Regular paper Novel half-mode substrate integrated waveguide bandpass filters using semi-hexagonal resonators Tahsin Khorand, Mohammad Sajjad Bayati ⇑ Department of Electrical Engineering, Razi University, Kermanshah, Iran article info Article history: Received 14 May 2018 Accepted 6 August 2018 Keywords: Bandpass filter Half mode substrate integrated Waveguide (HMSIW) abstract In this paper, a novel bandpass filter is presented, designed, and implemented by using a triple mode semi-hexagonal Half-Mode Substrate Integrated Waveguide (HMSIW) cavity, which has the advantages of compact size, low insertion loss, and high selectivity in upper and lower passband. To realize a triple mode filter, the first resonant mode is shifted to near the next two modes using a via hole perturbation. Two microstrip open stubs connected to open edge of HMSIW resonator are introduced to generate two transmission zeros in the lower passband. The position of transmission zeros could be controlled by adjusting the coupling gap between the microstrip open stub resonators. By etching an E-shape slot on the top plate of HMSIW resonator, two other transmission zeros are produced in the upper passband. A wide-band planar six-pole bandpass filter, which has the advantages of wide bandwidth and small size, is also proposed and fabricated by cascading two triple mode resonators. Measured results indicate that 29% and 47% fractional bandwidth, as well as approximately 1 dB and 1.1 dB insertion loss, are achieved for the proposed filters. Measured results of all those filters agree well with the simulated results. Ó 2018 Elsevier GmbH. All rights reserved. 1. Introduction Recently, planar microwave filters owning to their wide appli- cations have been developed as the key components of modern communication circuits such as wireless and RF/microwave cir- cuits. Multimode resonators have been widely utilized in the filter design process due to their capabilities in reducing the number of resonating elements, inherent size reduction, and improving per- formance in filter response’s selectivity. Triple mode filter is one kind of the multimode filters, having three resonances in one res- onator. One of the resonances is considered as a central frequency and the other two modes are located in close to edges of the pass- band. Several types of triple mode filters based on different struc- tures such as cylindrical and rectangular waveguide technology [1,2], microstrip structures [3,4], and planar structures with multi-layer resonators [5] have been proposed in the literature. Cavity waveguides, as well as multi-layer resonators, are bulky and complicated to fabricate and integrate with planar structures. Although planar structures could be integrated with planar cir- cuits, they have higher conductor loss and lower power capability. Substrate integrated waveguides (SIW) structure is considered as appropriate replacement for implementing microwave and millimeter components due to having the advantages of conven- tional metallic waveguides including, high quality factor, low insertion loss, low cost, easy fabrication process, ease of integration with planar structure [6–8]. Recently, HMSIW as a new structure has been proposed in which the size and the dominant mode are half of SIW [9–11]. The principal idea in HMSIW is that the sym- metric plane of SIW along the propagation direction is equivalent to a magnetic wall. Hence, HMSIW is obtained through bisecting SIW on the magnetic wall while the half field distribution is kept unchanged. Many filters based on SIW techniques with various res- onators such as split ring resonators (SRR) [12], stepped- impedance resonator (SIR) [13], compact microstrip resonator cell (CMRC) [14] and defected ground structure (DGS) [15], have been reported. These filters have appropriate performances, however, they are characterized with narrow bandwidth and most of their resonators operate in one mode. In [16], a triple mode filter has been designed by placing an additional via at the center of a circu- lar SIW cavity resonator in which its fractional bandwidth (FBW) is 15% in the central frequency of 33.5 GHz. In [17], a wideband filter has been proposed by placing u-shape slots on the top metallic plate of SIW which has the high selectivity in the upper side of the passband and its FBW is equivalent to 42% in the central fre- quency of 8.5 GHz. Furthermore, a triple mode filter has been introduced utilizing isosceles right triangular resonator based on quarter mode substrate integrated waveguide (QMSIW) with an https://doi.org/10.1016/j.aeue.2018.08.009 1434-8411/Ó 2018 Elsevier GmbH. All rights reserved. ⇑ Corresponding author. E-mail address: s.bayati@razi.ac.ir (M.S. Bayati). Int. J. Electron. Commun. (AEÜ) 95 (2018) 52–58 Contents lists available at ScienceDirect International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue