Abstract: Various embodiments are described of an antenna including a common ground plane, a first set of N approximately resonant elements with a length I2 and a second set of M approximately resonant elements with a length I1. The first set of N approximately resonant elements are wound to form a first helix with an initial diameter d2 and a height h2. The second set of M approximately resonant elements are wound in the opposite direction to the first set of N approximately resonant elements to form a second helix. The second helix is centrally disposed within the first helix, and d1 is less than d2 and h1 is greater than h2.

Abstract: A system and method of detecting Automatic Identification System (AIS) signals in space and decoding these signals. In one aspect, a system for performing this function is described which includes a receiver configured to receive the plurality of AIS signals and pre-process the plurality of AIS signals to produce digital input data, and a processor configured to process the digital input data to identify one or more candidate AIS message signals based on Doppler offsets associated with the digital input data, determine corresponding Doppler offset estimates and time estimates of the one or more candidate AIS message signals, decollide and decode the one or more candidate AIS message signals to obtain corresponding message segments and validate the decoded message segments for proper AIS formatting.

Abstract: Various embodiments are described of an antenna including a common ground plane, a first set of N approximately resonant elements with a length I2 and a second set of M approximately resonant elements with a length I1. The first set of N approximately resonant elements are wound to form a first helix with an initial diameter d2 and a height h2. The second set of M approximately resonant elements are wound in the opposite direction to the first set of N approximately resonant elements to form a second helix. The second helix is centrally disposed within the first helix, and d1 is less than d2 and h1 is greater than h2.

Abstract: An antenna including a common ground plane, a first set of n approximately resonant elements with a length l2 and a second set of n approximately resonant elements with a length l1. The first set of n approximately resonant elements are wound to form a first helix with an initial diameter d2 and a height h2. The second set of n approximately resonant elements are wound in the opposite direction to the first set of n approximately resonant elements to form a second helix. The second helix is centrally disposed within the first helix, and has an initial diameter d1 and a height h1 where d1 is less than d2 and h1 is greater than h2.