Studying the polarization and spectral distortion of the cosmic microwave background (CMB) in tandem with intensity fluctuations of the cosmic infrared background allows us to verify our assumptions on cosmic inflation and investigate the dynamics and evolution of galaxy clusters in the past 10 billion years. Because of its broadband emission and being an all-sky extended source, observing the entire CMB in detail is a very time-consuming and expensive exercise. Fortunately, in the past few years, the on-chip superconducting spectrometer technology has moved out of the lab and into the telescope. With its compact size and background-limited sensitivity, this family of instruments is particularly well-suited for fast and large area observations in a relatively unexplored range of the electromagnetic spectrum. However, recent examples of this technology do not yet reach the requirements needed for large spectroscopic and polarimetric surveys of the CMB. We formulate several of these requirements and introduce novel on-chip components and fabrication techniques. We introduce a crossover to enable distinguishing signal polarization, minimize signal loss by locally optimized lithography of a coplanar waveguide, lower the spectral resolution of microstrip filters by deposition of a dielectric layer, and increase the yield of the spectrometer array by removing individual line shorts. These together have culminated in the successful fabrication of a 14-spaxel integral field unit.

Context. The Deep Spectroscopic HIgh-redshift MApper (DESHIMA) is a broadband integrated superconducting spectrometer for millimeter (mm) and submillimeter (submm) wave astronomy based on kinetic inductance detectors (KIDs). The first generation, DESHIMA 1.0, was successfully tested in 2017. This paper describes the upgrade to DESHIMA 2.0 and presents its characterization in laboratory settings. Aims. We enhanced the performance by increasing the band coverage and efficiency while developing a fast sky-position chopper for the efficient removal of atmospheric fluctuations. Methods. The instrument features NbTiN superconducting microstrip (MS) filters with a low-loss a-SiC:H dielectric and an ultra-wideband leaky-wave antenna. A laboratory setup was designed, incorporating the cryostat housing cryogenic optics and integrated superconducting spectrometer chip comprising 339 KIDs connected to MS filters tuned for (sub)mm wave frequencies. Room-temperature mirrors on a hexapod stage allowed us to precisely position and align the optical elements. The sky-position chopper was positioned on a motor-controlled stage for a fine-tuned control over its position and alignment. The multiplexing capability of KIDs enabled us to simultaneously measure multiple performance metrics across the entire frequency range. Results. DESHIMA 2.0 achieved significant improvements in the performance compared to its predecessor: the measured instantaneous frequency coverage was 200–400 GHz with a mean filter Q_filter of 340 ± 50, the instrument efficiency reached ~8%, indicating a four times wider band coverage and a four times higher sensitivity. The yield rate for the MS filters exceeded 98%. The data loss caused by the sky-position chopper was limited to <20% without beam truncation. The estimated aperture efficiency from measured beam patterns agreed well with the designed value of approximately 70%. The telescope far-field beam patterns calculated from the measured patterns also agree well with the design specifications. We also demonstrated that a new method of absolute frequency calibration is valid using the data from the beam pattern measurement.