Parametric Study of Antenna Design: Impact of Lm2 and Ws1 on Performance

Several parametric studies were conducted to investigate and establish a design guideline for the proposed antenna. Each study only varied the investigated parameter, while keeping the rest of the parameters constant, as indicated in Table I.

The parametric study results for Lm2 are shown in Fig. 2. The value of Lm2 significantly affects the impedance matching of the antenna as it determines the length of the microstrip feeding line and feeding position on the slot. Fig. 2(a) demonstrates that the reflection coefficient varies greatly with different values of Lm2. However, the field distribution of the radiator is minimally affected by the value of Lm2, since the microstrip line is shielded by the metallic ground plane. Consequently, the axial ratio (AR) of the antenna only slightly changes with different values of Lm2.

Fig. 3 displays the parametric study results for Ws1. The value of Ws1 determines the size of the S-shaped patch or the M-dipole. The radiation impedance of the antenna and the radiation phase of the M-dipole differ with changes in Ws1. Consequently, Ws1 influences both the reflection coefficient and the AR of the antenna. As shown in Fig. 3(a), the best impedance matching is achieved when Ws1 is equal to 12 mm. Deviating from this value leads to a degradation in impedance matching. By carefully adjusting the value of Ws1, a resonance mode with a very small AR can be generated at high frequency, as depicted in Fig. 3(b). If Ws1 is too large, the resonance mode shifts to a lower frequency, resulting in a narrow AR bandwidth, as observed in the case of Ws1 = 14 mm. Conversely, if Ws1 is too small, the AR worsens within the operating band. When Ws1 is set to 12 mm, the antenna attains a wide 3-dB AR bandwidth.