On the integration of a 2.4 GHz ISM band antenna in proximity to transmission lines

In this contribution, a study of the interactions between a 2.4 GHz microstrip patch antenna and a microstrip transmission line integrated in close proximity on the same board, is presented. Our results reveal that the electromagnetic (EM) coupling between these components becomes very strong at or near the resonance frequencies of the TM-modes of the patch, especially when the distance of separation between the patch antenna and the transmission line is smaller than the difference between the physical length and the effective electrical length of the antenna, due to stray fields. Under these conditions, the antenna causes degradation of the insertion loss of the line. On the other hand, the presence of the transmission line leads to a shift in the resonance frequency of the antenna as well as a change in its impedance matching, due to fluctuations in the input impedance. To experimentally validate the simulation results, a test board was designed, fabricated and measured. A very good correlation was obtained between the measurement and simulation results.