Azimuth Angle Estimation for a Reduced Radiation Region Formed by a Metaspiral Antenna

A two-arm metaspiral antenna is presented, where the feeding voltage sources are expressed using excitation amplitude <inline-formula> <tex-math notation="LaTeX">$r$ </tex-math></inline-formula> and deviation angle <inline-formula> <tex-math notation="LaTeX">$\delta $ </tex-math></inline-formula>. This excitation is decomposed into the odd mode and even mode components. The odd mode component forms a circularly polarized (CP) axial beam and the even mode component forms a CP conical beam, whose maximum intensity is off the antenna axis. Superimposing the conical beam onto the axial beam forms a reduced radiation region in the elevation plane. The reduced radiation region is used for minimizing transmission in a particular <inline-formula> <tex-math notation="LaTeX">$\phi _{\mathrm {FBD}}$ </tex-math></inline-formula> direction or the rejection of interference signals from the <inline-formula> <tex-math notation="LaTeX">$\phi _{\mathrm {FBD}}$ </tex-math></inline-formula> direction. This paper presents a formula that estimates the azimuth angle of the reduced radiation region. The formula features the excitation mode ratio, <inline-formula> <tex-math notation="LaTeX">${m}$ </tex-math></inline-formula>, and the mode phase difference, <inline-formula> <tex-math notation="LaTeX">$\Delta \Phi $ </tex-math></inline-formula>. The formulated azimuth angle is validated by showing good agreement with the simulated azimuth angle obtained by searching for a null over the 3D radiation pattern. The formula is simple and hence supersedes the time-consuming 3D null search.