What is a Choke Ring Antenna?

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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

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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.

In modern geodetic research and satellite navigation systems, such as GPS, the accuracy and reliability of the data received play a crucial role. One of the key components that ensures high accuracy and minimizes the influence of external factors is the "Choke Ring" antenna. These antennas have gained popularity due to their unique characteristics, making them indispensable in various fields, from geodesy to scientific research.

The "Choke Ring" antenna type has several key advantages, especially in the fields of geodesy and satellite navigation systems like GPS:

1. Multipath Suppression: The main feature of the Choke Ring antenna is its ability to reduce multipath effects. This is achieved through the ring elements that surround the main part of the antenna. These rings block signals that are reflected off the ground or other surfaces, allowing the antenna to receive a clearer and more accurate signal.

2. High Accuracy: Due to the reduction of multipath effects, Choke Ring antennas provide high accuracy in location determination. This makes them ideal for use in geodesy, mapping, and any applications requiring high precision GPS navigation.

3. Reliability in Various Conditions: Choke Ring antennas perform well in various conditions, including complex urban and natural landscapes. They are less affected by the environment, which improves the stability and reliability of the signal.

4. Application in Scientific Research: These antennas are often used in scientific research, such as space geodesy and monitoring of the Earth's crust, where particular precision in measurements is required.

Because of these advantages, Choke Ring antennas are considered one of the best choices for tasks where precision and reliability of satellite signal reception are critically important.

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