# Multifunction RF Systems for Naval Platforms
## 3 MFRF System Design Considerations
### Practical Limitations and Trade-Offs
#### 3.2.2 Wideband vs. Multiband Operation
Their favourable output power and PAE specifications highlight the benefits of potentially using narrowband HPAs in conjunction with a multiband AESA such as the dual-band array described above. Regarding the digital receiver in the Rx channel of Figure 2, a critical specification is the number of bits of digitization that must be provided by the ADC to meet the highest dynamic range specification of 90 dB in Table 1. While ADC technology is evolving rapidly, ADCs with the roughly 15 bits required are not yet available at the 40 GSPS sampling rates needed to perform direct RF sampling over the full 0.5-40 GHz range of RF function operating frequencies. The current state-of-the-art in commercially available ADCs is represented by the entries in the table below [39]. It is observed that number of digitization bits decreases with increasing sampling rate. The 24-bit digitizer listed is applicable only for narrowband RF functions like naval radar. The ADC models with 14 and 16 bits may be suitable for all RF functions, while the 12-bit device could accommodate the ES function with its lower dynamic range specification of 60 dB. However, none of these ADCs have the bandwidth to allow direct RF sampling, except in the lower end of the operating frequency range. Consequently, an analog tuner would generally need to be included in the digital receiver in front of the ADC to translate the RF signal frequency down to an intermediate frequency that falls within the bandwidth of the ADC. This implies the need to have several AESAs or subarrays within the AESAs that are assigned to different bands which collectively cover the full operating frequency range, assuming that instantaneous coverage of the operating spectrum is an important goal (which would certainly be the case for the ES function). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Device** & **Frequency (GHz)** & **Gain (dB)** & **Output Power (W)** & **PAE (\%)** \\ \hline Analog Devices HMC930A & 0–40 & 13 & 0.25 & 10 \\ Analog Devices & 2–20 & 11 & 7 & 20 \\ HMC1087F10 & & 26 & 40 & 38 \\ Analog Devices HMC8205 & 0.3–6 & 26 & 40 & 38 \\ Qorvo TGA2590 & 6–12 & 35 & 30 & 25 \\ Qorvo TGA2813 & 3.1–3.6 & 22 & 100 & 55 \\ Qorvo TGA2635-CP & 8–11 & 26 & 100 & 35 \\ Qorvo TGA2595 & 27.5–31 & 23 & 9 & 24 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Representative specifications for HPAs [37; 38]. Finally, the DWG in the Tx channel must be able to generate waveforms with instantaneous bandwidths as high as 1 GHz, based on the EA function requirements listed in Table 1. This capability appears currently achievable with commercially available technology. For example, the Analog Devices AD9914 includes both a DDS and a 12-bit DAC on the same board, and supports output waveform bandwidths up to 1.4 GHz [40]. From a performance perspective then, currently available DWG technology appears to pose no significant limitation with regard to use in a naval MFRF system. As a general concluding observation, the discussion in this section points to ADC technology as representing the most severe impediment to wideband MFRF system implementation, given that the most stringent RF function dynamic range requirements can only be met when ADC bandwidths are restricted to 1-3 GHz.