A Dish / Grid antenna embodies a design that utilises a parabolic reflector, a curved surface with a cross-sectional shape of a parabola, to direct the radio waves. The primary function of this design is to collect and focus electromagnetic waves onto the antenna feed, similar to the way a satellite dish operates. The design of the Parabolic Reflector antenna is based on the principle of geometric optics. This principle allows the antenna to focus incoming waves onto a single point, the feed, thus enhancing the signal strength. The feed, located at the focal point of the reflector, is responsible for transmitting or receiving the radio waves to or from the reflector. The size of the dish is directly proportional to the wavelength of the signal: the larger the dish, the higher the gain and directivity, resulting in a more focused beam of radio waves. This characteristic makes a dish / grid antenna an excellent choice for long-distance microwave communication and radar systems. The construction of a Parabolic Reflector antenna can be either solid or mesh/grid. A solid dish, as the name suggests, has a continuous, unbroken surface that provides a high-efficiency reflection of radio waves. However, this design can be susceptible to wind loading due to its solid structure.
Dish vs Grid
A Grid is a specific variation of a parabolic antenna characterised by its grid-like reflective surface. Unlike a Dish Reflector antenna that has a solid parabolic surface, a grid reflector antenna uses a series of intersecting conductive elements, or 'grid', to form the reflector. This design significantly reduces wind load and weight, while still effectively focusing the radio waves onto the antenna feed. Despite minor losses due to the 'see-through' nature of the grid, these antennas can achieve comparable gain and directivity to their solid counterparts. Often found in outdoor wireless data systems and satellite communication applications, grid reflector antennas provide a practical solution when weight and wind resistance are critical considerations.
Cassegrain Reflector
This is a specialised type of parabolic reflector antenna, notable for its use of two reflectors - a primary parabolic reflector and a secondary hyperbolic or ellipsoidal reflector. Named after the Cassegrain optical telescope design, this antenna works by focusing the energy onto the small secondary reflector, which then projects the energy out towards the primary reflector and further on to the receiving device. This results in a high gain, or an increase in power, and a narrow beamwidth, which is the area over which the antenna transmits or receives signal effectively. Its design allows for reduced physical size of the antenna while maintaining high performance, making the Cassegrain reflector antenna commonly used in satellite communication and radio astronomy applications.