Grote Reber, a pioneer of radio astronomy who built an antenna dish in his back yard in Illinois in the 1930s and tuned it to radio signals from space, died Dec. 20 in Australia's southern island state of Tasmania.

The news of his death, two days short of his 91st birthday, was announced by Fred Lo, director of the National Radio Astronomy Observatory in Socorro, N.M. The cause was not reported.

Mr. Reber was the first person to build a radio telescope dedicated to astronomy, opening a window on the universe that eventually produced such landmark discoveries as quasars, pulsars and the remnant afterglow of the big bang, the observatory said in a statement. His self-financed experiments laid the foundation for today's advanced radio-astronomy facilities.

"Radio astronomy has changed profoundly our understanding of the universe," Lo said in the statement. "All radio astronomers who have followed him owe Grote Reber a deep debt for his pioneering work."

Mr. Reber, a graduate of the Illinois Institute of Technology, was working as a radio engineer in his native Chicago when he followed up Karl Jansky's 1933 announcement of the discovery of radio waves from space.

As a ham radio operator, Mr. Reber had made long-distance contacts on amateur shortwave bands to all of the continents, then quite an achievement. In his spare time in 1937, he built a 30-foot antenna dish in his back yard in Wheaton, Ill. It managed to pick up signals two years later.

The telescope's mirror, made of sheet metal 31 feet in diameter, focused radio waves to a point 20 feet above the dish. Its cylinder contained a radio receiver that amplified the faint cosmic signals by a factor of many million, making them strong enough to be recorded on a chart, according to the observatory.

Mr. Reber spent long hours every night scanning the skies with his telescope. He had to do the work at night because there was too much interference from the sparks in automobile engines during the daytime, an observatory history noted.

Lo said that Mr. Reber "was the first to systematically study the sky by observing something other than visible light. This gave astronomy a whole new view of the universe."

From 1938 to 1943, Mr. Reber made the first surveys of radio waves from the sky and produced the first radio map of the sky, the observatory history said. His articles in Astrophysical Journal in the early 1940s marked the beginning of intentional radio astronomy.

It became a major field of research following World War II as groups in many countries began building bigger and better antennas and receivers to follow up on his discoveries.

Mr. Reber's original dish antenna now is on display at the observatory site in Green Bank, W.Va., where he worked from 1957 to 1961.

Mr. Reber moved to Tasmania because it was a good place to study cosmic radio waves at very low frequencies.

In Australia, he was awarded an honorary research fellowship with the respected Commonwealth Scientific and Industrial Research Organization.