This paper presents a unidirectional, left handed circularly polarized (LHCP), single layered antenna array with improved interport isolation for simultaneous transmit and receive (STAR) or in-band full duplex (IBFD) wireless applications. The proposed IBFD antenna is comprised of three identical and sequentially rotated LHCP radiating elements where two R x patches are symmetrically placed with respect to a single T x patch. The symmetry of proposed antenna structure results in same amount of coupling or self interference (SI) from T x element and differentially driven R x patches achieve effective suppression of resulting SI to obtain improved T x-R x interport isolation required for STAR applications. The deployed feed network for differential-driven R x operation is composed of a simple 3dB/180 • rat-race coupler (ring hybrid coupler) with nice in-band amplitude and out-of-phase balance characteristics. The implemented single layer, compact (antenna elements and feeding network etched on single-layered PCB) antenna array achieves 10dB return-loss bandwidth ≥ 75MHz for both T x and R x ports. The prototype achieves ≥ 47dB interport isolation in 75MHz bandwidth and 3 dB axial ratio beam-width is ∼ 60 • for implemented antenna. INDEX TERMS Left hand circular polarized (LHCP) antenna, improved interport isolation, in-band full duplex, self interference cancellation (SIC), 3dB/180 • ring hybrid coupler.

This article presents a dual polarized, proximity-fed monostatic patch antenna (single radiator for both transmit and receive modes) with improved interport isolation for 2.4 GHz in-band full duplex (IBFD) applications. The proximityfed radiating patch offers comparatively wider impedance bandwidth for presented design. Very nice self-interference cancelation (SIC) levels for intended impedance bandwidth have been achieved through differential receive (R x ) mode configuration. The differential R x mode based on 180 ring hybrid coupler acts as a signal inversion mechanism for effective suppression or cancelation of in-band self-interference (SI) that is, the leakage from transmit port. The implemented prototype of proposed antenna achieves ≥87 dB peak isolation for dual polarized IBFD operation. Moreover, the recorded interport isolation for validation model ≥60 dB within 10 dB-return loss bandwidth of 90 MHz (2.36-2.45 GHz). The measured radiation characteristics of implemented antenna demonstrate nice gain and low cross-polarization levels for both transmit (T x ) and receive (R x ) modes. The dimensions of implemented antenna are 70 × 75 × 4.8 mm 3 . The novelty of this work is wide-band SIC performance for monostatic antenna configuration with compact structure of presented design. K E Y W O R D SDC interport isolation, differential feeding, dual polarization, full duplex antenna, high interport isolation, self-interference cancelation (SIC)

This paper presents a two-elements based, dual polarized, single layer, patch antenna array with improved isolation between transmit (Tx) and receive (Rx) ports for 2.4 GHz in-band full duplex (IBFD) or simultaneous transmit and receive wireless applications. The differential feeding deployed at the Rx port effectively suppresses the coupling which is termed as self-interference from the Tx port to achieve high Tx–Rx interport isolation. A simple 3 dB/180° ring hybrid coupler with nice amplitude and phase balance characteristics has been used for differential Rx operation. The mathematical description for a differential feeding based self-interference cancellation mechanism is also presented for the proposed dual polarized IBFD antenna array. The measurement results for the implemented prototype of the antenna array demonstrate very nice levels of Tx–Rx interport isolation. The implemented single layer, compact antenna array presents 10 dB return-loss bandwidth of more than 50 MHz for both Tx and Rx ports. The prototype achieves >80 dB peak interport isolation and 75 dB (65 dB) isolation in 20 MHz (50 MHz) bandwidth.

This work presents a unidirectional, co-circularly polarized (CP), printed antenna with highly decoupled or isolated transmit (T x ) and receive (R x ) ports for 2.4 GHz in-band full duplex (IBFD) applications. The presented antenna topology is based on four similar and sequentially rotated trimmed patches with right hand circular polarized (RHCP) characteristics. The symmetrical placement of two T x patches with respect to both R x elements results in equal levels of self interference (SI) which was suppressed through balanced excitation of T x mode. This mechanism results in effective suppression of SI at each R x patch. The residual SI is suppressed further through a second balanced feeding network deployed at R x port of proposed antenna topology. The employed balanced feeding networks provide superior performance of ≤ 0.5 dB and 6° magnitude and phase imbalances respectively between the two balanced output ports over the bandwidth of interest. The measured results for prototype of presented antenna achieve -10 dB bandwidth of better than 100 MHz for both T x and R x ports. The measured interport coupling for validation model ≤ -70 dB across the entire bandwidth of 100 MHz. As per best of authors' knowledge, the presented antenna is the first one to report such reduced levels of interport coupling over the whole impedance bandwidth of planar antenna with unidirectional radiation patterns and co-RHCP characteristics for both T x and R x modes across the overlapped bandwidth.INDEX TERMS Circularly polarized antenna, unidirectional radiation pattern, reduced interport coupling, self interference suppression, balanced feeding network.

This paper reports a bi-port, wideband, parasitic-fed, single/shared patch antenna with enhanced interport isolation for 2.4 GHz in-band full duplex (IBFD) applications. The employed parasitic feeding provides comparatively the wider impedance bandwidth and better gain for the presented antenna. The improved self-interference cancellation (SIC) levels across the required bandwidth are obtained through differentially-driven receive (Rx) mode operation. The differential Rx operation performs effective cancellation of in-band self-interference (SI) through signal inversion mechanism to achieve the additional isolation on the top of the intrinsic isolation of polarization diversity. The validation model for the presented antenna features ≥88 dB peak isolation between the dual-polarized Tx and Rx ports. In addition, the measured Tx–Rx isolation for prototype is >70 dB across the 10 dB return loss bandwidth of 100 MHz (2.42–2.52 GHz). The measured gain for each mode is better than 7.0 dBi. The novelty of this work is that compared to previously reported designs, the presented antenna offers wider impedance bandwidth and improved SIC levels in addition to superior gain performance. To the best of our knowledge, this is the first single/shared patch antenna which provides better than 70 dB interport isolation across the 10 dB return loss bandwidth of 100 MHz along with 7.0 dBi gain for Tx/Rx modes.