Abstract
In-band full-duplex radios demand simultaneous transmit and receive (STAR) antennas with high isolation, compact and ultra-low profiles, and simple feed networks. Current state-of-the-art designs rarely meet all of these requirements at the same time. In this paper, we present a characteristic-mode-based design approach to achieve high isolation using compact fully-planar STAR antennas with a simple feed structure. The proposed method utilizes two characteristic modes of a conducting object as transmit and receive chains to achieve high isolation without a complicated self-interference cancellation circuit. The design example in this work is fully-planar, and it has a physical height of 1.6 mm. The measured -10 dB overlapped $|S_{11}| ~{\mathrm {and}}~ |S_{22}|$ fractional bandwidth of this STAR antenna is 2.5% and the measured isolation between the transmit and receive ports is greater than 30 dB over the entire frequency band of operation.
Highlights
I N-BAND full-duplex (IBFD) wireless communication systems can simultaneously transmit and receive signals using the same frequency channel and have significant advantages over frequency division duplex (FDD) systems and time division duplex (TDD) systems as they can, theoretically, double the spectral efficiency [1]–[4]
In some IBFD applications, it is required that the simultaneous transmit and receive (STAR) antenna(s) and all the cancellation circuits in the wireless system contribute to a combined 110 dB–120 dB isolation [5], [6]
The existing techniques can be approximately categorized into the following classes [7]: a) separation in physical space, b) dual polarization, c) near-field cancellation, d) passive decoupling networks, e) surface treatments, and f) characteristic modes, as shown in Figure 1: a) Separation in physical space: The main idea of this method is to increase the distance between the TX and RX antennas, as the path loss increases with it
Summary
I N-BAND full-duplex (IBFD) wireless communication systems can simultaneously transmit and receive signals using the same frequency channel and have significant advantages over frequency division duplex (FDD) systems and time division duplex (TDD) systems as they can, theoretically, double the spectral efficiency [1]–[4]. We present a step-by-step method to comprehensively utilize the characteristic mode method for designing fully-planar STAR antennas with different (see Section III) or the same polarization (see Appendix A) for inband-full-duplex (IBFD) wireless communication systems. Since our main intention in this paper is to present a systematic method for designing compact planar STAR antennas with high isolation and simple feed structures using the characteristic mode theory, as opposed to presenting ready-for-launch products for IBFD applications, the design example in this paper is meant to serve as a proof-of-concept prototype.
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