IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 22, NO. 9, SEPTEMBER 2012 447 Mechanical Tuning of Substrate Integrated Waveguide Resonators Fermín Mira, Jordi Mateu, Senior Member, IEEE, and Carlos Collado, Senior Member, IEEE Abstract—This letter presents a novel approach for providing substrate-integrated waveguide tunable resonators by means of placing an additional metalized via-hole on the waveguide cavity. The via-hole contains an open-loop slot on the top metallic wall. The dimensions, position and orientation of the open-loop slot defines the tuning range. Fabrication of some designs reveals good agreement between simulation and measurements. Additionally, a preliminary prototype which sets the open-loop slot orientation manually is also presented, achieving a continuous tuning range of 8%. Index Terms—Open-loop slot, resonator, substrate-integrated waveguide (SIW), tuning. I. INTRODUCTION T HE development of substrate-integrated waveguide (SIW) technology has opened new perspectives for circuits and systems in the microwave and millimeter-wave frequency range. Based on a synthesized waveguide in a planar dielectric substrate with two rows of metallic vias [1], SIW structures exhibit a number of advantages, including easy fabrication, compact size, low loss, complete shielding and easy integration with active devices [2], [3]. Among the wide class of SIW components proposed in the literature, SIW filters have received particular attention, due to the possibility of achieving higher quality-factor and better selectivity, compared to classical planar filters in microstrip and coplanar-waveguide technology. A considerable amount of research has been conducted on the tuning of SIW resonators. Filters implemented in waveguide technology are tuned by introducing screws. Although the de- sign of SIW and waveguide filters is quite similar, this mechan- ical and easy tuning method is not adequate for SIW technology, due to their physical structure. In addition, mechanical toler- ances are typically higher in SIW technology and also the tol- erances in the dielectric permittivity of substrates introduce ad- ditional perturbation in the electromagnetic response. For this reason, tuning of SIW filters is crucial to compensate manufac- turing and material tolerances. Moreover, this tuning could be Manuscript received June 01, 2012; revised July 05, 2012; accepted July 09, 2012. Date of publication August 01, 2012; date of current version August 30, 2012. This work was supported in part by the Spanish Ministry of Science and Innovation under Grant TEC-2009-13897-C03-01/TCM and MAT2011-29269-C03-02, ENIAC ARTEMOS European Project (EUI2010-04252) and the COST Action IC0803 ‘RF/Microwave Com- munication Subsystems for Emerging Wireless Technologies (RFCSET)’. F. Mira and J. Mateu are with the Centre Tecnològic de Telecomunicacions de Catalunya, Barcelona 08034, Spain (e-mail: fermin.mira@cttc). C. Collado is with the Universitat Politècnica de Catalunya, Barcelona, Spain. Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LMWC.2012.2208735 Fig. 1. SIW cavity with tuning element. applied not only to compensate tolerances but also to change the band in case the tuning range is wide enough. Electrical tunable resonators have been proposed in [4] where a SIW cavity resonator is combined with a surface mounted var- actor with a measured continuous tuning range of 1.2%. In [5], the authors propose the inclusion of PIN diodes to obtain discrete electrical tuning. Discrete mechanical tuning is proposed in [6] by opening or shortcircuiting a capacitive circular slot, with a tuning range of 5%, or by using MEMS [7]. A more complex system is presented in [8] by introducing a cylinder of plasma in the res- onator, with only simulated results. In this letter, we propose a new concept for developing tunable SIW resonators based on the in- clusion of an additional metallized via-hole on the SIW cavity. In Section III of the letter, as illustrative example, we implement this method by means of a mechanical system, where tuning ranges up to 8% have been measured. II. TUNABLE SIW: CONCEPT AND FABRICATION The proposed structure is shown in Fig. 1. It consists of a conventional SIW resonator with an additional via hole inside of the cavity. The via hole is rounded by a circular slot connected to the top layer through a metallic contact placed at the angle . The via hole is located in the middle along the cavity and displaced from the center by . The existence of this via hole deviates the electromagnetic field distribution from the one in a uniform SIW resonator (see Fig. 2) and this variation gives rise to a change on the resonant frequency. The position of the via hole and its orientation define the path of the current and field distribution. In absence of contact with only the slot, the magnetic wall provides an electric field distribution similar to that for an empty cavity [see Fig. 2(a)], whereas with only the via hole in absence of slot, the electric field is compressed and the resonant frequency is highly increased [see Fig. 2(c)]. The inclusion of the metallic contact with angle provides field distributions and resonant frequencies between both the states described previously. For the contact is far from the maximum of the electric field and this case is more similar to the cavity with only the slot (see Fig. 2(b)). On the other hand, for the contact is close to the maximum of the electric 1531-1309/$31.00 © 2012 IEEE