The Technical Panel at I FATCA '87, Nairobi As in past years IFATCA '87 again offered the Corporate Members of the Federation a platform to directly address the conference participants. A large audience of delegates and observers attended the Panel, under the chairmanship of outg oing Executive Vice-President, Technical, A.F. W (Lex) Hendriks, and listened appreciatively to the presentations. The general discussion which followed the presentations was proof of the interest generated by the speakers and of the involvement of conference delegates and observers in the subject matters presented. At the head table, in addition to Lex Hendriks, were Ron Mahendran of Ferranti, the Corporate Members' Coordinator , Harry Cole of Marconi, Jim Pawson of Ferranti and Roger Kahane of Thomson-CSF. The first paper, presented by Roger Kahane, was 'The New Kenya Integrated Air Traffic Control Radar System '. Readers will recall that this paper was published in issue 2 1 8 7 of, The Controller' in the context of the Annual Conference in Nairobi. Henry W Cole of Marconi Radar Systems was the next speaker . Harry presented an intriguing concept:
Electronically Scanned Antennas (ESA) for Secondary Surveillance Radar (SSR) Introduction For once it is appropriate to start with the question 'What is an ESA?' and give the question 'Why?' second place. Curren t ly. surveillance radars use beams formed by an array which itself is mechanically rotated at a regular rate: so the beams it makes rotate. The data rate is tied to this. At 15 rpm rotation, new data on targets is called out every 4 s - whether needed or not, and never faster.
An Electronically Scanned Antenna (ESA) is a static non-rotating array producing beams which can be pointed in any direction at will . Changes of direction can be made almost instantaneously - in microseconds using modern fast switching microwave devices . ESAs are not new but until recently have been very expensive, being used in high power primary radars for defense purposes . The use of ESAs in SSR, with its much lower
(I to r) R. Kahane, L. Hendriks, J. Pawson, R. Mahendran. H. Cole
4
output powers, holds the promise of greatly reduced costs .
Why Have Them? Independently mounted rotating SSR antennas usually have about 5 to 10 hp motive power . Gene.rally, in still air, only about 2 or 3 kW of power is dissipated in turning the antenna. Even for 24 hours continuous operation the electricity bill is quite low about £5 (7 to 8 US dollars) a day at UK rates . Stresses both electrical and mechanical are relatively low and the likelihood of massive and expensive mechanical failure is very low indeed. Even though ESA operation requires less prime power, there's not much economic sense in replacing mechanical antenna rotation by static systems on this score. The need rests much more in making best use of time to gather target data at varying rates as the ATC situation warrants it . This becomes more important when Mode ·s· - particularly the Data Link facility with its Extended Length Messages (ELMs), are used . They last for 56 µs. ELMs are sometimes required to be transmitted as a train of 16 , separated by about 50 µs and thus can grow to 1440 µsin duration; at 15 rpm and beamwidth of 2 . 5 degrees the dwell-time on a particular aircraft will be 27 µs- enough for 10 ELMs
Opening of Technical Exhibit {I tor). R. Mahendran. Erik Sermijn , H. Cole, Kenya dignitaries.
THE CONTROLLER/ DECEMBER 1987