CANISTER MULTIPATH AND THE CLOSE COUPLED ANTENNA

Abstract

The effects of multipath in telemetry applications are very well known and the approaches to minimizing these effects are the subject of countless books, papers and articles. Multipath once again rears its head as the U.S. Navy fields the MK-41 Vertical Launching System (VLS), a launching system in which each missile is housed in a canister which is both magazine and launch mechanism. The Canister is designed to protect the missile from Electro Magnetic Interference (EMI), Radio Frequency Interference (RFI) and the environment. As can be expected, a canister designed to prevent Radio Frequency (RF) energy from entering should inherently prevent any RF from escaping, and renders the canister environment ripe with multipath. Pre-Launch telemetry checks, essential to the conduct of a missile flight test, become unreliable events which at times result in aborted missions. Today the “encanistered” missile system enjoys wide acceptance, in the U.S. as well as internationally. Since any missile radiating in a closed volume inherently suffers from these multipath degradations, it is important to disclose the results of Navy testing conducted on the canister as well as the mission observations of the multipath effects. The mission observations are described are “signature” traits of the degradations which should have been attributed to multipath. Clearly many missions and tests were affected, but most were simply ignored by an oblivious test team. A short summary of the canister multipath investigation follows,including unexpected findings, and finally a discussion is given on the Close Coupled Antenna and its effectiveness in mitigating the canister multipath.