1. Faisal Abedin Advisor: Dr. Mohammod Ali
Miniaturization and Gain Enhancement of Wideband Low-profile Antennas on Engineered Structures
Presented by -
Faisal Abedin
(Doctoral Candidate)
Department of Electrical Engineering
University of South Carolina, Columbia, SC 29208
Advisor: Dr. Mohammod Ali

2. Biography Education Research Interest Doctoral Candidate (GPA: 3.92)
Major: Electrical Engineering (Start Date: Spring 2003)
Department of Electrical Engineering
University of South Carolina, Columbia, SC
M.S. in Electrical Engineering, May 2001
Department of Electrical and Computer Engineering
North Carolina State University, Raleigh, NC
B.S. in Electrical Engineering, September 1999
Bangladesh University of Engineering and Technology, Dhaka, Bangladesh
Research Interest
Electromagnetic Band-gap (EBG) Structures and their Antenna Applications
Antenna miniaturization
Diversity antennas 2

3. Outline
Introduction
Novel concept to design ultra-thin Mobile Phone Antennas
Introduction to Engineered Structures called Electromagnetic Bandgap (EBG) structures
Three-dimensional EBG structures
Planar EBG structures
Phase profile of EBG structures
Application of Planar EBG structures 3

4. Personal Communication Systems Commercial & Defense Applications
Introduction
Personal Communication Systems
Commercial & Defense Applications
UAV
Satellite
Mobile Data System
GPS 3

5. Novel Design Concept for Mobile Antennas
Printed internal antenna
Cell phone back cover
Application: Mobile Antennas
90 mm
35 mm
h=10 mm
Feed
Metal Ground
Antenna
Ground
90 mm
h=4 mm
Feed
Ground
Metal
Gap
Antenna
Slide#1
A rapid growing market for wireless communication has created a significant demand for internal antennas for mobile phones. Traditional external antennas such as monopoles and helices increase the size of the handset and are more prone to breakage and damage. This problem is solved by researching and developing internal antennas. Such antennas can be easily placed internally within the housing of a mobile phone under the back cover of the phone right above the battery line.
Designing a mobile antenna for a portable wireless device is challenging because the antenna has to operate in close proximity to the ground plane, which degrades the antenna bandwidth significantly. The size of the ground plane and the antenna height affects the characteristics of the antenna. The primary challenge is to achieve necessary operating bandwidth, which requires that the antenna height be generally about 8-12 mm from the ground plane. This large antenna height makes the phone thicker.
The main objective of this research is to explore new types of ground planes in order to significantly reduce the height of antennas without deteriorating antenna bandwidth. A novel design concept is proposed to reduce the overall mobile phone thickness by introducing a newly designed antenna with meander-shaped slotted ground plane architecture. The meander-line configuration can be viewed as a slow-wave structure where the phase velocity of the propagating wave is reduced. Thus the geometry becomes electrically longer. There has been report that a longer and wider ground plane provides wider bandwidth (particularly around 900 MHz). Thus naturally if the ground plane can be modified to be electrically longer and wider that should help achieve better bandwidth. This proposed antenna operates at 900 and 1900 MHz. By utilizing this technique heights of antennas can be effectively reduced by more than 50% compared to a conventional antenna thereby reducing the overall phone thickness and make it more attractive to consumers.
The antenna is on top of a conventional mobile phone ground plane, which is suitable for dual band operation, GSM 900 MHz system and PCS 1900 MHz system. Note that the complete antenna assembly has just one feed. The ground plane dimensions are representative of present day mobile phones. The introduction of the slotted ground plane has increased the bandwidth by 3 to 4 times in both the frequency bands.
Based on this work we have a journal article published IEEE Antennas and Wireless Propagation Letters, 2003.
Dual band antenna on Conventional ground plane
Proposed a Novel Slow-wave Structure
Dual band antenna on Modified ground plane 4

6. Novel Design Concept for Mobile Antennas
Current Distribution
Conventional Antenna
Proposed Antenna
Higher Current Density
Maximum Current
Minimum Current
Accomplishments
Increases the antenna electrical length by uniformly spreading current
Increases the antenna bandwidth by 3 to 4 times
Reduces the antenna height by 2.5 times
Antenna prototype
Slide#1
A rapid growing market for wireless communication has created a significant demand for internal antennas for mobile phones. Traditional external antennas such as monopoles and helices increase the size of the handset and are more prone to breakage and damage. This problem is solved by researching and developing internal antennas. Such antennas can be easily placed internally within the housing of a mobile phone under the back cover of the phone right above the battery line.
Designing a mobile antenna for a portable wireless device is challenging because the antenna has to operate in close proximity to the ground plane, which degrades the antenna bandwidth significantly. The size of the ground plane and the antenna height affects the characteristics of the antenna. The primary challenge is to achieve necessary operating bandwidth, which requires that the antenna height be generally about 8-12 mm from the ground plane. This large antenna height makes the phone thicker.
The main objective of this research is to explore new types of ground planes in order to significantly reduce the height of antennas without deteriorating antenna bandwidth. A novel design concept is proposed to reduce the overall mobile phone thickness by introducing a newly designed antenna with meander-shaped slotted ground plane architecture. The meander-line configuration can be viewed as a slow-wave structure where the phase velocity of the propagating wave is reduced. Thus the geometry becomes electrically longer. There has been report that a longer and wider ground plane provides wider bandwidth (particularly around 900 MHz). Thus naturally if the ground plane can be modified to be electrically longer and wider that should help achieve better bandwidth. This proposed antenna operates at 900 and 1900 MHz. By utilizing this technique heights of antennas can be effectively reduced by more than 50% compared to a conventional antenna thereby reducing the overall phone thickness and make it more attractive to consumers.
The antenna is on top of a conventional mobile phone ground plane, which is suitable for dual band operation, GSM 900 MHz system and PCS 1900 MHz system. Note that the complete antenna assembly has just one feed. The ground plane dimensions are representative of present day mobile phones. The introduction of the slotted ground plane has increased the bandwidth by 3 to 4 times in both the frequency bands.
Based on this work we have a journal article published IEEE Antennas and Wireless Propagation Letters, 2003.
M. F. Abedin and M. Ali, “Modifying the Ground Plane and its Effect on Planar Inverted-F Antennas (PIFAs) for Mobile Phone Handsets,’’ IEEE Antennas and Wireless Propagation Letters, vol.2, no. 15, pp , 2003. 5

7. Antenna Miniaturization using Engineered Structures
Applications of Dipole Antenna Array
Ground-based
Vehicular
Air-borne applications
UAV Z X
height ≈ wavelength
Array of Dipole Antennas
Dielectric substrate
Metal Ground
Slide#2
In contrast to the miniature internal mobile antennas there are other types of conformal low-profile antennas, such as printed dipoles and slots, which are widely used in large arrays on ground-based, vehicular, air-borne and shipboard applications. To achieve a unidirectional beam such elements are operated against a metallic ground plane and eventually they suffer from serious performance degradation. To solve this problem they are placed at a height of approximately 0.25l from the ground plane, which makes the whole antenna structure thick and expensive. Two such array configurations are shown here.
We have proposed a new and unique methodology for antenna miniaturization based on novel engineered materials. The prime objective is to develop thin, miniaturized, wideband, directional antennas by designing 3-D EBG structures based on their reflection phase characteristics and placing it in between low profile thin wire antennas and metal ground plane. Schematic and cross-sectional view of such an Engineered structure is shown.
Conventional Dipole Array Configuration 6

8. Engineered Structure (EBG)
Antenna Miniaturization using Engineered Structures
Metal plates
Dipole Antenna
Metal Ground
Challenges
Generates surface wave
Costly
Increases Radar Cross-section
Reduces antenna efficiency
Requires 0.25 wavelength height
Proposed Solution
Engineered Structure (EBG)
Dipole Antenna
h= wavelength
Slide#2
In contrast to the miniature internal mobile antennas there are other types of conformal low-profile antennas, such as printed dipoles and slots, which are widely used in large arrays on ground-based, vehicular, air-borne and shipboard applications. To achieve a unidirectional beam such elements are operated against a metallic ground plane and eventually they suffer from serious performance degradation. To solve this problem they are placed at a height of approximately 0.25l from the ground plane, which makes the whole antenna structure thick and expensive. Two such array configurations are shown here.
We have proposed a new and unique methodology for antenna miniaturization based on novel engineered materials. The prime objective is to develop thin, miniaturized, wideband, directional antennas by designing 3-D EBG structures based on their reflection phase characteristics and placing it in between low profile thin wire antennas and metal ground plane. Schematic and cross-sectional view of such an Engineered structure is shown.
Thin antenna structure
Light-weight and compact
Directional
Wideband
Goals 7

9. Phase Profile of EBG Structures
Antenna Miniaturization using Engineered Structures
Phase Profile of EBG Structures
In phase
h = λ/4
Direct wave
Reflected wave
Metal Ground
h < λ/4
Out of phase
Dielectric Substrate
Antenna
h << λ/4
In phase
Engineered Structure
Phase profile
Slide#4
A detailed description of the dimension of the proposed EBG structure is shown in the figures. The vias connecting the metal plates with the ground plane provide the necessary inductance and the overlapping areas between the 2-layers of metal plates provide the capacitance. The 1st and 2nd layers of metal plates are placed at heights of 1.83 mm and mm, respectively from the ground plane. A thin (strip width=1 mm) printed dipole antenna of length 45 mm was designed to operate at 2.9 GHz. Based on the analytical study, one can easily determine the optimum values of design parameters (a and b) for an EBG structure, which in turn predicts the inductance (L) and capacitance (C) and eventually translates to the geometrical parameters of the EBG structure. A prototype of the proposed EBG and a printed dipole are shown.
The simulated and the measured data are shown, wherefrom it is clear that the dipole has distinct dual-band characteristics. The computed bandwidth of the antenna is 9%. Measured S11 data shows a bandwidth of 6%. The bandwidth for the measured case is slightly narrower compared to the computed case. The discrepancies between the measured and the computed data are due to fabrication imperfections. For comparison measured S11 data for the dipole in free space and computed S11 data for the antenna on a grounded dielectric substrate with the same thickness are plotted. It is observed that the antenna on a grounded dielectric substrate without the presence of the EBG structure has very poor return loss.
We have submitted a journal article in IEEE transactions based on this topic, which is currently under revision.
Phase (Degrees)
Metal Ground
EBG Surface
Frequency (GHz) 8

10. Antenna Miniaturization using Engineered Structures
2.8 mm ≡ 0.03λ
Metal Plates
Dipole Antenna
Dipole Antenna Performance on Proposed EBG Structure
Reflection (decibels)
EBG Top View
Slide#4
A detailed description of the dimension of the proposed EBG structure is shown in the figures. The vias connecting the metal plates with the ground plane provide the necessary inductance and the overlapping areas between the 2-layers of metal plates provide the capacitance. The 1st and 2nd layers of metal plates are placed at heights of 1.83 mm and mm, respectively from the ground plane. A thin (strip width=1 mm) printed dipole antenna of length 45 mm was designed to operate at 2.9 GHz. Based on the analytical study, one can easily determine the optimum values of design parameters (a and b) for an EBG structure, which in turn predicts the inductance (L) and capacitance (C) and eventually translates to the geometrical parameters of the EBG structure. A prototype of the proposed EBG and a printed dipole are shown.
The simulated and the measured data are shown, wherefrom it is clear that the dipole has distinct dual-band characteristics. The computed bandwidth of the antenna is 9%. Measured S11 data shows a bandwidth of 6%. The bandwidth for the measured case is slightly narrower compared to the computed case. The discrepancies between the measured and the computed data are due to fabrication imperfections. For comparison measured S11 data for the dipole in free space and computed S11 data for the antenna on a grounded dielectric substrate with the same thickness are plotted. It is observed that the antenna on a grounded dielectric substrate without the presence of the EBG structure has very poor return loss.
We have submitted a journal article in IEEE transactions based on this topic, which is currently under revision.
Dipole Antenna
Balun circuitry
Coaxial cable
Accomplishments
Reduced antenna height by 9 times
Attained sufficient antenna bandwidth
Increased antenna Gain and Efficiency
M. F. Abedin and M. Ali, “Effects of EBG Reflection Phase Profiles on the Input Impedance and Bandwidth of
Ultra-thin Directional Dipoles,’’ IEEE Transactions on Antennas and Propagation (under revision). 9

11. Novel Planar EBG Structures
Applications: Planar EBG
▪ Mobile phones ▪ Wireless LAN
▪ Satellite ▪ JTRS
▪ Global Positioning System
Unit cell of proposed Planar EBG Structure
Top-view
Slide#5
Construction technique of 3D EBG structures are complicated and expensive mostly for bulk commercial applications. We have proposed an alternative approach of designing a low frequency, uniplanar compact EBG structure. But the existing planar EBGs have stopband at frequencies higher than 10 GHz
And involves high dielectric constant (expensive) materials. Our primary focus is to develop compact planar EBGs operating at lower frequencies (f< 5 GHz), which have applications in Mobile phones, WLAN, GPS, Satellite, JTRS .To lower the stopband frequencies the unit cells of these EBG structures have to be increased in size which will require more board space and increase cost. So we focused on creating novel geometries that can increase the inductance and capacitance of the individual unit cells and thereby lower the stopband frequency. We will also focus on utilizing relatively low cost substrate materials including flexible film type materials.
Operation mechanism of this planar EBG can be explained by an array of LC filters, where the inductor L results from the meandered connecting lines and the capacitor C generates from the spacing between the adjacent patches. The top and bottom view of a planar EBG prototype fabricated in our lab is shown. The measured and computed S-parameter data of the proposed EBG reveals a stopband from 3.5 to 4.2 GHz.
Advantages: Planar EBG
▪ Extremely low cost
▪ Easy to fabricate
Transmission (decibels)
Stopband
3.5 – 4.5 GHz 10

12. Application of Planar EBG Structures
d = 51 mm
Dielectric Substrate
Dipole Antennas
Slide#6
In order to construct a compact integrated phased array system using printed circuit technology high dielectric substrates are more desirable. However, the utilization of a high dielectric constant substrate results in narrower bandwidth and generates severe surface waves. The generation of surface waves reduces antenna radiation efficiency and increases the mutual coupling of the antenna array. A low cost approach to resolve this problem is to utilize EBG structures to suppress the surface waves excited in such a configuration.
To facilitate the comparative study of the performance of dipole arrays in terms of mutual coupling in the presence of planar EBG, a single row of 6 unit cells of the proposed EBG elements is inserted in between the array of dipoles [shown in Fig.]. The planar EBG is designed in such a manner so that its stopband coincides with the operating frequency of the two dipoles, which is fc = 4.2 GHz.
The conventional dipole arrays in the absence of EBG have a bandwidth of 9.7%, while the arrays with the EBG give a bandwidth of 12.7%. Therefore, the insertion of the proposed EBG in between the dipole arrays increases the bandwidth by 31%. In the conventional case, the dipole arrays suffer from severe mutual coupling, which is -14 dB at the operating frequency (4.2 GHz). The insertion of the proposed EBG has significantly reduced the mutual coupling and brought it down to -27 dB. Normalized gain patterns for the conventional dipole arrays and arrays with the EBG at 4.1 GHz are shown in Fig.. For the conventional case one can observe blind spots at  =  45 in the gain pattern, which is created mainly due to the excitation of surface waves. Inclusion of EBG has smoothed out the gain pattern and eventually widened the scan angle of the array. Moreover, the dipole arrays with the EBG show better gain performance (gain = 6.7 dBi) compared to the conventional case (gain = 6 dBi).
A journal article based on this topic is prepared and we are planning to submit it within a week.
Mutual Coupling (decibels)
Coupling reduced by 13 dB 11

13. Application of Planar EBG Structures
Without EBG
With EBG
Nulls Eliminated
Null Points – No Signal
Accomplishments
Increased bandwidth by 31%
Reduced coupling by 13 dB
Eliminated Nulls in Radiation Pattern
Increased antenna Gain
Slide#6
In order to construct a compact integrated phased array system using printed circuit technology high dielectric substrates are more desirable. However, the utilization of a high dielectric constant substrate results in narrower bandwidth and generates severe surface waves. The generation of surface waves reduces antenna radiation efficiency and increases the mutual coupling of the antenna array. A low cost approach to resolve this problem is to utilize EBG structures to suppress the surface waves excited in such a configuration.
To facilitate the comparative study of the performance of dipole arrays in terms of mutual coupling in the presence of planar EBG, a single row of 6 unit cells of the proposed EBG elements is inserted in between the array of dipoles [shown in Fig.]. The planar EBG is designed in such a manner so that its stopband coincides with the operating frequency of the two dipoles, which is fc = 4.2 GHz.
The conventional dipole arrays in the absence of EBG have a bandwidth of 9.7%, while the arrays with the EBG give a bandwidth of 12.7%. Therefore, the insertion of the proposed EBG in between the dipole arrays increases the bandwidth by 31%. In the conventional case, the dipole arrays suffer from severe mutual coupling, which is -14 dB at the operating frequency (4.2 GHz). The insertion of the proposed EBG has significantly reduced the mutual coupling and brought it down to -27 dB. Normalized gain patterns for the conventional dipole arrays and arrays with the EBG at 4.1 GHz are shown in Fig.. For the conventional case one can observe blind spots at  =  45 in the gain pattern, which is created mainly due to the excitation of surface waves. Inclusion of EBG has smoothed out the gain pattern and eventually widened the scan angle of the array. Moreover, the dipole arrays with the EBG show better gain performance (gain = 6.7 dBi) compared to the conventional case (gain = 6 dBi).
A journal article based on this topic is prepared and we are planning to submit it within a week.
M. F. Abedin and M. Ali, “Application of EBG Structures to Reduce the Mutual Coupling between Linear Antenna Elements of an Array,’’ IEEE Antennas and Wireless Propagation Letters (submitted March 2005). 12

14. Broader Dissemination
Actively involved in disseminating knowledge to the broader community –
Mentored two High School Seniors through SPRI program in previous years
This summer an 11th Grade student will be mentored to conduct research
An undergraduate EE student of USC will be guided this summer funded through an NSF REU grant 13

15. Relevant Publications
M. F. Abedin and M. Ali, “Modifying the Ground Plane and its Effect on Planar Inverted-F Antennas (PIFAs) for Mobile Phone Handsets,’’ IEEE Antennas and Wireless Propagation Letters, vol. 2, no. 15, pp , 2003.
M. F. Abedin and M. Ali, “Effects of EBG Reflection Phase Profiles on the Input Impedance and Bandwidth of Ultra-thin Directional Dipoles,’’ IEEE Transactions on Antennas Propagation (under revision).
M. F. Abedin and M. Ali, “Application of EBG Structures to Reduce the Mutual Coupling between Linear Antenna Elements of an Array,’’ IEEE Antennas and Wireless Propagation Letters (submitted).
M. Ali and M. F. Abedin, “Designing Ultra-Thin Planar Inverted-F Antennas,” in Proc. IEEE Antennas and Propagation Society International Symposium Digest, vol. 3, pp , Columbus, OH, June 2003.
M. F. Abedin and M. Ali, “Application of EBG Substrates to Design Ultra-Thin Wideband Directional Dipoles,’’ in Proc. IEEE Antennas and Propagation Society International Symposium, vol. 2, pp , Monterey, CA, June 2004.
M. F. Abedin and M. Ali, “Designing Ultra-Thin Printed Dipole Arrays based on EBG Reflection Phase Profile,” IEEE Wireless and Microwave Technology (WAMI) Conference 2005, Clearwater, FL, April 2005 (accepted).
M. F. Abedin and M. Ali, “Reducing the Mutual-Coupling between the Elements of a Printed Dipole Array Using Planar EBG Structures,” IEEE Antennas and Propagation Society International Symposium, Washington, DC, July 2005 (submitted).
M. F. Abedin, M. Ali and P. F. Wahid, “Bandwidth, Efficiency and Pattern Characteristics of Miniaturized Embedded Antennas at 900/1900 MHz,” 9th edition of the Biennial International Conference on Electromagnetics in Advanced Applications.(ICEAA 2005), Torino, Italy, September 2005 (under preparation). 14