Frequency Scanned Radar basics
This page covers frequency scanned radar basics.It explains operation of frequency scanned radar including block diagram. Advantages and disadvantages of frequency scanned radar are also mentioned.
The radar in which beam steering is carried out using frequency control of array antenna type is known as frequency scanned radar.
It uses phased array antenna and it is useful for scanning beam in one angular co-ordinate. This radar consists of series fed array.
Following equation mentions relation between radar frequency and beam scan angle:
Δλ = 2*λo*(d/L)sinθs
Δλ = Wavelength change
λo = Wavelength which corresponds to broadside direction of beam
d = element spacing
L = length of line which connects adjacent elements
Frequency Scanned Radar operation with block diagram
Figure-1 depicts block diagram of frequency scanned radar type. The frequency scanned radar uses scanning of various types such as single beam scanning, multiple beam scanning, multiple frequency scan, scanning using reflector antenna etc.
The phase difference between two adjacent elements is expressed as follows:
Φ = 2* π * f * L / v
L = Length of line connecting two adjacent elements
v = Velocity of propagation
Beam steering in one dimension has been implemented by changing radar frequency. The equation for wavelength change for beam excursion of +/-θs is mentioned above.
This frequency scanned radar uses folded waveguide feed referred as serpentine feed. This is shown on left side of the figure. This configuration is useful for scanning pencil beam in elevation along with mechanical rotation which provides azimuth scan.
• Simple in construction
• It is not used for high range resolution, ECM as well as pulse to pulse frequency agility.
• Scan angle is limited due to possible existence of grating lobes.
• Bandwidth is limited.
• Frequency scanning in two dimentional coordinates is not used as it reduces bandwidth of the signal.