Parasitic spirals for enhancing bandwidth of a simultaneous transmit and receive patch antenna
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TECHNICAL PAPER
Parasitic spirals for enhancing bandwidth of a simultaneous transmit and receive patch antenna KueiJih Lu1 • Tuan Nguyen1
•
Nghi Tran2 • Tutku Karacolak1
Received: 28 October 2020 / Accepted: 3 November 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Two pairs of spiral-shape parasitic elements are proposed to improve the bandwidth of a microstrip patch antenna for simultaneous transmit and receive in 2.4–2.5 GHz ISM band. The antenna has two low-cost FR4 substrate layers and a ground plane between the layers. The top layer consists of the patch and parasitic spirals, and a modified 180° rat-race hybrid coupler is printed on the bottom layer. Adding the parasitic spirals enhance the antenna bandwidth by 15–25 MHz in both transmit and receive modes based on simulation and measured results. The hybrid coupler is used to maintain the high isolation between transmit and receive operations of the antenna. The antenna offers low-cross polarization for both modes at boresight (near 20 dB on the x–z plane and larger than 40 dB on the y–z plane). The design also has high selfinterference cancellation, a spherical directional radiation pattern, good impedance matching, and reasonable gain values.
1 Introduction Applications such as internet of things and wireless sensors employ numerous wireless devices, and the increasing number of wireless devices has crowded radio spectra and network traffic. One solution to this problem is recently emerged in-band full-duplex technology or simultaneous transmit and receive (STAR) systems, which could theoretically double the spectral efficiency compared to halfduplex and full-duplex communications by transmitting and receiving signals at the same time and the same frequency (Sabharwal et al. 2014). Because both signals are condensed down to a single frequency, more frequencies
& Tuan Nguyen [email protected] KueiJih Lu [email protected] Nghi Tran [email protected] Tutku Karacolak [email protected] 1
RF Research Laboratory, ENCS Department, Washington State University, ENCS Building, 14204 NE Salmon Creek Ave, Vancouver, WA 98686, USA
2
Department of Electrical and Computer Engineering, Auburn Science and Engineering Center, University of Akron, ASEC 352, Akron, OH 44325, USA
for the data communication will be available within a desired bandwidth, which increases the efficient use of the radio frequency spectrum (Bharadia and Katti 2016; Nguyen and Karacolak 2019). Implementing a STAR system requires sufficient self-interference cancellation (SIC) and isolation to prevent the system’s own transmit (TX) signals, which have higher magnitude than it’s receive (RX) signals, from overshadowing the system’s the RX signals. In general, self-interference suppression of 100 dB or more is needed to successfully implement a STAR system. This is mainly achieved in three stages (antenna, analog/RF, and digital cancellations) since a single technique cannot provide the required amount of can
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