Table 4. a detailed quantitative comparison for all of the mentioned tunable filters. Tuning Technique Based on Reference Filters Method II Method III Method IV Method VI fc (GHz) FTR BW Qu [40] 1.73 25% 2.3-3% 221-255 [41] 1.4 28% 3.7% 93-132 [46] 2.76 8.69% 2.8% - [60] 4.2 9.52% 1.5-2% - [53] + 12.8 10% [61] 10.875 7.81% - (simulation only) - [47] 0.9 84-206 66% Fixed BW of + 160 + 4.4% or tunable BW of 3-5% 4% each SIW cavity with perturbing via posts. A tuning range of 1.2-2.6 GHz is covered using 14 different tuning responses (states) with a very fine frequency resolution so as to behave such as a continuoustype filter. The insertion loss of the filter over this tuning range is below 4 dB. The magnitude of electric field distribution and resonance contour figures for the SIW cavity resonator are used to design a tunable filter with the highest tunability range possible. Packaged MEMS switches from Omron are used as the switching elements and are directly mounted on the biasing circuit layer of the filter. As a result, the parasitic effects are minimized. The quality factor of the filter varies from 93 to 132 over the tuning range. The stopband rejection performance is improved using two low-pass filters at the input/output ports of the filter. Figure 10(b) and (c) shows the measured S-parameter results for the presented RFMEMS tunable filter. Tunable SIW Bandpass Filters with p-i-n Diodes Armendariz et al. [40] presented a tunable SIW filter implemented using p-i-n diode switching elements. The perturbing via post method used in [41] is also used here. The biasing network and the SIW filter are completely separated using a two-layer structure. The performance characteristics of this filter are discussed in detail in [49] and are not repeated in this article. (a) 0 -5 Floating Patch Diode-Loaded Filters (Based on Method III) S21-Parameters (dB) -10 -15 Analog Tuning of Compact Varactor-Loaded Combline Filters in SIWs -20 -25 -30 -35 -40 4 4.5 5 5.5 6 6.5 7 7.5 Frequency (GHz) 8 8.5 9 (b) Figure 11. (a) The fabricated prototype of the varactor-loaded two-pole tunable filter and (b) the measured results at different states of 00, 01(10), and 11 [60]. 50 Sirci et al. [46] developed a two-pole tunable SIW coupled resonator filter. This filter is used as a demonstration of the tuning technique shown in Figure 1(c). Then, the application of this tuning method to the fine-tuning of the narrowband multipole filters in the postfabrication process is studied. The method enables fine-tuning of the center frequency without introducing degradation of the in-band performance. The filter in [60] also uses the same method. To initially evaluate the tuning concept, the authors fabricated a simple 2-bit tuned two-pole Chebyshev filter at June 2015