Physical Bounds for Antennas Above a Ground Plane

Abstract

Physical limitations of antennas above innite perfect electric conductor (PEC) ground planes are determined using the stored electromagnetic energy. Stored energies are computed with the method of moments (MoM) and the image theory. Convex optimization is used to derive the G/Q ratio and Q-factor for a reference geometry and the results are compared for dierent antenna types.

Minimization of Antenna Quality Factor

“…Because the structure possesses no geometrical symmetries, the procedure described in Section II can be followed without special treatment for degenerate modes. In order to find the parameter ν at which Q lb = Q lb , the bisection algorithm [14] can be employed to solve 2 the maximization problem in (13). The minimum quality factor Q lb occurs at ν ≈ 0.865, see Fig.…”

“…Certain antenna parameters (or their combinations) can be analyzed in the static limit [10] or be reformulated as convex optimization problems for larger structures [11], [12]. Effects of finite ground planes, lossy materials, or magnetic currents can also be included [5], [12], [13]. However, the unconstrained minimization of quality factor Q has not been formulated as a convex problem, making its solution much more difficult.…”

State‐space models and stored electromagnetic energy for antennas in dispersive and heterogeneous media

“…By offering a stable method of calculating the Q factor for inhomogeneous media the state‐space method opens up avenues of research for calculating optimal Q values for application‐based cases. This suggests the possibility to construct Q factor bounds for more applications than free space [ Gustafsson and Nordebo , ; Gustafsson et al , ] and infinite ground planes [ Tayli and Gustafsson , ].…”

Extremely Low-Profile Tunable Multiport Handset Antenna

“…This suggests that the difference in total efficiency is more due to deteriorated impedance matching than degraded radiation efficiency. As the large Q-factor is known to be a limiting factor for the operation of antennas with small height [25], [26], the presence of the lossy material of the user's hand can actually be beneficial by lowering the Q-factor. Antenna 1 has similar TARC with the user as in free space, leading to lower total efficiency due to lower radiation efficiency.…”

“…Decreasing the height of the antenna inevitably increases the Q-factor and as a consequence, either the achievable efficiency level or the bandwidth is reduced [25], [26]. One way to improve the performance while making the antenna smaller is to introduce tunable components in the matching networks or as aperture matching components to cover only part of the band instantaneously.…”