Chapter 1 Introduction
1.2 Introduction of WIFI
Wi-Fi is a wireless communication technology brand, the Wi-Fi Alliance (Wi-Fi Alliance) held, used on certified products based on IEEE 802.11 standards, the objective is to improve the standard IEEE 802.11-based wireless network Road interoperability.
1.3 Introduction of IEEE 802.11a/b/g
IEEE 802.11 is a set of standards for implementing wireless local area network (WLAN) computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802). The base current version of the standard is IEEE 802.11-2007.
The IEEE 802.11a standard uses the same data link layer protocol and frame format as the original standard, but an OFDM based air interface (physical layer). It operates in the 5 GHz band with a maximum net data rate of 54 Mbit/s, plus error correction code, which yields realistic net achievable throughput in the mid-20 Mbit/s. Since the 2.4 GHz band is heavily used to the point of being crowded, using the relatively unused 5 GHz band gives IEEE 802.11a a significant advantage. However, this high carrier frequency also brings a disadvantage: the effective overall range of IEEE 802.11a is less than that of 802.11b/g. In theory, IEEE 802.11a signals are absorbed more
readily by walls and other solid objects in their path due to their smaller wavelength and, as a result, cannot penetrate as far as those of IEEE 802.11b.
In practice, IEEE 802.11b typically has a higher range at low speeds (IEEE 802.11b will reduce speed to 5 Mbit/s or even 1 Mbit/s at low signal strengths). However, at higher speeds, IEEE 802.11a often has the same or greater range due to less interference.
IEEE 802.11b has a maximum raw data rate of 11 Mbit/s and uses the same media access method defined in the original standard. IEEE 802.11b products appeared on the market in early 2000, since IEEE 802.11b is a direct extension of the modulation technique defined in the original standard. The dramatic increase in throughput of IEEE 802.11b (compared to the original standard) along with simultaneous substantial price reductions led to the rapid acceptance of IEEE 802.11b as the definitive wireless LAN technology.
IEEE 802.11g is works in the 2.4 GHz band (like IEEE 802.11b), but uses the same OFDM based transmission scheme as IEEE 802.11a. It operates at a maximum physical layer bit rate of 54 Mbit/s exclusive of forward error correction codes, or about 22 Mbit/s average throughput.
1.4 Thesis Outlines
The organization of this is outlined as follows：
In Chapter 2, design of a sleeve dipole antenna for IEEE 802.11b/g, Introduction of basic omni-directional antenna in this chapter, and the simulated and measured results of optimized design are given as well.
In Chapter 3, design of a sleeve dipole antenna array for IEEE 802.11b/g, and the simulated and measured results of optimized design are given as well.
In Chapter 4, design of a Print sleeve dipole antenna array for IEEE 802.11a/b/g, improve taper efficiency of printed sleeve dipole antenna array in this chapter. The Print sleeve dipole antenna array is linear antenna array, when antenna elements are more and more, the taper efficiency is very important, this chapter, optimize taper efficiency to get best directivity.
In Chapter 5, design a Planar Inverted F Antenna for HSDPA, the operating frequencies are 850MHz、1900 MHz and 2100 MHz, and the simulated and measured results of optimized design are given as well.
Chapter 2
Design of Coaxial Sleeve Dipole Antenna
This chapter will discuss the omni-directional antenna. This section design the coaxial sleeve dipole antenna, however, the coaxial sleeve dipole antenna is evolved by the dipole antenna.
2.1 Theory of Sleeve Dipole Antenna
According to transmission line theory, when a transmission line is open circuit, if it add a feed in transmission line, which will form a dipole antenna, as shown in Fig 2.1, and the length of the transmission line will determine the operating frequency, when the length of the transmission line is half wavelength, would be generated the standing wave resonance to feed of the signal, and the current of dipole antenna is sinusoidal current distribution, the current distribution on the dipole antenna is given by
(2-1)
From (2-1), when the parameter Z is zero, in the center of antenna will get the largest current, and the current will equal to 0 at the antenna terminal.
The radiation pattern of dipole antenna is omni-direction. The ideal gain of
|)]
4 | ( [ I
)
( z MAX Sin z
I
impedance matching, because the impedance of dipole antenna is 73 + j42.5 ohms. The disadvantage is the length of dipole antenna must be half-wavelength.
2.1.1 Theory of Balun
Coaxial cable feed dipole antenna, unfortunately, the coaxial cable will produce the unbalance current, as shown in Fig. 2.2, however, the unbalance current will influence to the radiation pattern of dipole antenna, so it need to design a Balun. Balun is the abbreviations of "balance" and "Unbalance", which is used to transform the unbalanced input into balanced output and have wide range of applications.
In this research, the outer conductor connected to a quarter wavelength of the sleeve as a Balun, as shown in Fig. 2.3. The ratio of r2 over r1 will influence the length of the sleeve, when the ratio is set between 2 to 3, the length of Balun about is quarter-wavelength, if the ratio is set between 3 to 8, the length of Balun will be shorter than quarter-wavelength. The name of coaxial sleeve dipole antenna is combining of sleeve and dipole antenna.
2.2 Simulation of Coaxial Sleeve Dipole Antenna
The structure of simulation model is shown in Fig 2.4, coaxial sleeve
dipole antenna designed to be applied in IEEE 802.11 b/g, and operating frequency at 2.4 GHz, the quarter-wavelength is 3 cm, from Fig 2.5, the coaxial sleeve dipole antenna is combined with the dipole antenna and Balun, as is the dipole antenna, the ideal gain of dipole antenna is 2.15 dBi. The ratio of inner conductor and teflon will influence the impedance of cable, so it need to make sure the impedance of cable is 50 ohm, A simulation model by GEMS, The structure of the coaxial sleeve dipole antenna is shown in Fig 2.5, The parameter X and the parameter Y are about quarter-wavelength of operating frequency, the parameter A is diameter of inner conductor, the parameter B is diameter of teflon, the parameter C is a distance between the Balun to the outer conductor.
The optimization result for the length of coaxial sleeve dipole antenna are shown in table 1, when the parameter X is equal to 2.8 cm, the simulation result of S11 is -14.5 dB, the simulation result of efficiency is 93%, the simulation result of peak gain is 1.88 dBi, so when the parameter X is equal to 2.8 cm, which can get best result.
2.3 Simulation and Measurement Results of Sleeve Dipole Antenna
The fabricated of the coaxial sleeve dipole antenna is shown in Fig. 2.5, the simulation and measurement results of the reflection coefficient are shown in Fig. 2.6, the whole bandwidth covers the operating frequency. The
measurement environment of coaxial sleeve dipole antenna is shown in Fig.
2.7. The measurement system is SATIMO Star-Lab. It is a spherical Near-Field measurement system. The simulation and measurement results of efficiency are shown in Fig. 2.8. The measurement result of efficiency is about 85%. The simulation and measurement results of peak gain are shown in Fig. 2.9. The measurement result of peak gain is about 1.9 dBi. The simulation and measurement result of E-plane radiation pattern at 2.45 GHz are shown in Fig. 2.10. The simulation and measurement result are almost the same. The simulation and measurement results of H-plane radiation pattern at 2.45GHz are shown in Fig. 2.11. The radiation pattern at H-plane is almost omni-direction.
2.4 Summary
The peak gain of coaxial sleeve dipole antenna is about 1.9 dBi, the efficiency is about 85%. The radiation pattern at H-plane is almost omni-direction.
λ /2 λ /2
Fig 2.1 Structure of dipole antenna
Fig 2.2 Structure of sleeve antenna
2.75
Fig 2.3 Structure of sleeve Balun
Fig. 2.4 Structure of coaxial sleeve dipole antenna Unit：mm
A 0.4
B 1.4
C 2
X Efficiency at 2.45GHz S11 at 2.45GHz Peak Gain at 2.45GHz
3 cm 80 % -9 dB 1.32 dBi
2.8 cm 93 % -14.5 dB 1.88 dBi
2.75 cm 92 % -12.5 dB 1.87 dBi
2.7 cm 91 % -11.5 dB 1.82 dBi
Table 1 Optimization for X length of coaxial sleeve dipole antenna
Fig. 2.5 Fabricated of the coaxial sleeve dipole antenna
1/4 wavelengt h 波長 1/4
wavelength
1/2 wavelengt
h 波長 Unit：mm
Frequency (GHz)
2.0 2.1 2.2 2.3 2.4 2.5 2.6
|S 11|(dB)
-20 -15 -10 -5 0
Simulated Meassured
Fig. 2.6 Simulation and measurement result of reflection coefficient
Fig. 2.7 Measurement environment of coaxial sleeve dipole antenna
Frequency (GHz)
2.30 2.35 2.40 2.45 2.50 2.55 2.60
E ff icie nc y (% )
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Simulated Measured
Frequency (GHz)
2.30 2.35 2.40 2.45 2.50 2.55 2.60
P eak Gain(dB i)
-8 -6 -4 -2 0 2 4 6
Simulated Measured
Fig. 2.8 Simulation and measurement results of efficiency
Fig. 2.9 Simulation and measurement results of peak gain
-35 -30 -25 -20 -15 -10 -5 0
Fig. 2.10 Simulation and measurement results of E-plane radiation pattern at 2.45GHz
Fig. 2.11 Simulation and measurement results of H-plane radiation pattern at 2.45GHz
Chapter 3
Design of Coaxial Sleeve Dipole Antenna array
In chapter 2, the peak gain of the coaxial sleeve dipole antenna is about 1.9 dBi. For long distance WiFi communication, the antenna gain is very important, so in this chapter, will design sleeve dipole antenna array to increase antenna gain.
3.1 Motivation
The radiation pattern of coaxial sleeve dipole antenna is omni-direction, it can cover any direction, Unfortunate, for long distance WIFI communication, the antenna gain is very important, so in this chapter, it design sleeve dipole antenna array to increase antenna gain. The sleeve dipole antenna array has high gain, and the radiation pattern like the coaxial sleeve dipole antenna is omni-direction too.
3.2 Theory of Antenna Array
An antenna array is an antenna that is composed of more than one antenna elements, each antenna elements has the same amplitude and phase, the interval between each antenna elements is about half-wavelength.
antenna array are more high directivity and peak gain.
The radiation pattern of antenna array is sum of the radiation pattern of each antenna elements, the radiation pattern of antenna array is shown in Fig 3.1. Generally, the main beam generate in the middle of the antenna array, when the antenna elements are more and more, the antenna gain is more higher, but the main beam will be narrower.
a. Theory of Array Factor
If there are N elements along x-direction with spacing d, the total field intensity with identical element pattern
(3-1)
In which a
n is the amplitude excitation. F(θ) is nth antenna element
pattern.Then the total electric field intensity is[Element pattern x Array Factor] (3-2)
sin
So Array Factor is
(3-3) Exclude the phase term, the AF is a SINC function with maximum value is with half-wavelength element spacing.
b. Theory of Array Admittance
The sleeve dipole antenna array is linear antenna array, when an antenna element is more and more, the taper efficiency is very important.
Follow R.S.ELLIOTT paper [2] “On the Design of Traveling-Wave-Fed Longitudinal Shunt Slot Arrays”, equivalent circuit of traveling-wave linear array is shown in Fig. 3.2, Y
n
A
is the admittance of antenna element, βL is the space distance, Go is match load. The equation of voltage and current can write(3-4)
And power radiated from each antenna element is
)
So
(3-6)
When P1=P2=P3=….Pn, we can get the best taper efficiency, Eq. (3-5) and (3-6) combined to give
(3-7)
From (3-7), when power radiated of each antenna element are equal, sleeve dipole antenna array have the best taper efficiency. So the linear antenna array can change admittance of each antenna element to get best taper efficiency. Chapter 4, will optimize of taper efficiency to get best antenna directivity.
3.3 Simulation of Coaxial Sleeve Dipole Antenna array
The structure of the coaxial sleeve dipole antenna array is shown in Fig.
3.3, it add a helix to construct an array, which can make electric field in the same direction to increase antenna gain by shifting the phase, and parameter H is equal to half-wavelength, which is second antenna element. In the coaxial sleeve dipole antenna array, the helix is very important, the length of the helix is about half-wavelength, when the length is equal to
equal half-wavelength, the main beam will be scan, in WiFi communication, this is very serious problem. Because the coaxial sleeve dipole antenna array is dipole antenna, so the length of each antenna elements must equal half-wavelength.
In Fig. 3.3, the defining parameters of the conventional helix are the helix radius, R ,the total length of the helix, CL ,the turn-to-turn spacing, TD ,and the axial length, Z.
3.4 Simulation and Measurement Results of Sleeve Dipole Antenna Array
The fabricated of the coaxial sleeve dipole antenna array is shown in Fig.
3.4, the measurement environment is shown in Fig 3.5. The simulation and measurement results of the reflection coefficient are shown in Fig. 3.6, the whole bandwidth covers the operating frequency. The simulation and measurement results of efficiency are shown in Fig. 3.7, the measurement result of efficiency is about 90%. The simulation and measurement results of peak gain are shown in Fig 3.8, the measurement result of peak gain is about 4.2 dBi. The simulation and measurement result of E-plane radiation pattern at 2.45 GHz are shown in Fig 3.9, the simulation and measurement result is almost the same. The simulation and measurement result of H-plane radiation pattern at 2.45 GHz are shown in Fig 3.10, from Fig 3.10, it can find
the radiation pattern of coaxial coaxial sleeve dipole antenna is belonging to omni-direction.
3.5 Summary
The gain of the coaxial sleeve dipole antenna array is about 4.2 dBi, and the efficiency is about 90%, and the radiation pattern at H-plane is almost omni-direction.
Fig. 3.1 Structure of antenna array
Fig. 3.2 Equivalent circuit of traveling-wave linear array
βL βL
Fig. 3.3 Structure of coaxial sleeve dipole antenna array
Fig. 3.4 Fabricated of the coaxial sleeve dipole antenna array
H R
TD Z
Unit：mm 17
X
57 H
11 Z
2.5 TD
2 R
62.8 CL
Unit：mm
Frequency (GHz)
2.0 2.1 2.2 2.3 2.4 2.5 2.6
|S 11|(dB )
-20 -15 -10 -5 0
Simulated Meassured
Fig. 3.5 Measurement environment of coaxial sleeve dipole antenna array
Fig. 3.6 Simulation and measurement result of reflection coefficient
Fig. 3.7 Simulation and measurement result of efficiency
Fig. 3.8 Simulation and measurement result of peak gain
Frequency (GHz)
2.30 2.35 2.40 2.45 2.50 2.55 2.60
Ef fi cienc y (%)
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Simulated Measured
Frequency (GHz)
2.30 2.35 2.40 2.45 2.50 2.55 2.60
Peak Gain (dBi)
-8 -6 -4 -2 0 2 4 6
Simulated
Measured
Fig. 3.9 Simulation and measurement result of E-plane radiation pattern at 2.45 GHz
Fig. 3.10 Simulation and measurement result of H-plane radiation pattern at 2.45 GHz
Chapter 4
Sleeve Dipole Antenna array by Print Circuit Board
In Chapter 4, a sleeve dipole antenna array by print circuit board will be designed for IEEE 802.11a/b/g, and improving taper efficiency in this chapter, the sleeve dipole antenna array by print circuit board will add an reflector to change radiation pattern. The sleeve dipole antenna array is linear antenna array, when antenna elements are more and more, the taper efficiency is very important, in this chapter, we optimize of taper efficiency to get best directivity.
4.1 Introduction of Sleeve Dipole Antenna array by Print Circuit Board
Fig 4.1 is show WiFi apply in town, the base station at town center, unfortunately, for long distance client need high antenna gain to connect base station.
In this chapter, design of the sleeve dipole antenna array by print circuit board, and add a reflector to increase antenna gain, the radiation pattern of the sleeve dipole antenna array will be change. The sleeve dipole antenna array is wideband antenna array, Unfortunately, the main beam will scan at different frequency.
4.2 Simulation of Sleeve Dipole Antenna array by Print Circuit Board
The sleeve dipole antenna array is designed to be applied in IEEE 802.11a and IEEE 802.11b/g, operating frequency are from 2.41 GHz to 2.46 GHz and 5.2 GHz to 5.8 GHz, due to operating frequency of IEEE 802.11a is wider, so the main beam will obvious scan.
a. Simulation of Sleeve Dipole Antenna array for IEEE 802.11 b/g
Simulation model of sleeve dipole antenna array is shown in Fig. 4.2. The substrate is FR4 with thickness 0.08 cm. The size of substrate is 16 cm in length and 2.1 cm in width. The operating frequency of IEEE 802.11 b/g is from 2.41 GHz to 2.46 GHz. The parameter X is about quarter-wavelength, the parameter Y is distance of each antenna element, and the main beam can scan at different frequency. The sleeve dipole antenna array will add a reflector, which increase antenna gain is about 6 dB. The height of the sleeve dipole antenna array to the reflector is about 2 cm.
b. Simulation of Sleeve Dipole Antenna array for IEEE 802.11a
Simulation model of sleeve dipole antenna array is shown in Fig. 4.3. The substrate is FR4 with thickness 0.08 cm. The size of substrate is 12.5 cm in
3 2
1 Y Y
Y
length and 1.3 cm in width. The operating frequency of IEEE 802.11 a is from 5.2 GHz to 5.8 GHz. The parameter X is about quarter-wavelength, the parameter Y is distance of each antenna element, and the main beam can scan at different frequency. The sleeve dipole antenna array will add a reflector, which increase antenna gain is about 6 dB. The height of the sleeve dipole antenna array to the reflector is about 0.75 cm.
c. Optimization of Antenna Admittance
When the operating frequency is higher, the wavelength is shorter, the sleeve dipole antenna array can contain more antenna element in the same size. The sleeve dipole antenna array is linear antenna array, when an antenna element is more and more, the taper efficiency is very important. From the chapter 3, which can know, when P1=P2=P3=….Pn, we can get the best taper efficiency, from Eq. 3-7, which can know the linear antenna array can change admittance of each antenna element to get best taper efficiency.
Follow R.S.ELLIOTT paper “On the Design of Traveling-Wave-Fed
Longitudinal Shunt Slot Arrays” [1], the equation of voltage can write
(4-1)
antenna array has the best taper efficiency. This paper design of sleeve dipole antenna array by print circuit board, due to the print circuit board have insertion loss, the current will be weaken. The equivalent circuit of the sleeve dipole antenna array by print circuit board is shown in fig 4.4, the a
1
and a2
are admittance of insertion loss. The antenna element more and more, the antenna admittance is larger.In Fig 4.3, the parameter D is space of feed, which can control the array admittance. Fig. 4.5 and Fig. 4.6 are show simulation result of admittance with thickness 0.08 cm and 0.04 cm, the parameter D and admittance are in direct proportion.
The simulation models of sleeve dipole antenna array by print circuit board are shown in Fig 4.7. The each antenna element has equal admittance is shown in Reference, optimization of the antenna admittance are shown in CASE1 and CASE 2. The simulation results of the return loss are shown in Fig 4.8. The whole bandwidth covers the operating frequency, from 5.2 GHz to 5.8 GHz. The simulation results of efficiency are shown in Fig. 4.9. The efficiency of the reference is about 60%. The efficiency of the CASE2 is about 65%. The simulation results of directivity are shown in Fig. 4.10. The directivity of the reference is about 7.5 dBi. The directivity of the CASE2 is about 8 dBi. The simulation results of peak gain are shown in Fig. 4.11. The peak gain of the reference is about 5 dBi. The peak gain of the CASE2 is about 5.5 dBi. After optimization of antenna admittance, the peak gain has been increased 0.5 dBi, the directivity has been increased 0.5dBi, and the
efficiency has been also increased.
4.3 Simulation and Measurement Results of Sleeve Dipole Antenna array by Print Circuit Board
The fabricated of the sleeve dipole antenna array by print circuit board is shown in Fig 4.12. The substrate is FR4 with thickness 0.08 cm, The size is 16 cm in length and 2.1 cm in width. The height of the sleeve dipole antenna array to the reflector is about 2 cm. The simulation and measurement result of the reflection coefficient are shown in Fig. 4.14, whole bandwidth covers the operating frequency. The simulation and measurement results of efficiency are shown in Fig. 4.15. The measurement result of efficiency is about 60%.
The simulation and measurement results of peak gain are shown in Fig. 4.16, the measurement result of peak gain is about 8.5 dBi. The simulation and measurement results of E-plane radiation pattern at 2.41 GHz are shown in Fig. 4.17. The simulation and measurement results of H-plane radiation pattern at 2.41 GHz are shown in Fig. 4.18.The simulation and measurement results of E-plane radiation pattern at 2.44 GHz are shown in Fig. 4.19. The simulation and measurement results of H-plane radiation pattern at 2.44 GHz are shown in Fig. 4.20. The simulation and measurement results of E-plane radiation pattern at 2.46 GHz are shown in Fig. 4.21. The simulation and measurement results of H-plane radiation pattern at 2.46 GHz are shown in Fig. 4.22. From E-plane, the simulation and measurement results are almost the same.