## 6 Experimental Validation  
A prototype of the basic patch antenna and the proposed CDNG-MTM loaded ESA are fabricated on a low-cost FR-4 substrate with relative permittivity (\(\epsilon_{r}\)) 4.4, loss tangent (tan\(\delta\)) 0.02, and substrate height (\(h\)) 1.6 mm. The designed antenna is tested using a vector network analyser. All the simulations and optimisations are carried out using ANSYS(r) HFSS [38]. Even though the parametric analysis shows that the designed antenna can resonate up to 1.8 GHz in the lower band and 4.5 GHz in the higher band, the prototype is designed and tested at the resonance of 2.4 GHz and 5.2 GHz because they are the most commonly used application bands in wireless communications. All the mathematical calculations are done based on the lower resonance frequency 2.4 GHz. A photograph of the CDNG-MTM loaded ESA is shown in Figure 12. The simulated and measured return loss characteristics of the CDNG-MTM loaded ESA are shown in Figure 13. The figure shows that the ESA is operating at two bands with centre frequencies 2.43 GHz and 5.2 GHz. The percentage bandwidth of the basic patch antenna is 3.5%. CDNG loading results in antenna miniaturisation with enhanced bandwidth. The CDNG loaded ESA has a percentage bandwidth of 1.63% at 2.4 GHz and 13.15% at 5.2 GHz. It has, \(k=51.47\) rad/m at the first resonant frequency 2.4 GHz, a = 14.14 mm and therefore \(ka=0.72<1\). When these values are applied in Equation (6), the \(Q_{\text{min}}=4.07\) whereas the actual \(Q\) radiated (\(Q_{rad}\)) obtained is 61.3%. Hence, by definition, the proposed antenna is electrically small [1]. \[Q_{\text{min}}=\frac{1}{k^{3}a^{3}}+\frac{1}{ka} \tag{6}\]  
Figure 11: Variation in resonant frequency with respect to position of CDNG-MTM. The maximum bandwidth can also be expressed using Chu limit as  
\[FBW_{\text{max}}=\frac{VSWR-1}{Q_{\text{min}}\sqrt{VSWR}} \tag{7}\]  
where \(FBW_{\text{max}}\) represents the maximum fractional bandwidth. On applying (6) and (7), the \(FBW_{\text{max}}\) that can be achieved at \(VSWR=2\), is 17.37% and the bandwidth of 1.63% obtained is well below the maximum limit of bandwidth. Radiation characteristics of the proposed ESA at 2.4 GHz and 5.2 GHz are plotted in Figure 14. E-plane and H-plane show omni-directional characteristics in both the bands. A comparative analysis of the parameters of the basic patch with the proposed CDNG-MTM loaded antenna is presented in Table 2. The comparison shows that the proposed modified structure has distinct advantages in terms of size, operating bands, and bandwidth. Figure 12: Prototype of the proposed ESA. (**a**) Top view. (**b**) Bottom view. Figure 13: Simulated and measured return loss characteristics of the proposed ESA. A comparative study of different types of electrically small antennas in terms of overall size, _ka_ value, percentage miniaturisation, resonant frequency, gain, number of bands, and percentage bandwidth is summarized in Table 3. The comparison of the overall size of the antenna is done in terms of '\(\lambda\)' wherever available, because it standardizes the electrical size of different antennas operating in different frequencies. A comparison of the overall size of various antennas reveals that all the antennas are larger than the proposed one. In conventional antennas, the increase in substrate permittivity normally decreases the antenna size. In the proposed antenna, the introduction of the CDNG-MTM on the FR4 substrate alters its permittivity so that the size of the antenna is reduced more considerably than the size reduction achieved by other MTM based antennas in Figure 13.0 The proposed