1000-1450 MHz Feed

This feed was designed and constructed by the Millimeter Wave Laboratory of the Raman Research Institute. It is of the corrugated horn type - known for its high aperture efficiency and very low cross-polarization levels. In any horn, the antenna pattern is severely affected by the diffraction from the edges which can lead to undesirable radiation not only in the back lobes but also in the main lobe. By making grooves on the walls of the of a horn, the spurious diffractions are eliminated. Such horns are called ``Corrugated horns''[4]. Our feed at 1420 MHz. has fins instead of grooves, since the whole assembly is made out of brass sheets. The flare-angle of the horn is $120^{\circ}$. The dimensions of the feed are:

• Aperture diameter : $\:3.65\:{\lambda}$
• Horn length : $\:4.48\:{\lambda}$

The phase center has been found out to be at the apex of the cone - at a depth of 200 mm from the aperture plane. This feed has an impressive bandwidth: 580 MHz, starting from 1000 MHz to 1580 MHz, as can be seen from Fig 19.15

Figure 19.15: The VSWR as a function of frequency for the 1420 MHz feed.

Radiation patterns, including the cross-polar pattern is shown in Fig 19.16.

Figure 19.16: Radiation Pattern of the 1420 MHz feed.

The edge taper is $-19$ dB and the cross-polar peak is $-24$ dB. The front-end electronics is housed in a rectangular box,on the back side of the horn, forming one integral unit. The entire band is divided into 4 subbands, each 140 MHz wide and centered on 1390, 1280, 1170 and 1060 MHz. There is also a bypass mode in which the entire bandwidth is available.