# Development of Enabling Technologies for Ku-Band Airborne SATCOM Phased-Arrays
## 4 Developed Devices
### Digital Vector Modulator (DVM)  
A DVM in Ku band to control in amplitude and phase the radiating elements has been designed, manufactured and tested. It consists of a MMIC (Monolithic Microwave Integrated Circuit) in GaAs (Gallium Arsenide) technology integrating a 5-bit attenuator (ATT), a 5-bit phase shifter (PS) and a serial to parallel converter (S2P), as reported in Figure 15.  
The DVM development allows to realize T/R Modules in Ku band with mechanical dimensions and interconnections reduced with respect to that available on the market, i.e., separated digital attenuator and phase shifter (Figure 16).  
To realize a S2P on GaAs technology the E-mode and the D-mode transistors should be realized on the same wafer. To do this, the TQPED (MMIC technological process) process has been selected. A 10 bit S2P has been customized by TriQuint in line with Airbus Italy requirements summarized in Table 3.  
Each attenuator and phase shifter cell have been designed separately. The position of the cells in the MMIC chain has been properly chosen considering the RF performances and the layout arrangement.  
Figure 16: Rx module with (left) and without (right) DVM.  
\begin{table}
\begin{tabular}{l l} \hline \hline
**ITEM** & **Value** \\ \hline Phase Shifter Cells & 180\({}^{\circ}\), 90\({}^{\circ}\), 45\({}^{\circ}\), 22.5\({}^{\circ}\), 11.25\({}^{\circ}\) \\ Attenuator Cells & 0.75, 1.5, 3, 6, 12 dB \\ Rx Band & 10.7 \(\div\) 12.75 GHz \\ Tx Band & 14 \(\div\) 14.5 GHz \\ Command Line & Clock, Data, LE \\ Bias & +5; \(-\)5 V \\ Power Consumption & \(<\) 350 mW \\ I/O Return Losses & \(>\)12 dB \\ \hline \hline \end{tabular}
\end{table}
Table 3: Basic characteristics of the DVM.  
Figure 15: GaAs digital vector modulator (DVM) MMIC.  
The DVM MMIC and the stand alone main block have been manufactured on a 5 by 10 mm\({}^{2}\) tile in a multi project wafer (MPW). The manufactured MMIC has been mounted on an aluminum carrier and tested by means of a probe station. The pictures of the DVM under microscope is reported in Figure 17.  
The RF measurements are hereafter provided: Relative amplitude and phase variations (Figure 18), measured insertion loss with only phase shifter variation and phase error due to the attenuation states (Figure 19), return loss port 1 and return loss port 2 (Figure 20).  
Figure 17: picture under microscope of the manufactured DVM.  
Figure 18: DVM chip performance: (**a**) measured relative attenuation with 1 dB step; (**b**) measured relative phase with 11.25 degrees step.  
The performances of the 11.25\({}^{\circ}\), 90\({}^{\circ}\) and 180\({}^{\circ}\) phase shifter cells in the DVM MMIC were very good in terms of relative phase shift: An average error of 1\({}^{\circ}\) has been measured. Vice versa, the measurement of the 22.5\({}^{\circ}\) and 45\({}^{\circ}\) cells shows a phase shift higher than the target value (8\({}^{\circ}\) and 4\({}^{\circ}\), respectively). It has to be highlighted that the phase errors of the 22.5\({}^{\circ}\) and 45\({}^{\circ}\) cells in the stand alone main blocks is the half respect the same cells inside the DVM MMIC.  
The performance of the attenuator cells agree with the expected ones, except for the phase stability vs. gain variation in Tx band which presented an undesired phase shift for attenuation higher than 17.25 dB. However, such deviation for the specific parameter is generally also present in commercial devices and is not considered significant for the specific project.  
The insertion loss of the reference state was about 11.2 dB and flat in band. Considering the combination of the two COTS (Commercial of-the-shelf) component employed in the antenna demonstrator we experienced an overall insertion loss of 13 dB. Taking into account the inductive effect of the wire bonding interconnections, the return losses of both ports are below 10 dB.  
Finally, the power consumption of the S2P, designed by TriQuint, was 250 mW. This could be drastically reduced (up to 120 mW) with the implementation of some identified technical solutions.