Sep 9 2008
The ability to determine one's exact position at any spot in the world is now more or less taken for granted thanks to Global Navigation Satellite Systems (GNSS) like the Global Positioning System or GPS.
GPS was originally developed for military purposes, but its enormous application potential quickly led to widespread use of the system in civil segments like road traffic, sea and air travel, surveying and agriculture. For applications that are dependent on centimeter-accurate positioning, such as the precise working of farmland, GPS's accuracy of around 10 meters is not sufficient. For precision guidance of a tractor by an automatic steering system, additional correction signals are needed from reference stations or networks.
To receive signals inside such networks, choke ring antennas are used, for example the AT504 (GG) model from Leica Geosystems AG, a leading supplier of surveying instruments headquartered at Heerbrugg, Switzerland. The cover that protects the sensitive instrument from the effects of the weather is made by Emaform AG, Gontenschwil, Switzerland, from Baydur® 60, a polyurethane integral skin foam from BaySystems®. BaySystems® is Bayer MaterialScience's umbrella brand for its global polyurethane systems business, and embraces many decades of know-how in the field of polyurethane in conjunction with close customer support.
Choke ring antennas consist of a number of conductive cylinders arranged concentrically around a central antenna. The design on which the Leica
AT504 model was based was developed by the US space authority NASA and the Jet Propulsion Laboratory (JPL), and is regarded as a global standard for permanent GNSS reference networks. The antenna is noted among other things for its good signal-to-noise ratio and high resistance to radio frequency interference signals. The polyurethane material satisfies the strict specifications relating to undisturbed reception and is highly resistant to all kinds of weather. The material is also unaffected by bird droppings. It offers exceptional design freedom so that even complex molding geometries can be created. This allows designers to optimize the shape of the protective cover to ensure that it is exactly the same distance from the mechanical center of the antenna element at every point. This is necessary to keep the remaining influence on the signal reception constant over the entire horizon and for every elevation angle. The new Leica antenna AR25 is also equipped with this cover.
The protective cover is 45 cm high and has a diameter of 40 cm. The use of inexpensive aluminum molds ensures very economical production. At the end of the production process, the part is coated, printed by pad printing, furnished with installation materials, and delivered to the customer.
"Leica Geosystems benefits from our flexibility and our proximity to customers, and also appreciates our consistent quality," says Christian Merz, head of Sales and Marketing at Emaform.
The high performance of the devices is opening up additional applications in very different fields. Only recently, the British Highways Agency decided to award Leica Geosystems a contract for GPS/GNSS instruments, motorized total stations, services and training programs, significantly extending its capabilities for accident investigation.