L-Band radars do not need to have large antennas. Since they have a longer wavelength and a smaller frequency they can travel further, that is why airports use L-band radars when detecting incoming airplanes at a long range, and communication between GPS, GLONASS, and Galileo systems.
First...The L-band is of a lower freq than the X-band...
Radar - Wikipedia, the free encyclopedia
From the source above, the L-band is 1-2 ghz and the X-band is 8-12 ghz.
Second...Radio communication is not the same as radar detection, even though both may uses the exact same signal. Explanation why below.
Finally...The B-2, F-117, F-22 and F-35 are considered 'non-cooperative' targets. Civilian airports searches for 'cooperative' targets. Airliners
WANT to be seen. Military aircrafts usually do not. So the example of airports using the L-band is inappropriate.
There is a reciprocal relationship between beam width, which affect target resolutions, and antenna dimensions. The narrower the beam, the greater the target resolutions, such as altitude, airspeed and aspect angle to the seeking radar.
RADAR BEAM CHARACTERISTICS
Beamwidth varies directly with wavelength and inversely with antenna size.
For any desired beam width, either we change the antenna dimension or we change the transmitting freq. In other words, for any transmitting freq, the larger the antenna, the narrower the beam. That mean the antenna using the L-band will be larger than another antenna using the X-band for the same beam width. If we cannot change antenna size but want to affect beam width, we must change the transmit freq to affect/produce the desired beam width.
Beam width affect a radar detection property called 'resolution cell'...
Definition: radar resolution cell
The volume of space that is occupied by a radar pulse and that is determined by the pulse duration and the horizontal and vertical beamwidths of the transmitting radar. Note: The radar cannot distinguish between two separate objects that lie within the same resolution cell.
So even though the L-band in this small wing mounted antenna may have longer reach than the larger X-band nose mounted radar, which I highly doubt, against a target whose body is designed to deliberately affect radar surface wave behaviors, a 'non-cooperative' body, target resolutions will be so poor that the pilot will not be able to determine beyond the %50 certainty threshold that he is seeing a target, let alone the possibility that there may be more inside the large resolution cell created by the L-band beam width. By the time this L-band radar is able to produce any target resolutions, the pilot will be on his way to meet Charon.
Keep in mind 3 very important items in radar detection:
- Antenna size
- Beam width (transmit freq)
- Resolution cell
Their relationship and effects on each other cannot be separated.