Image: Dipole radar altimeter antenna

Description: A dipole antenna of a radar altimeter from an advertisement in a 1947 radio magazine. It was mounted on the bottom surface of an aircraft and transmitted radio waves which reflected from the ground. The altitude of the aircraft was calculated from the time it took the radio waves to return. This is a half-wave dipole; composed of two symmetrical elements each 1/4 wavelength long, insulated from each other with the white insulator. It is mounted 1/4 wavelength below the aircraft's body, so the aircraft's aluminum skin functioned as a reflecting surface to reinforce the outgoing wavefront. It is made of painted brass tubing, and was mounted parallel to the airstream to reduce air drag. The text gave no information about the operating frequency, but if the antenna is roughly 20 cm, long as it appears to be, the wavelength is around 40 cm so the operating frequency was in the UHF range, around 700 MHz. A coaxial cable feedline attached to the connector, bottom.
Title: Dipole radar altimeter antenna
Credit: Retrieved June 15, 2014 from Tele-Tech magazine, Caldwell-Clements Inc., Bristol, Connecticut, Vol. 6, No. 5, May 1947, p. 7 on American Radio History website
Author: Unknown
Permission: This image is from an advertisement without a copyright notice published in a 1947 magazine. In the United States, advertisements published in collective works (magazines and newspapers) are not covered by the copyright notice for the entire collective work. (See U.S. Copyright Office Circular 3, "Copyright Notice", page 3, "Contributions to Collective Works".) Since the advertisement was published before 1978 without a copyright notice, it falls into the public domain.
Usage Terms: Public domain
License: Public domain
Attribution Required?: No