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Exposing the near field of an antenna to varying dielectric environment causes changes of the antenna input impedance and, thus, unwanted feed mismatch. Feeding such an antenna at different points, and selecting an appropriate feed for best match at a given scenario, may solve the problem. For the case of two scenarios of different dielectric environments and an antenna with two feed points, this work presents a passive power divider network, which keeps the antenna matched to the source in either scenario. Specific impedance transformations in the two branches of the divider network realize power transfer in a first scenario from the source to complex feed impedance at the first antenna feed, while in a second scenario, with now different antenna feed impedances, matched power transfer is from the source to the second antenna feed. Analytical formulae are derived for the design of the divider network. An experiment uses an example antenna with two feeds and a microstrip divider network, connected to a common 50 ohm port. Measurements are conducted with the antenna radiating, first, in air and, secondly, into butter. The measurements show antenna match at 1 GHz in either case and agree well with the analytical results.

Attaching a wireless transmission system comprising a radio frequency (RF)-chip and a dipole antenna to dielectric material of largely different permittivity leads to strong variation of the antenna feed impedance. Due to the severe impedance mismatch between the RF-chip and the antenna, the performance of the system may deteriorate drastically. The proposed antenna provides three feed points, which show respective feed-point match to 100 Ohm balanced feeds for three different dielectric environments (free-space and half-spaces of permittivity 4 and 42, respectively). Thereby, the RF-chip incorporates three 100 Ohm balanced output ports that are connected to the antenna from whom only one can be selected to provide the output signal. The respective other two output ports are shorted by an internal switching circuit that is controlled by external DC voltages. The measurement of the reflection coefficient of the stand-alone antenna and the chip agree well with the simulations, allowing to interconnect these two components. Further, the radiation pattern of the whole system is measured for two different scenarios showing good functionalities.