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Abstract
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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 0:02λ00:035λ0 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 S11 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.
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