Downwinders Act This bill expands eligibility for and extends a program that compensates individuals who were exposed to radiation from atmospheric nuclear testing and subsequently developed specified cancers. Under current law, the program compensates, among others, individuals who were present in a designated geographic area during a period of nuclear testing. The bill expands that area to include all of Utah and specified counties in New Mexico. In addition, individuals may submit claims for compensation for 10 years following this bill's enactment (currently, the program terminates on July 10, 2022). To support the program, the National Telecommunications and Information Administration must auction 100 megahertz of electromagnetic spectrum assigned or allocated to the federal government with a portion of the proceeds to be deposited into the Radiation Exposure Compensation Trust Fund in the Treasury. The bill extends this trust fund for 10 years following the bill's enactment. In addition, the Department of Health and Human Services must study which counties in Nevada and New Mexico were affected by radiation fallout from open air nuclear testing.