# Development of Enabling Technologies for Ku-Band Airborne SATCOM Phased-Arrays
## 4 Developed Devices
### Self-Diplexing Radiating Element Design  
The first criticality in the design of Tx/Rx radiators is the capability to separate the transmitted signal from the received one. A typical approach consists in designing a radiating element covering the entire band and then connecting a diplexer or a circulator. However, this configuration has the drawback to increase the overall dimensions and the ohmic losses at the Low Noise Amplifier (LNA) input.  
Figure 4: EIRP vs. elevation angle over the horizon (with and without mask constraint).  
Figure 5: Typical azimuth (**a**) and elevation (**b**) Tx antenna pattern at 14.25 GHz, 30 degrees elevation over the horizon.  
A more efficient solution consists of implementing, for each radiating element, two different ports: One for Tx and one for Rx signal. This type of configuration is called a self-diplexing solution. This approach offers better electrical performance and permits the reduction of the manufacturing complexity.  
The radiating element is realized using two different substrates of RT/Duroid 5880 with 0.508 mm thickness separated by a foam with 1 mm thickness.  
Starting from the ground, the first two metallizations are dedicated to the receive capabilities: The first patch has a diameter of 8.5 mm and it is fed by a UT047 coaxial cable; while the second patch, with a diameter of 10.4 mm, implements the stacked configuration, by the foam spacer, that allows to operate over the large frequency band. The transmit radiating configuration uses a single patch of 7.4 mm diameter and it is fed directly by UT047 coaxial cable taking advantage of the upper receive metallization for the ground. The Figure 6a shows a sketch of the self-diplexing radiating element assembly; while in Figure 6b the 3D model used in full wave analysis is shown.  
The radiating element provides four ports able to operate in dual linear orthogonal polarizations both for transmission and reception.  
A prototype of the radiating element is shown in Figure 7a, while the engineered radiator is shown in Figure 7b. The hexagonal ground makes support functionality and it circumscribes a circle of 22 mm of diameter.  
Return loss at Rx and Tx ports and isolation are reported in Figures 8 and 9, respectively. It is important to note that the isolation between the Rx and Tx ports over the entire Tx band is better than 20 dB.  
The gain for the Rx and Tx radiating elements have been measured vs. frequency. The results are reported in Figure 10a,b. The gain in free space condition is better than 8 dB for the receive ports over the frequency band with VSWR of 2:1; while at transmit ports 7 dB gain are guaranteed.  
Figure 6: Sketch of the self-diplexing radiating element (**a**) and 3D model (**b**).  
Figure 7: Radiating element prototype (**a**) and engineered radiator (**b**).  
In Figure 11, the measured radiation patterns of the radiating element in free space configuration are reported for the extreme frequencies of the operating receive band, while for the transmitting band it shows the central frequency in the same conditions. The reported measured radiation patterns are compared with the simulation analysis results demonstrating an excellent agreement.  
Figure 8: Return loss of the radiating element (simulation and measurements) at Rx ports (**a**) and Tx ports (**b**).  
Figure 10: Measured gain: (**a**) Rx radiating element; (**b**) Tx radiating element.  
Figure 9: Isolations of the radiating element (simulation and measurements): (**a**) at Rx1 vs. Rx2 and Tx1 vs. Tx2; (**b**) Rx ports vs. Tx ports.