Regular magnetic field structures can be derived from the Faraday rotation measures (RM) of polarized background sources observable at 1.4 GHz with the SKA. At lower frequencies ($<250$ MHz) polarimetry of radio sources with the Low Frequency Array (LOFAR) will allow the investigation of extremely small RM, to detect and map weak regular fields in halos and outer parts of spiral galaxies, and in the interstellar and intergalactic medium. Very little is known yet about the number density of polarized sources at low frequencies. Observed distributions of polarized sources at 350 MHz and 1.4 GHz and perspectives to detect weak magnetic fields with LOFAR are presented. Test observations of polarized radio sources with the Westerbork Synthesis Radio Telescope (WSRT) and the Giant Metrewave Radio Telescope (GMRT) are discussed.
Exploring the Cosmic Dawn through the 21 cm Forest and High-redshift Radio Sources with the SKA
Max Planck Institute for Astrophysics（马克斯·普朗克天体物理学研究所）；Gifu Shotoku Gakuen University（岐阜女子大学）；Kobayashi Maskawa Institute, Nagoya University（名古屋大学小林益川研究所）；Northeastern University（东北大学）；Liaoning Normal University（辽宁师范大学）；University of Nevada, Las Vegas（内华达大学拉斯维加斯分校）；Yunnan University（云南大学）；Nagoya University（名古屋大学）；Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；The Institute of Statistical Mathematics（统计数学研究所）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；University of Tsukuba（筑波大学）
The topology of the magnetic field in Abell 2255 out to its virial radius. Results from the LOFAR Galaxy Cluster Ultra-Deep Field
INAF - IRA（意大利国家天体物理研究所-博洛涅分院）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Institute for Advanced Study（普林斯顿高等研究院）；Dipartimento di Fisica e Astronomia, Università di Bologna（博洛尼亚大学物理与天文学系）；Center for Astrophysics Harvard & Smithsonian（哈佛&史密森尼天体物理中心）；Department of Astronomy, University of Wisconsin-Madison（威斯康星大学麦迪逊分校天文学系）；ASTRON, the Netherlands Institute for Radio Astronomy（荷兰射电天文研究所）；Hamburger Sternwarte, Universität Hamburg（汉堡大学汉堡天文台）；INAF - IASF Milano（意大利国家天体物理研究所-米兰天文物理研究所）
Investigating the radio emission in the Perseus cluster with LOFAR sub-80 MHz LBA
INAF – Istituto di Radioastromia（意大利国家天体物理研究所射电天文学研究所）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Université Laval（拉瓦尔大学）；Dunlap Institute for Astronomy and Astrophysics, University of Toronto（多伦多大学邓普天文学与天体物理学研究所）；Università di Bologna（博洛尼亚大学）
The Large-Scale Structure of the Universe through the SKA lenses
University of Bologna（博洛尼亚大学）；Manipal Academy of Higher Education（马尼拉高等教育学院）；University of Hamburg（汉堡大学）；MIT Art, Design and Technology University（麻省理工学院艺术、设计与技术大学）；Tata Institute of Fundamental Research（塔塔基础研究所）；University of Tartu（塔尔图大学）；National Astronomical Observatory of Japan（日本国立天文台）
Radio Halos in Galaxy Clusters as unveiled by the SKA telescope
Indian Institute of Technology Indore（印度理工学院印多尔分校）；Rhodes University（罗德岛大学）；Naval Research Laboratory（海军研究实验室）；National Centre for Radio Astrophysics, Tata Institute of Fundamental Research（国家射电天体物理中心，塔塔基础研究所）；University Catholic of Lyon- University of Lyon（里昂天主教大学-里昂大学）；National Tsing Hua University（国立清华大学）；Leiden University（莱顿大学）
Exploring future synergies for large-scale structure between gravitational waves and radio sources
Queen Mary University of London（伦敦大学皇家玛丽学院）；Instituto de Astrofisica e Ciências do Espaço, Universidade do Porto CAUP（波尔图大学CAUP天体物理学与空间科学研究所）；University of the Western Cape（西开普敦大学）；Universidade do Porto（波尔图大学）；Institute of Cosmology and Gravitation, University of Portsmouth（朴茨茅斯大学宇宙学与引力研究所）
