Experimental results of structurally modified high power ultra broadband phased array antenna for extending the operating frequency range and improving the VSWR

Phased array antennas find many applications in modern electronic systems like radars, satellite communications, trackers, jammers etc. Jammers normally use high power antennas and in military applications, the jammer antennas are mission critical and need to operate continuously over long periods and transmit high power RF signals in a particular direction to provide effective jamming on the threat fire control radars, supporting the missiles. Many types of antennas mounted on rotary platforms were in use for jamming applications over few decades, but steering of the radiation beams electronically with very less reaction time with phased array antennas, fed with a dynamic phase shift network (DPSN) came into existence over past few years, provides highly directive beams for effective jamming. The radiated powers are in the order of few hundreds of power (approx. 300 Watts of CW), generated by TWTs, over wide frequency coverage with BWR >3. In such applications, the ports of the phased array antenna elements are simultaneously fed with high power UWB TWT amplifiers. In this type of applications where high power transmissions are involved, VSWR is an important parameter, which determines the amount of the transmitting power and controls the temperature at the feed point due to heating and many times poor VSWR, damages the feed connector and high cost UWB TWTs. A research has been carried out to improve the VSWR of an eight element 8-18 GHz phased array antenna and improved the VSWR over the extended frequency range of 6-18 GHz, without changing the dimensions of the array. Many conventional methods like dielectric loading, stub matching, etc., [1] were experimented, though little improvement is observed in VSWR performance in certain frequency bands of 8-18 GHz, but could not achieved the required VSWR over 6-18 GHz frequency range. Therefore structural modifications to the aperture of the array have been studied and many experiments have been carried out to evolve mechanism for improving the VSWR over entire frequency range. The experiments were successful and VSWR results were satisfactory over 6-18 GHz. These experiments and the measured results are presented in this paper and the authors would like to promote these methods for any type of aperture antennas.