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Design and experimental validation of dual‐band circularly polarised horn filtenna

2017; Institution of Engineering and Technology; Volume: 53; Issue: 10 Linguagem: Inglês

10.1049/el.2017.0145

1350-911X

Mirko Barbuto, Fabrizio Trotta, Filiberto Bilotti, Alessandro Toscano,

Antenna Design and Analysis

Electronics LettersVolume 53, Issue 10 p. 641-642 Antennas and propagationFree Access Design and experimental validation of dual-band circularly polarised horn filtenna M. Barbuto, Corresponding Author M. Barbuto mirko.barbuto@uniroma3.it Department of Engineering, ‘Niccolò Cusano’ University, Rome, ItalySearch for more papers by this authorF. Trotta, F. Trotta Antenna Department, Elettronica S.p.A, Rome, ItalySearch for more papers by this authorF. Bilotti, F. Bilotti Department of Engineering, ‘Roma Tre’ University, Rome, ItalySearch for more papers by this authorA. Toscano, A. Toscano Department of Engineering, ‘Roma Tre’ University, Rome, ItalySearch for more papers by this author M. Barbuto, Corresponding Author M. Barbuto mirko.barbuto@uniroma3.it Department of Engineering, ‘Niccolò Cusano’ University, Rome, ItalySearch for more papers by this authorF. Trotta, F. Trotta Antenna Department, Elettronica S.p.A, Rome, ItalySearch for more papers by this authorF. Bilotti, F. Bilotti Department of Engineering, ‘Roma Tre’ University, Rome, ItalySearch for more papers by this authorA. Toscano, A. Toscano Department of Engineering, ‘Roma Tre’ University, Rome, ItalySearch for more papers by this author First published: 01 May 2017 https://doi.org/10.1049/el.2017.0145Citations: 16AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract A simple and cheap solution is proposed to transform a wideband and linearly polarised horn antenna in a dual-band circularly polarised horn filtenna. The filtering and polarisation transformation capabilities are achieved by inserting inside the throat of the horn a complementary electrically small resonator etched on a thin metallic sheet. In this way, the overall structure is well matched in two frequency ranges (13–14 and 16.4–17 GHz) and radiates left-handed and right-handed circularly polarised fields in the lower and upper frequency bands, respectively. The measurements performed on a realised prototype confirm the good performance of the proposed structure, which may be employed in satellite communication systems requiring different circular polarisation for the up- and down-link frequency ranges. Introduction Filtering antennas (filtennas) have recently received considerable attention, allowing the integration in a single element of two fundamental operations (electromagnetic radiation and filtering functions) required in a communication system. In about one decade, a wide variety of filtennas have been designed and successfully realised [1-8], exhibiting both passband or notch-band behaviours and working for either linear or circular polarised (CP) fields. Among them, passband CP filtennas are particularly useful in satellite communication systems. In fact, CP fields are less affected by weather events and multipath effects. Moreover, satellite communication systems typically employ narrowband signals that, at the receiver front end, should be properly discriminated by the out-of-band noise. To the best of our knowledge, the first attempt to design a CP horn filtenna is reported in [5], where a complementary resonator has been inserted inside the throat of a standard horn to reduce its impedance bandwidth and convert the linear polarised mode of the feeding waveguide in a CP field received/radiated by the horn. However, in some satellite systems a dual-band CP antenna is required in order to create two different channels for the up- and down-link. In this case, the horn filtenna should be able to radiate/receive left-handed (LH) and right-handed (RH) CP signals centred at two different frequencies. A first attempt in this direction has been presented in [8], where the authors placed a chiral metamaterial slab at the aperture of a standard linearly polarised horn antenna. In this way, the whole structure effectively works around 12.4–12.5 and 14.2–14.4 GHz, exhibiting LH and RH polarisations at the two frequency bands, respectively. Although this solution allows introducing a dual-band behaviour, it requires two copper patterns to be etched on a dielectric laminate; whose lateral dimensions should be large enough to cover the entire horn aperture. This increases complexity and reduces power-handling compared with the single-band structure reported in [5] that, instead, consists only of a properly etched metallic sheet. Moreover, it does not introduce good filtering functions, having a reflection coefficient magnitude with several deep minimums in the entire operating bandwidth of the horn. In this Letter, we properly modify the filtering module used in [5], in order to obtain a dual-band behaviour. Then, by inserting the resulting filter inside the throat of a horn antenna, we design and experimentally characterise a dual-band CP horn filtenna working in two orthogonal polarisations at the two operating frequencies. Design and numerical simulations The filtering module proposed in [5] consists of two orthogonally crossed meandered slots with a subwavelength dimension drilled on a metallic screen. As shown in [9], by applying Babinet's principle to its complementary structure, i.e. two meandered metallic dipoles, the operative frequency of the filter can be determined as a function of its geometrical dimensions. Moreover, by using two slots with slightly different dimensions, a 90° phase shift between them can be obtained, leading to the generation of a CP transmitted field. However, in order to obtain a filtering module working in CP at two different frequencies, we need to properly modify its geometrical shape. In particular, we consider here the structure reported in Fig. 1a, consisting of four meandered slots drilled on a thin metallic sheet. The idea is to design two pairs of slots working around two different operating frequencies, each of them consisting of two slightly different elements in order to achieve a CP operation in both frequency bands. By using the commercial software CST Microwave Studio, we have analysed the behaviour of the structure shown in Fig. 1b, where the proposed module has been integrated inside a regular corrugated conical horn to design a dual-band CP horn filtenna. In particular, the two slots of each pair of elements of the filter have been first designed with equal dimensions. In this way, we can fix the resonant frequencies of the slots pairs in two different operating bands (around 13.5 and 16.75 GHz). Then, through a numerical optimisation procedure, the length of each slot has been properly modified to obtain an LHCP and an RHCP field for the lower and upper frequency bands, respectively. The optimised dimensions in millimetres are as follows: A1 = 1.63, A2 = 1.21, A3 = 0.97, A4 = 0.94, B1 = 1.62, B2 = 1.20, B3 = 1.44, B4 = 1.22, C1 = 1.15, C2 = C4 = 0.9, C3 = 1.15, h1 = 0.66, h2 = 0.57, h3 = 0.72, h4 = 0.55, w1 = w2 = w3 = w4 = 0.25, s = 0.7, Ds = 6.3, Lg = 33, Lh = 25.6, Lt = 5, Ws = 1.3, and Wr = 1.3, where the numerical subscripts, referring to Fig. 1a, indicate the corresponding slot. Fig 1Open in figure viewerPowerPoint Geometrical sketch of a Proposed dual-band CP filter (slots have different colours to simply identify pairs working at different frequencies) b Proposed filter placed inside corrugated conical horn Fig 2Open in figure viewerPowerPoint Reflection coefficient magnitude of dual-band CP horn filtenna As shown in Fig. 2, after optimising the filter dimensions, a good impedance matching (|S11| lower than −10 dB) has been obtained at the two operating bands 13.2–14.1 and 16.3–17.1 GHz. Please note that these bands do not cover the entire frequency bandwidth of the standard horn-waveguide system (12.4–18 GHz), confirming the filtering behaviour of the particle. Moreover, the axial ratio in the main beam direction, reported in Fig. 3, indicates that the deviation from circular polarisation is <3 dB in the ranges 13.2–13.6 and 16.8–16.9 GHz, which fall within the matching bands of the proposed structure. Finally, the realised gain patterns, reported in Fig. 4, confirm that the horn radiates an LHCP field at the lower-frequency band and an RHCP field at the higher band. Experimental validation To further test the effectiveness of the proposed filtering module, a prototype of the dual-band CP horn filtenna has been assembled, as shown in Fig. 5, by using commercial components (a regular corrugated horn antenna and a coaxial-to-waveguide transition) and the manufactured filtering module. The latter has been realised by drilling the four meandered slots, with dimensions reported in the previous section, on a 0.1-mm-thick copper foil by using an LPKF Protomat-S milling machine. The matching properties of the overall structure have been measured with an Anritsu vector network analyser Master MS2028C, while its radiating properties have been measured using a near-field antenna measurement system Satimo StarLab. Fig 3Open in figure viewerPowerPoint Axial ratio in main beam direction of dual-band CP horn filtenna Fig 4Open in figure viewerPowerPoint Realised gain patterns of proposed horn filtenna a xoz-plane at 13.5 GHz b yoz-plane at 13.5 GHz c xoz-plane at 16.85 GHz d yoz-plane at 16.85 GHz Fig 5Open in figure viewerPowerPoint Photographs showing prototype of dual-band CP horn filtenna a Front view showing filter placed inside throat of horn b Side view of overall antenna structure All the measured results are reported in Figs. 2-4, for comparison with the corresponding simulated ones. From these figures, we can see that simulation and measurements are in good agreement, confirming the effectiveness of the proposed module in transforming a broadband linearly polarised horn antenna in a dual-band CP horn filtenna. Moreover, we remark here that the gain of the proposed structure in the two operating bands is degraded by only 0.1 dB compared with the horn without the filtering module. Conclusion In this Letter, the numerical design and the experimental characterisation of a dual-band CP horn filtenna are presented. The proposed structure consists of a thin metallic sheet with a proper engraving placed inside a standard corrugated conical horn. The shape and the geometrical dimensions of the engraving are designed to allow the efficient electromagnetic radiation/reception of an LHCP field around 13.5 GHz and RHCP field around 16.85 GHz. In this way, a standard wideband and linearly polarised horn antenna can be easily adapted to be used in satellite systems, where two frequency channels operating in CP with opposite handedness are required. Results obtained from measurements confirm the effectiveness of our approach. Acknowledgment The authors thank Elettronica S.p.A. for providing measurement instrumentation. References 1Hsieh, C.Y., Hsun, C.H., Ma, T.G.: ‘A compact dual-band filtering patch antenna using step impedance resonators’, IEEE Antennas Wirel. Propag. Lett., 2015, 14, pp. 1056– 1059 (https://doi/org/10.1109/LAWP.2015.2390033) 2Zhang, X.Y., Duan, W., Pan, Y.M.: ‘High-gain filtering patch antenna without extra circuit’, IEEE Trans. Antennas Propag., 2015, 63, pp. 5883– 5888 (https://doi/org/10.1109/TAP.2015.2481484) 3Pan, Y.M., Hu, P.F., Zhang, X.Y., Zheng, S.Y.: ‘A low-profile high-gain and wideband filtering antenna with metasurface’, IEEE Trans. Antennas Propag., 2016, 64, pp. 2010– 2016 (https://doi/org/10.1109/TAP.2016.2535498) 4Luo, G.Q., Hong, W., Tang, H.J. et. al.,: ‘Filtenna consisting of horn antenna and substrate integrated waveguide cavity FSS’, IEEE Trans. Antennas Propag., 2007, 55, pp. 92– 98 (https://doi/org/10.1109/TAP.2006.888459) 5Barbuto, M., Trotta, F., Bilotti, F., Toscano, A.: ‘A combined band pass filter and polarization transformer for horn antennas’, IEEE Antennas Wirel. Propag. Lett., 2013, 12, pp. 1065– 1068 (https://doi/org/10.1109/LAWP.2013.2280151) 6Barbuto, M., Trotta, F., Bilotti, F., Toscano, A.: ‘Varying the operation bandwidth of metamaterial-inspired filtering modules for horn antennas’, Prog. Electromagn. Res. C, 2015, 58, pp. 61– 68 (https://doi/org/10.2528/PIERC15051402) 7Barbuto, M., Trotta, F., Bilotti, F., Toscano, A.: ‘Horn antennas with integrated notch filters’, IEEE Trans. Antennas Propag., 2015, 63, (2), pp. 781– 785 (https://doi/org/10.1109/TAP.2014.2378269) 8Ma, X., Huang, C., Pan, W., Zhao, B., Cui, J., Luo, X.: ‘A dual circularly polarized horn antenna in Ku-band based on chiral meta material’, IEEE Trans. Antennas Propag., 2014, 62, (4), pp. 2307– 2311 (https://doi/org/10.1109/TAP.2014.2301841) 9Barbuto, M., Bilotti, F., Monti, A., Ramaccia, D., Toscano, A.: ‘ Engineered electromagnetic surfaces and their applications’, in A. Tiwari, R. Wang, B. 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