## 3 Experimental Results and Discussion  
In this section, an extensive experimental characterization is reported, both for what concerns the RF-MEMS phase shifters physical samples, as well as for the standalone micro-switches they employ. The mentioned testing comprises the analysis of the RF characteristics and the electromechanical behavior of the available RF-MEMS samples. Figure 5: Simulated reflection (**a**), transmission (**b**), and phase shift (**c**) for several configurations of the Ka band RF-MEMS reconfigurable phase shifter (center frequency at 29.3 GHz). The S-parameters (scattering parameters) are measured using a probe station equipped with Ground-Signal-Ground (GSG) CPW microprobes (250 \(\upmu\)m pitch), a Vector Network Analyzer (VNA) with an operating frequency range from 10 kHz up to 40 GHz and a voltage source. The VNA is calibrated with the SOLT (Short Open Load Thru) method using an on-wafer GSG calibration kit. The discussed phase shifters require actuating four DC signal pads and one ground (GND) pad. Thus, we exploit a setup featuring five DC probes and two RF probes to fully characterize the physical devices. The probes setup is shown in Figure 6.  
In the first place, the attention is concentrated on the standalone RF-MEMS switching unit electromagnetic characteristics. In this regard, the transverse and longitudinal ohmic micro-relays previously discussed in Section 2 and reported in Figures 2 and 3 are measured up to 40 GHz. The following Figures 7 and 8 show the comparison of measured and simulated S-parameters of transverse and longitudinal switches, respectively, in the OFF and ON state. Figure 6: Photograph of the measurement setup featuring both RF and DC microprobes. Figure 7: Measured versus simulated S-parameters characteristics of the transverse ohmic switch reported in Figures 2a and 3a 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. Concerning the isolation (S21) in the OFF state, the simulated traces predict quite accurately the experimental behavior, as visible in Figures 7b and 8b. A more articulated discussion has to be developed for the ON state of both switches as the disagreement between measurements and simulations is relevant. In particular, the measured reflection (S11) is worse than simulations for both switches, as emerged in Figures 7c and 8c, with particular reference to the latter case (longitudinal switch). Relevantly, the losses (S21) of the physical samples are significantly larger than expected, being them worse than simulations of an extent ranging from 0.2-0.3 dB up to 0.8-0.9 dB. In particular, the measured S21 of the transverse switch employed in the K band phase shifter is \(-\)0.8 dB at 19.5 GHz, while the simulated prediction is \(-\)0.1 dB (see Figure 7d). The experimental S21 of the longitudinal switch employed in the Ka band phase shifter is \(-\)1 dB at 29.3 GHz while the simulation predicts a value slightly larger than \(-\)0.1 dB (see Figure 8d). Despite such a rather severe performance drift in terms of larger attenuation, its explanation is straightforward and the solution quite easy as the cause is related to a known technology aspect. The physical samples available at the time of this paper's writing are coming from the first wafer of the RF-MEMS fabrication batch processed in the facility. In such a wafer, which was considered a preliminary test, strict control on the cleaning of through-oxide vias to the aluminum underpass (after their opening) was not performed [16]. This happened for a technical problem and led to larger contact resistance between gold and aluminum, detected when measuring a few test structures for process control. This non-ideality also affects S-parameters leading to the bad performance shown in Figure 7c,d and Figure 8c,d for the switches in the ON state.