Multi-band front to back lobe ratio (FTBR)

Multi-band SIW antenna with modulated metasurface at 5GfrequencyPriya Suresh Nair 1, Amalendu Patnaik 2, M.V.

Kartikeyan 3Millimeter and THz Laboratory, Dept. of Electronics and Communiction Engineering, Indian Institute of Technology Roorkee, Roorkee-247667, Uttarakhand, [email protected], [email protected], [email protected] — This paper proposes a multi-band SIW an-tenna which is linearly polarized. The antenna consists ofa T-shaped radiator inscribed on the upper side of thedielectric substrate.

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This radiator is responsible for multi-band occurrence. The operating frequency is chosen to be28 GHz, which is a valid selection for 5G applications.An aperiodic modulated metasurface is employed as theground plane for the proposed antenna. Modulated MTSis a great alternative to the metal ground as it enhancesthe gain and subsequently the front to back lobe ratio(FTBR) of the antenna. The substrate used is FR4 epoxywith a thickness of 0.8 mm. The simulations are done usingANSYS HFSS. Only simulated results are presented as theantenna fabrication is under process.

Keywords —T-shaped radiator, multiband ,metasurface(MTS), articial magnetic conductor (AMC)I. INTRODUCTIONThe reason for increased researches in multi-bandantennas is due to the expeditious development of radarand satellite communication systems. One of the mostprominent choices for the implementation of the multi-band antennas is slot antenna. It offers various advan-tages such as higher bandwidth, low prole, low costetc. among many other factors. 9,10,11,12 describelatest developments and trends in the eld of broad-bandand multi-band antennas. Despite this, the main factorthat limits its performance is the bidirectional radiationpattern it produces.

Substrate integrated waveguides (SIWs) or laminatedwaveguides have replaced the conventional transmissionlines at high frequency millimeter wave communication.Propagation characteristics and ease of construction arethe main reasons among many others due to which itis suitable waveguide structure at very high frequencies.Its physical construction consists of two metallic platessandwiching the dielectric substrate. The metallic platesare connected through arrays of cylindrical metallicgrooves. The wave propagation in the structure is boundbetween these two arrays of cylindrical vias. SIWs alsoprovide easy integration of planar circuits. Microsrtiptransition is used to excite the SIW structure.

Themain reason foe choosing this over other techniques is low return loss, low insertion loss and also it providessufcient bandwidth for the desired purpose. Metallic grounds are conductive surfaces that act asreectors. They reverse the phase of the reected EMwaves. They also support surface waves. These tworeasons are sufcient enough to prove the fact thatmetallic grounds have deleterious effects on antennaperformance. By introducing special periodic patternson the conductive surface, its surface properties canbe altered provided the period of this texture is muchsmaller than the wavelength of the EM wave. Variousapplications of the modulated MTSs are listed in 4.

Theproposed antenna uses its application to control surfacewaves. Recent years have seen researchers workingon non-periodic MTSs. The periodicity is taken as aconstant on the aperture and the variation of impedanceis achieved by varying the geometry, thereby giving anon-periodic MTS structure.

5G is one of the most sought after wireless technol-ogy. The answer to increasing demand for efcient, highspeed and secular communication is 5G as it utilizesthe unexplored high frequency bands. In this paper, thefrequency band under consideration is 22-40 GHz. In section II the design of the proposed antenna is ex-plained. In Section III, HFSS simulations and its resultsare given. The conclusions drawn from the proposeddesign and its simulations are given in Section IV.

II. DESIGN OF THE PROPOSED ANTENNAA. Antenna Design The geometry and design parameters of the proposedSIW antenna at 28 GHz is shown in Fig. 1. The designconsists of a single layer substrate of FR4 epoxy havinga relative permittivity ( r) of 4.4 and loss tangent (tan ) of 0.02 with a substrate thickness of 0.

8mm. Thediameter(d) and pitch (p) values are chosen accordingto 6,7,8 in order to ensure that leakage of poweris minimized. The diameter of the periodic metallicvia is chosen to be 0.8mm whereas the chosen pitchvalue is 0.87mm. There is a tapered transition betweenmicrostrip feed line and SIW.

The tapering prole isused to overcome the challenges of impedance matchingin a wide frequency range at millimeter-wave bands. Thecombination of a tapered prole and SIW technologyis implemented 5. One of the several reasons thathas been standing out for the tapering prole to beeasily integrated is the exibility in the SIW design. Theoptimized numerical values of all the design parametersare given in table 1. Fig. 1: T-radiator SIW antennaB. AMC unit cell The unit cell of the proposed modulated articialmagnetic conductor (AMC) is shown in Fig.2.

It consistsof 3X3 array of circular patches of different radii. Thesize of each square element of AMC is 3.1mm X3.1mm. The reason for incorporating non-periodicity inthe AMC texture is the reduction in area with almostsame performance characteristics. Fig. 2: Geometry of AMC unit cellC. Design of antenna with aperiodic modulated MTS The metallic ground of conventional antenna is re-placed with 3X2 array of the above mentioned mod-ulated aperiodic AMC or MTS unit cell.

This AMCsurface does not allow the propagating surface waves within the frequency band of interest and hence im-proves the antenna radiation characteristics. The proper-ties of in-phase reection and non propagation of surfacewaves lead to the replacement of conventional metallicground plane with modulated AMC. The constant radius(0.6mm) circular patches on the ground plane belowthe length of T-radiator is to ensure that the EM wavesreected by T-radiator is in phase with the incident ones. Fig. 3: T-radiator SIW antenna with with modulatedaperiodic AMCTABLE I: Antenna design parameters Design parameters Numerical values(mm) Substrate length (L) 17.5Substrate width (W) 8.

5Substrate thickness (th) 0.8Length of SIW (L1) 3.6Width of SIW (w3) 6Diameter of the vias (d) 0.

8Pitch (s) 0.87Width variation of tapered section (w1-w2) 2.5 to 3Length of rst part of T-radiator (L3) 3Length of second part of T-radiator (L2) 6.5Width of T-radiator (w4) 1.5Radii of circular patches (r1, r2, r3) 0.

15,0.3,0.45Length of AMC unit cell (L5) 3.

1Width of AMC unit cell (w5) 3.1III. SIMULATIONS AND RESULTA. Reection coefcient comparison From the graph, it can be clearly stated that the intro-duction of modulated metasurface results in decreasedrefelction loss . The multi-band occurrence is due to theT-radiator etched on the upper side of the FR4 epoxysubstrate.B.

Radiation pattern comparison Gain of the antenna without modulated MTS is about3 dBi whereas gain of the proposed antenna with mod-ulated MTS is 4.03 dBi. It is evident from the polarplots that the increase in gain is about 1 dBi with thereplacement of conventional metal ground with modu-lated aperiodic AMC or MTS. Therefore the proposedFig.

4: Reection coefcient T-radiator SIW antennawith and without AMC Fig. 5: E-plane radiation pattern comparisonantenna is an efcient radiator with decreased back lobeand increased gain.IV.

CONCLUSIONThis work presents an antenna design that is easy tofabricate and utilize at 5G frequency bands. The papermainly focuses on how the introduction of modulatedaperiodic metasurface (MTS) or AMC improves gainof the antenna by 1 dBi and also enhances the FTBRof the antenna when compared to the antenna withmetallic ground plane. This is clearly visible in theradiation pattern simulated using HFSS as shown inFig. The presence of T-radiator in the antenna design isresponsible for multi-band and SIW along with taperedmicrostrip feeding ensures low reection loss.RE F E R E N C E S1Y. Zhang, D.

Shen, X. Li, Jun Su, Ming Dong, “A triple-bandsubstrate integrated waveguide antenna base on metamaterials”, 11 thInternational Symposium on Antennas, Propagation andEM Theory (ISAPE), 20162K. Goodwill, Vibha Tripathi, M.V.

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