Abstract
A design method of large-sized square-loop and circular-loop frequency selective surface (FSS) filters for protection of mm-wave imagining receivers is presented. Due to fine cell structure requirements, the performance of the FSS structures at mm-wave frequencies can be significantly affected by fabrication tolerances, especially involved with large-size panel fabrication. Through a comprehensive parametric variation study on the performance of square-loop and circular-loop FSS structures, it is found that the circular-loop FSS structure performs much less sensitively to the fabrication tolerances, thereby producing better and consistent performances with given design values. As a design example, square-loop and circular-loop notch filters resonating at 105 GHz were designed and the performances were evaluated with multiple prototypes. The resonant frequencies of the implemented circular-loop FSS filters deviated by only about 0.5 GHz from the accurate designed value, which can be easily adjusted in the design process. The implemented square-loop and circular loop FSS filters provided low-loss in the pass-band and high rejection of 23 dB at the resonant frequency with good oblique angle performance.
Highlights
A frequency selective surface (FSS) consists of an array of identical metallic structures arranged as a single or multi-dimensional periodic surface
The periodic structures have extensively been used in series of microwave, millimeter-wave and terahertz (THz) applications such as band-stop filters, dichroic reflectors and circuit absorbers [1]
These electric charge densities are accumulated at the horizontal (x-direction) strips of the loops, creating the capacitive part “C.” Whereas, the magnetic field is induced around the vertical (y-direction) strips of the loops due to the flow of electric current that forms of an inductive part “L” in the equivalent circuit model (ECM)
Summary
A frequency selective surface (FSS) consists of an array of identical metallic structures arranged as a single or multi-dimensional periodic surface. With small-sized FSS structures [27,28,29], high-precision fabrication technique can be applied without difficulty, but, as the size of the FSS panel becomes bigger, significant increase in fabrication cost can occur In this regard, recently, our group has developed and reported a low-cost fabrication technique for large-size FSSs (~19.7 × 6.3 inches at 170 GHz) with high performance at mm-wave range to protect the mm-wave ECEI receiver [6]. A comprehensive comparative parametric analysis including the effect of fabrication tolerances on the performance for square- and circular-loop FSS structures at the millimeter-wave frequency range is presented. To the best of authors’ knowledge, the configurations of circular-loop FSSs have not been yet employed previously in the mm-wave imaging systems
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