Antenna Details
 

Dear All,

I'm a student at Liverpool University and I'm currently carrying out some research on antenna theory. I have been looking into TCAS antennas but there seems to be little technical information on them. Does anyone have any detailed technical information on any antenna that is on any current commercial aircraft?
Thanks

LW

TCAS Antenna
 

I couldn't find any detailed information in my books. However, it might be worth contacting Rockwell Collins UK Ltd, Unit 68, Sutton Business Park, Earley, Reading, RG6 1AZ. They may be able to provide you with some technical information. Their TCAS systems are certainly used on many Boeing 737-300s. Certainly worth a try. Good luck.

Don't know if this is any help - from the 737CL AMM:


3 . Directional Antenna (Fig. 2)
A. The directional antenna is an electronically steerable phased array that
has four top loaded monopole elements. The directional antenna is
connected to the TCAS computer with four coaxial cables that have TNC
plugs on the antenna end.

B. The TCAS uses two directional antennas. One is installed on top and the
other is installed on the bottom of the airplane. These antennas
transmit to and receive signals from intruder airplanes.

C. Each of the four elements of the directional antenna has a resistor that
goes from the antenna element to ground. Each of the four resistors has
a different value. The TCAS Processor regularly does a continuity test
on the antenna ports and will see the correct resistance value if the
port is not shorted and not open.

During TCAS receptions, each of the four directional antenna elements accepts any 109O-MHZ rf signal that is present. The phasing of these received signals is determined by the direction
from which the rf energy is received. These signals are directed onto the same four cables that connect transmit signals between theTCAS processor and directional antenna. The ANT-81A is a passive device and therefore does not require input power.

Some more:

The directional antenna lets the TCAS computer transmit
interrogations and receive replies on one of four antenna beams.
The TCAS processor electronically points the antenna beam in one of
four different directions to find the bearing of intruder airplanes.
The antenna does not have to move. The TCAS adjusts the drive level
and phase of each of the four antenna elements in the directional
antenna to point the beam.

TCAS transmits 1030 MHz messages from the top and bottom TCAS
antennas to interrogate ATC transponders in other airplanes. The
TCAS receives 1090 MHz messages from ATC transponders through the
top and bottom directional antenna.

Later in the troubleshooting, it states those resitance values mentioned in my first reply, fo the four segments of the antenna:

C4 (RED) 9.7K TO 10.3K OHMS
C3 (BLUE) 6.46K TO 7.14KOHMS
C2 (BLACK) 3.7K TO 4.1KOHMS
C1 (YELLOW) 1.7K TO 1.89K

Livewarrior. TCAS Antenna are "L Band" If you google "L Band Aircraft Antenna" you will find a wealth of information out there. Good luck!