# Design and Development of a Wideband Planar Yagi Antenna Using Tightly Coupled Directive Element
## 5 Antenna Fabrication and Measurements  
The designed antenna was fabricated using a conventional chemical-based fabrication process. A moisture and dust green-solder mask was used to protect the metalized layers from oxidation. The spacing used between the plated-through holes of 1-mm in diameter was 1.6 mm. These holes were fabricated using a conventional drilling and plating process. The overall dimensions of the proposed antenna structure are \(60\times 140\) mm\({}^{2}\). A photograph of the fabricated Yagi antenna is shown in Figure 6. The measured and simulated reflection coefficient results (parameter S\({}_{11}\)) are presented in Figure 7. The reflection coefficient values (parameter S\({}_{11}\)) of the proposed antenna are less than \(-10\) dB in the frequency range 2.6-4.3 GHz, which is equivalent to a fractional bandwidth of 49.3%. The simulated and measured E-plane (xy-plane) and H-Plane (yz-plane) radiation patterns at 3 GHz, 3.5 GHz, and 4.0 GHz are presented in Figure 8a-c, respectively. Good agreement is observed between measured and simulation results. The proposed antenna exhibits excellent radiation characteristics with the maximum value of the side-lobe level (SLL) being less than \(-10\) dB compared to the main lobe. Other radiation parameters, such as the half-power beam width (HPBW), cross-polarization, realized gain, and side-lobe levels for the E-plane and H-plane radiation patterns at different frequencies are summarized in Table 3.  
Figure 5: Comparison of (**a**) input impedance (real) and (**b**) input impedance (imaginary) parameters of the proposed antenna element, without and with tightly coupled wide directive element. Figure 6: Photograph of the fabricated proposed antenna (**a**) front view (**b**) back view. The 3D-radiation pattern graphs at 2.75 GHz and 3.5 GHz are presented in Figure 9a,b, respectively. At higher frequencies, the antenna beams become more directive and concentrates toward the end-fire direction. A snapshot photograph presenting the electric field distribution over the top plane of the antenna's surfaces with and without plating via-holes is shown in Figure 10a,b, respectively. It can be observed that via-holes concentrate maximum energy toward the end-fire direction. On the other hand, in the antenna without via-holes, a strong electric field near the edges is observed. The antenna gain was measured using standard gain horn-antenna measurements. Initially, the free-space transmission coefficient (parameter S\({}_{21}\)) was measured using (i) a broadband horn antenna (LB-10180) from the A-info company and (ii) a standard-gain horn (SGH) antenna from the NSI company. Next, the standard-gain horn antenna was replaced by the antenna under test (printed Yagi), and the S\({}_{21}\) measurements were recorded. The gain values were calculated by consulting the SGH data-sheet and comparing both readings. A comparison between the simulated and measured gain performance is shown in Figure 11a. Both simulated and measured results are in good agreement with a difference not exceeding \(\pm\) 0.8  dB. Commonly, such difference may occur due to connector's insertion loss, fabrication tolerances, radiation pattern measurements performed in non-anechoic chamber environment, difference in substrate material definition used in simulation and real fabrication especially the dissipation factor (tan8) value. From the parametric analysis, it can be discovered that antenna's performance parameters especially the reflection coefficient and the gain values are significantly affected by the varying structural parameters in the order of few millimeters. The simulated antenna's directivity and gain at 3.5 GHz are found to be 9.93 dBi and 8.31 dBi, respectively. This difference might be due to the fabrication tolerances of the antenna manufacturing process. Secondly, we considered that the substrate used in fabrication may have exhibited more dissipation loss than that one used in our simulation setup.