# Highly Integrated Wideband Transmit/Receive Module for X-Band SAR Applications
## 4 Experimental Tests  
The design of the RF transitions discussed in Section 3 and the complete assembly of the TRM with the SCFE, the core-chip, and the auxiliary amplifiers (LLA and driver) in Figure 1 led to the manufactured TRM shown in the experimental setup in Figure 12 for testing the fully assembled TRM B, whose output (antenna) power was detected by Port 2 of the VNA through the semirigid coaxial cable connected at the TRM antenna connector. The input power was provided to the TRM B by VNA Port 1 through the input coaxial connector placed under the TRM. The output power is a derived value from the input power set at the Port 1 and the gain (S\({}_{21}\)) measured by the VNA. Due to the expensive SCFE and core-chip devices, only two TRMs were fully assembled, whereas the other two were equipped with coaxial connectors for the verification of the passive interconnects.  
A PCB card was developed in order to correctly route all the DC and digital control signals to the TRM and generate the pulsed voltage to switch the gates of the power amplifiers of the SCFE. The quad-module TRM was mounted on an aluminum carrier for thermal and mechanical requirements and was screwed to the large PCB. All DC signals, properly RF filtered, were routed on the PCB from the TRM DC pads at the bottom of the module to a multipin connector and, from this, with an appropriate wiring, to the power supply. As for DC signals, all digital signals (i.e., clock, data) were routed, through the  
Figure 12: (**a**) Experimental setup of the quad-TRM. (**b**) Schematic overview of the complete setup.  
PCB and a dedicated connector, from the digital pads of the TRM to the parallel port of the controller PC.  
The relevant experimental data that characterize the TRM in transmit mode are the gain and the transmitted power. They are reported in Figure 13 as the function of the input power for the three frequency values toward the limits and in the middle of the band of interest at 8 GHz and 12 GHz and then 10 GHz, respectively. The gain in Figure 13a is quite constant for input power level below \(-25\) dBm, as expected; then, it decreases while getting close to the maximum power that can be provided by the final HPA stage of the SCFE. In fact, the output power \(\mathrm{P_{out}}\) reaches its maximum of 41.5 dBm when the input power \(\mathrm{P_{in}}\) exceeds \(-10\) dBm. The transmitting amplification chain is not expected to work in the linear region, but instead in the compressed region to ensure a more constant gain over frequency. Figure 13c shows the gain as the function of frequency evaluated at the 12 dB compression point (c.p.) after setting the input power  
The receive mode is also experimentally characterized by measuring the input and output return loss and the RX gain. The RX chain works in the linear region due to the very low power expected from the antenna. The S\({}_{11}\) (from the antenna port) and S\({}_{22}\) (from the RXout Port) are shown in Figure 14a, whereas the S\({}_{21}\) (RX gain) is reported in Figure 14b. The noise figure (NF) is the last parameter that requires a careful evaluation, since it greatly impacts the sensitivity of the overall RX chain and thus the level of the minimum detectable signal received by the antenna. The procedure for measuring the NF is described by the following steps:  
* The Spectrum Analyzer Rohde&Schwarz FSW--Signal and Spectrum Analyzer 2 Hz \(-\)50 GHz was set in noise figure mode;
* The noise source HP 346C was connected to the SA to perform the calibration;
* The TRM was placed in the thermal chamber to perform the measurement at a specific temperature;
* The noise source was connected to the antenna connector through a cable with known loss (the loss value was used to de-embed the noise contribution of the cable loss), whereas the RX output connector from the TRM was connected to the SA;
* The NF was measured using the SA.  
Figure 14: _Cont._  
The NF is within the required limits within the band of interest.