A new broad K/Ka-band receiver (18.0–32.3 GHz) for the Yebes Observatory’s 40 meter radio telescope^★

¹ Centro de Desarrollos Tecnológicos, Observatorio de Yebes (IGN), 19141 Yebes, Guadalajara, Spain
² Observatorio Astronómico Nacional (OAN, IGN), Calle Alfonso XII, 3, 28014 Madrid, Spain
³ Departamento de Astrofísica Molecular, Instituto de Física Fundamental (IFF-CSIC), Calle Serrano 121, 28006 Madrid, Spain

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Received: 23 September 2025
Accepted: 19 November 2025

Abstract

Since 2010, the 40 m radio telescope of the Yebes Observatory has been devoted to very long baseline interferometry (VLBI) and single-dish observations. Up until 2019, it covered frequency bands between 2 GHz and 90 GHz in discontinuous and narrow radio windows that met the needs of the European VLBI Network (EVN) and the Global Millimeter VLBI Array (GMVA). The situation changed in 2019 when new receivers were built and installed at the telescope for the Q- (31.5–50 GHz) and W- (72–90.5 GHz) bands in the frame of the Nanocosmos¹ project, a synergy project funded by the European Research Council. The 18.5 GHz instantaneous bandwidth is now fully covered in the two polarisations with 16 fast Fourier transform (FFT) spectrometers of 38 kHz resolution. This has allowed us to achieve an unprecedented level of ultra-sensitivity for line surveys, leading to the discovery of around 95 molecules in space over the last six years. These results have encouraged the construction of a new low-noise cryogenic receiver between 18 GHz and 32.3 GHz for the 40 m radio telescope with orthogonal polarisations (H & V) and 19 kHz of spectral resolution. Due to the frequency resolution requirement and the limited number of FFT boards, the band has been split into two sub-bands for each polarisation: low-band (18–26 GHz) and high-band (26–32.3 GHz), with eight FFT spectrometers of 1 GHz instantaneous bandwidths per sub-band and per polarisation. Alternatively, the receiver can be configured to analyze the full receiver band (18–32.3 GHz) in a single polarisation (either H-pol or V-pol). Here, we present the characteristics of the receiver and the first astrophysical results demonstrating its performance. A detailed analysis of the radio frequency interferences (RFIs) generated by satellite down-link communications and its impact on spectroscopic studies of the interstellar and circumstellar media is also provided. In this context, we conclude that the radio astronomy community must continue to strive to protect the still RFI-free K/Ka radio windows from harmful radiocommunication signals.