# K/Ka-Band Very High Data-Rate Receivers: A Viable Solution for Future Moon Exploration Missions
## 4 Receiver Architecture  
The block diagram of the K/Ka-band receiver (RX) is illustrated in Figure 3. The receiver exploits a dual conversion superheterodyne architecture [15; 16]. The novelty of the proposed design is related to the adoption, for space applications, of commercial components originally developed for the military and for the automotive markets, i.e., for sectors where miniaturization and low cost are traditionally associated to high reliability levels. The receiver front-end operates a first down-conversion to an IF of 3.7 GHz. It consists of a two stages low noise amplifier (LNA), an image rejection filter (F2), a sub-harmonically pumped (\(\times 2\)) mixer (M1), an IF filter (F3) and a first stage of IF amplification (A1). The half frequency LO is generated by a microwave phased locked loop (PLL) synthesizer, this ensures a low near-carrier phase noise as well as frequency stability and agile channel selection. In the system, a pair of notch filters (F5, F4) are used to get rid of the spurious synthesizer signals and of the mixer feed through. For the K-band the LO frequency varies from 9.425 to 9.725 GHz; for the Ka-band, instead, the LO is in the range between 11.900 to 13.150 GHz. At the front-end input a ferrite isolator and a preselection bandpass filter (F1) ensure a good input matching and an out-of-band interference limitation (including that originated by the downlink transmitter) respectively. Since, in this position, the insertion losses are critical, rectangular waveguide components will be adopted (WR34 for the K-band and WR28 for the Ka-band). For the same reason the image reject filter (F2) is placed after two LNA stages. In this way it is possible to: (i) minimize the RX noise; (ii) reduce the impact of the image filter attenuation on the overall noise figure. The second point is very important, since low cost filter implementations can be adopted. Among several possibilities, the substrate integrated waveguide (SIW) technology was selected as the candidate for preliminary experiments. This is a planar approach that leads to self shielding, compact structures: in such a way the image filter can be directly integrated in the front-end printed circuit board (PCB), with advantages in terms of compactness and reliability. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Time** & **Ground** & **Path Loss** & **Atm. Loss** & **Doppler** & \(T_{a}\) & \(C/N\) & \(E_{b}/N_{0}\) \\
**(UTC)** & **Stations** & **(dB)** & **(dB)** & **(kHz)** & **(K)** & **(dB)** & **(dB)** \\ \hline \multirow{3}{*}{1 January 2025; 10:00} & ESRN & 231.2 & 1.2 & +17.65 & 57.7 & 18.5 & 15.5 \\  & New Norcia & 231.1 & 1.7 & \(-\)21.43 & 75.1 & 17.9 & 14.9 \\  & Guiana S.C. & & & out of visibility & & & \\ \hline \multirow{3}{*}{17 January 2025; 00:00} & ESRN & 231.4 & 0.4 & +7.65 & 21.8 & 19.6 & 16.6 \\  & New Norcia & 231.5 & 11.4 & \(-\)31.36 & 223.5 & 6.3 & 3.3 \\  & Guiana S.C. & 231.5 & 81.7 & +29.77 & 242.7 & \(-\)64.2 & \(-\)67.2 \\ \hline \hline \end{tabular}  
* 10 m dish antenna with 100 W TX power at 22.85 GHz; QPSK modulation with 50 MHz signal bandwidth.  
\end{table} 
Table 3: Results of the Mission Scenario Simulations carried out with Systems Tool Kit (STK). Figure 3: Block diagram. Simplified block diagram of the K/Ka band very-high data rate receiver. In the figure the Low-Noise Amplifier stages are indicated with LNA; F1 is the pre-selection filter; F2 is the image-rejection filter; M1 is the first mixer; VOO is the Voltage Controlled Oscillator that is stabilized by a Phase Locked Loop (PLL). The Reference signal is provided by a Temperature Compensated Crystal Oscillator (TCXO). Radio Frequency (RF) signal, Local Oscillator (LO) signal and Intermediate frequency (IF) signal identify the down-conversion mixer operation. The second frequency conversion occurs within the software defined radio (SDR) connected after the front-end.