# Upgrading of the L-P Band Cryogenic Receiver of the Sardinia Radio Telescope: A Feasibility Study
## 3 Study of the Receiver Criticalities and Workflow for the Upgrading Feasibility Study
### Mitigation of the RFIs Derived from the Surrounding Area  
In recent years, as technology advances, the generation of radio frequency and microwave signals has grown exponentially. All this involves a continuous evolution of the RFI scenario, which represents a very relevant issue for radio telescopes. In fact, the periodic monitoring, and the resulting knowledge of unwanted man-made RFI signals, represents a crucial operation for preventing to mask weak cosmic signals detected by the telescopes involved in radio astronomy research activities. Certain radio observatories design and develop ad hoc hardware fully dedicated to RFIs detection [45]; some others prefer to dedicate a low percentage of the observing time with the aim to accomplish the activities of RFIs monitoring. This option has the benefit of taking advantage of the telescope's high sensitivity to identify the RFIs, but at the cost of taking time to conduct the astronomical research. In the case of our radio observatory, other than using SRT for activities of RFIs detection, two ad hoc systems are available:  
* One of the Vivaldi antennas of the new Sardinia Aperture Array Demonstrator (SAD) telescope, with its dedicated signal acquisition chain [45; 46], is shown in Figure 6. This system is located close to the SRT area and it is designed to cover the frequency range 50-500 MHz, with an antenna gain of about 8 dBi. It represents a useful fixed station, operating automatically and remotely in order to guarantee continuous data acquisition 24 h per day, and 7 days per week. In this way, it is possible to map the RFI scenario around SRT, detecting both continuous and impulsive signals. Further details of the system are described in [45; 46]. * The RFI mobile laboratory, depicted in Figure 7, that was designed with the aim to have a very high sensitivity and a large linear dynamic range, without neglecting to limit the generation of self-produced RFIs [47]. The system is equipped with an aluminum retractable telescopic mast that can lift one antenna and can be rotated in azimuth electronically or manually. The whole RF receiving system works up to 18 GHz and its front-end was accurately characterized by using microwave instruments with high performances. Further details are reported in [47]. As concerns the P- and L-bands, the RFI mobile laboratory is equipped with a P-band log-periodic dipole antenna (LPDA) that covers, with a gain of about 12 dBi, the frequency range 0.29-0.45 GHz, and a L/S-band LPDA with a gain of about 11 dBi between 1.2 and 3.3 GHz [47]. This system, being a mobile station, is useful for surveys aimed at verifying the RFIs distribution in the neighborhood of the telescope, with the possibility to choose different locations such as a realistic and more pessimistic view of the expected spectrum receivable by SRT. When the L-P band receiver was installed on SRT, there was a RFIs situation less critical than now. In fact, the uptake of broadband telecommunications networks (both civilian and  
Figure 6: Schematic of the RFI monitoring system based on one of the Vivaldi antennas of the Sardinia Aperture Array Demonstrator (SAD) [45; 46]. Figure 7: The RFI mobile laboratory [47]. military) and third, fourth and five generations cellular phones have led to an increase in the RFIs in the P and L frequency bands. Despite the recurring RFI measurement campaigns performed with the aim to update the RFI maps around the telescope, a new detailed campaign is necessary to determine if there is the necessity to install new microwave filters, for latest RFIs rejection, on the upgraded receiver. These filters are to be engineered to cut all main RFIs with levels of amplitude too high and guarantee a more or less cleaned band of observation. The new RFI campaign is conducted using the RFI monitoring system based on SAD, for the P-band, and SRT, for both P- and L-bands. Using two different systems, it is possible to compare several data with the goal to identify the vast majority of undesired signals present in receiver bandwidth.