5.337 The use of the bands 1 300-1 350 MHz, 2 700-2 900 MHz and 9 000-9 200 MHz by the aeronautical radionavigation service is restricted to ground-based radars and to associated airborne transponders which transmit only on frequencies in these bands and only when actuated by radars operating in the same band.
5.423 In the band 2 700-2 900 MHz, ground-based radars used for meteorological purposes are authorized to operate on a basis of equality with stations of the aeronautical radionavigation service.
5.424 Additional allocation: in Canada, the band 2 850-2 900 MHz is also allocated to the maritime radionavigation service, on a primary basis, for use by shore-based radars.
G2 In the bands 216.965-216.995 MHz, 420-450 MHz (except as provided for in G129), 890-902 MHz, 928-942 MHz, 1300-1390 MHz, 2310-2390 MHz, 2417-2450 MHz, 2700-2900 MHz, 3300-3500 MHz, 5650-5925 MHz, and 9000-9200 MHz, use of the Federal radiolocation service is restricted to the military services.
G15 Use of the band 2700-2900 MHz by the military fixed and shipborne air defense radiolocation installations will be fully coordinated with the meteorological aids and aeronautical radionavigation services. The military air defense installations will be moved from the band 2700-2900 MHz at the earliest practicable date. Until such time as military air defense installations can be accommodated satisfactorily elsewhere in the spectrum, such operations will, insofar as practicable, be adjusted to meet the requirements of the aeronautical radionavigation service.
US18 In the bands 9-14 kHz, 90-110 kHz, 190-415 kHz, 510-535 kHz, and 2700-2900 MHz, navigation aids in the U.S. and its insular areas are normally operated by the Federal Government. However, authorizations may be made by the FCC for non-Federal operations in these bands subject to the conclusion of appropriate arrangements between the FCC and the Federal agencies concerned and upon special showing of need for service which the Federal Government is not yet prepared to render.

Wiki entries

Airport Surveillance Radar (ASR-11)

Current Use 2700–2900 MHz Airport Surveillance Radar (ASR-11) primary radar band

According to the FAA:

Airport Surveillance Radar (ASR-11) is an integrated primary and secondary radar system that has been deployed at terminal air traffic control sites. It interfaces with both legacy and digital automation systems and provides six-level national weather service calibrated weather capability that provides enhanced situational awareness for both controllers and pilots.

The primary surveillance radar uses a continually rotating antenna mounted on a tower to transmit electromagnetic waves that reflect, or backscatter, from the surface of aircraft up to 60 nautical miles from the radar. The radar system measures the time required for radar to echo to return and the direction of the signal. From this, the system can then measure the distance of the aircraft from the radar antenna and the azimuth, or direction, of the aircraft in relation to the antenna. The primary radar also provides data on six levels of rainfall intensity and operates in the range of 2700 to 2900 MHz. The transmitter generates a peak effective power of 25 kW and an average power of 2.1 kW. The average power density of the ASR-11 signal decreases with distance from the antenna. At distances of more than 43 feet from the antenna, the power density of the ASR-11 signal falls below the maximum permissible exposure levels established by the Federal Communications Commission (FCC).

The secondary surveillance radar uses a second radar beacon antenna attached to the top of the primary radar antenna to transmit and receive area aircraft data for barometric altitude, identification code, and emergency conditions. Military, commercial, and some general aviation aircraft have transponders that automatically respond to a signal from the secondary radar by reporting an identification code and altitude. The air traffic control centers uses this system data to verify the location of aircraft within a 60-mile radius of the radar site. The secondary radar also provides rapid identification of aircraft in distress. The secondary radar operates in the range of 1030 to 1090 MHz. Transmitting power ranges from 160 to 1500 watts.

NEXRAD Weather Radar

Current Use 2700–3000 MHz NEXRAD Weather Radar

In the United States, NEXt-generation weather RADars (NEXRAD) operate in the band 2700-3000 MHz. The radars are WSR-88D (Weather Surveillance Radar - 1988 Doppler) models. According to the National Weather Service, there are 160 operational NEXRAD radars throughout the U.S. and at some overseas locations.
According to NTIA technical report 13-490, the lowest tuned frequency for any NEXRAD is 2705 MHz, and the radars have the following technical characteristics:

Peak transmitter power	750 kW
Transmitter type	klystron tube
Operational frequency range	2700-3000 MHz
Antenna type	9 m (28 ft) diameter parabolic reflector with microwave feed horn at power center
Antenna gain	45.5 dBi
Antenna height above ground	24 m (80 ft)
Antenna beam width	0.95 deg (3 dB width) 0.15 deg (boresight accuracy)
Antenna sidelobe levels	At least 27 dB below main-beam gain
Antenna beam scanning protocol	conical scan, +0.5 deg to +20 deg elevation
Antenna beam scanning rate	6 rpm (10 sec/scan revolution interval)
Transmitted pulse widths	short pulse: 1.6 microsec long Pulse: 4.5 microsec
Transmitted pulse modulation	P0N (unmodulated CW pulses)
Transmitted pulse repetition rates	short pulse: 318 to 1304 pulses/sec long pulse: 318 to 452 pulses/sec
Receiver bandwidth	0.795 MHz