Pune, India, 13 – 15 December 2010

ITU-T Kaleidoscope 2010Beyond the Internet? - Innovations for

future networks and services

Mrs. Jayashree P. ShindeSinhgad Academy of Engineering,

Kondhwa, Punejpspaper10@ymail.com

RESONANT FREQUENCIES OF A CIRCULARLY POLARIZED NEARLY

CIRCULAR ANNULAR RING MICROSTRIP ANTENNA WITH SUPERSTRATE

LOADING AND AIRGAPS

Introduction of Microstrip Antenna

The use of microstrip antennas (MSA) in various applications of portable wireless equipment.

Versatile characteristics like compactness, conformal nature, cost effective and ease of design.

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 2

Introduction contd..

Analysis TechniqueThe proper choice of structure geometry, material selection, thickness, feeding techniques, polarization and far field radiation pattern.

Which predicts accurately the behavior of the antenna under consideration viz. the resonant frequency, and impedance bandwidth.

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 3

MSA with Superstrate

The antenna to be placed out of the sight of the consumer beneath plastic covers.To protect the MSA from environmental damage like accumulation of snow, oxidation or corrosion.

Shifts antenna resonant frequency due to change in the effective permeability. The shifts in the ‘fo

’are required to be considered while designing of MSA.

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 4

Circularly Polarized Nearly Circular ARMSA.

Circular disc MSA is mapped in nearly circular annular ring geometry.

Nearly Circular annular ring is loaded with superstrates with different dielectric constants and thickness along with air gaps of various spacer heights.

Circular polarization are expected from a slightly elliptical radiator, fed along a line 45 from its major axis by a coaxial line through a dielectric substrate or by a microstrip line.

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 5

Nearly circular disc

‘a’ being radius along X-axis & ‘b’ being radius along Y-axis.The nearly circular metallic disc has a ‘b/a’ aspect ratio of 0.98.For the same aspect ratio, the radii are reduced from 70mm to 17.5mm

Pune, India, 13 – 15 Dec 010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 6

FR4 as substrate material with thickness h=1.53mm and εr= 4.3

Structure under InvestigationThree such Nearly Circular ARMSA viz. 1st, 2nd and 3rd ARMSA are printed

Top view of nearly circular ARMSA with diagonal coaxial feed

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 7

Types of ARMSA

1st ARMSAOuter radius =70mm, Inner radius =35mmFeed Position= (-35,-35)mm

2nd ARMSAOuter radius =35mm, Inner radius=17.5mmFeed Position= (-18.2,-18.2)mm

3rd ARMSAOuter radius=17.5mm, Innerradius=8.75mmFeed Position= (-8.75,-8.75)mm

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 8

Environmental Effects on MSA

Side View of Nearly Circular ARMSA with Air gap and Superstrates

For analyzing the effect of superstrates and air gap over the ARMSA, the air gap spacers of various heights are introduced between the actual radiating patch and the superstrates.

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 9

Analysis of Annular Ring MSA

The cavity model of a nearly circular ring is obtained by replacing its peripheries with magnetic walls.Since there is no variation of the fields along the z-direction, the modes are designated as TMnm modes.

where n, m are variations in the azimuthal and radial directions respectively.

The radial component of the surface current must vanish along the edges at = a and = b to satisfy the magnetic wall boundary conditions.

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 10

Geometry of a circular ring MSA

Application of these boundary conditions leads the characteristic equation for the resonant modes:J'n(kb)Y'n(ka) - J'n(ka)Y'n(kb) = 0

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 11

• Jn and Yn are respectively, the Bessel's and Neuman's functions of first and second kind, order n.• knm is the resonant wave number. • The value of knm is such that the usual magnetic wall boundary conditions (H = 0) are satisfied at the ring edges ( = a and = b).

1. Simple Nearly circular ARMSA

For an Annular ring MSA with inner radius ‘a’ and outer radius ‘b’ with b/a=2; and given values of n and εr , solving the

characteristic equation for knm the resonant

frequencies are determined from;

The %Error is calculated using the expression % error = (fexp - fcalc)/ fexp*100

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 12

Where xnm = knma

r

nmnm

a

cxf

2

Table1. Simple 1st, 2nd & 3rd ARMSA without air gap and superstrate

Patch Type modes fo1 fo2 fo3 fo4 fo5

1st ARMSAb = 70mma = 35mm

fexp GHz 0.905 1.330 1.735 2.120 2.500

fcal GHz 0.907 1.326 1.722 2.100 2.470

% Err -0.221 0.315 0.714 0.943 1.200

2nd ARMSAb = 35mma=17.5mm

fexp GHz 0.940 1.820 2.645 3.440 4.188

fcal GHz 0.958 1.856 2.694 3.480 4.242

% Err -1.900 -1.98 -1.875 -1.16 -1.29

3rd ARMSAb=17.5mma=8.75mm

fexp GHz 1.960 3.770 5.450 7.055 8.625

fcal GHz 1.954 3.815 5.431 6.966 8.581

% Err 0.290 -1.21 0.229 1.261 0.505

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 13

Simple 1st ARMSA measurements on VNA ZVA- 40

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Simple 2nd ARMSA measurements on VNA ZVA- 40

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 15

Simple 3rd ARMSA measurements on VNA ZVA- 40

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 16

Comparison of resonant frequencies for Simple ARMSA‘s of Table 1.

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 17

Return loss(dB)

2. Nearly circular ARMSA with Superstrate Cover Table2 includes the resonant frequencies of all

modes with one superstrate of FR4 material of ‘h’=1.64 mm, εr= 4.3 above the ARMSA.

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 18

Patch Type modes fo1 fo2 fo3 fo4 fo5

1st ARMSAb = 70mma = 35mm

fexp GHz 0.897 1.317 1.715 2.105 2.490

fcal GHz 0.894 1.307 1.694 2.065 2.470

% Err 0.334 0.767 1.236 1.900 0.803

2nd ARMSAb = 35mma=17.5mm

fexp GHz 0.927 1.804 2.614 3.380 4.102

fcal GHz 0.931 1.810 2.618 3.377 4.110

% Err -0.431 -0.332 -0.175 0.080 -0.21

1st ARMSA with FR4 cover measurements on VNA ZVA- 40

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 19

2nd ARMSA with FR4 cover measurements on VNA ZVA- 40

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 20

Comparison of resonant frequencies for ARMSA‘s of Table 2 with FR4 cover

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 21

Return loss(dB)

3. ARMSA with spaced dielectricTable 3. 2ndARMSA with spaced superstrate of FR4

22

1) Airgap h2= 0.26mm, εr2=1 & cover1 of FR4 h3=1.64mm, εr3= 4.3

Patch Type modes fo1 fo2 fo3 fo4

2nd ARMSAb =35mma=17.5mm

fexp GHz 0.927 1.805 2.615 3.381

fcal GHz 0.943 1.893 2.667 3.445

% Err -1.70 -1.88 -1.88 -1.89

2)Airgap h2= 0.52mm, εr2=1 & cover1 of FR4 h3=1.64mm, εr3= 4.3

2nd ARMSAb =35mma=17.5mm

fexp GHz 0.928 1.827 2.659 3.425

fcal GHz 0.955 1.857 2.692 3.478

% Err -2.90 -1.600 -1.241 -1.547

3)Airgap h2= 1.307mm, εr2=1 & cover1 of FR4 h3=1.64mm, εr3= 4.3

2nd ARMSAb =35mma=17.5mm

fexp GHz 0.929 1.828 2.660 3.426

fcal GHz 0.955 1.854 2.692 3.480

% Err -2.700 -1.400 -1.200 -1.576

Comparison of resonant frequencies for ARMSA‘s of spaced dielectric

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 23

4. Nearly circular ARMSA with two superstrates

Table 4. 2nd ARMSA with two superstrates of RT Duroid & FR4.

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 24

Patchtype modes fo1 fo2 fo3 fo4

2nd ARMSATwo covers h1=0.787mm εr1=2.2 &h2=1.64mmεr2=4.3

fexp GHz0.927 1.804 2.638 3.402

fcal GHz0.935 1.819 2.639 3.406

% Err-0.862 -0.853 0.003 -0.126

RESULTS AND DISCUSSION

Several set of measurement of the Nearly Circular ARMSA viz:

SimpleSingle FR4 coverIntroducing various air gaps Two different superstrate materials as cover

For all ARMSA the resonant frequency measurements use the minimum return loss specification of resonance.

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 25

RESULTS AND DISCUSSION CONTD..

The measured data as well as the calculated resonant frequencies using the formulations are comparable.

Percentage errors use experimental resonant frequency as a reference for the dominant mode as well as for the higher harmonics.

% error = (fexp - fcalc)/ fexp*100Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 26

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 27

1. Simple ARMSA:The average percent error between the experimental and calculated values for 1st ARMSA is found to be 0.59%. For the 2nd and 3rd ARMSA the percent error is found as -1.64% and 0.216% respectively.

2. Single FR4 cover:The average percent error in the resonant frequencies of the dominant as well as the higher harmonics between the experimental and calculated values for the 1st, 2nd and 3rd ARMSA with FR4 cover is found to be 1%,

-0.214% and 2.317% respectively.

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 28

3. Introducing various air gaps:

With one air gap of height 0.26mm between substrate and one superstrate of FR4 with ‘h’=1.64 mm, εr= 4.3 above the ARMSA.

The average percent error for the 1st, 2nd and 3rd ARMSA is found to be 0.538%, 1.816% and 1.188% respectively.

With air gap of height 0.52mm each, the average percent error for the 1st, 2nd and 3rd ARMSA is found to be 0.15%, -1.71% and 0.545% respectively.

4. Two different superstrate materials as cover:

Two superstrates, one of RT Duroid having ‘h’=0.787 mm, εr=2.2 and another of FR4 with ‘h’=1.64 mm, εr = 4.3 above the ARMSA.

The average percent error in the resonant frequencies between the experimental and calculated values for the 2nd and 3rd ARMSA is found to be -0.377%, 1.794%

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 29

Conclusions

The resonant frequencies of a nearly circular ARMSA employing circular polarization with superstrate loading and air gaps between them were analyzed for various radii of the inner and outer nearly circular discs. The full wave analysis of the resonant frequency of ARMSA were presented which incorporates the fringing field variations due to different modes excited.

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Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 31

The three types of ARMSA were fabricated and comparison is made between the experimental and calculated values of the resonant frequencies for various harmonics. The model demonstrates less than 1% errors on average for simple, single cover, various air gaps and two covers of various dielectric constants.Such study is useful for calculating the effect on resonant frequency, gain and bandwidth of portable antennas.

Future scope

To verify the multilayer effect on the shift in the resonant frequency using the quasi-static capacitance.

Study the circular polarization characteristics in a multilayer ARMSA.

To determine the Axial Ratio band width for the various types of ARMSA studied.

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 32

Thank You

Pune, India, 13 – 15 Dec 2010: 33