Self-interference suppression improvement by employing circular polarized antennas

Full-duplex base-stations with half-duplex nodes, allowing simultaneous uplink and downlink from different nodes, have the potential to double the spectrum efficiency without adding additional complexity at mobile nodes. Hybrid beam-forming is commonly used in millimeter wave systems for its implementation efficiency. An important element of hybrid beam-forming is quantized phase shifters. In this paper, we ask if low-resolution phase shifters suffice for beamforming-based full-duplex millimeter wave systems. We formulate the problem of joint design for both self-interference suppression and downlink beamforming as an optimization problem, which we solve using penalty dual decomposition to obtain a near-optimal solution. Numerical results indicate that low-resolution phase shifters can perform close to systems that use infinite phase shifter resolution, and that even a single quantization bit outperforms half-duplex transmissions in both low and high residual self-interference scenarios.

Radiation patterns are presented for planar equiangular spiral antennas at wavelengths of approximately 10 micrometers . These antennas are fabricated using integrated-circuit processes on silicon substrates and are coupled through dielectric lenses. Patterns are presented over a full 2D scan for orthogonal linear polarizations, and for left- circular (LCP) and right-circular (RCP) polarizations. The antennas respond preferentially to left-circularly polarized radiation, as expected for the left-handed sense of the spiral arms. Cross-polarization ratios as large as 10 dB in circular polarization are obtained, corresponding to an axial ratio of 1.2. No difference in response between horizontally and vertically polarized radiation is observed, as expected for circularly polarized antennas. Directivities as large as 14 dB in left-circular polarization have been obtained. The cross-polarized directivity is considerably lower than the co-polarized directivity. All patterns are approximately circularly symmetric about the (theta) equals 0 axis. The cross-polarization ratio and pattern symmetry strongly depend on the alignment of the antenna and detector response is antenna coupled, even at radiation wavelength of the same order of magnitude as the resolution limit of the optical lithography used to define the antenna geometry.

The use of bandwidth for mobile and cellular networks has been increasing at an unprecedented rate, with applications in emergent areas such as smart vehicles and civil infrastructure, telemedicine, and remote education. The predicted increase of mobile network utilisation requires a high data rate capacity to transfer information through the network. The current limited capacity of the fourth generation (4G) mobile network is not expected to satisfy the predicted high data demand by 2020. To meet this requirement, a new fifth generation (5G) mobile network has been proposed. In order to reach the high capacity demands, the 5G requires a wide frequency bandwidth, which is not available in the sub-3 GHz frequency spectrum. Therefore, many international organisations have assigned the millimetre-wave band (mm-Wave), which includes 24, 28, 37, 39, and 60 GHz, as a frequency band for 5G. Using mm-Wave raises many challenges such as an increase in the path loss, radiation field absorbed by the human body, signal polarisation misalignment, and MIMO antenna footprint inside the mobile handset. Therefore, designing beam-steering, reconfigurable circular polarization, and compact MIMO antenna systems for 5G applications is important to cope with these challenges. Although there are some antenna systems were reported recently for mm-Wave 5G, they had limited steering angles, one polarization types or bulky antenna size. This thesis aims to solve the current challenges mentioned above by developing mm-Wave 5G antenna systems and in doing so makes three main contributions to the field of mm-Wave 5G antenna systems.As the path loss and radiated fields absorbed by surface layers of the human body increase at mm-Wave, emphasis is given into the development of the beam-steering antenna system, which is the first contribution of this thesis. The beam-steering technique aims at reducing the effects of electromagnetic field exposure on the human head, as well as maintain a consistent connection between the handset and the base station. A novel compact three-dimensional (3-D) beam-steering system of mobile handsets at 28GHz is proposed. It consists of dipole antenna arrays, power dividers and digital phase shifters. Nevertheless, a novel technique of connecting p-i-n diodes to build a phase shifter is proposed for better performance. The proposed design has the ability to steer the beam in a wide angle in 3-D. it relies on using both sides of a printed circuit board for a two-dimensional antenna array. Moreover, to further improve the performance of the beam-steering system, a tunable power divider for mm-Wave 5G is presented. It is used to tune the feeding amplitude of the beam-steering antenna array, and thus reduces the side-lobe level (SLL) of the antenna radiation pattern.n nThe second contribution is the development of two reconfigurable circular polarisation (CP) structures for 5G applications at mm-Wave. CP is an effective technique to mitigate signal polarisation misalignment, phase deviation and multipath effect problems. Electrical reconfigurable methods are used to switch the CP type by using p-i-n diodes. Firstly, an open-ended stub concept with a simple feed circuit is used to build a novel reconfigurable CP patch antenna. Then the same concept is developed to build a reconfigurable CP antenna array system using branch-line couplers, power divider, and 4 p-i-n diodes. The open-ended stub concept is found to be efficient in both designs by reducing the complexity and the number of the p-i-n diode switches compared to the reported existing CP antenna systems in the literature.MIMO is a major technology of 4G mobile antenna system and also has disruptive potential for mm-Wave 5G. Therefore, the third contribution is the development of new design approaches to integrate the current 4G with futurist 5G MIMO antenna systems. Integrating these two technologies in one structure leads to a reduction of the total MIMO antenna footprint significantly within handsets, where the available space is limited. To that end, two novel 5G/4G MIMO antenna systems are built. First, 5G/4G MIMO antenna system is proposed by using one structure; and it covers multiband mm-Wave spectrums (28, 37 and 39) GHz for 5G as well as sub 3 GHz for 4G.n Moreover, to further improve the gain especially at mm-Wave band, an antenna array structure is deployed to build another 5G/4G MIMO antenna system. This design integrates 5G and 4G operations into a single structure; and covers a wideband 23-29 GHz for 5G and frequency-tuning 2.05-2.70 GHz for 4G.The developed antenna systems reported in this thesis positively contribute to the antenna design domain and are expected to encourage safety, compactness, reliability, and a multiband antenna system for the mm-Wave 5G industry in near future.n

A new simple single-feed method for circularly polarized ring antennas has been investigated. Experimental and theoretical investigation show that either right-handed (RH) or left-handed (LP) circular polarization (CP) can be easily achieved by selecting one of the two input ports of the antennas. The proposed U-shaped microstrip feed line excites the fundamental TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode of the ring radiating elements through proximity coupling along the semi-annular section of the line. The induced rotating surface currents on the ring radiators contribute to the circular polarization behavior of the antennas. Two types of rings have been investigated. Square ring prototypes operate at 2.7 GHz have been designed, fabricated and evaluated to show the basic operating principles of the antennas, while annular ring radiating elements operate at 2.255 GHz are realized to demonstrate the reconfigurable capability of the new feeding structure. In the reconfigurable design, a high isolation RF switch is used to direct the input signal between the two input ports. With suitable biasing arrangement of the RF switch, the antenna is capable to radiate at either types of circular polarization. The reconfigurable design is fed by a single microstrip line. Return losses, axial ratios, gains and radiation patterns of the prototype antennas have been measured for verifications. A parametric study of the new feeding structures with a square ring has been carried out for important design guidelines.

We present the design, fabrication and testing of a low-temperature superconducting (LTS) analog microwave variable attenuator. The two-port circuit includes two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$90^{\circ }$</tex-math></inline-formula> hybrid couplers and a phase shifter to realize a variable attenuation at the output port. The wideband analog phase shifter is implemented using LTS microstrip transmission line (TL) coupled to an array of radio frequency superconducting quantum interference devices (rf-SQUIDs). The phase shift is achieved by passing a dc current through a TL adjacent to the SQUID-loaded microstrip line which controls the flux through the rf-SQUIDs. The proposed variable attenuator shows more than 30 dB of precise analog flat attenuation tuning range over 8 GHz to 12 GHz with a dc control current ranging from 0 mA to 4.5 mA. The device exhibits a wideband operation with variable attenuation seen not only in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X-</i> band but also in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ku-</i> band. The device is fabricated using a multilayer niobium-based superconducting process SFQ5ee by MIT Lincoln Laboratory, and has a compact footprint of 1.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{mm}^{2}$</tex-math></inline-formula> . To the best of our knowledge, this is the first implementation of a variable attenuator using distributed rf-SQUIDs. This device has implications in a variety of applications such as cryogenic receivers and qubit circuit measurements.

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.

Beam-frequency-scanning detection and point-to-point communication typically differ significantly in bandwidth and polarization characteristics, requiring two separate antennas in conventional designs. This paper proposes a method to integrate a dual-mode radiation of narrowband circular polarization (CP) into a broadband linearly polarized (LP) beam-scanning leaky-wave antenna (LWA) using a full spoof surface plasmon polariton (SSPP) system. First, a grooved SSPP unit and its complementary structure are used with periodic mode modulation to achieve continuous vertically polarized (V-pol) dual-beam scanning from backward to forward. By periodically embedding spoof localized surface plasmon (SLSP) units, strong coupling between SLSPs and SSPPs is enabled under resonant conditions. Then, CP radiation is generated due to the rotating electric-field vectors of SLSPs. Experiment and simulation results demonstrate continuous V-pol beam scanning from −30° to 22° across 4.25–6.75 GHz, including effective broadside radiation. Notably, at 5.4 GHz, the antenna radiates right-handed circularly polarized (RHCP) and left-handed circularly polarized (LHCP) waves in opposite broadside directions. Compared with existing technologies, the insertable CP radiation allows the antenna to enable two significantly different operating modes, which can be applied in combined beam-scanning detection and narrowband satellite emergency communication, greatly improving system integration.

An S-band dual circular polarizer has been designed and tested with low power in the paper, which will be applied in a spherical cavity pulse compressor. It converts the TE $$_{10}$$ mode in rectangular waveguide into two polarization degenerated TE $$_{11}$$ modes in cylindrical waveguide. The general scattering matrix of the dual circular polarizer has been deduced based on the properties of the passive microwave network, which is suitable for the usual 3 dB coupler, as well as the left/right hand circular polarizer. Based on the 3D code software CST, the dual circular polarizer was numerically simulated. Then, two prototypes have been manufactured and tested with the vector network analyzer (VNA). The simulation results show that the magnitudes and phase difference of the two TE $$_{11}$$ modes are − 3.0103/− 3.0104 dB and 89.79 degrees, respectively. The cold test results show good agreement with CST simulation. The method of analyzing the relationship between the voltage standing wave ratio (VSWR) and the errors of the magnitudes and phase difference of the two TE $$_{11}$$ modes was given, which can be used to qualitatively analyze the properties of the circular polarizer. The S-band waveguide dual circular polarizer can be applied in the pulse compressor, phase shifter or other frequency bands.

In this paper, a wide-angle beam scanning circularly polarized (CP) phased array element, which consists of a concentric tightly coupled dipole array (TCDA) element with a two-layer parasitic ring structure and a wideband 90° phase shifter, is proposed. To solve the problem of the scanning blindness zone caused by a concentric layout, the grounded coupling patch for the traditional TCDA element is ‘split’ into a combination of a grounded parasitic ring and coupling patch. This combination structure can not only suppress the in-band common-mode resonance but also destroy the scanning blind zone mode formed by the dipole and grounded coupling patch. In addition, a two-layer parasitic ring structure is introduced to obtain a wider axial ratio (AR) beamwidth relative to a single-layer structure, so a wide-angle beam scanning AR is realized. An 8 × 8 left-handed CP planar array based on the proposed wide-angle beam scanning CP elements is designed and prototyped. Results show that the array can operate over a 3.2:1 (3.75–12.0 GHz) overlapping bandwidth, meeting an AR < 3 dB in the main beam and an active voltage standing wave ratio <2.8 within a ±60° angle scanning range.

Nonreciprocal ferrite phase shifters usually rely for their operation on the two different scalar permeabilities exhibited by counter-rotating circularly polarised magnetic waves in a magnetised ferrite medium. One classic way to establish planes of circular polarisation in a coaxial transmission line is to partially load it with a dielectric material. Although this structure has been widely used in the construction of coaxial resonance isolators, it has not been experimentally employed in the design of nonreciprocal ferrite phase shifters. This paper describes the development of a 3.7–4.2 GHz 90° phase shifter with a figure of merit of 600°/dB using a half-dielectric-filled coaxial line suitably loaded with ferrite sheets.

A wideband multi-polarized square-horn antenna based on an orthogonal mode transducer (OMT) is developed for working in the whole W-band in this paper. The designed antenna is capable of radiating multiple polarization modes as horizontal polarization (HP) and vertical polarization (VP) when as single-port excitation and left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) when as dual-port excitation, owing to the characteristic of the OMT with the transmitting of orthogonally polarized waves. A CNC-layered fabrication approach is proposed, which means that the antenna prototype integrating with a Boifot-type OMT, turning waveguide, twisting waveguide and phase shifter is divided into three layers along the vertical direction to be fabricated based on computerized numerical control (CNC) technology. In the design, the turning waveguide and twisting waveguide are employed to achieve plane consistency of the antenna branch ports. Furthermore, a phase shifter is designed to compensate the orthogonally polarized waves, which can keep the phase of the orthogonally polarized waves consistent in a wideband frequency range from 75 GHz to 110 GHz. A prototype is fabricated and measured to verify the performance of the proposed multi-polarization antenna, and the measured results agree well with the simulation ones. In the whole W-band, the value of return loss is better than 10 dB of all polarization modes, and the value of AR of the LHCP and RHCP is below 3.5 dB. The maximum gain of the antenna reaches up to 18.8 dBi at 110 GHz. In addition, regarding the layered structure, the possible layered assembly error analysis is discussed, which verifies the feasibility of the layered machining for this antenna.

A high-gain circularly polarized (CP) holographic antenna (HA) based on impedance-modulated surface (IMS) is proposed in this paper, which is composed of a source antenna and the IMS. A monopole antenna working around 11.4 GHz can drive the IMS. Surface wave generated by the monopole can be converted into directional CP wave through the IMS. The radiation characteristics of the three kinds of phase modulated HAs are compared and 12-phase modulated HA is selected as the proposed antenna at last. The peak gain of the presented CP HA is up to 18.7 dBi at 11.4 GHz. The operating band of the CP HA is from 10.5 to 13.5 GHz (25 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">%</sup> ). In addition, a good agreement is achieved between simulation and measurement. Moreover, the proposed antenna has the advantages of simple production process and low cost.

A new kind of circular polarization leaky-wave antenna with N-shaped slots cut in the upper side of substrate integrated waveguide (SIW) is investigated and presented. The radiation pattern and polarization axial ratio of the leaky-wave antenna are studied. The results show that the width of N-shaped slots has significant effect on the circular polarization property of the antenna. By properly choosing structural parameters, the SIW based leaky-wave antenna can realize circular polarization with excellent axial ratio in 8 GHz satellite band.

20. Phase Shifter

In this paper, we verified an arbitrary waveform generator based on a nonlinear transmission line (NLTL). The fabricated arbitrary waveform generator consists of a NLTL harmonic generator, 10dB coupled line couplers, Wilkinson power dividers, band pass filters, low noise amplifiers (LNA), variable attenuators, and NLTL phase shifters. By controlling the bias voltage of attenuators and phase shifters, it is possible to generate a desired arbitrary waveform such as a triangle waveform and a sawtooth waveform in a microwave frequency range.