Contents
What are side lobes in ultrasound?
Side lobes are multiple beams of low-amplitude ultrasound energy that project radially from the main beam axis (,Fig 1). Side lobe energy is generated from the radial expansion of piezoelectric crystals and is seen primarily in linear-array transducers (,3,,6).
Why do grating lobes occur?
Grating lobes will occur whenever the size of individual elements in an array is equal to or greater than the wavelength, and there will be no grating lobes when element size is smaller than half a wavelength.
How do you get a grating lobe?
Consider a linear array of seven elements spaced one-half wavelength apart. This array contains no grating lobes. When you increase the element spacing to one wavelength, the number of side lobes increases. When you increase the element spacing to 1.5 wavelengths apart, the grating lobes appear in the visible region.
Why are the side lobes of an antenna so important?
The longer the antenna relative to the radio wavelength, the more lobes its radiation pattern has. In transmitting antennas, excessive side lobe radiation wastes energy and may cause interference to other equipment. Another disadvantage is that confidential information may be picked up by unintended receivers.
What is the radiation pattern of an antenna?
A typical directional antenna radiation pattern in polar coordinate system representation, showing side lobes. The radial distance from the center represents signal strength. A typical antenna radiation pattern in cartesian coordinate system representation showing side lobes.
What causes the side lobe of a radar to return?
When a radar is pointed toward the horizon, there is a very large area of ground covered by the side lobes in the negative elevation region. The large reflective area covered by the side lobe can cause significant side lobe returns despite the antenna attenuation.
Where does the ground return come from on an antenna?
The ground return comes though the antenna side lobe, known as side lobe clutter. Ground return is often high due to the amount of reflective area at close range, which results in a strong return despite the side lobe attenuation of the antenna. The ground return is at short range, essentially the altitude of the aircraft.