**4.1 Single-chip front-end (SCFE)**

As described in Section 2.2, RF TRMs are usually realized by interconnecting several functionalities fabricated on separate MMICs. Such an approach is somehow the result of the inability of a single compound semiconductor technology to properly carry out the main features normally required by an RF TRM. In some applications, such as active electronically scanned array (AESA), this multichip approach could result in a suboptimal overall system. Indeed, the density of the radiating

*UWB Technology - Circuits and Systems*

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**Figure 20.**

**Figure 19.**

**Figure 18.**

*Operational characteristics of a THREE-base harmonic IFM receiver.*

*Functional block diagram of a THREE-base harmonic IFM receiver.*

*UWB frequency measurement circuit simplified schematic.*

**Figure 21.** *Two MMIC compact TRM.*

elements, and thus the performance of the array, is directly related to the physical size of the overall TRM that is adopted behind each elementary radiating element. Thus, the availability of highly integrated front ends with sensible smaller foot print and weight could be very useful for such systems, since it would allow the increase of radiating elements density, leading to the performance maximization.

Recently, with the advance of highly performing and reliable commercial GaN processes, the concept of single-chip front end (SCFE) was investigated as a possible alternative to multichip TRMs.

Essentially, an SCFE is a single MMIC that integrates the three functionalities that are required for a half-duplex TRM, i.e. the HPA, the LNA, and the single-pole double-throw (SPDT) switch. GaN offers remarkable advantages in terms of reliability, robustness, heat dissipation and power handling capability, as compared to GaAs counterparts for this specific application.

The limiter inserted before the LNA, in **Figure 21**, is optional, and depends on the maxim incident power and the LNA's robustness.

**Figure 22** depicts the schematic block diagram and implementation of a recently published SCFE [14].
