at the end.
• Many more references on gap waveguides can be found in the following book chapter: – A. Uz Zaman, P.-S. Kildal, “Gap Waveguides”, to appear in Handbook of Antenna Technologies, Springer 2016.
• The soft and hard surfaces and gap waveguides are lectured in the course on “Metasurfaces for Antennas” organized by European School of Antennas every third year. The next appearance is 5-9 October 2015 in Zagreb.
View PDFGap Waveguides and PMC packaging: Octave Bandwidth mmand submm-Wave Applications of Soft & Hard Surfaces, EBGs and AMCs