# Highly Integrated Wideband Transmit/Receive Module for X-Band SAR Applications
## 2 TRM Architecture  
The block diagram in Figure 1 illustrates the architecture of each transmit/receive chain of the single TRM within the combined quad-module assembly. The following main functional blocks may be distinguished:  
- Control;  
- Receiver;  
- Transmit;  
- Calibration. The control block is composed of an integrated core-chip. Its main functions are to compensate the module-to-module amplitude and delay dispersion, to compensate the module amplitude and delay variation over temperature, to allow antenna beam shaping by selecting the appropriate insertion amplitude and delay, and to route the RF signal through the appropriate path depending on the selected operative mode. The receiver block is composed of the receive section of an integrated single-chip front-end (SCFE) and a low-level amplifier (LLA). This block has the function to amplify the signal received from the radiating element, while adding a low noise to it and keeping its linearity. The transmitter block is composed of the transmit section of an integrated SCFE and a driver amplifier. This block has the function to amplify the signal to be delivered to the radiating element and be transmitted by it. The calibration block is composed of a directional coupler. The core-chip includes the phase shifting capability implemented using a true delay line (TDL) that is able to add the required time delay or phase shift, with minimum values of 1.56 ps corresponding to 5.625\({}^{\circ}\) at the center frequency (10 GHz). The delay (phase shift) can range from 0 to 100 ps, thus from 0 to 360\({}^{\circ}\) based on a 6-bit command for switching on and off the appropriate amplifier stages placed on each TDL section. The two main modes of operation are the transmit and receives modes highlighted in Figure 1a,b, respectively, by the solid red lines. However, for the purpose of module calibration, both paths need to be evaluated and appropriately adjusted by varying the signal amplitude and phase; therefore, the corresponding calibration modes should be applied. This is done by defining the transmit calibration mode by measuring the transmitted signal once it is partially (of \(-\)30 dB) diverted toward the calibration port (Cal Port) through the directional coupler, as identified by the dashed green line. The receive calibration mode instead is highlighted in Figure 1b by the green dashed line, since a known reference signal is injected into the receive path by the Cal Port through the directional coupler. The T/R module housing was manufactured using ISP (integral substrate package) technology. This means that the substrate hosting the T/R module circuits acts as part of  
Figure 1: Identification of the paths of the electrical signals for the (**a**) TX mode of operation and (**b**) RX mode of operation. The corresponding calibration modes of operation involve also the directional coupler and the calibration port (Cal Port). the housing as well. Each housing hosts four T/R modules, this allows for the shrinking of the overall dimensions and thus compliance with the radiating elements pitch required by operations up to 12 GHz. Indeed, grouping the T/R modules allows for the avoidance of double walls and gaps between them. The selected disposition with the connectors toward the radiating element at the module periphery allows for TRM fixation points at the corners (thus assuring a good thermal and mechanical contact of the whole module) and ensures the proper fixation point to the radiating board. In addition, this leads to the simplification of the product structure (allowing for a single cover/frame) and enables future development with multichannel core-chips. The housing is illustrated in Figure 2.  
The complete packaging solution is composed of:  
* A molybdenum carrier, which acts as a heat spreader due to its high thermal conductivity;
* A LTCC (low-temperature co-fired ceramics) multilayer substrate [33], which hosts the T/R module circuits;
* A Kovar ring and a Kovar cover, which enclose the top of the substrate.