Pseudorandom Coding for Improved Antenna Range Measurements

The autocorrelation function for pseudorandom binary codes is such that these codes are ideal for suppressing unwanted reflections on antenna ranges. The method presented here depends on amplitude modulating the transmitted signal with a maximum-length linear recurring modulo-two sequence (PN code) and correlating it at the receiver with a delayed version of the code. In this way reflections whose path transit times are greater than 1 bit time from the direct path transmission time are reduced in amplitude by a factor inversely proportional to the length of the code word. Also presented is a simple means for generating the maximum-length shift-register codes using delay lines and mixers that makes this method especially practical for most antenna range applications.