Dual-band full-duplex antenna with high isolation using differential fed and dual-polarization

This study proposes a new design approach for a dual-band full-duplex antenna to achieve high interport isolation using the differential fed technique. It consists of a single radiating patch, a differential fedline, and a direct fedline. A slotline-based balun is used in the design to implement the differential fed, which offers minimum phase and magnitude imbalances to the patch of the antenna. The differential fed and direct-fed lines are orthogonally connected to the radiating patch to realize dual polarization. Both the dual-polarization and differential fed techniques help to improve the interport isolation of the antenna. It offers an interport isolation of more than 51 and 53 dB over the entire lower and higher operating bands, resonating at 3.22 and 4.1 GHz with 84 and 110 MHz bandwidths. To validate the proposed antenna, a prototype has been fabricated on an FR-4 substrate with the dimensions of (1.79 x 1.79 x 0.017)lambda(g) (lambda(g) is the guided wavelength in the substrate at the lower frequency f(1)), with measured results consistent well with simulations. The far-field measurement exhibits that the proposed antenna provides a unidirectional broadside radiation pattern and achieves a minimum cross-polarization of less than -38 dB in all directions and less than -42 dB in the direction of the main lobe in both E- and H-planes at the resonant frequencies. The antenna has insignificant backward radiation with the front-to-back ratio >= ${\boldsymbol{\ge }}$20 dB when port1 is active and the front-to-back ratio >= ${\boldsymbol{\ge }}$30 dB when port2 is active. Moreover, the proposed antenna design is simple and easy to fabricate as the differential fed is implemented using the slotline-based balun within the same general purpose FR-4 substrate layer. This eliminates the need for any additional and separate circuits for differential fed and minimizes the overall volume of the antenna.