Effects of dielectric substrates on circular patch antennas’ characteristics using electromagnetic wave equation

Abstract

This study investigates whether circular patch antennas designed using the Fundamental Electromagnetic Wave Equation (FEWE) can yield realistic performance when compared with substrate-inclusive cavity model designs at an operating frequency of 2.4 GHz. Circular patch antennas were designed using FEWE and the cavity model. The FEWE-based design assumed free-space conditions, while the cavity model incorporated substrate permittivity. Three dielectric substrates, namely Duroid ( = 2.2), Rogers Ultralam 1217 (= 2.17), and FR4_epoxy ( = 4.4) were evaluated at a constant substrate thickness of 0.1575 cm. All antennas were modeled and simulated in Ansys HFSS using a probe-fed configuration. Performance parameters, including gain, directivity, return loss, VSWR, and input impedance, were extracted for comparative analysis. The FEWE-based antenna exhibited negative directivity (−7.021 dB) and gain (−7.045 dB), poor return loss (−0.30 dB), a very high VSWR (57.00), and an input impedance of 308 Ω, indicating severe mismatch. In contrast, cavity-model designs achieved positive radiation performance: Duroid (6.909 dB directivity, 6.839 dB gain), Rogers Ultralam 1217 (6.940 dB, 6.890 dB), and FR4_epoxy (5.477 dB, 2.401 dB). However, impedance matching remained poor (return loss −1.69 to −1.80 dB; VSWR 9.66 to 10.29; input impedance 193Ω to 321Ω). Increasing dielectric constant reduced antenna size but degraded radiation performance. These findings conclude that including a dielectric substrate is essential for physically realistic circular patch antenna design. While FEWE is unsuitable as a standalone design tool, substrate-inclusive models, such as the cavity model, are necessary to achieve meaningful radiation characteristics in practical wireless applications.