Sparse MIMO for ISAC: New Opportunities and Challenges Sparse MIMO is a promising technology for 6G communication systems, offering enhanced spatial resolution and sensing capabilities. Unlike conventional compact MIMO, which uses half-wavelength spacing between antenna elements, sparse MIMO allows for larger array apertures without increasing the number of elements. This results in improved spatial resolution, larger virtual apertures for sensing, and better performance in both communication and sensing tasks. Sparse MIMO architectures include uniform sparse arrays (USA) and non-uniform sparse arrays (NUSA), such as minimum redundancy array (MRA), modular array (MoA), nested array (NA), and co-prime array (CPA). These architectures enable the formation of larger virtual apertures through difference or sum co-arrays, enhancing sensing degrees of freedom (DoF) and spatial resolution. Sparse MIMO provides several advantages for integrated sensing and communication (ISAC), including finer spatial resolution, larger sensing DoF, enlarged near-field regions, reduced mutual coupling, and more flexible deployment. However, it also presents challenges such as grating lobes, beam splitting, and the need for advanced beam codebook design and array geometry optimization. The main design issues for sparse MIMO include beam pattern synthesis, signal processing, grating lobe suppression, beam codebook design, and array geometry optimization. Simulation results demonstrate that sparse MIMO outperforms compact MIMO in terms of spatial resolution, sensing accuracy, and spectral efficiency. For example, sparse MIMO with larger array apertures achieves finer angular and distance resolutions, leading to better performance in near-field communication and sensing. Additionally, sparse MIMO can reduce hardware, energy, and signal processing costs by requiring fewer activated antennas. Future research directions for sparse MIMO in ISAC include the development of sparse intelligent reflecting surfaces (IRS)/reconfigurable intelligent surfaces (RIS), advanced beam control and tracking techniques, and physical layer security methods. These advancements aim to enhance the capabilities of 6G ISAC systems, enabling more accurate sensing and communication in dense environments.Sparse MIMO for ISAC: New Opportunities and Challenges Sparse MIMO is a promising technology for 6G communication systems, offering enhanced spatial resolution and sensing capabilities. Unlike conventional compact MIMO, which uses half-wavelength spacing between antenna elements, sparse MIMO allows for larger array apertures without increasing the number of elements. This results in improved spatial resolution, larger virtual apertures for sensing, and better performance in both communication and sensing tasks. Sparse MIMO architectures include uniform sparse arrays (USA) and non-uniform sparse arrays (NUSA), such as minimum redundancy array (MRA), modular array (MoA), nested array (NA), and co-prime array (CPA). These architectures enable the formation of larger virtual apertures through difference or sum co-arrays, enhancing sensing degrees of freedom (DoF) and spatial resolution. Sparse MIMO provides several advantages for integrated sensing and communication (ISAC), including finer spatial resolution, larger sensing DoF, enlarged near-field regions, reduced mutual coupling, and more flexible deployment. However, it also presents challenges such as grating lobes, beam splitting, and the need for advanced beam codebook design and array geometry optimization. The main design issues for sparse MIMO include beam pattern synthesis, signal processing, grating lobe suppression, beam codebook design, and array geometry optimization. Simulation results demonstrate that sparse MIMO outperforms compact MIMO in terms of spatial resolution, sensing accuracy, and spectral efficiency. For example, sparse MIMO with larger array apertures achieves finer angular and distance resolutions, leading to better performance in near-field communication and sensing. Additionally, sparse MIMO can reduce hardware, energy, and signal processing costs by requiring fewer activated antennas. Future research directions for sparse MIMO in ISAC include the development of sparse intelligent reflecting surfaces (IRS)/reconfigurable intelligent surfaces (RIS), advanced beam control and tracking techniques, and physical layer security methods. These advancements aim to enhance the capabilities of 6G ISAC systems, enabling more accurate sensing and communication in dense environments.