A Planar Shared-Aperture Co-Polarized Array Antenna With a High Isolation for Millimeter-Wave Full Duplex Communication

With the continuing progress of RF technologies and capabilities, multifunction is a key paradigm allowing for efficient use of space and low-cost systems. A critical factor to fully take advantage of multifunction is the use of true full-duplex simultaneous transmit and receive (STAR) without any traditional forms of multiplexing (spatial, time, frequency, polarization). An important consideration for true STAR systems is the first layer of transmit (Tx) and receive (Rx) isolation provided by the antenna front-end. These front-ends can be realized in bistatic configurations where the physical separation and/or high-impedance surfaces separating the Tx and Rx antennas provide the necessary isolation [1] ; a more desirable configuration, however, is the so-called quasi-monostatic configuration where the Tx and Rx antennas share the same footprint.

In this study, a 77 GHz phased array antenna based on substrate-integrated waveguide (SIW) is proposed. The proposed phased array antenna includes two columns of transmitting (TX) linear antenna arrays and two rows of receiving (RX) linear antenna arrays, which form a rectangular ring distribution. These TX and RX antennas are vertically polarized cavity antennas fed by SIW slots. Simulation results show that the TX antennas and RX antennas have good phased scanning capabilities of ±30° in the elevation direction and ±45° in the azimuth direction at 75–81 GHz, respectively. In order to verify the performance of the proposed antenna, we excite each one of the TX and RX linear phased array antennas using two SIW power dividers and two WR12 waveguide ports. The measured bandwidths of the TX and RX antenna arrays with voltage standing wave ratio less than 2 are 14.5% from 73.7 to 85 GHz and 13.7% from 72.5 to 83.2 GHz, respectively. The measured boresight gains of the TX and RX antenna arrays at the operating frequency band are around 12 and 11.5 dBi, respectively.

Array antennas for 77GHz automotive radar application are designed and measured. Linear series-fed patch array (SFPA) antenna is designed for transmitters of middle range radar (MRR) and all the receivers. A planar SFPA based on the linear one and substrate integrated waveguide (SIW) feeding network is proposed for transmitter of long range radar (LRR), which can decline the radiation from feeding network itself. The array antennas are fabricated, both the performances with and without radome of these array antennas are measured. Good agreement between simulation and measurement has been achieved. They can be good candidates for 77GHz automotive application.

In this communication, a dual-orthogonal-port stacked annular ring microstrip patch antenna for polarization diversity applications and full-duplex communications is presented. Vertical pins that extend from SMA connector inner pins have been employed to implement a port coupling cancellation mechanism and achieve high isolation between the two ports. Furthermore, the structure is completely symmetric and does not require any feed network bridge (differently from differential feeding structure), making it very suitable for simultaneous transmit and receive (STAR) applications that employ balance feeding structures and, therefore, require very similar port performance. An antenna prototype has been designed for the ultrahigh-frequency (UHF) radio frequency identification (RFID) bandwidth, and the measurement has revealed excellent isolation performance, with a peak of 42 dB at the frequency of 922 MHz.

Full-duplex wireless communication is deemed to have remarkable application prospect for the possibility in enhancing the spectrum efficiency by 2 times. However, the strong transmitted leakage signal causes serious self-interference for the full-duplex system. To address this question, a new sectional type full-360° phase-shifter and a gm-tunable LNA are proposed for the feed-forward self-interference suppression, which provide fine phase and amplitude tuning precision smaller than 0.5° and 1.5dB respectively. Moreover, a noise attenuator factor is introduced in the LNA for noise reduction. The NF of the proposed LNA is 6.3dB and the effective signal gain is 18.3dB. Benefited from the proposed phase-shifter and LNA, the self-interference suppression depth is larger than 32dB, which demonstrate the effectiveness of the proposed circuits for self-interference suppression for RFID or other full-duplex wireless communication systems.

A shared antenna aperture for simultaneous transmit and receive (STAR) operating from 0.5 to 45GHz with isolation >50dB over the entire band is discussed. The proposed system utilizes four distinct band breaks: 0.5–2.5GHz, 2–7GHz, 619GHz, and 18–45GHz. The transmitting and receiving apertures of each band are designed, fabricated, and integrated on 46cm×46cm ground plane. A monostatic STAR system based on a lens-loaded cavity-backed four-arm spiral antenna is used to cover 0.5–2.5GHz band requirements. Other bands have dual-polarization capability and rely on physically displaced TX and RX antennas, engineered antenna patterns, and implementation of high impedance surfaces (i.e. bed of nails) to achieve desired isolation level. A dual-polarized Vivaldi array recessed in a cavity and quad-ridge horns are employed for the 2–7GHz and 6–45GHz bands; respectively.

Various experimental results have stated that the self-interference (SI) in full-duplex communication can be mitigated to properly detect the intended signal. However, relatively little is known about the cancellation limits of these systems. A good SI-cancellation strategy passes first by a proper understanding of the nature of this SI. This is highly related to the physical implementations of radio-frequency (RF) transceivers that suffer from a variety of non-idealities defying the perfect knowledge of the received SI. In this chapter, we investigate the various factors that can limit the SI-cancellation performance in full-duplex wireless communications systems. We first classify the known SI-cancellation architectures based on where the reference signal is taken to cancel the SI. By combining the effects of the transceiver impairments, estimation error and SI channel, our analysis reveals that the main bottleneck SI-cancellation turns out to be either the quantization noise, the local oscillator phase noise or the estimation error, depending on the selected SI-cancellation architecture. We provide illustrative numerical results that can facilitate the SI-cancellation architecture selection to meet the specific target system requirements.

In this paper, a wideband dual-circularly polarized simultaneous transmit and receive (STAR) antenna is designed at ISM band. Four sequential rotated microstrip patch elements are excited by two sets of feeding networks: the feeding network of transmit (TX) antenna on the top side of the substrate for left hand circular polarization (LHCP), and the feeding network of receive (RX) antenna on the bottom side for right hand circular polarization (RHCP), or vice versa. The parasitic patches with an air gap are used to enlarge the gain bandwidth. The cancellation technique based on the phase cancellation and geometrical symmetry of antenna is employed. The simulation and measurement results show good agreement and demonstrate the good TX/RX isolation of greater than 35 dB across a wide bandwidth of 5–6 GHz. The TX/RX isolation reaches 48.5 dB @ 5.18 GHz, and the axial radio is better than 3 dB across the entire ISM band, which further proves the feasibility of this design methodology and the application in STAR and sensory integration.

In this paper, a waveguide antenna is designed and fabricated for side and rear radar sensor of vehicles in UWB (Ultra Wide Band) high band (center frequency : 9.5 GHz, -10 dB bandwidth : 600 MHz (6.4 %)). For the radar antenna, a probe fed rectangular waveguide antenna having simple structure and wide bandwidth is used. An important performance factor in this antenna is the isolation between transmitting (TX) and receiving (RX) waveguide antennas because this radar system uses TX and RX antennas separately. Thus the isolation between two antennas was simulated for E-plane and H-plane array. As a result, it was verified that the isolation of the H-plane array of the antennas is better than E-plane array, due to the TE10 mode. Therefore, H-plane arrayed waveguide antennas were mounted on a T-shaped radar module and performance of antennas was investigated. The -10 dB bandwidth of the TX and RX antenna mounted on T-shaped radar module was measured as 1000 MHz (10.52 %) and 1090 MHz (11.47 %) respectively and the isolation is less than -50 dB in the operation band. The peak gain is 7.65 dBi for the TX antenna and 7.26 dBi for the RX antenna and the beamwidth of H-plane of TX and RX antenna was measured as and respectively. Consequently, we verified that the proposed waveguide antenna is appropriate for a vehicle radar applications.

Residual self-interference (SI) cancellation in the digital baseband is an important problem in full-duplex (FD) communication systems. In this paper, we propose a new technique for estimating the SI and communication channels in a FD communication system, which is inspired from superimposed signaling. In our proposed technique, we add a constant real number to each constellation point of a conventional modulation constellation to yield asymmetric shifted modulation constellations with respect to the origin. We show mathematically that such constellations can be used for bandwidth efficient channel estimation without ambiguity. We propose an expectation maximization (EM) estimator for use with the asymmetric shifted modulation constellations. We derive a closed-form lower bound for the mean square error (MSE) of the channel estimation error, which allows us to find the minimum shift energy needed for accurate channel estimation in a given FD communication system. The simulation results show that the proposed technique outperforms the data-aided channel estimation method, under the condition that the pilots use the same extra energy as the shift, both in terms of MSE of channel estimation error and bit error rate. The proposed technique is also robust to an increasing power of the SI signal.

To improve the bandwidth of the SIW, a planar ridged substrate-integrated waveguide (RSIW) with a center line of cylindrical posts is proposed. Theoretical design formulas are derived. The bandwidth is defined as between the cutoffs of TE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</inf> and TE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</inf> modes of the RSIW. The modes are made equivalent to those of a transmission line cavity, across the transverse plane, and the cavity is loaded by a ridge of capacitive posts. Good agreements are observed between the theoretical formulas and numerical simulations. A 37% bandwidth enhancement is achieved. Higher enhancement is possible.

A simultaneous transmit and receive (STAR) metasurface system configuration based on shared aperture methodology is proposed for in-band full-duplex millimeter-wave communication. It is fulfilled by two separated circularly polarized (CP) feeds on both sides and the arrangement of dual-mode wideband meta-atoms that utilize CP selective property. High isolation between the transmitter (Tx) and receiver (Rx) ports of the system is realized by polarization mismatch between the Tx's CP feed and the CP selective metasurface. A wider operating bandwidth is realized by the compound geometric phase responses for both the Rx and Tx subsystems. To validate the proposed concept, a STAR metasurface system prototype to generate directional beams for a millimeter-wave communication system is designed and implemented in Ka-band. The measured port isolation is greater than 33 dB over the system operating bandwidth from 25.5 to 40 GHz (44.3%). The system prototype realizes excellent radiation performance of a joint 3-dB gain/axial-ratio bandwidth of 30.9% and 36.9%. The proposed SATR metasurface system doubles the channel throughput and enhances spectral efficiency, and thus employed to deal with congestion of the electromagnetic spectrum for high-throughput wireless communication.

A dual-slot feeding structure is used in the design of a two-layer E-band substrate integrated array antenna to realize the wideband or dual-band characteristic. Several metallic vias, which are equivalent to open-ended air-filled circular waveguides, are fabricated through printed circuit board process to form wideband radiating elements. They are fed by a parallel substrate integrated waveguide (SIW) feeding network underneath these radiating elements to obtain a compact configuration. First of all, a single antenna element is modeled and investigated to recognize the characteristics of the feeding dual-slot and the radiation via. Then, a 16×16 high-gain wideband array antenna is fabricated. Its measured |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> |<;-10 dB bandwidth is 10.5%, and measured realized gain is in the range of 28.2-30.7 dBi within the same bandwidth. Maximal total radiation efficiency is measured to 61.7%. After that, a dual-band 8 8 array antenna is designed and fabricated as well. Its measured |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> |<;-10 dB bandwidths are 70.6-72.4 GHz and 80.8-82.2 GHz, and measured realized gains are 24.2-25.2 dBi and 24.6-25.8 dBi, respectively. Maximal total radiation efficiency is measured to 72.4%. Considering its wide-band, high-gain and compact configuration, this type of substrate integrated antenna array presents an excellent candidate for E-band multi-gigahertz capacity wireless communication systems.

To address the limited spectrum, current communication systems employ either frequency division duplex (FDD) or time division duplex (TDD) transceivers. These duplexing techniques exploit orthogonality of the time/frequency resources, to reuse the spectrum. A popular approach for implementing full duplex communication without increasing resource utilization is the simultaneous transmit and receive (STAR) scheme. However, the implementation of STAR systems is hindered by the high power transmitted signal which inevitably couples to the receiver, causing higher interference in the band of interest. It is therefore necessary to suppress this interference. In this paper, we present the design and implementation of a 2-stage interference cancellation at the RF and analog domain. This results in 50dB suppression of the coupled signal across a wide bandwidth of 500MHz.

This paper proposes measurement scheme of radar cross section (RCS). The measurement of quasi monostatic radar channel is done in anechoic chamber. The time gating technique is used for removing the effect of mutual coupling between transmitter (Tx) and receiver (Rx) antennas. The personal computer (PC) case is used as the target under test (TUT). The vector network analyzer (VNA) is used to measure transmission coefficient in frequency range covered ultra wideband (UWB) that is 3–11 GHz. The double-ridged waveguide horn antennas are used as Tx and Rx antennas with vertical polarization. The complex frequency transfer function at each angle is used to evaluate the RCS of TUT. The RCS with time gating are shown and compared with that without time gating. From the results, we can see that the proposed measurement scheme can be increased the accuracy of RCS that evaluated from quasi monostatic radar with dense mutual coupling between Tx and Rx antennas.