JICAMARCA RADIO OBSERVATORY

JRO

ANTENNAS

ANTENNAS

The main Jicamarca ISR consists of an array of 18,432 half-wave dipoles covering an area of 290 m by 290 m, divided up into 64 modules of 144 crossed dipoles that can be phased and/or connected in any way, but any changes must be done by hand by changing cables, which can take a couple of hours for major changes. There are three separate transmitter modules, each capable of transmitting more than one megawatt of peak power (maximum duty cycle of 6%, minimum pulse length of 1 µs, giving a range resolution of 150 m). These can be run together or separately, feeding different antennas if desired. There is a 65th module about 200 m to the west of the main array which, together with four or five of the 64 modules, is used on reception (only) for imaging experiments (visit http://landau.phys.clemson.edu to look at some images from F and E region irregularities). Many experiments do not need the full power of the large transmitters, therefore, for such studies we can save power and manpower by using only the 100 kW driver stages or even smaller transmitters that deliver about 30 kW.

The big array points essentially vertically. The two-way half-power beam width is about 0.7° which can be steered off axis by about 3° in any direction by phasing. These pointing positions include positions that are perpendicular to the geomagnetic field. Also, there are several other smaller antennas that can be directed at large angles to the vertical, usually also normal to B. There are two “mattress” arrays that are fully steerable in the east-west direction: an array of 4 COCO (coaxial, co-linear) antennas and an array of Yagi antennas (both of the latter arrays also look in the E-W plane). This last array consists of 16 widely-spaced, tilted Yagi antennas, phased so that the beam is directed westward at a zenith angle of approximately 45 degrees (this angle could be changed if desirable for a particular experiment). The half power full beamwidth is approximately 2 degrees. With it can be observed coherent backscatter from E and F region plasma irregularities lying west of the Jicamarca radar. Observations of the electrojet and of bottomside and topside spread F have already been made with the new array during test runs.

There is a lot of land around the Observatory for additional antennas for special experiments. Arrays of a kilometer or more in length could be set up (in certain directions).