The $\vec E$ field in a rectangular waveguide of inner dimensions a$\times$b is given by $\vec E$= $\dfrac{\omega \mu}{h^2} \left( \dfrac{\pi}{a} \right)$H₀ sin $\left( \dfrac{2\pi x}{a} \right)^2$sin ($\omega t - \beta z$$\widehat y$
Where H₀ is a constant, and a and b are the dimensions along the x-axis and the y-axis respectively. The mode of propagation in the waveguide is