Submitted to the IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES 1 Abstract—This paper presents a novel class of substrate integrated waveguide (SIW) filters, based on periodic perforations of the dielectric layer. The perforations allow to reduce the local effective dielectric permittivity, thus creating waveguide sections below cutoff. This effect is exploited to implement immittance inverters through analytical formulas, providing simple design rules for the direct synthesis of the filters. The proposed solution is demonstrated through the design and testing of several filters with different topologies (including half-mode SIW and folded structures). The comparison with classical iris-type SIW filters demonstrates that the proposed filters exhibit better performance in terms of sensitivity to fabrication inaccuracies and rejection bandwidth, at the cost of a slightly larger size. Index Terms—Filters, resonator filters, substrate integrated waveguide, tolerance analysis. I. INTRODUCTION HE SUBSTRATE INTEGRATED WAVEGUIDE (SIW) technology has been the object of intense and ever- growing research activities in the last decade [1], [2]. The SIW technology combines the complete shielding and fairly low losses, with the simple and cost-effective manufacturing, thus representing the ideal platform for the development of the next generation of wireless systems. Besides the traditional SIW, several novel structures have been proposed, to reduce the size, increase the single-mode bandwidth, and decrease losses. Among them, the folded SIW [3], [4] allows to reduce by half the width of the waveguide (at the cost of a dual-layer manufacturing), the half-mode SIW [5], [6] reduces the width and increases the single-mode bandwidth of a factor two, the slab SIW [7] allows to increase the single-mode bandwidth, the ridge SIW [8], [9] increases the bandwidth and reduces the size (at the cost of a higher Paper submitted 23 December 2016; revised 7 April 2017. This paper is an expanded version from the 2016 IEEE MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization, Beijing, China, July 2016. L. Silvestri, E. Massoni, M. Bozzi, and L. Perregrini are with the University of Pavia, Department of Electrical, Computer and Biomedical Engineering, Pavia, Italy (e-mail: lorenzo.silvestri01@ateneopv.it, enrico.massoni02 @ateneopv.it, maurizio.bozzi@unipv.it, luca.perregrini@unipv.it). C. Tomassoni is with the University of Perugia, Department of Engineering, Perugia, Italy (e-mail: cristiano.tomassoni@unipg.it). A. Coves is with the Dept. de Ingenieria de Comunicaciones, Universidad Miguel Hernandez, Elche, Spain (angela.coves@umh.es). (a) (b) Fig. 1. SIW filter with periodic perforations: (a) Physical geometry of the filter; (b) Equivalent structure based on the homogeneous permittivity of the perforated area. fabrication complexity), and the empty SIW [10] cuts dielectric losses and extends the power handling capabilities (at the cost of a slightly larger size). Similarly, a number of novel SIW filter configurations have been presented to improve filter performance, reduce losses, and minimize the footprint [11]-[13]. Half-mode [14], folded [15], and quarter-mode [16] SIW cavities have been adopted to reduce the filter size, and the substrate integrated coaxial line [17] has been used to obtain wide stopband and compact size. The use of defected ground structures and of extracted poles have been proposed in [18], [19] for improving the out- of-band rejection. Miniature SIW cavities adopting interdigital capacitors [20] have been proposed to reduce filter dimensions. The use of empty surface-mounted waveguide cavities in [21] allows to implement filters with higher quality factor. Recently, the preliminary investigation of a band-pass filter based on a periodically drilled SIW structure has been proposed [22]: perforations in the dielectric substrate (Fig. 1(a)) allow to reduce the local effective permittivity, thus creating waveguide sections below cutoff (Fig. 1(b)). Further developments of this class of filters have been reported in two conference papers [23], [24], adding flexibility to the design and extending this concept to half-mode SIW structures. In this paper, a systematic investigation of the properties of Substrate Integrated Waveguide Filters Based on a Dielectric Layer with Periodic Perforations Lorenzo Silvestri, Student Member, IEEE, Enrico Massoni, Student Member, IEEE, Cristiano Tomassoni, Member, IEEE, Angela Coves, Member, IEEE, Maurizio Bozzi, Senior Member, IEEE, and Luca Perregrini, Fellow, IEEE T