Closely-packed Antenna Research Articles

Scattering Suppression of Closely-Packed Cross-Band Patch Antennas Using Absorptive/Reflectionless Filtering Techniques

This paper presents a novel method for cross-band scattering cancelation in closely-spaced antennas inspired by absorptive/reflectionless filtering principles. Prior-art approaches that combine a bandpass-filter (BPF) unit and an antenna in multiple-input multiple-output (MIMO) systems can improve cross-band isolation between the antenna ports. However, such procedure is ineffective in suppressing cross-band scattering, which leads to radiation-pattern distortion. This is because in closely-packed antennas each radiating element behaves as an external source for the others, so that it induces currents into them. To overcome this problem, a method originating from absorptive/reflectionless filtering techniques is reported here and applied to a dual-antenna scenario. In complementary-diplexer-based reflectionless BPFs, an absorptive bandstop-filter-(BSF)-type branch loaded by a resistor is utilized to absorb the out-of-band RF power not transmitted by the main BPF channel. By using this concept in a first patch-type antenna and owing to the reciprocity principle, the RF coupled energy or induced currents in the first antenna due to the surrounding antenna can be absorbed. Thus, radiation-pattern distortion for the surrounding antenna is avoided. Equivalent-circuit, simulated, and measured results are provided to show the effectiveness of this engineered scattering-suppression method, which is believed to be promising for application in cross-band multi-antenna systems.

Reduction of mutual coupling between closely-packed antenna elements using defected ground structure

A simple ground plane structure that can reduce mutual coupling between closely-packed antenna elements is proposed. The structure consists of a dumb-bell-like pattern etched in a single ground plane. It is found that isolation of more than −40 dB can be achieved between two parallel individual planar inverted F antennas sharing a common ground plane. Influence of the designed defected ground plane structure on the radiation pattern is also investigated.

Reduction of Mutual Coupling Between Closely-Packed Antenna Elements

A simple ground plane structure that can reduce mutual coupling between closely-packed antenna elements is proposed and studied. The structure consists of a slitted pattern, without via's, etched onto a single ground plane and it is therefore low cost and straightforward to fabricate. It is found that isolations of more than -20 dB can be achieved between two parallel individual planar inverted-F antennas (PIFAs) sharing a common ground plane, with inter-antenna spacing (center to center) of 0.116 lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> and ground plane size 0.331lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . At 2.31 GHz it is demonstrated that this translates into an edge to edge separation between antennas of just 10 mm. Similarly the structure can be applied to reduce mutual coupling between three or four radiating elements. In addition the mutual coupling between half wavelength patches and monopoles can also be reduced with the aid of the proposed ground plane structure. Results of parametric studies are also given in this paper. Both simulation and measurement results are used to confirm the suppression of mutual coupling between closely-packed antenna elements with our slitted ground plane.