The dual-band LP feed system for the Sardinia Radio Telescope prime focus

Abstract

We present the design of the passive feed system of the dual-band receiver for the prime focus of the Sardinia Radio Telescope (SRT), a new 64 m diameter radio telescope which is being built in Sardinia, Italy. The feed system operates simultaneously in P-band (305-410 MHz) and L-band (1300-1800 MHz). The room temperature illuminators are arranged in coaxial configuration with an inner circular waveguide for L-band (diameter of 19 cm) and an outer coaxial waveguide for P-band (diameter of 65 cm). Choke flanges are used outside the coaxial section to improve the crosspolarization performance and the back scattering of the P-band feed. The geometry was optimized for compactness and high antenna efficiency in both bands using commercial electromagnetic simulators. Four probes arranged in symmetrical configuration are used in both the P and the L-band feeds to extract dual-linearly polarized signals and to combine them, through phased-matched coaxial cables, into 180 deg hybrid couplers. A vacuum vessel encloses the two P-band hybrids and the two L-band hybrids which are cooled, respectively at 15 K and 77 K. For the P-Band, four low loss coaxial feedthroughs are used to cross the vacuum vessel, while for the L-Band a very low loss large window is employed. The P-band hybrids are based on a microstrip rat-race design with fractal geometry. The L-band hybrids are based on an innovative double-ridged waveguide design that also integrates a band-pass filter for Radio Frequency Interference (RFI) mitigation.

An infrastructure for multi back-end observations with the Sardinia Radio Telescope

“…Two channels (CH3, CH4) are dedicated to the L-band, the other ones (CH1, CH2) to the P, C or K-band. Figure 5 shows a block diagram of the system: Taking advantage of the dual-frequency L-P receiver [9] and with the exception of XARCOS, up to four IFs may be processed by all other back-ends. The first two channels (CH1, CH2) are merely amplified through a Mini Circuits ZKL-2R5+, split using a Mini Circuits ZFSC-2-372-S+ and then sent to the three back-ends.…”

Space Debris Detection in Low Earth Orbit with the Sardinia Radio Telescope

“…In full operational mode, the SRT is able to host up to 20 remotely controllable receivers and to observe the sky with high efficiency in the frequency range between 0.3-116 GHz [13]. In order to observe the signal sent from FTS and scattered by the debris, the coaxial dual-feed L-P band (0.305-0.410 GHz, 1.3-1.8 GHz) cryogenic receiver of SRT has been used ( Figure 1) [14][15][16][17]. The features of the transmitter and receiver antennas at 410 MHz are reported in Table 1.…”

Superconducting filter for radio astronomy using interdigitated, capacitively loaded spirals

“…The telescope operates with high efficiency in the 0.3-116 GHz frequency range. The microwave filters will be installed in the low frequency chain of the coaxial dual-polarization dual-frequency cryogenic receiver for P-band (305-410 MHz) and L-band (1.3-1.8 GHz) designed for the primary focus of the SRT [12]. The main feature of this receiver is the ability to measure the variable effects of the interstellar medium in the line-of-sight between the source and receiver.…”