Wideband planar array antenna based on SCRLH-TL for airborne synthetic aperture radar application

This paper presents empirical results of a novel planar microstrip array antenna based on a simplified composite right/left-handed transmission line (SCRLH-TL) for application in circularly polarized synthetic aperture radar (CP-SAR) systems operated in UHF, L, S, and C-Bands. The array antenna consists of 6x6 matrix of spiral-shaped radiating elements that are excited through proximity-coupled, single feed-line. Pattern synthesis technique is used to determine the excitation coefficients (amplitude and phase) to apply to the individual array elements to achieve the required pattern shape. The array antenna has dimensions of 111.5x96.06mm(2). The measured impedance bandwidth of the antenna is 3.85GHz for S-11<-10dB from 300MHz to 4.15GHz, corresponding to a fractional bandwidth of 173%. Maximum gain and radiation efficiency measured are 4.8 dBi and 79.5%, respectively, at 2.40GHz. The antenna has a 3-dB axial-ratio bandwidth of 3.94GHz from 144MHz to 4.66GHz. The antenna's beamwidth in azimuth and elevation planes vary between 60 degrees and 120 degrees across its operational frequency range from 300MHz to 4.15GHz. The antenna design fulfills the challenging electrical and physical specifications required for CP-SAR employed onboard unmanned aerial vehicle (UAV).