Improvement of gain in dual fed X band isoflux Choke horn antenna for use in LEO satellite mission

For high image data rate transmission from LEO satellites in X band frequency range, horn antenna is generally used for this purpose. Due to high data rate transmission, there is a requirement of high EIRP from space segment. This EIRP requirement is met by using antenna of high gain as much as possible with wide beamwidth due to the limitation of RF power transmission onboard the satellite. Recently, Isoflux choke horn antennas are been used in LEO satellite programs which provides an added advantage of maintaining a near to constant signal to noise ratio over the complete communication path. Isoflux Choke horn antenna used in commercial & space applications have uniform length of choke rings which provides near to Isoflux pattern. In this paper, gain enhancement has been done by introducing nonlinear size of choke rings which results an additional link margin value. Improvement of 1.5 dB gain is achieved by introducing this concept. Circular polarization is achieved using dual fed mechanism. The optimized design shows low side lobe and back lobe levels with excellent cross polarization achieved, which ensures better polarization purity and that only required polarization signal is received at the receiving end. Prototype measurement results are in close conformance with the simulated results. Measured Isoflux pattern has a gain of > 7 dB over horizon to horizon earth coverage with axial ratio <; 3 dB. VSWR value in the desired X band frequency range is <; 2.