## 3 Experimental Results and Discussion
In the next wafers of the same fabrication batch, still to be finalized, the issue of vias opening was correctly performed and we expect significantly lower values of contact resistance and, in turn, reduced losses. To provide an experimental indication of the low-losses typically achieved by the RF-MEMS technology employed for implementing the phase shifters here reported, it can be helpful  
Figure 8: Measured versus simulated S-parameters characteristics of the longitudinal ohmic switch reported in Figures 2b and 3b with reference to (**a**) reflection (S11) in the OFF state; (**b**) isolation (S21) in the OFF state; (**c**) reflection (S11) in the ON state; (**d**) transmission (S21) in the ON state. referring to [8; 19]. In such works, RF-MEMS series ohmic switches with through-oxide vias properly opened and cleaned showed measured values of the S21 parameter better than \(-1\) dB up to 50 GHz when conducting (ON state) and, more importantly, better than \(-0.3\) dB up to 30 GHz. Of course, the employment of switching units with the increased losses just reported affects negatively the RF characteristics of the phase shifters. In this respect, one should bear in mind that, regardless of the particular configuration of 4 bits, the RF signal has to travel through eight ON switches. Therefore, the S11 and S21 simulated characteristics previously shown in Figure 4a,b and Figure 5a,b cannot be met by the physical samples, as it is going to be discussed in the following. To conclude the discussion on the testing of standalone switches, it must be reported that the DC characterization of the pull-in behavior of the physical samples showed a satisfactory agreement with the actuation voltages previously discussed in Tables 1 and 2. This consideration applies to all the tested replicas of the transversal and longitudinal RF-MEMS micro-relays, which showed variations of the pull-in voltage always in the range of a few percent with respect to simulations. Further details are not provided for the sake of brevity, leaving proper room to the upcoming RF characterization of the phase shifters. The 4-bit phase shifters, regardless of the operating frequency band, have four actuation pads for each reference line, four pads for the respective four different phase delays and a single ground pad (labeled as GND). A layout top-view of both devices is provided in Figure 9.  
The reference phase pads are labeled as S\({}_{0}\) and placed at the top of the scheme. The pads named \(S_{22.5}\), \(S_{45}\), S\({}_{90}\), and \(S_{180}\) route the DC signal to the branches realizing the corresponding phase delays. The K and Ka bands RF-MEMS phase shifters have a silicon chip footprint of 10.5 mm \(\times\) 7.5 mm and 7.5 mm \(\times\) 8.5 mm, respectively. The desired bits combinations are obtained imposing a 45 V DC signal to the corresponding pads (i.e., above pull-in) and 0 V to the ground pad. For the sake of clarity, in the following, we show measurements for just a few bits combinations, namely 0, 45, 67.5, 90, and 180 degrees of phase shift. We measured the reflection (S11), insertion loss (S21), and phase delay in a 2 GHz frequency range for the K and Ka band operating frequencies, taking into account the diversity of the two proposed design concepts. The S-parameters measurements are reported in the following Figures 10 and 11, for the K and Ka band phase shifters, respectively. Figure 9: Top-view layout topology of the (**a**) K band (19.5 GHz center frequency) and of the (**b**) Ka band (29.3 GHz center frequency) RF-MEMS phase shifters design concepts. The measured reflection of the observed configurations ranges between \(-15\) and \(-25\) dB at the center frequency (see Figure 10a), while the simulated values are comprised between \(-25\) dB and \(-43\) dB (see Figure 4a). More relevantly, the measured transmission is between \(-6.8\) and \(-8.6\) dB at the center frequency (see Figure 10b), while the simulations show an S21 between \(-1.4\) and \(-1.8\) dB (see Figure 4b).