Patch antennas with ring hybrid feeding structures and defected ground structure for full-duplex applications

Carlene Goodbody

With the rise of the internet of things (IoT), recent years have seen an explosion of the wireless trend. As a result, wireless communication spectra have become very crowded and the limitations in current radio technology evident. Current communication systems apply a time/frequency-division approach to enable bidirectional communications. These techniques divide time or frequency resources into orthogonal portions for transmission and reception. If these systems were to attempt communication at the same time and frequency the received signal would be overwhelmed by the transmit signal which is of a significantly higher power. Finding a solution to the phenomenon of self- interference could theoretically double the capacity of current communication networks[1][2]. Further because of the increased number of applications for wireless technology there is a significant need to achieve self- interference cancellation while maintaining a very small footprint. In this work, two microstrip antenna system designs are presented for in-band full-duplex application. The elements of the design include a probe-fed patch, modified 180o hybrid (in splitter/combiner configuration) and nested defected ground structure (DGS) respectively. Both models utilize the modified 180o hybrid to reduce interference between the transmit and receive ports of a single patch antenna. They are designed to operate in the ISM band of 2.4 to 2.5 GHz. The first design, a probe-fed patch antenna, has an isolation bandwidth of 90 MHz, 3.67% of 2.45 GHz. While the second design, a patch antenna with DGS, has an isolation bandwidth of 100 MHz, 5% of 2.45 GHz. Measured in a reflective environment, the probe fed patch antenna has measured isolation below - 50 dB with peak isolation of - 65 dB and the DGS antenna has measured isolation below -50 dB with peak isolation of -76 dB. Both designs have good gain and radiation patterns presenting a spherical directional pattern. Both antennas present an envelope correlation coefficient, calculated from far fields, of ≥ 0.005 at all frequencies suggesting almost no mutual coupling between the transmit and receive ports across the band of interest well below the accepted 0.3 thresholds for multiple input multiple output systems used to quantify our results for full-duplex operation.

Patch antennas with ring hybrid feeding structures and defected ground structure for full-duplex applications

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