**5. Application of waveguide port approach**

The obtained approach has been applied to practical EMC problems for microwave antennas fed by coaxial waveguides. Such waveguides are the most commonly used to excite microwave antennas and electronic devices. This excitation usually uses microwave coaxial connectors, such as BNC and SMA.

#### **5.1 Modeling of two branches feeding large printed UWB antenna**

First, based on the measurement data [28], a printed ultra-wideband (UWB) antenna is considered. **Figure 13** shows a schematic view of a large printed UWB antenna with a two-branch-feed, the bottom of which is connected to the core of a 50 Ω SMA connector with waveguide excitation, the covering of which is connected to a metal plate serving as a reflector. The bottom end of the connector is accepted as a waveguide port, and the input impedance of the UWB antenna at the waveguide port is measured and simulated.

The model of a printed UWB antenna is a square metal patch with a length *La* = 40 mm and a width *Wa* = 40 mm, printed on a dielectric substrate with a length *Lb* = 43 mm, a width *Wb* = 47.5 mm, a thickness *t* = 1.5 mm and material parameters *εrd* = 4.4 and tanδ*<sup>d</sup>* = 0.02. The antenna is connected to a two-branch-feeding strip with a total width *t*<sup>1</sup> = 15 mm, a distance between the branches *t*<sup>2</sup> = 11 mm, and a height of the branches *h*<sup>1</sup> = 3.5 mm. The UWB antenna is placed at a height *h*<sup>2</sup> = 3 mm above a metallic plate of a length *L* = 275 mm and a width *W* = 207 mm and is connected to the SMA connector. The model of the SMA connector is represented by a coaxial waveguide with an outer radius *D*/2 = 2.125 mm, inner radius *d*/2 = 0.635 mm, and a length *L*con = 6.8 mm, filled with a polyethylene dielectric with relative permittivity *ε<sup>r</sup>* = 2.24 and loss tangent tan δ = 0.005.

**Figure 14** shows a comparison of simulated input impedances of a printed UWB antenna at the waveguide port with measurement results [28]. Comparison of the simulated results with measurement data shows a good agreement between them in a wide frequency range from 1 to 10 GHz. This validates the developed approach to modeling the composite antenna geometries fed by coaxial waveguides with dielectric filling.

#### **5.2 Coupling problem between GPS and SDARS antennas**

In conclusion, based on the measurement data [28], the coupling between the GPS and SDARS patch antennas was analyzed in the frequency range from 1 GHz to 3 GHz. **Figure 15** shows the measurement setup (a) and its schematic view (b) for studying

**Figure 13.**

*Schematic view of a large printed UWB antenna with two branch feed connected to a coaxial waveguide port.*

#### **Figure 14.**

*Comparison of the simulated and measured input impedances of a printed UWB antenna.*

**Figure 15.**

*Measurement setup (a) and its schematic view (b) for the coupled GPS and SDARS patch antennas.*

the coupling between active GPS and passive SDARS antennas, separated by a distance of *d* = 4 cm. Both antennas are fed by 50 Ohm coaxial lines with standard SMA connectors with parameters described in Section 5.1.

The parameters of the setup are the following. The SDARS antenna is a square metallic patch of 32 mm 32 mm size with two opposite cut corners, printed on a dielectric substrate with dimensions 34 mm 34 mm 3.25 mm and *ε<sup>r</sup>* = 4.1. The GPS antenna is constructed by a square metallic patch of 21 mm 21 mm size with truncated corners, printed on a 25 mm 25 mm 4 mm dielectric substrate with ε*r*<sup>1</sup> = 20.34. Both patch antennas are mounted on a 190 mm 145 mm metal plate.

**Figure 16** shows a comparison of the transmission coefficient between active GPS and passive SDARS patch antennas, obtained by the developed MoM approach and measurements. A pretty good agreement between the simulated results and measured data in the frequency range of 1–3 GHz is observed. This comparison validates the developed waveguide port approach with measurements to model coupling problems between different composite geometry antennas with coaxial waveguide ports.

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

**Figure 16.**

*Transmission coefficient between GPS and SDARS patch antennas.*
