A. I. Semenikhin - Ph.D. (Eng.), Professor of Department of Antennas and Radiotransmission Devices, Southern Federal University. E-mail: airpu@tgn.sfedu.ru
D. V. Semenikhina - Dr.Sc. (Eng.), Professor of Department of Antennas and Radiotransmission Devices, Southern Federal University
Yu. V. Yukhanov - Dr.Sc. (Eng.), Professor, Head of Department of Antennas and Radiotransmission Devices, Southern Federal University
N. I. Bobkov - Head of Sector, Rostov Research Institute "Gradient" (Rostov-on-Don). E-mail: g2645@mail.ru

Electrodynamic models and the main radio engineering characteristics of a quad-ridged ultrawideband horn feed of reflector antenna (RA) for control devices of a radio electronic situation for work in the range of 2-18 GHz at two orthogonal linear the polarization are considered. The feed has to provide a high directivity of RA through azimuth and the wide-angle simultaneous review of space through elevation; phase-frequency characteristics of two orthogonal channels have to be identical, the isolation between them in the band of operating frequencies shouldn't be less than 25 dB, and the amplitude-frequency characteristic of the realized gain (RG) has to be close to the characteristic of an optimum horn. The HFSS electrodynamic modeling results of such feed with various form of the back resonator in the area of ridge feed for the purpose of VSWR realization no more than 3 and satisfaction of requirements to frequency characteristics are given. The feed was conditionally divided into three parts: two coaxial-to-waveguide transitions with the back resonator, tapered horn section with four wedge-shaped ridges and a horn nozzle. During the modeling, optimization of coaxial-to-waveguide transitions of a feed with various forms of the resonator (from rectangular to pyramidal) is performed. For elimination of a half-wave resonance of currents at end faces of ridges additional elements were entered into internal space of the resonator. During the modeling it was established that frequency characteristics of RG and beamwidth of a feed without diaphragm significantly differ from the corresponding characteristics of an optimum horn because of excitement and distribution of the highest modes at some frequencies in the extending part and aperture of a horn. For elimination of this advantage the size of cross section of the waveguide section is optimized and the diaphragm with the rectangular window which size also is optimized is used. More technological crests extended to a short-circuiting wall of the resonator are offered. The position of a diaphragm in the waveguide transition and length of the waveguide section were chosen to achieve the smallest level of the return losses. In a range 2-18 GHz the feed with extending ridges and a rectangular diaphragm has VSVR no more than 2,8, a polarization isolation between channels at least 30 dB; the phase-frequency characteristics of channels differ no more than at 15°; the width of the pattern in the H-plane decreases with frequency growth therewith.