Amc his_ris_structure application in antenna engineering

HIS/AMC/RIS/METASURFACE APPLIED IN MICTROSTRIP(PATCH) ANTENNA DESIGN

Ntawangaheza Jean de Dieu( 金利 )[email protected]

(PPT3ofPPt3)

mailto:[email protected]

OUTLINE

MPA antenna back ground

MAC/RIS/HIS/EBG applied in antenna design

MPA size reduction using high , gain and bandwidth enhancement using AMC structure.

Wire dipole, patch antenna AMC GND performance comparison and UWB notched bands antennas.

Patch antenna mutual coupling , X_pol. Level reduction and partial reflecting surface antenna(PRs).

Antenna beam tilting/steering using AMC structure.

MICROSTRIP (PATCH) ANTENNA

Microstrip (patch) antenna radiation principle can be seen as an extension of its counterpart microstrip line, the latter fringing fields are tightly bounded to the sub’s edge( small width on high dielectric constant)

Whereas, for a microstrip patch antenna fringing fields are strengthened thorough use of low dielectric constant sub and a radiator with a relatively larger width . MPA origin can be dated back in 1953, but it became popular in early 1970s.

According to the cavity model MPA is bounded by two E walls top and bottom and 4 H walls in the sidesThus one can make change on either top radiator or bottom GND to change the antenna performance

Ref .Custodio Peixuero,” Microstrip antennas Papers in the IEEE transactions on antennas and propagation, IEEE antenna and propagation magazine, February 2012, Debatosh Guha,” Microstrip and printed antennas: New trends techniques and applications, WILEY 2011

AMC/HIS/RIS/EBG STRUCTURES IN ANTENNA DESIGN

Ref , Debatosh Guha,” Microstrip and printed antennas: New trends techniques and applications, WILEY 2011; Li peng et al. UWB band notched monopole antenna design using an EBG structure, IEEE microwave theory and technique, April 201;Kush agarwal et al. wideband circular polarized AMC reflector backed aperture antenna, IEEE AP March 2013; Abbas Pirhadi et al.,” wide high directive aperture MPA design by using a FSS superstrate layer,IEEE AP April 2012; Ian T. McNachel,” A method for determining optimal EBG reflection pahse for low profile dipole antennas, IEEE AP May 2013; Sang il Kwak et al. design of PIFA with metamaterial for bdy body SAR reduction in wearable applications,IEEE EM compatibility February 2017;B Sanz Izquierdo et al. an application of an active FSS to reconfigurable antenna technology,IEEE conference 2016; Wen lu xie et al. A RPA with wide band higher order harmonic suppression using compact defect microstrip structure, PIERS 2016; Chandrakanta Kumar et al., Asymetrical geometry of DGS for rectangular Microstrip: A new approach to reduce its X-P fields, IEEE AP June 2016; Chandrakanta Kumar et al,” DGS integrated Microtrip antenna array for improved radiation properties, IEEE antennas and wireless propagation letters,2017

AMC/HIS/RIS IN ANTENNA DESIGN

Now that we understand what surface waves are and how to design and characterize an artificial magnetic conductor(AMC), it is time to investigate their use in antenna design.

During the discussion, AMC means that the periodic structure has both in phase reflection and band gap properties in the frequency range of interest.

In phase reflection serve to minimize the antenna’s profile while the surface band gap helps to suppress surface waves, thus achieving a low profile with enhanced efficiency antenna and BW.

In some cases, both AMC features are not required, for instance dipole antenna fed by microstrip line(via tapered balun) will only require in phase properties, and for mutual coupling suppression only surface wave band gap may be required in the plane of their propagation(1D AMC is enough)

Ref. Ian T. McNachel,” A method for determining optimal EBG reflection phase for low profile dipole antennas, IEEE AP May 2013, :Peter Kovacs et al., EBG structures practical tips and advice for antenna engineers, Radioengineering,2012, You feng Cheng et al., Reduction of mutual coupling between patch antennas using a polarization conversion isolator.

AMC/HIS/RIS/EBG APPLIED TO ANTENNA DESIGN

Planar printed antenna main issues

Reference : Peter Kovacs et al., EBG structures practical tips and advice for antenna engineers, Radioengineering,2012, Girish Kumar broadband MP,Artech House 2003;, Dr R.B waterhouse, MPA a designer's guide, RMIT university 2003

In all planar printed antenna designs, two dissimilar materials are used, and EM energy is trapped along the interface, forming into SW(except for an air sub).

Mounting a dipole antenna above an uniform lossless dielectric sub with a times more power is trapped into the sub, an EM wave reaching the sub-air interface at an angle of () will have a total reflection.

The following formula should be used to predict the number and mode of excited SWs, strong SWs are excited on a thicker with a high substrates.

Surface waves effect can be neglected for ().

. n =0,2,4… for TM modes n=1,3,5 … for TE Modes

AMC/RIS/EBG/HIS APPLIED TO ANTENNA DESIGN

Why AMC structures are so important in printed antenna design?

reference : Peter Kovacs et al., EBG structures practical tips and advice for antenna engineers, Radioengineering,2012, : Fan Yang and Rahmat, EBG structures in antenna engineering,, Cambridge 2009 , , Dr R.B waterhouse, MPA a designer's guide, RMIT university 2003

Methods such as drilling air cavity under the antenna, optimizing antenna size such that the TM0 is not excited, use of superstrate and stair steps substrate were widely used to suppress SWs.

However, they result into larger size, more complicated design and narrow bandwidth than the original one( narrow 3dB and VSWR BWs).

AMC structures are compact and compatible with MMIC/RF, and can successful suppress SWs if they are correctly implemented. It can be made conformal to the host object( without affecting mechanical and aerodynamic properties of the vehicle)

By using AMC structures a smooth symmetric pattern is expected( with less SSL ,X_pol and increased FBR). Moreover, antenna gain is significantly enhanced with increasing the AMC unit cell number.

AMC APPLIED IN ANTENNA DESIGN

when AMC structures should be considered to improve antenna performance ?

Ref : Peter Kovacs et al., EBG structures practical tips and advice for antenna engineers, Radioengineering,2012, Ian T. McMichael et.al, Method for determining optimal reflection phase for low profile antenna, IEE AP 2013.

If an antenna substrate supports both SWs polarization(TM and TE), in order to successfully suppress SWs , the working frequency should be since is inevitable.

If antenna structure or feed does not support TM polarized SWs, via less structure can be used to suppress TE SWs.

Failing to satisfy both TE and TM SWs suppression, will result in minor or no improvement in antenna’s radiation properties.

In Patch antenna and probe fed dipole antenna implementation, vias should always be present in design of AMC_GND.

Antenna characteristics depends upon on the number of EBG cells and the thickness of the sub, as the row numbers increase the parasitic loading decrease while the cavity effect increases, increasing antenna gain(FBR) at BW sacrifice.


AMC surrounding radiating element.Problems:

Goals: Minimize antenna size while keeping its BW in acceptable range. Use AMC SWs band gap to increase antenna gain, minimize back lobe

radiation( increase FBR) as well as side lobe level(SSL). Integration with MMIC/OEIC circuits.

Miniaturization techniques such as shorting pin, dielectric/magnetic loading, meandering/ cutting slots, fractal geometry, generally result in low antenna efficiency, high cross polarization and narrow BW.

Antenna size and profile could be reduced if a high substrate is employed, which in turn increases surface waves excitation probability.

Ref : Fan Yang and Rahmat EBG structures in antenna engineering,, Cambridge 2009, Frank B. Gross Frontiers in antennas, Mc Graw Hill 2011 Dr R.B waterhouse, MPA a desgner’s guide, RMIT university 2003.


MPA as a resonant type antenna, its size and quality factor Q depend heavily on the operating frequency which in turn adversely affect both BWs(VSWR and AR)

A high dielectric substrate considerably reduces antenna profile and size in addition to compatibility with MMIC/OEIC, albeit severe surface waves are excited..

Surface waves excitations have several detrimental effects on antenna performance including: narrow BW, low radiation efficiency with a poor radiation patterns.

The antenna BW can be recovered by utilizing thick substrate, still radiation efficiency and patterns are severely degraded.

Ref. : Fan Yang and Rahmat EBG structures in antenna engineering,, Cambridge 2009, , YI Huang and Kevin Boyle antennas from theory to practice, Wiley 2008; Dr R.B waterhouse, MPA a designer’s guide, RMIT university 2003.

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AMC surrounding a MPA radiating element on a high substrate

AMC/EBG/RIS/EBG APPLIED TO ANTENNA DESIGN

Reference : Fan Yang and Rahmat EBG structures in antenna engineering,, Cambridge 2009, YI Huang and Kevin Boyle antennas from theory to practice, Wiley 2008 .

Advantages and disadvantages of high substrate. A RMPA design example at 2.4GHz(ISM) band with the same sub. Height and variable (RT5880 and RT 6010).

Substrate

Parameter(mm) L=40.5 W=48.5 H=1.588 Feed=9

Substrate TR 6010(=10.2)Parameter(mm) 25.87 18,96 1.588 3.52

With similar antenna’s heights, replacing =2.2 with =10.2 antenna size is remarkable reduced( nearly to a half).

SIMULATION RESULTS/ PERFORMANCE COMPARISON

Source : Fan Yang and Rahmat EBG structures in antenna engineering,, Cambridge 2009, , YI Huang and Kevin Boyle antennas from theory to practice, Wiley 2008 . .

Antenna BW increases with increasing sub_height, with a 2.1 to 4.1% BW for RT5880 and 1 to 2.1% for RT6010

However, antenna directivity decreases with increasing antenna height( for both cases)

Thick substrate with high yields high FBR, SLL and thus reduced directivity and efficiency due to surface wave excitation.

AMC UNIT CELL DESIGN AND CHARACTERIZATION

Ref. : Fan Yang and Rahmat EBG structures in antenna engineering, Cambridge 2009, Dr R.B waterhouse, MPA a designer's guide, RMIT university 2003 .

Using RT6010 substrate of 3.176mm thickness, a square unit cell operating at 2.45GHz should be 3.8x3.8 with 0.25mm gap see left Fig.

Only TM0 SWs is supported at this frequency since the TE1 starts at 7.78GHz.

Using CST MWS a square unit cell with both 2 properties is optimized and ready to be incorporated into the design.

Minimum Transmission(SW band gap) does not necessary correspond to zero phase.

SURFACE WAVE SUPPRESSION WITH AMC SURROUNDING MPA

Reference : Fan Yang and Rahmat EBG structures in antenna engineering, Cambridge 2009 , Frank B. Gross Frontiers in antennas, Mc Graw Hill 2011, Peter Kovacs et al., EBG structures practical tips and advice for antenna engineers, Radioengineering,2012; M. Rahman et al. circular polarized patch antenna with periodic structure, IEEE-Proc Antennas propagation June 2002,Andrea Neto et al. on the optimal radiation BW of printed slot antennas surrounded by EBG structures, IEEE AP April 2006 .

Enclosing a PA with an AMC will prohibit surface wave propagation, diffraction and reflection.

Antenna BW is maintained and radiation properties are improved thanks to HIS （ SSL, gain and 3dB beam width ） .6.4dBi,-15.4dB,97.3deg Vs 8dBi,-21dB and 74.1deg.

An HIS is designed so that both in phase and surface wave band gap cover antenna operating BW.

Antenna AMC spacing should be ( or ). Antenna has smooth symmetric pattern with higher FBR and lower SLL. Whereas max achievable antenna BW and gain depends on the number of unit used.

ENHANCING ANTENNA BW USING AMC GND

Reference :D. Qu , L. Shafai, improving MPA using EBG substrates,IEE proc-micro 2006, Alireza Foroozesh performance enhancement of compact MP using AMC ground, IEEE2009, Nayana Chaskar et al. effect of dimensions, spacing periodicity of RIS on resonant and BW of 2x2 planar array, IEEE conference 2016, Elkualkadi handbook of research on advanced trends in microwave and communication Engineering,IGI2016; WanChen Yan, wide band and high gain edge fed patch antenna and array using AMC structure,IEEE antennas and wireless propafation letters,2013

In most MPA design PEC GND is used, thus antenna current and image current are out of phase, reducing both antenna and BW.

Unlike previous case, now AMC structure serve as antenna GND which affects both near field and far field properties.

Contrary to other MPA BW enhancing techniques, AMC increases considerably both gain and BW （ 4.56dBi Vs 4.74dBi ） antenna size 0.38x0.27x0.05 including GND. back radiation is eliminated, whereas 3dB beam width is increased.This method is also applicable to antenna 2D array and other feeding scheme like inset feed microstrip line.

AMC in low compact dipole/monopole antenna design(printed&wire)

Traditional vertical monopole and dipole wire antennas

Simple and low cost with a wide bandwidth, monopole antenna requires at least a GND with a radius of .

Dipole in free space radiates in isotropic manner, causing interferences into its surroundings, moreover both monopole and dipole are relatively large at UHF range.

Modern Mobile and wireless devices require hidden, compact wide band low profile （ VSWR BW of atleast 10% and less ） antennas which are shield from other circuit( conductors). By 1995 users consume almost 50% of the antenna’s power.

A quarter wavelength thick substrate or EM energy absorber materials were initially used for a low profile design, albeit efficiency is significantly degraded, and in low RF and Microwave frequency range this substrate thickness requirement is unfeasible.

Ref. Frank B. Gross Frontiers in antennas, Mc Graw Hill 2011, YI Huang and Kevin Boyle antennas from theory to practice, Wiley 2008 , M . Jensen et.al; EM interaction of handset antenna and a human in personal communication proc. IEEE 1995.

AMC in low compact dipole antenna design (wire/ printed)

A modern approach MPAs are widely used in handheld devices, however, they are easily detuned by

surrounding conductor whereas wire antenna are less detuned by nearby conductor.

The in phase property of the EBG/AMC can minimize antenna's profile and size ( and BW of 24.4% 8.7dBi at 1.3GHz), while surface wave band gap suppresses the excited SWs, thereby improving both gain and BW.

AMC provides lower back radiation( for both far and near fields), reducing antenna-user interaction, enabling lower SAR and high efficiency design. Leading to a compact small size devices( small battery).

High substrate is used to decrease the unit cell size, albeit its in phase BW also decrease considerably.

Ref. Daniel Frederic Sievenpiper, High impedance EM surfaces,, PhD dissertation UCL, 1999 ， Zhan Li, Antenna designs for handset applications multiple antenna integration and interaction with the human head, PhD dissertation uCL,2005, Tngajie Yuan Dual layer EBG structures for low profile ‘ bent’ monopole antenna, PIR 2013, G Goussetis et al. Miniaturization of EBG structure for mobile applications, Radio science 2005,Kwok Hung Chan et al.,” Effects of phase difference in dipole phased array antenna above and EBG substrates on SAR,IEEE antennas and wireless propagation letters 2013.

AMC in low compact dipole/monopole antenna design(printed/wire)

AMC low profile monopole/dipole antenna designs tips and considerations.

If an antenna or feeding structure does not support TM SW mode, then no-via FSS structure can be used( capacitive reactance FSS), to cancel out TE.

Non via AMC such as UC EBG has a narrow in phase BW and tend to resonate at relatively high frequency, thus they are well suited for high frequency use.

A good design practice should separately consider to characterize EBG structure Zs plot, then design a dipole antenna with desired return loss( dipole’s self and mutual impedance), and finally map the dipole( antenna) Zin to the Zs plot.

Decision can be made if a capacitive/inductive FSSS or EBG is desired to suppress SWs. In phase BWs depend on antenna self Zin and the height above an EBG/FSS. The higher the Zin/height the wider the BWs, unfortunately when the BW falls out the AMC BW, antenna’s radiation characteristics deteriorates considerably.

Ref. Method for determining optimal reflection phase for low profile antenna, IEE AP 2013, Fan Yang and Yahya, EBG structures in antenna engineering, Cambridge university press 2009.

Low profile wire antenna Vs patch antenna above EBG GND (example ) / VSWR BW

MPA is a well known low profile antenna by so far, however by using an AMC GND, wire dipole antenna can be put horizontally closer the AMC GND, leading to high eff.and wide VSWR BW. A comparison of these low profile antennas in terms of VSWR BW is needed.

Ref. Fan Yang and Yahya, EBG structures in antenna engineering, Cambridge university press 2009.

Dipole antenna exhibits wide BW of 22%, while patch antenna BW increases from 9 to 30% when placed on the same AMC GND.

The profile of the patch is even lower than that of wire, to increase coupling between patch and FSS unit cell.( yielding wider BW)

Wider BW for dipole can be achieved by increasing the height, however the pattern will degrade.

Patch BW on EBG GND depends on its aspect ratio

Low profile wire antenna Vs patch antenna above EBG GND (example )/Radiation pattern

MPA is a well known low profile antenna by so far, however by using an AMC GND, wire dipole antenna can be put horizontally closer the AMC GND, with high efficiency and wide VSWR BW. A comparison of these low profile antennas is needed.

Ref. Fan Yang and Yahya, EBG structures in antenna engineering, Cambridge university press 2009.

Both patch and wire yield broadside pattern with almost the same directivity.

However, wire_EBG has an off broadside E plane, due to excitation of vertical vias of the EBG. Further, H plane directivity is lower than patch ones.

Patch antenna on EBG_GND also yield pattern steering behaviors.

By introducing beam tilting, the antenna’s gain is decreased (8.5-5.5dBi)

AMC in UBW band notching

UWB antenna operates in the frequency range of 3.1-10.6GHz(VSWR<2 110%BW) offered by the FCC in 2002, as prominent solution for high data transmission, low power consumption(less interference ), precise positioning as well as low cost of production.

Other bands exist in this spectrum range, namely middle(3.3-3.7GHz) and upper WiMAX(5.6GHz), WLAN(5.15-5.85GHz) satellite TV in C band(3.7-4.2 GHz) and 8.14GHz satellite TV which may interfere with the UWB communication system.

Approximate and cut/try methods exist to notch out the above frequency bands such as slots/slits cut in the GND or on antenna element, slot in the feeding microstrip line or addition of stub()/parasitic strips as well as filters. However, in addition to adversely impacting antenna’s matching, efficiency, time delay and pattern shape, they increase antenna size cost along with antenna design complexity.

Since single notch band antenna suffers from both poor skirt characteristics and gain suppression, multi-resonators are used to achieve wide or multiband notch operation, albeit the antenna efficiency and pattern may further deteriorate.

Ref. Mohammad Yazdi et al,,” Design of a band ntoched monopole antenna by means of an EBG structure,IEEE antennas and wireless propagation,2011;Lin Peng et al., UWB band nothced monopole antenna design using EBG structures, IEEE transactions on microwave theory and techniques April 2011.

UBW and band notch design requirement

Debatosh Guha and Yahia, Microstrip and printed antennas new trends techniques and applications, Wiley 2011, , Elkualkadi handbook of research on advanced trends in microwave and communication Engineering, IGI2016, . Mohammad Yazdi et al,,” Design of a band ntoched monopole antenna by means of an EBG structure,IEEE antennas and wireless propagation,2011;Lin Peng et al., UWB band nothced monopole antenna design using EBG structures, IEEE transactions on microwave theory and techniques April 2011.

VSWR BW lay within the 3.1-10.6GHz with consistent gain, Beam width, polarization and linear phase( group delay, good fidelity factor)

Compact low profile() at low edge frequency and ease of integration with other MMIC circuit.

Less dependent on the GND size, inexpensive with band notch( low gain), ease of installation and mechanically robust with minimal tuning.

UWB antenna with 3 notched bands using an EBG( design example)

It is a well known fact that any smooth surface( circular, ellipse, disc, corner truncated rectangular patch antenna with slots) fed by partial ground plane( coplanar wave guide CWP), yield an ultra wide BW behavior.

However, antenna performance depends heavily on the size of the GND( lower frequency edge is given by the sum of the GND and antenna size ) whereas the radiating element-GND interspacing determines antenna’s matching.

By coupling an EBG structure(LC filter) to antenna’s feed line, band rejection( with good skirt shape and low gain) at desired fr can be achieved, note that the interaction is not linear, thus further optimization is needed for a satisfactory result.

Determine the band gap using reflection phase gap. Design an UWB antenna operating in the FCC frequency range. Integrate both parts and do the required optimization.

Notched UWB antenna design procedure:

UWB antenna with 3 notched bands using an EBG( design example) results

Three unit cells are designed in isolation with their band gap responses estimated using reflection phase.

An UWB antenna operating in frequency range 3.1-10.6GHz is designed, with antenna dimensions of ( wavelength at 3GHz)

Both antenna and EBG(LC filters ) are integrated together to achieve an UWB antenna with 3 band notches, band notch refers to VSWR>2

Notice that the integration is non linear, therefore for an optimum antenna performance, one needs to re-optimize antenna_EBG system.

For brevity only impedance BW is shown, pattern, time delay not shown herein.

AMC/RIS/HIS in low profile wideband resonant cavity (RCA)antenna design

Also known as Fabry Perot cavity antenna, EBG resonant antenna(PRS/ERAs) and 2D leaky wave antennas, is a broadband unidirectional directive antenna. It was initiated by Von Trentini 1956, it is now gradually replacing reflectors, dielectric lens, waveguide horns and especially 2D antenna array.

Traditionally, FPC antennas are narrow band due to their resonant nature and non uniform aperture phase and amplitude distribution. To enhance antenna’s radiation 3dB BW, peak gain, aperture efficiency and VSWR BW, a wideband antenna should excite a FPC with a phase correction structure(PCS).

FPC antennas are highly directive, light weight, low cost and ease of scalability for sparse array configuration, planar structure with simple feeding schemes, making them attractive for modern high speed wireless communication.

Phase correcting structure include use of multilayer( stacked slabs/unprinted) and planar structures consisting of different width with different dielectric constant(printed). While its profile is reduced through use of an AMC GND.

Arslan et al.,” A planar feeding techniques for low profile wideband resonant cavity antennas, IEEE conference 2016, Basit A Zeb et al. Performance analysis of classical and phase corrected EBG corrected resonator antennas with all dielectric superstrates, IET 2016

PRS design

Beside, the cavity’s E field phase and amplitude, its height too influences considerably the antenna performance, the heights , less than and yield optimum, VSWR degradation and high peak gain performances, collectively.

The antenna’s 3dB gain, peak gain, efficiency depends upon the reflectivity of the cavity, which is a function of the of the superstrate, and it can be well controlled using an AMC/FSS superstrate, albeit phase error increases with the AMC size. The higher the reflectance of the PRS layer, the higher the antenna peak gain and the narrower the 3dB BW due to the cavity’s high Q.

The cavity’s resonant frequency is given by N=0, 1,2,… for fundamental mode N=0, plus PEC GND , in addition to PCS, other methods exist to widen the 3dB BW, such mutli-source feeding (increased design complexity and losses), tapered AMC( similar to stepped impedance matching).

FPC antennas are good candidates for modern base station antennas, to avoid complex and lossy 2D arrays, however the determining key parameters is the volume(0.5-0.25) and lateral size(8-10)

Naizhi wang et al. Wideband fabry perot resonant antenna with two complementary FSS Layers, IEEE AP May 2014 Raheel M. Rashmi et al., wideband high gain EBG resonator antennas with small footprints and all dielectrics superstrates, IEEE transactions on antennas and propagation, 2014, , Basit A Zeb et al. Performance analysis of classical and phase corrected EBG corrected resonator antennas with all dielectric superstrates, IET 2016

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PRS antenna design example results prediction

Though one of DCM or RSM methods, can be used to predict the performance of the narrow 3dB bandwidth(5-6%), for a wide band 3dB(>15%) design, both methods have to be combined. The overall directivity depends on feed antenna and PRS ‘s reflectance, from which the overall aperture size of the antenna can be derived.

Moreover, single layer printed PRS superstrate is preferable over unprinted and printed multiple layers superstrates due to its simplicity and low cost.

and whereas the aperture size can be determined using


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For our antenna the gain is 8.34dBi at 5GHz and PRS reflectivity is about 0.72, giving total directivity and aperture size of 16.22dBi and 5.27 , however the size of the aperture can be reduced to approx. 2.65 . when a PEC GND is used as a backing plane for an FPR cavity( for fundamental mode N=0 )

PRS design example simulation

for a wide 3dB BW, high peak gain and improved aperture efficiency operation, the FPC cavity must have an ascendant phase slope, maximum reflectivity magnitude(RSM>0.6) and wide band defect mode cavity(TDCM>0.7).

Thus 3 steps are required for an optimum FPA design, one a feed antenna design, second unit cell reflectivity, transmissivity analysis( both quantities must be max>0.7), and phase( ascendant slope), finally system assembly(antenna-cavity).


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PRS antenna design example results analysisParametric study


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At 5.5 thus the cavity must be less than 27mm, as indicated in (1) the PRS phase vary with height, causing antenna directivity degradation.

A Wide 3dBi BW is obtained at 22mm, which is about 18% with a peak gain of 15.8dBi, very close to 16.2dBi theoretical one and is the range predicted by the phase slope and RSM/TDCM.

Though the feed antenna has a wide VSWR BW, it is limited by the PRS reflectivity BW, Thus the antenna should operate in the 5WLAN band for high directivity requirement.

PRS antenna design example results analysisOrigin antenna Vs PRS antenna


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As expected antenna gain is increased drastically in the frequency range of interest 5-6GHz from 8-16dBi( doubled).

However, further antenna impedance matching is needed to achieve a satisfactory VSWR<2 result in this band.

In H plane and E plane PRS antenna yields 3dB beam width of 29 Deg, gain 16dBi while the reference antenna has 74.2Deg and 8dBi; and 28Deg with a 16dBi against 76Deg with 8dBi, respectively.

Both antenna has lower X_pol level, which less in Hplane for the PRS case, SSL is higher for the latter also it is obvious that the latter has significant back radation.

Mutual coupling reduction using an AMC/EBG structures

Surface waves not only deteriorate an antenna element performance but also reduce antenna array gain(efficiency & increase blind scan in phased array case) by increasing EM coupling between elements constituting an array.

Mutual coupling increases with an increase in both substrate thicknesses and dielectric constant in E plane array configurations( elements direction coincides with SW direction and antenna E current direction).

The same observations are achieved in H plane configuration for antenna array on thick low sub( SW have less effect since they are orthogonal to the antenna element direction), due to an increase in antenna size.

Thus an EBG( with SW band gap) can be put in between antenna array elements to prevent SW propagation, especially when antenna array is designed on higher and thicker sub. Though 2D EBG structures are widely used, 1D EBG also can achieve the same amount of improvements while reducing the required space considerably, EBG can be etched between elements or on the ground plane(DGS).

Ref. Fan yang and YaHYA, EBG structures in antenna engineering, Cambridge university press 2009, Chao Ming Luo et al.,” Isolation enhancement of e very compact UWB MIMO slot antenna with two DGSs,IEEE wireless, 2015, R.Anita et al. ,”enhanced isolation with DGS in MIMO antenna, Electronic letter nov.2014,Qian Li et al.,” Miniaturized double layer EBG structure for broadband mutual coupling reduction between UWB monopole antennas,IEEE AP March 2015.

Mutual coupling reduction using an AMC/EBG structures( example)

Although, techniques such as cavity backed MPs, substrate removal between array elements and multilayer techniques are employed to reduce EM coupling, they are outperformed by the EBG( SW BG BW must be wider than the antenna’s VSWR BW).

Ref. Fan yang and YaHYA, EBG structures in antenna engineering, Cambridge university press 2009, Chao Ming Luo et al.,” Isolation enhancement of e very compact UWB MIMO slot antenna with two DGSs,IEEE wireless, 2015, R.Anita et al. ,”enhanced isolation with DGS in MIMO antenna, Electronic letter nov.2014,Qian Li et al.,” Miniaturized double layer EBG structure for broadband mutual coupling reduction between UWB monopole antennas,IEEE AP March 2015, R. Saleem et al.,” eight elements UWB array with three distinct isolation mechanism, Electronics letters February 2015.

Good design practice should consider to simulate both in phase and SW BW behaviors, since SW BG width depends on the number of unit cell and not generally coincide with in phase BW, nevertheless, reflection phase curve is a good approximation.

Coupling decreases as the number of EBG rows increases,

Trade off between size and performance

EBG cells interact with antenna, frequency shifts.

Enhancing antenna’s polarization purity with EBG/DGS

In MPAs design, the main sources of high cross polarization are: monopole like radiation from the feeding coax, surface waves ， fringing fields at the edge of the patch and more importantly the excitation of higher order mode having polarization orthogonal to the dominant one.

X_pol problem can be tackled using EM coupling feeding, differential feed and EBG etched on the GND known as defected ground structure(DGS) which was introduced for the first time in 2005. The latter is the most easier to implement at relatively low cost with no additional volume, loss and weight, albeit it reduces FBR.

Polarization purity comes into play in duplex communication, which employs two frequencies with orthogonal polarizations to efficiently utilize frequency spectrum, it also major design requirements for circular polarization design.

A physical measure known as X-pol level is usual used to express how the desired and non-desired polarization influence each other ( max co-polarization over the max cross pol. In a specific direction/plane )

Ref Chandrakanta Kumar et al., “ Asymetric Geometry of DGS for RMPA: A new approach to reduce its X_pol fields, IEEE AP June 2016, Chandrakanta Kumar Microstrip patch with nonproximal symmetric DGS for improved polarization properties over principal radiation plane, IEEE wireless letters, 2015, abhijyoti et al., “RMPA on slot-type defect ground for reduced cross polarization radiation, IEEE antennas and wireless prop.letters, 2015, Kai feng Lee, Microstrip patch antennas, Imperial college press,2011

Enhancing polarization purity with EBG/DGS( design example)

To show the effectiveness of the defected ground structure(DGS), the previous antenna(2.5GHZ on RT5880) is redesigned by incorporating two slots in the GND in H plane direction to stress down the higher order mode excitation.

Ref Chandrakanta Kumar et al., “ Asymetric Geometry of DGS for RMPA: A new approach to reduce its X_pol fields, IEEE AP June 2016, Chandrakanta Kumar Microstrip patch with nonproximal symmetric DGS for improved polarization properties over principal radiation plane, IEEE wireless letters, 2015, abhijyoti et al., “RMPA on slot-type defect ground for reduced cross polarization radiation, IEEE antennas and wireless prop.letters, 2015, Kai feng Lee, Microstrip patch antennas, Imperial college press,2011

DGS is designed so that it does not affect both radiation and impedance matching of the antenna, approximately 13dB reduction is achieved in H plane inn angle range of .

Beam tilting/ steering using an EBG structure for future 5G base station

Electronically and mechanically beam tilted base stations are often used to enhance the overall system capacity and combat co-channel interference in cellar network.

However, the former suffers from considerable gain losses( the overall array is tilted while the element its self is not) while the latter presents a very changeling mechanical configuration, though, it yields a high gain within a wide tilt angle.

AMC/EBG has proved an effective method for the design of low profile antenna, in this case both antenna and EBG GND are in close proximity to each other( EBG is in near field zone), thus by modifying EBG current distribution, the antenna pattern can be tilted in the desired direction.

By using a fixed single beam tilted element as a basic building block for the array antenna design, a high gain with beam tilted capability can be achieved( fixed down-tilt beam), and this antenna type falls in the category of radiation pattern reconfiguration.

Compared to frequency reconfigurable, polarization reconfigurable, spatial diversity angular diversity has proved to increase the MIMO antenna performances.

Ref. llKYu et al. EBG dipole sub-array antennas creating an enhanced tilted beams for future base stations, IET 2015,Frooq Sultan et al., “ superstrate based Beam scanning of Fabry perot cavity antenna, IEEE antennas and propagation wireless,2016, Badreddine at al., “ design of phase modulated metasurfaces for beam steering in Fabry Perot cavity antennas, IEEE antennas and propag. Wireless 2017,Abdelhamid Tayebi et al., “ application of EBG structures to the design of a multibeam reflector feed, IEEE antenna and propagation magazine, october 2014; Osama M. Haraz et al., Dense dieletric patch antenna array with improved radiation characteristics using EBG GND structures and dielectric superstrate for future 5 cellular networks, IEEE Access 2014;M.M. Saad et al.,” A review on compact slot antenna for wireless MIMO communication system,IEEE conference 2014.

Beam tilting/ steering using an EBG structure for future 5G base station( design example)

Antenna rad. pattern can be tilted along E to increase signal reception or along H plane to combat co-channel interference with the nearby base stations antennas.

Ref. llKYu et al. EBG dipole sub-array antennas creating an enhanced tilted beams for future base stations, IET 2015,Frooq Sultan et al., “ superstrate based Beam scanning of Fabry perot cavity antenna, IEEE antennas and propagation wireless,2016, Badreddine at al., “ design of phase modulated metasurfaces for beam steering in Fabry Perot cavity antennas, IEEE antennas and propag. Wireless 2017,Abdelhamid Tayebi et al., “ application of EBG structures to the design of a multibeam reflector feed, IEEE antenna and propagation magazine, october 2014; Osama M. Haraz et al., Dense dieletric patch antenna array with improved radiation characteristics using EBG GND structures and dielectric superstrate for future 5 cellular networks, IEEE Access 2014.

Unlike active beam tilt antenna, AMC can achieve a desired beam tilt angle without additional losses and space.

Even for a standard EBG wire antenna design, the E plane is off broadside direction, without any modification to the unit cell.

However antenna gain decreases as the tilt angle increases, for 20, 26 and 37Deg, their gain are 8.5,7.6,7.23dBi, respectively.

Conclusion

Since their conception, EBG/AMC/RIS/HIS structures have proved to effectively improve antenna performance including X-pol and mutual coupling reduction, antenna miniaturization, band width enlargement (VSWR and AR), gain enhancement(FBR) with good radiation pattern shape( surface wave suppression).

at the very beginning 2D array well used for low profile high gain design, due to their complexity and losses, nowadays FPR antennas are used to replace the latter as well as other type of antennas such as dielectric lens, reflector(dish) and wave guide horns.

More than one techniques among the ones discussed in this presentation can be applied for high performance antenna design, for instance FPR’s bandwidth and gain can increased using multi source exciter(array), mutual coupling and x_pol reduction techniques may also be incorporated therein.

Knowing all these techniques may come in handy during the design of a more stringent application, also may help to decide whether FPR or 2D array antennas are required.

Date post:	21-Mar-2017
Category:	Engineering
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