DoD has authority to acquire articles and services from foreign sources per the Competition in Contracting Act (CICA), Federal Acquisition Regulations (FAR) and Defense Federal Acquisition Regulations Supplement (DFARS). The requirements of these laws and regulations which emphasize the importance of conducting full and open contract competitions with potential U.S. and foreign sources to meet validated DoD mission requirements apply.
The question indicates that the article to be acquired (a Doppler Radar) is a commercial item. If so, it is very likely that the DoD Contracting Activity could accomplish this procurement by providing DoD Unclassified, publically releasible information to prospective foreign source(s) during the contracting process to accomplish the procurement. However, in the unlikely event that DoD would be required to provide prospective foreign source(s) with either Controlled Unclassified Information or Classified Information during the contracting process, appropriate Technology Security and Foreign Disclosure (TSFD) approvals from the cognizant Foreign Disclosure Organization within the DoD Component would be required prior to release of such information to the prospective foreign source(s). Moreover, the prospective foreign source(s) would be asked to comply with U.S. international security programs and export control laws, regulations and policies in writing at an early stage of the contracting process to be considered responsive. Consult DAU's ACQuipedia article on this subject at URL https://www.dau.mil/acquipedia/pages/articledetails.aspx#!250 for further details.
The question background also indicates that the country where the potential foreign source is located is Denmark. DoD has a Reciprocal Defense Procurement Memorandum of Understanding (RDP MOU) with Denmark. DAU recommends the questioner consult the A&S/Defense Pricing and Contracting International Contracting website at URL https://www.acq.osd.mil/dpap/cpic/ic/index.html for additional information on international contracting with Danish sources to ensure they are taking full advatange of the provisions of the U.S. - Denmark RDP MOU..