Compact Antennas for In-Band Full-Duplex Applications

This paper presents two compact antennas for in-band full duplex wireless communication systems. One of the most critical tasks in designing this type of antenna is mutual coupling suppression. The conventional decoupling networks employ external circuits which are positioned below, above, or between the radiating elements, leading to large overall dimensions. This paper shows two approaches to designing compact in-band full duplex antenna systems. The first approach employs a self-decoupling technique to avoid using any external decoupling circuit. Alternatively, the second approach is a combination of compact radiating elements and defected ground structure. In both cases, the isolation is about 40 dB with extremely small element spacings, which are just about <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.016\lambda(\lambda$</tex> is a free-space wavelength at the operating frequency) for the first approach and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.008\lambda$</tex> for the second approach. Meanwhile, the overall antenna dimensions can reach a compact size of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.49\lambda\times 0.37\lambda\times 0.01\lambda$</tex>.