European Space Agency

Cuva.me Compact UHF and VHF Antennas for Maritime Emergencies

Objectives

The main classes of antennas found in commercially available rescue transponders are vertical whips, wire, helical and patch antennas. Blade antennas are mentioned but don’t really apply to the applications we target. These antennas are most often integrated with a product and tend to operate on a single band (COSPAS or AIS-SART, for example). A few dual-band examples also operate on the COSPAS-SARSAT band and the 121.5 MHz aeronautical rescue frequency. 
In this project, the goal is to develop a compact dual band 406/162MHz antenna for use in the latest generation of search and rescue beacons (to be possibly extended to special low-rate data-gathering applications). The focus will be on managing the complementary requirements of antenna size and electrical performance suitable for satellite and terrestrial service. Furthermore, a secondary objective is the development of a numerical model of the antenna (or antennas) studied as part of this project.

Challenges

The most significant challenge will be striking the right balance between physical size and electrical performance. Small antennas suffer severe constraints on bandwidth and efficiency that are defined by fundamental physical principles.  Therefore, a significant part of this project is dedicated to managing these fundamental constraints while allowing us to satisfy, in some minimal sense, the requirements needed for reliable emergency beacon operation.

Benefits

The main classes of antennas found in present commercially available rescue transponders are vertical whips, wire, helical and patch antennas. Most of these antennas are single band (usually operating in the COSPAS-SARSAT 406 MHz band). The main benefits of this work are found in our design of dual band antennas that permit simultaneous operation on the 406 MHz and 162 MHz bands.  There is a dearth of compact antennas for these applications on the market. By the end of this project, we would like to make compact, dual band antennas available to the market that will find use in both hand-held personal locators as well as vessel-based distress beacons.

Features

Based on the results of an initial study, we focus on the following tentative antenna architectures:

  • A cylindrical dielectric loaded helical antenna. Quadrifilar varieties conveniently provide circular polarization from all viewing angles, but are not low-profile antennas. 
  • A planar antenna where a couple of design options are available:
    • Parallel plate mode and/or normal patch mode and/or higher mode. A dual band antenna will require two modes. Selection of the modes depends on the required radiation pattern and size constraints. The radiation pattern shape depends on the selected services.
    • Planar fractal or genetic algorithm techniques may be used where applicable 
  • A fixed and/or standalone automatic antenna tuner may be required depending on the final selection of the antenna design and end user equipment. This applies to both the helical and the planar antenna option.

Planar circular polarized antenna.

Plan

The project starts off with a preliminary study of the state of the art as well as understanding the special requirements and operational demands of the proposed dual-band antenna.  An exploration of the combination of services that might best satisfy the “mission requirements” is carried out. This then allows the definition of a set of antenna requirements. 
A prototype “breadboard” design will be carried out to test the proof of concept, satisfying as many of the electrical and mechanical constraints as needed.  The test results are then used to verify and update the antenna model. 
We then move on to producing a comprehensive design of the final antenna, taking into account all electrical, mechanical and environmental requirements.  A full suite of electrical, mechanical and environmental tests, performed in the laboratory as well as under expected environmental conditions is carried out.

Current status

At this point in the project, we have completed a market survey and a preliminary study of some candidate antenna designs. We are presently engaged in the preliminary design process. Numerous simulations and optimization cycles are being carried out in order to improve the simulation model as well as to settle on a set of antenna architectures to fabricate as part of the breadboard process. Once we clear the Preliminary Design Review process, we shall fabricate a set of antennas for extensive preliminary testing.

Status date

Monday, November 24, 2014 - 08:23