A Novel TM$_01$–TE$_11$Circularly Polarized (CP) Mode Converter

A novel mode converter that converts a TM₀₁ mode to a CP TE₁₁ mode was developed. In the converter, the TM₀₁ mode is transformed into a coaxial transverse electric and magnetic (TEM) mode first, then the coaxial TEM mode is split in space into multiple TE₁₁ sector waveguide modes by eight plates in the coaxial waveguide, which further subject the TE₁₁ sector waveguide modes to different signal paths and hence effectively convert the TEM mode into a CP TE₁₁ mode. A mode converter at 4GHz was designed. The conversion efficiency of TM₀₁-to-TE₁₁ is 99% at center frequency with an axial ratio of 0.7dB. Over the frequency range of 3.8-4.3GHz, the conversion efficiency exceeds 90%, and the axial ratio is less than 2.7dB. A good agreement between experiments and simulations was observed