# Wideband Versatile Receiver for CubeSat Microwave Front-Ends
## 3 Receiver Design, Simulation and Components Characterization  
Designing high-performance CubeSat receivers equipped with double frequency conversion stages for higher spurious rejection was a challenge until a few years ago. This was mainly due to the lack of suitable components, especially for the high-frequency filtering section, which was limited in terms of working bandwidth, rejection level and cost. The first mixer in the receiving chain was specifically designed to up-convert the input signal to a higher frequency, then the second mixer down-converts again the signal to a lower frequency, namely the intermediate frequency (IF). Even though this circuital topology increases the complexity of the receiver and adds a certain number of components, it offers different advantages, e.g., it is beneficial where high spurious rejection is required. Another important point to consider is the presence of the so-called image frequency. This occurs when an additional tone, i.e., additional with respect to the signal of interest, enters the mixer and generates an output at the same IF frequency as the desired one. This makes the detection of the main signal very challenging. This issue can be mitigated by filtering the signal at the input of the chain, but considering wide input bandwidths, such as the 16 GHz bandwidth of the present contribution, it might be nearly impossible to find a suitable variable microwave filter that can be placed at the input of the chain. By introducing a first up-conversion stage, it is possible to increase the frequency separation between the signal of interest and the other frequency components, thus facilitating the task of filtering unwanted tones. The block diagram of the proposed receiver, designed within the Cadence AWR Microwave Office design environment, is reported in Figure 1.  
Every component was accurately simulated and tested. Indeed, the components' losses, if not adequately compensated by means of amplification stages, might underdrive the LO inputs of the different mixers, thus generating undesired behaviors. On the other hand, the dynamic range of the amplifiers must be taken into account to avoid the compression of their gain. The input signal, after being received by the antenna and amplified, is the MM2-0530 HS mixer by Marki Microwave, Inc., Morgan Hill, CA, USA. This block upconverts the signal up to the frequency of 29 GHz. To make possible the up-conversion of the 2-18 GHz input signal, an LO signal spanning from 27 GHz to 11 GHz was required to exploit the sum frequency components at the output of the mixer. To lower the costs required to generate such a high-frequency signal, a 13.5-5.5 GHz signal was injected in a frequency doubler stage by exploiting the MMD 1030 HS by Marki Microwave, Inc. Multiple multiplication stages could have been employed, but this solution would have been dramatically increased the number of spurious. The proper operation of the frequency doubler was tested by verifying its performance over all the bandwidth. For the sake of brevity, only the output spectrum was measured with an Agilent MXA N9020A spectrum analyzer and by injecting a 5.5. GHz signal at the input of the component is reported. The output spectrum was reported in Figure 2. By taking into account the losses of the employed cables, the overall attenuation of the frequency doubler was measured as equal to 11 dB. Figure 1: Schematic of the proposed microwave receiver. Figure 2: Frequency spectrum at the output of the frequency doubler MMD 1030 HS. The input signal was centered at 5.5 GHz. The first stage mixer requires an LO signal level at least equal to 15 dBm. Considering the doubler conversion loss of around 11 dB, an LO amplifier stage was employed. In detail, the APM-6849 by Marki Microwave, Inc. was chosen for its low-phase noise. The scattering parameters of the amplifier were measured by means of the vector network analyzer ES364A by Agilent Technologies (45 MHz-50 GHz; Figure 3) in order to verify the component performance and tune the system accordingly.