Corner reflector antenna
A directional VHF/UHF antenna with moderate gain and wide bandwidth.
A corner reflector antenna is a directional antenna designed for VHF and UHF frequencies. It was created by John D. Kraus in 1938. The design places a dipole driven element in front of two flat, rectangular reflecting screens that meet at an angle, typically 90 degrees. This antenna produces linearly polarized radio waves and can be oriented for either horizontal or vertical polarization.
These antennas offer moderate gain, usually between 10 and 15 dB, along with a high front-to-back ratio of 20 to 30 dB and a wide bandwidth. Common uses include UHF television receiving antennas, point-to-point communication links, data links for wireless WANs, and amateur radio antennas on the 144, 420, and 1296 MHz bands. A corner reflector antenna is distinct from a corner reflector, which is a passive device that simply bounces radio waves back toward their source.
The reflecting surfaces are often made of wire screen or rod elements parallel to the driven element, rather than solid metal sheets, to cut down on weight and wind resistance. The spacing between these rods should not exceed 0.06 of the wavelength. While the angle between the sides is most often 90 degrees, narrower angles down to 45 degrees have been used; gain improves as the angle shrinks, but the benefit below 90 degrees is small and requires longer reflector screens. The distance from the driven element to the point where the reflectors meet is roughly 0.5 wavelengths, though this is not critical—for a 90-degree antenna, gain varies by less than 1.5 dB when the spacing ranges from 0.25 to 0.75 wavelengths. Adjusting this spacing also changes the dipole's radiation resistance, allowing it to be matched to the feed line. For wideband applications like TV antennas, bowtie-shaped driven elements are common.
This antenna can be seen as a type of directive antenna with gain falling between that of a plane reflective array and a parabolic dish. It is especially useful when a broadband directional antenna about one to one-and-a-half wavelengths in size is needed, since a parabolic dish of that size offers no gain advantage and the corner reflector is simpler to build.
Several variations exist.
- Inventor
- John D. Kraus
- Year invented
- 1938
- Frequency bands
- VHF and UHF
- Typical gain
- 10–15 dB
- Front to back ratio
- 20–30 dB
- Typical angle
- 90°
- Driven element spacing
- approximately 0.5 λ
Lore & Background
The corner reflector antenna was invented by John D. Kraus in 1938. It is a form of directive antenna with gain intermediate between a plane reflective array antenna and a parabolic antenna. The flat reflecting surfaces can be metal sheets, but are more often made of wire screen or rod elements parallel to the driven element to reduce weight and wind loads. The spacing of the rods should not be more than 0.06 (6%) of the wavelength. The angle between the sides is most commonly 90°, though angles down to 45° have been used. Gain increases as the angle narrows, but the increase below 90° is minimal and requires longer reflector screens. The spacing of the driven element in front of the point where the reflectors meet is approximately 0.5 λ but is not very critical; for 90° antennas the gain does not vary more than 1.5 dB for spacing between 0.25 λ and 0.75 λ. The radiation resistance of the dipole increases with this spacing, so the spacing can be adjusted to match the driven element to the feed line. Bowtie driven elements are often used for wide bandwidth applications like television antennas.
Reader's Guide
The corner reflector antenna is widely used for UHF television receiving antennas, point-to-point communication links and data links for wireless WANs, and amateur radio antennas on the 144, 420, and 1296 MHz bands. It is particularly suitable in applications where a broadband directional antenna around one to 1+1⁄2 wavelengths in size is needed. A parabolic dish this size has no advantage in gain over the corner reflector, so its simplicity of design and construction make it attractive. Several variations exist: the single driven element can be replaced by a Yagi array, and UHF Yagi television antennas very often use a corner reflector. These antennas function more like two separate antennas: the corner reflector and driven element provide broad bandwidth gain at the lower end of the UHF band, while the Yagi array gives extra gain at the high end. Monopole versions for use at lower frequencies have been built by placing vertical reflecting screens behind a vertical monopole antenna. The corner reflector antenna should not be confused with a corner reflector, a passive device used to reflect radio waves back toward the source.
Did You Know?
- It has a typical gain of 10–15 dB and a front-to-back ratio of 20–30 dB.
- The reflecting screens are often made of wire screen or rod elements to reduce weight and wind loads.
- The antenna can be mounted for either horizontal or vertical polarization.
Frequently Asked Questions
Who is the Corner Reflector Antenna and who brought it into the world?
The Corner Reflector Antenna is a directional antenna design that was developed by John D. Kraus back in 1938. It has remained a staple of VHF and UHF radio engineering ever since.
What are the Corner Reflector Antenna's key stats and 'powers'?
It typically delivers a moderate gain in the 10-to-15 dB range while maintaining a strong front-to-back ratio of 20 to 30 dB. It also enjoys a notably wide operating bandwidth compared to many other directional designs.
How is the Corner Reflector Antenna physically built?
At its heart sits a dipole driven element positioned in front of two flat, rectangular metal screens that meet at a right angle (usually 90 degrees). This geometry lets the antenna radiate linearly polarized waves and be aimed for either horizontal or vertical polarization.
Which frequency bands does the Corner Reflector Antenna cover?
It is designed to operate across both the VHF and UHF bands, making it a versatile choice for a broad range of mid-frequency radio applications.
Why does the Corner Reflector Antenna matter in real-world radio work?
Its combination of moderate gain, excellent front-to-back rejection, and wide bandwidth makes it a go-to option for UHF television reception and point-to-point radio links. It has been a reliable workhorse in those roles for nearly a century.
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