確認（シミュレーション）

x2 = {1, 0};      
y2 = {Cos[θ], Sin[θ]};       
A = 
      RA*Exp[I*θA]; 
B = RB*Exp[I*θB]; 
A*x2 + B*y2  //  ComplexExpand

ta = 
        45  °;
tb = 
        ta + θ + π;
nframe = 
        4;
xyreg = 
        0.5;
Do[
ParametricPlot[
          Evaluate[
            x2*Cos[t + ta] + 
                y2*Cos[t + tb]  /.  {θ -> 30  °}], {t, 
            0, (2*π)*(i/
                  nframe)}, 
PlotRange -> {{-xyreg, xyreg}, {-xyreg, xyreg}}, 
Frame -> 
            True, 
AspectRatio -> 
            Automatic];
, {i, 1, 
        nframe}
]