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Electrically tunable evanescent mode half mode substrate integrated waveguide (HMSIW) resonators are implemented for S band applications. An HMSIW loaded with a complementary split ring resonator (CSRR) achieves forward electromagnetic wave transmission below the characteristic waveguide cutoff frequency due to evanescent wave amplification. A variable capacitor connected to one of the conductors of the CSRR changes its effective capacitance to ground, resulting in frequency tuning of the resonator. Three different configurations are investigated with a varactor diode connected between the ground and three different contact points of the CSRR. The external Q factor is slightly affected by the frequency tuning. More than 15% tunability is achieved around 3.4 GHz. Full wave structure simulation results are in good agreement with those of measurement.Index Terms-Complementary split ring resonator (CSRR), half mode substrate integrated waveguide (HMSIW), tunable resonator, varactor diode.

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This work presents a non-invasive, reusable and submersible permittivity sensor that uses a microwave technique for the dielectric characterization of liquid materials. The proposed device consists of a compact split ring resonator excited by two integrated monopole antennas. The sensing principle is based on the notch introduced by the resonators in the transmission coefficient, which is affected due to the introduction of the sensor in a new liquid material. Then, a frequency shift of the notch and the Q-factor of the proposed sensor are related with the changes in the surrounding medium. By means of a particular experimental procedure, commercial liquids are employed to obtain the calibration curve. Thus, a mathematical equation is obtained to extract the dielectric permittivity of liquid materials with unknown dielectric properties. A good match between simulated and experimental results is obtained, as well as a high Q-factor, compact size, good sensitivity and high repeatability for use in sensing applications. Sensors like the one here presented could lead to promising solutions for characterizing materials, particularly in determining material properties and quality in the food industry, bio-sensing and other applications.

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A millimeter-wave bandpass filter (BPF) using complementary split-ring resonator (CSRR) loaded quarter mode substrate integrated waveguide (QMSIW) cavities is presented in this work. The CSRR-Ioaded QMSIW cavity resonates below the original QMSIW resonance frequency, which further reduces the size with respect to its SIW counterpart. The reduced quality factor Q of the cavity makes it useful for BPFs with broad fractional bandwidth (FBW). A micromachined 4thorder Chebyshev BPF is demonstrated at the unlicensed 57 GHz to 64 GHz frequency band. A FBW of more than 11.6% with an in-band return loss of better than 15 dB, and an insertion loss of less than 2.5 dB are obtained.Index Terms -Bandpass filter (BPF), complementary split ring resonator (CSRR), quarter-mode substrate integrated waveguide (QMSIW).