What are Gregorian Antennas?

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- everything RF

Apr 12, 2024

The Gregorian antenna, named after astronomer James Gregory is a type of reflector antenna that uses two parabolic reflectors to focus radio waves into a tight beam. The primary reflector is larger in size and collects incoming electromagnetic waves and focuses them towards a secondary, smaller reflector positioned in front of it. This secondary reflector, also parabolic in shape, further concentrates the waves before directing them towards the antenna's receiver or transmitter located at the focal point of the system.


One of the key features of the Gregorian antenna is its ability to produce a narrow, focused beam with minimal aberrations. This is achieved through careful design and optimization of the two reflectors' shapes and relative positions. By precisely controlling the curvature and separation of the reflectors, engineers can ensure that the reflected waves converge at the desired focal point, resulting in high gain and improved signal-to-noise ratio.

Gregorian antennas can operate across a broad range of frequencies, from the microwave to millimeter-wave bands. The specific frequency range depends on the size of the reflectors used. Large Gregorian antennas (diameters exceeding 10 meters) are used for low-frequency (below 1 GHz) applications like radio astronomy. The smaller the Gregorian antennas the higher its operating frequency. These antennas can be designed to support any frequency from a few GHz to over 100 GHz.

Gregorian antennas can also be designed to operate with various polarizations, such as linear or circular, depending on the specific application requirements.

The material used to construct the reflectors of a Gregorian antenna plays a very important role in determining its RF characteristics. Metals like aluminum or copper offer good conductivity at lower frequencies, while specialized materials like machined surfaces or dielectric materials are used for higher frequencies to minimize signal loss. 

Advantages of Gregorian Antennas 

The Gregorian antenna offers several advantages over other antenna configurations, making it particularly well-suited for long-distance communication and satellite applications: 

  • High Gain & Directivity: The dual-reflector design of the Gregorian antenna allows for exceptionally high gain, enabling reliable communication over vast distances without the need for excessively high transmitter power.

  • Low Side Lobes: The dual reflector design of Gregorian antenna's minimizes its side lobes, reducing the risk of signal interference and improving signal clarity.

  • Low Noise Temperature: The focused nature of the antenna's beam helps to minimize noise pickup from the surrounding environment, resulting in a lower noise temperature and improved signal reception quality.

Applications of Gregorian Antennas 

Gregorian antennas are most used in Satellite Communication and Radio Astronomy. In SATCOM they are used by satellite ground stations for both receiving/transmitting signals from orbiting satellites. Their high gain and low noise characteristics are particularly valuable in this context, where reliable communication with spacecraft over vast distances is required. In the field of radio astronomy, Gregorian antennas play a crucial role in observing distant celestial objects and phenomena in space. Their ability to capture weak signals makes them ideal for astronomers seeking to unravel the mysteries of the universe.