# K/Ka-Band Very High Data-Rate Receivers: A Viable Solution for Future Moon Exploration Missions
## 5 Results
(**a**) Ka-band front-end breadboard operating from 27.5 to 30 GHz, (**b**) SDR and custom FPGA define both-based modem board. The 3.7 GHz IF signal is obtained by a sub-harmonically pumped mixer. The half-frequency LO is in the range between 11.90 to 13.15 GHz and it is generated by a PLL synthesizer. IF output is about \(-128.9\,\mathrm{dBm}/\mathrm{Hz}\) (see marker) and is clearly shaped by the 300 MHz bandwidth of the image reject filter (i.e., the rectangular waveguide filter mounted on the breadboard prototype). The IF spectrum of Figure 8b, instead, corresponds to a \(-60\,\mathrm{dBm}\), \(28.65\,\mathrm{GHz}\) CW signal at the input. The delivered IF power is \(-19.6\,\mathrm{dBm}\) (see marker), thus resulting in a transducer power gain of 40.4 dB. As a consequence, the input spectral noise density can be estimated as: \(-128.9-40.4=-169.3\,\mathrm{dBm}/\mathrm{Hz}\) which, for a 50 MHz signal bandwidth, gives a receiver noise floor of about \(-96\,\mathrm{dBm}\), in agreement with the previous system analysis. A more accurate characterization of the receiver noise performance requires the measurement of its noise figure. This was done exploiting the Y-factor method, as described in [32; 33]. The N9918A Field-Fox from Keysight (in spectrum analyzer mode) was used to measure the delivered noise power at the 3.7 GHz IF output. In order to reduce the systematic errors due to the spectrum analyzer noise figure, a 15 dB preamplifier was adopted, setting to \(F_{SA}\approx 22\,\mathrm{dB}\) the overall noise figure of the measurement system. This value was used in the correction of the measured data according to ([32], p. 14). The measurements were carried out with the Y-factor method using a 40 GHz, FSW series, Rodhe & Schwarz spectrum analyzer (equipped with internal pramplifier and noise figure option). The 346C-K01 noise source from Agilent was adopted for the calibration: Its excess noise ratio is \(ENR=11.73\,\mathrm{dB}\) at 28 GHz, whereas the input reflection coefficient is less than \(-16\,\mathrm{dB}\) in the on condition. The measurements are reported in Figure 8c,d for the available power gain and the noise figure versus frequency respectively. The receiver front-end overall noise figure is 3.4 dB whereas the corresponding gain is 40 dB. These values include the coaxial-to-CPW end launcher and the feeding  
Figure 7: Image filter. 29.1 GHz image reject filter implemented in substrate integrated waveguide (SIW) technology: (**a**) layout; (**b**) experiment. The filter is realized on RO4350 material with \(h=0.25\,\mathrm{mm}\), \(\epsilon_{R}=3.48\) and \(\tan\delta=0.004\). The measured insertion loss is of about 3.6 dB including the feeding lines and the two coaxial-to-coplanar waveguide (CPW) end launchers. The return loss is around \(-20\,\mathrm{dB}\) at center frequency. The three measured prototypes show very close frequency responses, testifying the reproducibility of the fabrication process. line insertion losses. With a separate set of measurements (carried out with a vector network analyzer), these have been evaluated at about 1.5 dB. As a result, de-embedding these losses from the receiver noise figure, a final value of about \(F_{RX}\approx 3.4-1.5=1.9\) dB is obtained. It is worth noting here that the 2 dB ripple in the gain response is due to the mismatch between the two LNA stages and the transmission line length between them. The large signal gain of the receiver is depicted in Figure 9 as a function of the available input power at 28.65 GHz. For an input power of \(-100\) dBm the gain is 46 dB, in agreement with that illustrated in Figure 8d. The input-referred 1 dB compression point is \(P_{1 dB}=-37\) dBm, which is suitable for the target moon receiver. As a final test, the constellation in the I/Q plane at the output of the receiver breadboard (Ka-band front-end, SDR and demodulator) is measured for a QPSK signal at 40 Msym/s (see Figure 10). The modulated signal is centered at 28.6495 GHz, has a roll-off factor of 0.25 and a bandwidth of 50 MHz.