# Broadband Microstrip Antenna for 5G Wireless Systems Operating at 28 GHz
## 6 Optimization Process and Discussion of Simulation Results
During the optimization process, the length and width of the antenna base with the screen (W\({}_{\text{s}}\), W\({}_{\text{e}}\), L\({}_{\text{s}}\), and L\({}_{\text{e}}\)), the length and width of the radiator (L\({}_{\text{p}}\) and W\({}_{\text{p}}\)), the length and width of the power line (L\({}_{\text{f}}\) and W\({}_{\text{f}}\)) and the length and width of the patch inset (Y\({}_{0}\) and X\({}_{0}\)) were changed. Other structural elements, such as thickness and permittivity of the substrate, were not changed [28; 29; 30; 31]. In the next step, we define the range of parameters to be changed, specifying their minimum, maximum, and initial values. For each optimization parameter, a minimum value and a maximum value must be defined, and optionally, an initial value can be given as well. The initial value will influence the optimization process when using particle swarm optimization or genetic algorithm. If the starting value is not specified by the user, the value in the middle of the range of the parameter will be taken as the starting point of the optimization. In our optimization process, we selected the minimum, maximum, and start values based on calculated parameters of the rectangular patch and the center frequency. In the next step, we define an optimization mask. An optimization mask is a set of user-defined values forming a continuous line. The mask is a criterion to which the optimal solution must adhere. It is specified that the optimized solution is smaller, equal, or larger than the mask. When calculating an optimal solution, the target values are compared with the mask. If the mask criterion is met, the values are added to the value table. We do not define an optimization mask in our optimization process. The last step of the optimization process is the selection of the optimization target. The objectives, which need to be defined, specify the desired state that the optimization process should try to achieve by changing certain parameters of the antenna model. For each optimization search, goals should be defined to determine the desired state that the optimization process should aim to achieve. Many goals can be defined, but a correct optimization search must include at least one goal. During the optimization process we define the following goals:  
* Impedance goal (input impedance, input admittance, reflection coefficient (S\({}_{11}\)), transmission coefficient, VSWR, return losses, current);
* electric field, H field
- magnetic field, directional component, coordinate system);
* Radar Cross Section);
* S-parameter goal (coupling coefficient, reflection coefficient, transmission coefficient, VSWR, return losses);
* SAR (Specific Absorption Rate) goal;
* Power goal (efficiency, active power, power loss);
* Transmission/reflection coefficients goal (reflection, transmission, co-polarization, and cross-polarization);
* Receiving antenna power goal (efficiency, active power, and power loss). In our optimization process, we chose an impedance target (reflectance and VSWR) with a target minimization operator. The impedance target provides optimization related to the impedance and admittance of any voltage or current source, which is solved within the FEKO model. The reflectance ratio is calculated in relation to the indicated reference impedance. In the case of an impedance target, the reflection factor is calculated directly from the observed input impedance. Therefore, this value is the active reflection factor, and may differ from the S\({}_{11}\), which was calculated during the calculation of the S parameter in the multiport model. The voltage standing waveform factor for the observed input impedance is considered in relation to the indicated reference impedance. Once the parameters of the optimization process have been defined, we can run \"OPTFEKO\" to calculate the optimal solution for the specified parameters. Once the optimal values for the model are obtained, the FEKO model with the optimal parameters is created.