Miniaturized design of coupled bi‐element array antenna using sequential inductive and interdigital capacitive circuits

Abstract

An electrically small array antenna (ESAA) is proposed including two tightly coupled half-monopole antennas (TCMAs) as a single radiation element with two excitation ports. By properly using two consecutive inductive-capacitive loadings in the conventional bi-element monopole, total electrical length of the resonant frequency is increased, significantly and then the frequency migrates from 4 to 0.5 GHz as a frequency sample (i.e., an 88% reduction). This combination consists of several stubs on each of the monopoles and an interdigital capacitor designed in the dead space between them so that only a compact overall size of 0:02λ 0 Â 0:035λ 0 at 0.5 GHz is occupied. The studies on different subsections of the TCMA are done and additionally an extended circuit model and simplified one are presented which agrees well with simulation. Due to the fully symmetrical design and elimination of the cross currents, a stable omni-directional radiation pattern with high polarization purity and radiation efficiency over 20 dB and 78% is achieved, respectively. An implemented prototype exhibits an improved impedance matching and measured 10 dB S 11 bandwidth of 34% which are in good agreement with simulation. The proposed TCMA can be a good candidate for compact wireless systems such as RFID sensors.