This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES 1 A Wideband Correlation and Detection Module Based on Substrate-Integrated Waveguide Technology for Radio Astronomy Applications Juan Luis Cano , Enrique Villa, Angel Mediavilla, and Eduardo Artal, Member, IEEE Abstract—A wideband (30% relative bandwidth) corre- lation and detection module based on substrate-integrated waveguide (SIW) technology intended for a radio astronomy polarimeter is presented. The SIW circuit is a six-port network with two input ports that are correlated in two hybrid couplers and their corresponding output signals are routed to Schottky diode detectors, which are designed using microstrip technology and assembled within the same system. The designed SIW structure includes hybrid couplers, power dividers, a 90° phase shifter, and 90° bends, providing a real implementation of a functional system with improved bandwidth performance from 35 to 47 GHz. Experimental results are in concordance with simulations, and they validate the module operation for the proposed application. Index Terms— Correlation, polarimeter, radio astronomy, radiometer, substrate-integrated waveguide (SIW), wideband. I. I NTRODUCTION S UBSTRATE-INTEGRATED waveguide (SIW) is a rela- tively new technology that is having an increasing interest since it was proposed by Deslandes and Wu [1]. The main reason for its success is the combination of the advantages of planar technology, such as lightness, compactness, and reduced manufacture cost, with those of waveguide technology, such as low insertion loss and higher quality factors. On the other hand, radio astronomy is among the most demanding applications because a slight improvement in the receiver sensitivity has a huge impact on the observing time and the scientific knowledge itself. In particular, the study of the cosmic microwave background (CMB), both in inten- sity and in polarization, pushes the technology to its limits, requiring state-of-the-art subsystems, due to the faintness of the received signals. The most critical components affecting the sensitivity of a radiometer or polarimeter are the first subsystems in the receiver chain. A high insertion loss degrades the equivalent noise temperature, and therefore these elements, such as feedhorns, polarizers, and orthomode transducers (OMT), are Manuscript received September 28, 2017; revised January 11, 2018; accepted March 16, 2018. This work was supported by the Spanish Min- istry of Economy and Competitiveness under Project AYA2013-49759-EXP. (Corresponding author: Juan Luis Cano.) The authors are with the Departamento de Ingeniería de Comuni- caciones, Universidad de Cantabria, 39005 Santander, Spain (e-mail: juanluis.cano@unican.es). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMTT.2018.2823305 designed using the waveguide technology. They are normally cooled to cryogenic temperatures to reduce even more its noise contribution. However, not only low losses are an important guideline for these kinds of receivers but also the number of receivers (pixels) that can be accommodated in the instrument has a significant influence in the overall performance. For this reason, modern radio astronomy receivers are multipixel cameras, where the increasing number of pixels is the current trend. In this context, the SIW technology has a clear opportu- nity for the development of light, compact, highly integrated, and relatively cheap back ends. The QUIJOTE project [2], [3] is a multipixel radio astron- omy ground-based experiment with the aim of characterizing the CMB polarization, among other scientific goals, through the measurement of the Q, U , and I Stokes parameters simultaneously from 10 to 47 GHz in different subbands. The calculation of these Stokes parameters is carried out through the correlation and detection of the incoming signals. These operations are performed in a specific unit in each pixel called correlation and detection module (CDM). Although the final election for the design of the CDM in the QUIJOTE project was the waveguide technology, this paper presents the development of a full system implementing the correlation, detection, and level accommodation functionalities in Q-band (35–47 GHz, 30% instantaneous bandwidth) with most of the RF circuitry implemented in the SIW technology. Once correlated, the signals are detected using Schottky diode detectors implemented in the planar technology and integrated in the same module. Finally, the system incorporates adjustable video amplifiers to accommodate the detected voltages to suitable values for the subsequent data acquisition electronics unit. The proposed CDM scheme demonstrates the feasibility of the SIW technology to perform complex operations, beyond its individual parts, in highly demanding applications such as radio astronomy. Section II presents the pixel scheme and the CDM block diagram in order to explain its principle of operation. Sec- tion III provides detailed information about the CDM design focusing on each subsystem separately. CDM measurement results are presented in Section IV, whereas the conclusion is presented in Section V. II. PRINCIPLE OF OPERATION The polarimeter scheme, before the CDM, selected for each pixel in the QUIJOTE project (30- and 40-GHz bands) is 0018-9480 © 2018 IEEE. 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