**3.4 Validation of the developed approach for composite geometry**

The developed approach has been validated to simulate the scattering characteristics of a single monopole antenna, fed by waveguide excitation from a flanged coaxial line with dielectric filling. **Figure 5a** shows a schematic view of such antenna with a height *ha* = 10 mm placed above a square metallic plate of 20 mm � 20 mm, which serves as a reflector. The coaxial line has an outer diameter *D* = 6.98 mm, an inner diameter *d* = 2 mm, and a length *hb* = 15 mm. The line bottom end is accepted as a waveguide port, and the input impedance of the antenna at this port is simulated for various dielectric fillings of the line.

**Figure 6** shows a comparison of the input impedances, calculated by the developed approach for the model of **Figure 5a** with *ε<sup>r</sup>* ¼ 1*:*0001 , by the WPE approach for the conducting model of **Figure 5b**, and by discontinuous Galerkin time-domain (DGTD) method [28]. An excellent agreement between the obtained results is seen, which confirms the equivalence and correctness of both WPE approaches (for conducting and composite geometries) for very low dielectric fillings of coaxial lines.

**Figure 5.** *Single monopole antenna fed by a flanged coaxial line: (a) with dielectric filling; (b) without dielectric filling.*

#### **Figure 6.**

*Comparison of the input impedances of a monopole antenna in the port plane, calculated by the MoM for ε<sup>r</sup>* ¼ 1*:*0001 *and ε<sup>r</sup>* ¼ 1 *with DGTD method.*

*Waveguide Port Approach in EM Simulation of Microwave Antennas DOI: http://dx.doi.org/10.5772/intechopen.102996*

#### **Figure 7.**

*Comparison of the input impedances of a monopole antenna in the port plane for the dielectric filling of a coaxial line ε<sup>r</sup>* ¼ 2*:*25 *calculated by MoM and DGTD method.*

**Figure 7** shows a comparison of the input impedances, calculated for the model of **Figure 5a** with *ε<sup>r</sup>* ¼ 2*:*25 using the developed approach and DGTD method. An excellent agreement between both results is seen, which validates our approach to treat arbitrary dielectric and geometric parameters of composite structures with waveguide port excitation.

Comparison of **Figures 6** and **7** shows that the use of dielectric filling of the coaxial line shifts the resonances of the input impedance to lower frequencies. In addition, this leads to a change in the line's characteristic impedance from 75 Ω in **Figure 6** to 50 Ω in **Figure 7**. Thus, the developed WPE approach for composite geometries covers a wider area of geometries and provides more control over the characteristics of the analyzed structures.
