Trilogy of novels (I am almost certain they were paperback originals), by an American author and published in the late 1970s or early 1980s. Nazis develop flying saucers & flee Germany at the end of WWII. They relocate to either the North Pole or the South Pole (can't remember which) and are thusly responsible for all UFO sightings, flaps, plane crashes and missing time forever after (the author threw in just about every UFO trope you can think of.) I know they had a Master Plan but I don't know what it was because I only read the first book.
The ultimate conspiracy begins... W.A. Harbinson started to uncover the nightmarish truth about Unidentified Flying Objects (UFOs) in the research for his bestseller GENESIS. Now, he has taken that groundbreaking work and expanded it, going back decades to create another astounding epic. INCEPTION is a terrifying story based on documented historical fact that reveals what is really known about UFOs while holding its readers spellbound with a breathtaking thriller about organized evil, global conspiracy - and the secret future of our world... INCEPTION - THE FIRST BOOK OF THE EPIC PROJEKT SAUCER SERIES. 'A Herculean conspiracy epic... superbly written, crammed with food for thought.' -Los Angeles Times
This review mentions Antarctica.
The core idea of Projekt Saucer, which were not written in the order presented above, revolves around an Earth-based source for flying saucers, or UFOs. Rather than blaming them on aliens, the flying saucers are created by an awesome conspiracy, created by a Doctor Wilson. (Someone called Wilson, BTW, featured in some of the first reports of unknown airships in America.) Through the first book, Wilson takes his ideas to Nazi Germany – incidentally creating the Foo Fighters along the way – and then into a colony in the frozen continent – Antarctica. In the years that follow, Wilson’s flying saucers give rise to the entire UFO phenomenon – apart from much more primitive saucers flown by the US and the USSR - including alien abductions, UFO bases, UFO theories, UFO encounters, UFO dangers…
It looks there used to be a dedicated page for the series, now only available via the Wayback Machine.
I lucked out that they were one of the first results for
science fiction trilogy nazi saucers
There's a copy of the first book available on Openlibrary.