Integrated Filtering Antennas for Wireless Communications

In traditional radio frequency (RF) front-end subsystems, the passive components, such as antennas, filters, power dividers and duplexers, are separately designed and cascaded via the 50 ? interfaces. This traditional approach results in a bulky and heavy RF front-end subsystem, and suffers from compromised efficiency due to the losses in the interconnections and the mismatching problems between different components. The frequency responses of the antennas such as the frequency selectivity and bandwidth are usually degraded, especially for microstrip antennas. To improve the frequency responses and reduce the size of RF front ends, it is important to investigate novel highly integrated antennas which exhibit multiple functions such as radiation, filtering, power dividing and combining or duplexing, simultaneously. In this thesis, several innovative designs of compact, multi-functional integrated an-tennas/arrays are proposed for wireless communication applications. First, new methods of designing integrated filtering antenna elements with broadband or dual-band performance are investigated. These antennas also feature high frequency selectivity and wideband harmonic suppression. Based on these studies, several integrated filtering array antennas with improved gains and frequency responses are developed for the first time. Compared with traditional array antennas, these proposed antennas exhibit improved bandwidths, out-of-band rejection and wideband harmonic suppression. The application of the filtering antennas in millimeter-wave (mm-Wave) frequency band is also investigated as it can potentially reduce the cost of the mm-Wave front-end subsystems significantly while providing the improved impedance bandwidth. The integrated design techniques are further developed to design novel dual-port highly integrated antennas with filtering and duplexing functions integrated. Such a new concept and the prototypes could find poten-tial applications in wireless communication systems and intelligent transportation system (ITS). In this thesis, comprehensive design methodologies and synthesis methods are provid-ed to guide the design of the integrated filtering antennas. The performance is evaluated with the help of full-wave electromagnetics (EM) simulations. All of the prototypes are fabricated and tested for validating the design concepts. Good agreement between the simulation and measurement results is achieved, demonstrating the integrated antennas have the advantages of compact size, flat gain performance, low losses and excellent harmonic suppression performance. These researches are important for modern wireless communication systems

Stub-loaded resonator-fed filtering patch antenna with improved bandwidth

A method of designing a patch antenna with wideband and filtering characteristics is proposed in this paper. Different from traditional aperture-coupled patch antenna, a stub loaded resonator (SLR) is employed as the feed. This coupled SLR-patch produces three reflection zeros (dual-mode from the SLR and one from the patch) and therefore a wider bandwidth. Due to the resonant property of the SLR, the antenna exhibits a filtering performance and good out-of-band rejection. This integration approach eliminates the 50 Ohm interfaces between the traditionally cascaded filter and antenna. This contributes to a more compact and simplified RF frontend. Methods to control the modes of the SLR are investigated. The simulation and measurement results agree well with each other, showing an excellent performance in terms of bandwidth, frequency selectivity and radiation patterns

A Ku-Band Filtering Duplex Antenna for Satellite Communications

In this paper, a dual-polarisation shared-aperture duplex antenna is presented for satellite communications at the standard microwave Ku-band, based on the integrated filtering-antenna concept and co-design approach. The design relies on the use of resonators coupled to the radiating dual-band dual-polarisation antenna. The resonant patch antenna forms one pole of each channel filter, resulting in a third-order filter in the Rx channel and a second-order filter in the Tx channel. The Rx and Tx ports of the antenna take in horizontal and vertical linear polarisations, respectively. The integrated duplexer helps to increase the isolation between the ports and the selectivity of each channel. The integration between the filter and the antenna is achieved by electromagnetic coupling, without the need of external matching circuits. Thus it attains a compact footprint. The operation frequencies of the demonstrated duplexantenna are from 11 to 12.5 GHz (12.8%) for the downlink to the Rx port, and from 13 to 14.4 GHz (10.2%) for the uplink at the Tx port. High port-to-port isolation of over 40 dB is realized to reduce channel interference. Flat in-band average gains are achieved to be 8.3 and 8.6 dBi, for the low- and high-bands, respectively

Multi-mode resonator-fed dual polarized antenna array with enhanced bandwidth and selectivity

A novel design concept of multi-mode filtering antenna, which is realized by integrating a multi-mode resonator and an antenna, has been applied to the design of dual-polarized antenna arrays for achieving a compact size and high performance in terms of broad bandwidth, high frequency selectivity and out-of-band rejection. To verify the concept, a 2×2 array at C-band is designed and fabricated. The stub-loaded resonator (SLR) is employed as the feed of the antenna. The resonant characteristics of SLR and patch as well as the coupling between them are presented. The method of designing the integrated resonator-patch module is explained. This integrated design not only removes the need for separated filters and traditional 50 Ω interfaces, but also improves the frequency response of the module. A comparison with the traditional patch array has been made, showing that the proposed design has a more compact size, wider bandwidth, better frequency selectivity and out-of-band rejection. Such low-profile light weigh broadband dual polarized arrays are useful for space-borne synthetic aperture radar (SAR) and wireless communication applications. The simulated and measured results agree well, demonstrating a good performance in terms of impedance bandwidth, frequency selectivity, isolation, radiation pattern and antenna gain

An Ultra-Wideband Circularly Polarized Asymmetric-S Antenna With Enhanced Bandwidth and Beamwidth Performance

This paper introduces an ultra-wideband circularly polarized (CP) asymmetric-S antenna with wide axial ratio beamwidth (ARBW) for C-band applications. The proposed antenna is realized by bending a linearly polarized dipole into asymmetric-S shape with variable trace width, which achieves CP radiation. Unlike the reported symmetric-S antenna, the proposed antenna is constituted with two unequal curved arms to enhance the bandwidth and beamwidth performances. Compared with the symmetric-S antenna, the proposed antenna demonstrates much wider AR bandwidth and wider ARBW over broader frequency range. A prototype is fabricated to verify the design principle. The measured and simulated results are very consistent and both indicate that the proposed antenna has a wide impedance bandwidth (VSWR <; 2) of 70.2% (3.58 to 7.46 GHz), and a wide 3-dB AR bandwidth of 84.8% (2.75 to 6.8 GHz). Moreover, maximum ARBW of 153° is achieved, and a 3-dB ARBW of more than 100° is maintained within a wide operation bandwidth of 46.3% (3.65-5.85 GHz)

A Knotted Meta-molecule with 2-D Isotropic Optical Activity Rotating the Incident Polarization by 90{\deg}

Optical activity is the ability of chiral materials to rotate linearly-polarized (LP) electromagnetic waves. Because of their intrinsic asymmetry, traditional chiral molecules usually lack isotropic performance, or at best only possess a weak form of chirality. Here we introduce a knotted chiral meta-molecule that exhibits optical activity corresponding to a 90{\deg} polarization rotation of the incident waves. More importantly, arising from the continuous multi-fold rotational symmetry of the chiral torus knot structure, the observed polarization rotation behavior is found to be independent of how the incident wave is polarized. In other words, the proposed chiral knot structure possesses two-dimensional (2-D) isotropic optical activity as illustrated in Fig. 1, which has been experimentally validated in the microwave spectrum. The proposed chiral torus knot represents the most optically active meta-molecule reported to date that is intrinsically isotropic to the incident polarization