Antennas in 3G Applications

1. Antennas in 3G Applications

2. CONTENTS • Introduction • Planar spiral antenna with EBG configuration • Frequency independent antennas • Spiral antenna • PBG structure • PIFA antenna • Modifications in PIFA antenna to operate at multiple bands • Conclusion • References 

3. Introduction • Cellular mobile services were initially offered using analog radio technologies and these were considered as the first generation systems (1G). • In 2G GSM(global system for mobile communication) technique was adopted. • IN 3G (third generation), a more advanced version of technology was adopted to provide a wide range of multimedia applications.

4. Usually 3G services are used to operate over the range 1800MHz-2100MHz and around 900MHz also. • The data rates available with 3G are 2Mbps and bandwidth of 5-20MHz is provided for services. • Applications like, video streaming, video calls, high speed net access, location based applications can be accessible in mobile phones.

5. Planar spiral antenna with EBG structures • Frequency independent antennas: • These kind of antennas are self scaling antennas. Ex : Spiral antenna, log periodic antenna etc. • The shape of these antennas are defined in terms of angles . • If the physical dimensions of the antenna are reduced/increased by a factor of ’k’, then the characteristics doesn’t change if the frequency of operation increased/reduced by the same factor of ’k’.

6. Spiral antenna • The shape of antenna is defined in terms of angle by the relation

7. R is a constant that controls the initial radius of the spiral antenna. • Flares of the spiral antenna is controlled by ‘a’. The value of ‘a’ depends on the change of frequency and angle of rotation. C is the angle of rotation • The two arms of the antenna are dual to each other and satisfies the Babinet’s principle.

8. Four edges of two arms are four helical curves with equal angle. The equations of helical curves are is the origin angle difference. Feeding is done in a way to satisfy the symmetry of spiral antenna

9. The ends of arms are truncated in order to provide better matching termination. • The lower of operation depends on the length of the arm. • The upper frequency of operation is limited by the inner radius R of helical curve. • The wave radiated is circularly polarized. • The patterns are Bidirectional and single lobed.

10. EBG configuration EBG structures consists of periodic arrangement of materials with different dielectric constants.

11. EBG structures

12. The band stop conditions depends on the periodicity of dielectric structure. • K=propagation constant • P=periodicity • n=integer • The refractive index ratio of the base material and the impurity should be atleast 2:1

13. If the EBG structure is created by a patch the Centre frequency of the band gap depends on the structure dimensions. The L and C values are H F

14. The pass band ripples reduces and band gap depth increases with periodicity. • The depth and width of band gap and pass band ripples increases with fill factor. • The forward radiation being enhanced and the back & side lobes restricted, unidirectional radiation is achieved. • The EBG structures can be of any shape and of uniform dimensions on the ground plane.

15. EBG structures doesn’t allow the propagation of wave in some bands. • EBG structures reduces the surfaces waves propagation and mutual coupling. • By creating line defects in the structure it acts as a resonator or a wavegiude depends on the direction of propagation. • These kind of structures used to improve the radiation efficiency.

16. FR-4 is selected as the material for the antenna medium substrate, whose permittivity is 4.4 and thickness is 0.08cm. • Return loss without PBS structure for planar spiral antenna with R= 0.3 cm, a = 0.221, Return loss S11 of antenna without PBG

17. The substrate is in square shape with 5 cm length and in the figure L = 1.9 cm, W = 1.3 cm, h0 = 0.2 cm, h1 = 0.4 cm, h2 = 0.3 cm • PBG structure on the back side of the ground plane of planar spiral antenna. fig.2 PBG structure

18. The operating frequency band width reduces by applying PBG structure. Return loss with PBG structure

19. The widths W1, W2 and W3 of apertures at the first, second and third columns are changed as 0.9 cm, 1.4 cm and 1.5 cm respectively. EBG structure with different periods

20. Return loss radiation pattern • The RF working frequency range of this system is 1920-2170 MHz, with 250 MHz frequency bandwidth and 13% relative bandwidth with 2GHz as centre frequency. • It is used in WCDMA systems.

21. PIFA ANTENNA • PIFA is abbreviated as planar inverted F antenna. • It structures is simple and it consists of rectangular patch element, ground plane, short circuiting pin and feeding mechanism.

22. Patch is roughly quarter wavelength long. • The short plane width is used to adjust the resonant frequency. • The feed position changes the impedance of the antenna.

23. We can reduce the size of the antenna even more by truncating the plane after compensating with a capacitor. • There would be some radiation loss by truncation.

24. PIFA has high current density on the under surface of the planar element and the ground plane compared to the upper surface of the element. • The maximum current distribution present at the region close to the short pin and decrease away from it. • The dominant component of the electric field is zero at the short-circuit plate while the intensity of this field at the opposite edge of the planar element is significantly large. • The draw back of the PIFA is its narrow bandwidth. To increase band width: • 1) Vary the size of the ground plane. 2) Use of thick air substrate to lower the Q. 3) Use parasitic resonators with resonant lengths close to main resonant frequency. • This antenna usually operate at frequency 1900-2100Mhz.

25. Modifications in PIFA • By making slots in the plane of antenna we can create multiple resonances. • Using varactor diode in the PIFA to tune to particular frequency of operation. • The PIFA antenna with slots and varactor diode in it can be used to operate at multiple frequencies.

26. PIFA with slots in the plane and with varactor diode

27. By changing the dc supply voltage we can the change the capacitance provide by the varactordiode. • As there are three slots in the plane it operates at three resonant frequencies 2GHz, 5.35GHz, 5.8GHz. • This antenna can cover the frequency ranges of services like Bluetooth, DCS, PCS,UMTS,WLAN and ISM for different capacitance values of varactor diode. The gain of this antenna is 1.84-2.41dB .

28. Conclusion For the antennas to be used in 3G applications they should have large bandwidth, no side lobes, small size and could be able to operate at multiple frequencies in order to provide enhanced and multifunctional performanceand can be mounted easily on PCB of mobile phones.

29. References • [1]Baiqiang You, Jianhua Zhou, Hao Chen, “The Application of PBG Configuration in Spiral Antenna,” IEEE International Workshop 2007. • [2] C.A.Balanis, Antenna Theory Analysis And Design, 2nd ed. New York: John Wiley & Sons, Inc., 1997 • [3] Hu Rong, Zhang Xuexia, “The study of PBG configuration characteristics and its applications in antennae,” [J].Transaction of Electron, Vol. 12 (12): pp.1765-1770, 2003. • [4] Viet-Anh Nguyen, Rashid-Ahmad Bhatti, and Seong –Ook Park, “A Simple PIFA-Based Tunable Internal Antenna for Personal Communication Handsets,” IEEE Antennas and Wireless Propagation Letters, vol. 7, 2008. • [5] N. Behdad and K. Sarabandi, “A varactor-tuned dual-band slot antenna,” IEEE Trans. Antennas Propag., vol. 54, no. 2, pt. 1, pp.401–408, Feb. 2006 .  Websites: • [1] www.antenna-theory.com

30. Queries ??