###### Abstract  
This article presents the methodology to design a single-fed circularly-polarized antenna with low front-to-back ratio (FBR). A circular-patch (CPatch) antenna has been incorporated within the rectangular-cavity, made of, substrate integrated waveguide (SIW). The size of the CPatch and the SIW cavity has been chosen appropriately, in a manner, that the both resonators dominant mode coincide. This arrangement has been adopted to realize the basic radiating unit with no surface-wave and the significantly lower FBR. The circularly polarization has been excited through shorting the periphery of CPatch radiator to the \"one of the two metallic grounds\" of this SIW cavity. The patch periphery has been shorted from two distinct points, separated by the quarter wavelength--over center frequency of working band. The antenna has been designed and manufactured over Rogers RT/Duroid 5880 substrate with dielectric constant (\(\epsilon_{r}\)) of 2.2, loss-tangent (tan \(\delta\), at 10 GHz) of 0.0009, and substrate height of 0.508 mm. Southwest(r) end launcher (SEL) along with SIW-to-GCPW (Grounded Co-Planar Waveguide) transition has been used here to facilitate the measurement of antenna's electrical and the radiation performance. The designed antenna's impedance bandwidth and the 3 dB axial-ratio (AR) bandwidth is 9.5% and the 2.3%, respectively. It's simulated and the measured peak gain, within working frequency band, is higher than 8.5 Bic. The proposed antenna's FBR is antenna is significantly lower than the conventional circularly-polarized antennas. Through comparative study, with work in open literature, it has been demonstrated that the designed antenna, based on proposed method, can a potential candidate for applicable in satellite and in the other spaceborne communication system's module--at ground and in the space station. circular polarization; circular-patch antenna; substrate integrated waveguide (SIW); cavity-backed antenna; millimeter-wave; satellite communication; front-to-back ratio (FBR); grounded coplanar waveguide (GCPW) +
Footnote †: journal: Electronics Letters  
total antenna performance through secondary effects. Especially in phased array antenna system and in the high-gain antenna array--fed through corporate-feed network. Over millimeter wave (MMWave) and the higher frequencies this 90\({}^{\circ}\) broadband balun might degrade the antenna's polarization purity caused by coupling between feed lines of the two adjacent radiator and the surface-wave--that could be excited in the substrate of feeding network. The 2 \(\times\) 2 array of the (c) do provides the excellent performance over wider bandwidth; however, the radiators based on this method could not be used in phased-array design due to their larger size. If applied, as per the antenna array theory the larger grating lobes could emerge in array's radiation pattern--as the spacing between two basic radiators might be greater than one full wavelength [6] in free space. Therefore, over the MMWave frequencies the most suitable technique to design CP antennas--especially for the array design--would be the single-feed method. The new dimensions, in the antenna's performance improvement, could be added through \"surrounded the main-radiator via cavity\" to shield the spurious radiations and the back scattering. Such antennas are called the cavity-backed (CB) antenna. CB antennas are not new and has been studied widely [7; 8], let's take the example of the metallic waveguide-based CB CP antenna, over sub-6 GHz frequency band presented in [7], where the waveguide not merely improves the FBR but also guaranteed the higher polarization purity--over wider beamwidth. Nevertheless, metallic waveguides are bulky and hinders the antenna integration with other RF components, especially over MMWave frequencies, where the antennas use cases and the deployment scenarios are quite different.