Tech Chat | Should I Choose A Choke Ring Antenna For My Reference Station?

-04-11

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Since our SV100 GNSS receiver was released half a year ago, many users have shown great interest and got positive feedback about it. Most of our users have used the SV100 as a reference station for their CORS or monitoring projects.

When supporting our SV100 users building reference stations, one of the most frequently asked questions is - should I use a choke ring antenna for SV100? What are the advantages of choke ring antenna over geodetic antenna?

In today's blog, we will give a brief introduction of Choke Ring antenna and hope this will help you to make a decision.

What Is Choke Ring Antenna?

The structural design of the choke ring antenna has been proven worldwide to effectively reduce the strength of most multipath signals. It consists of a circular ring with a number of slots or gaps in it, which effectively act as wave guides to cancel out the reflected signals. The ring is typically made of a conductive material, such as metal, and is placed above a ground plane to further reduce interference.

A choke ring antenna is a type of GNSS antenna that is designed to mitigate the effects of multipath interference. It is usually a quarter wavelength deep, in order to create a high impedance surface that prevents propagation of surface waves near the antenna and excitation of undesired modes. The net effect is a very smooth controlled pattern with low susceptibility to multipath.

What Is Multipath Interference?

Multipath interference occurs when the satellite signal is reflected off a surface, such as a building or a vehicle, and arrives at the antenna at different times, causing errors in the GNSS measurements. 

When GNSS signals reach the choke ring antenna, they pass through the gaps between the rings and are received by the antenna element. The reflected signals, on the other hand, are blocked by the rings and are not received by the antenna element. This helps to ensure that the signals received by the antenna are only the direct signals from the GNSS satellites, which results in more accurate positioning.

Therefore, choke ring antennas are commonly used in high-precision GNSS applications to reduce the multipath error, such as national CORS and large monitoring projects etc.

Is the Choke Ring Antenna Essential?

In addition to the choke antenna, there is also a small type of GNSS antenna that can be used in reference stations &#; the geodetic antenna. Judging from the market feedback, it also has a good performance and is worth recommending.

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Compared with geodetic antennas, choke ring antennas are obviously more professional. But correspondingly, the price of the choke ring antenna is also quite high, generally four or five times higher than that of the geodetic antenna.

In conclusion, for users who have sufficient budget and plan to build a professional CORS network, the choke ring antenna is the first choice. But if you just build a station for your own use without strict project requirements, geodetic antennas will be your cost-effective solution.

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A choke ring antenna is a type of omnidirectional antenna that is used for GNSS applications. Its design consists of a central antenna element, which is surrounded by several concentric conductive rings. These antennas are known for their ability to reject multipath signals (a reflection of satellite signals from nearby objects) from a source. This includes signals reflected from ground and water surfaces, buildings, topography, vegetation, and other sources. Choke ring antennas have specially designed filters, inserted in each groove, which reduces multipath signals in both the L1 and L2 bands within the same antenna configuration. 

Since the path that a signal takes from a transmitter to a receiver can be used to measure the distance between the two, this makes it highly suitable for GPS applications in surveying and geological measurement (forestry applications). The reduction of multipath can greatly increase the accuracy of GPS recordings, especially in environments where signal attenuation is difficult. As a result, centimeter-level accuracy might theoretically be obtained when choke ring antennas are connected to mapping-grade GPS receivers. 

Construction

Choke ring antennas are generally machined from a single billet of aluminum and consist of several concentric rings (3 to 5) of equal depth around a central ring that holds an antenna receiver. The choke rings are usually a quarter wavelength deep, in order to create a high impedance surface that prevents propagation of surface waves near the antenna and excitation of undesired modes. The net effect is a very smooth controlled pattern with low susceptibility to multipath. The entire choke ring is usually 300-450 mm in diameter and 60 mm in depth and weighs approximately 7 kg. These dimensions result in unhandy field measurement studies and thus limit its application in forestry. Choke rings function to eliminate the electromagnetic energy reflected from the Earth&#;s surface. The design of a choke ring is relatively standard, although some variations occur in the vertical arrangement of the rings, from flat to conical, the latter of which is used to assist in increasing signal quality from low elevations.

Due to the way this antenna is constructed, it is often enclosed in a protective cover when used for outdoor applications.

Limitations

An inherent disadvantage of the typical choke ring design is reduced antenna gain at low elevation angles (below 20°). The reduced antenna gain results in signal strength reduction followed by poor positional accuracy.

If you want to learn more, please visit our website MINI Choke ring antenna.