Pune, India, 13 – 15 December 2010 ITU-T Kaleidoscope 2010 Beyond the Internet? - Innovations for future networks and services Mrs. Jayashree P. Shinde Sinhgad Academy of Engineering, Kondhwa, Pune 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 Technique The 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 f o 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 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 ε r = 4.3

Structure under Investigation Three such Nearly Circular ARMSA viz. 1 st, 2 nd and 3 rd 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 1 st ARMSA Outer radius =70mm, Inner radius =35mm Feed Position= (-35,-35)mm 2 nd ARMSA Outer radius =35mm, Inner radius=17.5mm Feed Position= (-18.2,-18.2)mm 3 rd ARMSA Outer radius=17.5mm, Innerradius=8.75mm Feed 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 TM nm 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 J n and Y n are respectively, the Bessel's and Neuman's functions of first and second kind, order n. k nm is the resonant wave number. The value of k nm 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 ε r, solving the characteristic equation for k nm the resonant frequencies are determined from; The %Error is calculated using the expression % error = (f exp - f calc )/ f exp *100 Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 12 Where x nm = k nm a

Table1. Simple 1 st, 2 nd & 3 rd ARMSA without air gap and superstrate Patch Typemodesf o1 f o2 f o3 f o4 f o5 1 st ARMSA b = 70mm a = 35mm f exp GHz f cal GHz % Err nd ARMSA b = 35mm a=17.5mm f exp GHz f cal GHz % Err rd ARMSA b=17.5mm a=8.75mm f exp GHz f cal GHz % Err Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 13

Simple 1 st 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 14

Simple 2 nd 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 3 rd 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 ARMSAs 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, ε r = 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 Typemodesf o1 f o2 f o3 f o4 f o5 1 st ARMSA b = 70mm a = 35mm f exp GHz f cal GHz % Err nd ARMSA b = 35mm a=17.5mm f exp GHz f cal GHz % Err

1 st 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

2 nd 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 ARMSAs 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 dielectric Table 3. 2 nd ARMSA with spaced superstrate of FR4 22 1) Airgap h 2 = 0.26mm, ε r2 =1 & cover1 of FR4 h 3 =1.64mm, ε r3 = 4.3 Patch Typemodesf o1 f o2 f o3 f o4 2 nd ARMSA b =35mm a=17.5mm f exp GHz f cal GHz % Err )Airgap h 2 = 0.52mm, ε r2 =1 & cover1 of FR4 h 3 =1.64mm, ε r3 = nd ARMSA b =35mm a=17.5mm f exp GHz f cal GHz % Err )Airgap h 2 = 1.307mm, ε r2 =1 & cover1 of FR4 h 3 =1.64mm, ε r3 = nd ARMSA b =35mm a=17.5mm f exp GHz f cal GHz % Err

Comparison of resonant frequencies for ARMSAs 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. 2 nd 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 Patchtypemodesf o1 f o2 f o3 f o4 2 nd ARMSA Two covers h1=0.787mm ε r1 =2.2 & h 2 =1.64mm ε r2 =4.3 f exp GHz f cal GHz % Err

RESULTS AND DISCUSSION Several set of measurement of the Nearly Circular ARMSA viz: Simple Single FR4 cover Introducing 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 = (f exp - f calc )/ f exp *100 Pune, 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 Simple ARMSA: The average percent error between the experimental and calculated values for 1 st ARMSA is found to be 0.59%. For the 2 nd and 3 rd 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 1 st, 2 nd and 3 rd ARMSA with FR4 cover is found to be 1%, % and 2.317% respectively.

Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services Introducing various air gaps: With one air gap of height 0.26mm between substrate and one superstrate of FR4 with h=1.64 mm, ε r = 4.3 above the ARMSA. The average percent error for the 1 st, 2 nd and 3 rd 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 1 st, 2 nd and 3 rd 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, ε r =2.2 and another of FR4 with h=1.64 mm, ε r = 4.3 above the ARMSA. The average percent error in the resonant frequencies between the experimental and calculated values for the 2 nd and 3 rd ARMSA is found to be %, 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. Pune, India, 13 – 15 Dec 2010: ITU-T Kaleidoscope 2010 – Beyond the Internet? Innovations for future networks and services 30

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