Something to share about antenna. Try to make as simple as possible

1. sulaim_qais@yahoo.com
Mac 2013
ANTENNA DESIGN

2. INTRODUCTION
A rough outline of some major antennas and their discovery /
fabrication dates are listed:
 Yagi-Uda Antenna, 1920s
 Horn antennas, 1939. Interesting, the early antenna literature
discussed waveguides as "hollow metal pipes".
 Antenna Arrays, 1940s
 Parabolic Reflectors, late 1940s, early 1950s? Just a guess.
 Patch Antennas, 1970s.
 PIFA, 1980s.
Current research on antennas involves metamaterials
(materials that have engineered dielectric and magnetic
constants that can be simultaneously negative, allowing for
interesting properties like a negative index of refraction). Other
research focuses on making antennas smaller.
Rectangular patch antenna Array

3. INTRODUCTION
In 1913, the Eiffel Tower was used an antenna. Back when communication was
at very low frequencies, the antennas had to be very large to get any sort of
radiation. The Eiffel Tower fit this bill well, and was used to communicate with
the United States Naval Observatory in Arlington, Virginia.

4. How wave propagates ?
Using Dipole antenna as an example
Understand this :
 Electric field will produce magnetic field
 Changing in magnetic field will produce electric field
This process rotate continuously , thus creating waves.

5. Frequency band
Several standard for radio spectrum naming such as :
 ITU radio bands
 IEEE bands
 EU, NATO, US ECM
 waveguide frequency band
Frequency Band Name Frequency Range Wavelength (Meters) Application
Extremely Low Frequency
3-30 Hz 10,000-100,000 km Underwater Communication
(ELF)
AC Power (though not a
Super Low Frequency (SLF) 30-300 Hz 1,000-10,000 km
transmitted wave)
Ultra Low Frequency (ULF) 300-3000 Hz 100-1,000 km
Very Low Frequency (VLF) 3-30 kHz 10-100 km Navigational Beacons
Low Frequency (LF) 30-300 kHz 1-10 km AM Radio
Medium Frequency (MF) 300-3000 kHz 100-1,000 m Aviation and AM Radio
High Frequency (HF) 3-30 MHz 10-100 m Shortwave Radio
Very High Frequency (VHF) 30-300 MHz 1-10 m FM Radio
Ultra High Frequency (UHF) 300-3000 MHz 10-100 cm Television, Mobile Phones, GPS
Satellite Links, Wireless
Super High Frequency (SHF) 3-30 GHz 1-10 cm
Communication
Extremely High Frequency
30-300 GHz 1-10 mm Astronomy, Remote Sensing
(EHF)
400-790 THz 380-750 nm
Visible Spectrum Human Eye
(4*10^14-7.9*10^14) (nanometers)
ITU radio bands

6. Field surrounding an antenna
Divided into 3 principle region :
1. Reactive Near Field - E- and H
fields are out of phase by 90 degrees to each other (recall that for
propagating or radiating fields, the fields are orthogonal (perpendicular)
but are in phase).
2. Radiating Near Field or Fresnel Region
reactive fields are not dominate; the radiating fields begin to emerge.
However, unlike the Far Field region, here the shape of the radiation
pattern may vary appreciably with distance. Note that depending on the
values of R and the wavelength, this field may or may not exist.

7. Field surrounding an antenna
3. Far Field or Fraunhofer Region
the most important region, determines the antenna's radiation pattern, so
this is the region of operation for most antennas
Must satisfied all these equation :
R = distance
D= antenna dimension /diameter
λ = wavelength frequency
λ= c /f = [speed of light]/[propagating frequency]

8. General effect of antenna size
Small antenna will produce low directivity. Big antenna will
produce high directivity
 if you use an antenna with a total size of 0.25 - 0.5 λ (a quarter- to a half-wavelength
in size), then you will minimize directivity. That is, half-wave dipole antennas or half-
wavelength slot antennas typically have directivities less than 3 dB, which is about as
low of a directivity as you can obtain in practice.
 we can't make antennas much smaller than a quarter-wavelength without
sacrificing antenna efficiency.
 for high directivity, we'll need antennas that are many wavelengths in size. That is,
antennas such as dish (or satellite) antennas and horn antennas have high directivity, in
part because they are many wavelengths long.

9. Understand Efficiency, Directivity, Gain
efficiency is defined as the ratio between the input and the output of such system.
You could have an antenna that has high directivity, but, due to losses
(conductor losses, dielectric losses, measured by the antenna efficiency or
deficiency) your antenna sucks and the overall antenna radiation is not the one
desired. That's why we introduce the Gain

10. Understand Efficiency, Directivity, Gain

11. Understand Efficiency, Directivity, Gain
 The Gain is defined as the directivity of antenna after being affected by such
losses. The gain is always related to the main lobe and is specified in the direction
of maximum radiation unless indicated.
 An antenna with a gain of 3 dB means that the power received far from the
antenna will be 3 dB higher (twice as much) than what would be received from a
lossless isotropic antenna with the same input power.
 In general gain is measured and directivity is calculated.
To be more precise, the term ‘realized gain’ is sometimes used to differentiate
the gain defines by IEEE.

12. Why we need matching circuit ?
Matching is the process of removing mismatch loss due to wave travelling
through different impedance.
Reduce the power reflected from the load (the antenna)
 maximize the power delivered to the antenna.
The reflection coefficient given by:

13. Why we need matching circuit ?
Simulation shows a standing wave when 100%
reflection. When reflection coefficient equal to 1

14. Why we need matching circuit ?
Example : A 50 Ω transmission line is connected to a 30 Ω antenna . Calculate
the reflection coefficient.
ZL Γ = (ZL-ZA) / (ZL+ZA)
= (50-30)/(50+30)
= 0.25
Picture above shows circuit model of an antenna connected to signal source, V.
ZL = line characteristic impedance
ZA = antenna impedance
Notes: Uniform transmission line impedance do not dependent on its length,
the value is the same no matter how long the transmission is. Therefore, it is
known as characteristic impedance. However, the characteristic impedance
depends on the line width, dielectric and propagating frequency. Transmission
line normally affects the higher frequency which the transmission line is longer
than the wavelength.

15. Why we need matching circuit ?
Impedance normally consists of real and imaginary part.
The real part of the antenna impedance represents power that is either radiated
away or absorbed within the antenna.
The imaginary part of the impedance represents power that is stored in the near field
of the antenna.
Both are non-radiated powers.
Maximum power transfer occur when:
Zs* (conjugate)
If ZA=50-j20 , then Zs = 50 + j20

16. Bandwidth
Bandwidth is typically quoted in terms of VSWR. For instance, an antenna may
be described as operating at 100-400 MHz with a VSWR<1.5.
Described in Return loss S11=20 log (0.2)= -13.98 dB.
Take note :
S11 is a measure of the reflection from an antenna. 0dB means that all the power is reflected, hence the matching is not
good. -10dB means that 10% incident power is reflected, meaning 90% power is accepted by the antenna. However, a good
S11 response does not necessarily mean the antenna is radiating. S11 is still typically used though to show an antenna's
response; the underlying assumption is that the losses are not so great.
There are also other criteria which may be used to characterize bandwidth :
 polarization over a certain range, for instance, an antenna may be described as
having circular polarization with an axial ratio < 3dB (less than 3 dB) from 1.4-1.6 GHz.
This polarization bandwidth sets the range over which the antenna's operation is
approximately circularly polarized.
 Fractional Bandwidth (FBW). The FBW is the ratio of the frequecny range (highest
frequency minus lowest frequency) divided by the center frequency. The antenna
Q also relates to bandwidth (higher Q is lower bandwidth, and vice versa).

17. Several common antennas bandwidth

18. Beamwidth and sidelobes
Figure shows the radiation pattern of an antenna
 main beam is the region around the direction of maximum radiation (usually the
region that is within 3 dB of the peak of the main beam). The beamwidth of the main
beam is sometimes called Half Power Beamwidth (HPBW) just beamwidth.
 sidelobes are smaller beams that are away from the main beam. These sidelobes are
usually radiation in undesired directions which can never be completely eliminated.
 Null to Null Beamwidth. This is the angular separation from which the magnitude of
the radiation pattern decreases to zero (negative infinity dB) away from the main
beam.

19. Polarization

20. Polarization
Circular polarization is a desirable characteristic for many antennas. Two antennas that are both
circularly polarized do not suffer signal loss due to polarization mismatch. Antennas used in GPS systems
are Right Hand Circularly Polarized.
Suppose now that a linearly polarized antenna is trying to receive a circularly polarized wave.
Equivalently, suppose a circularly polarized antenna is trying to receive a linearly polarized wave.
What is the resulting Polarization Loss Factor?
Recall that circular polarization is really two orthongal linear polarized waves 90 degrees out of phase.
Hence, a linearly polarized (LP) antenna will simply pick up the in-phase component of the circularly
polarized (CP) wave. As a result, the LP antenna will have a polarization mismatch loss of 0.5 (-3dB), no
matter what the angle the LP antenna is rotated to.
Circular polarization

21. Friss Transmission Equation
Friis Transmission Equation is used to calculate the power received from one antenna
(with gain G1), when transmitted from another antenna (with gain G2), separated by a
distance R, and operating at frequency, f or wavelength, λ.
Received power, R
Gain 1 Gain 2
In general, for two linearly polarized antennas that are rotated from each other by an angle ø, the power
loss due to this polarization mismatch will be described by the Polarization Loss Factor (PLF).
Friis Transmission Equation says that the path loss is higher for higher frequencies. The
importance of this result from the Friis Transmission Formula cannot be overstated. This is
why mobile phones generally operate at less than 2 GHz. There may be more frequency
spectrum available at higher frequencies, but the associated path loss will not enable
quality reception.However, lower frequency making the antenna bigger. The challenge for
antenna designer is to build antenna for lower frequency with smaller size.

22. Antenna material (Radiator)
High relative permittivity means that the material is magnetic which mean it attracts to
magnet. A positive relative permeability greater than 1 implies that the material
magnetizes in response to the applied magnetic field. Generally these elements are not
suitable for making antenna/radiator parts.
I can say that carbon (graphite) is also a good material of making antenna

23. Some of antenna design
1. Dipole antenna
Antenna length= 0.48λ
Normally using 70Ω transmission line
Can get higher gain with L= 3λ/2
Increase the BW by using thicker wire
L

24. Some of antenna design
2. Monopole antenna
Monopole antenna is twice the directivity of dipole antenna

25. Some of antenna design
3. Helical/ Helix antenna
A wide bandwidth, is easily constructed, has a real input
impedance, and can produce circularly polarized fields.
Helix antennas of at least 3 turns will have close to circular
polarization in the +z direction
C=πD
Typically, the pitch angle is
taken as 13 degrees
pitch angle,

26. Some of antenna design
4. Yagi-Uda antenna
Driven element normally used dipole antenna

27. Some of antenna design
5. Planar Inverted-F Antenna (PIFA)
Side view
Top view
λ/4 = L+W1-W2
Making shorter W2 will get lower bandwidth… having higher the value have
higher bandwidth
Create dual band antenna

28. Some of antenna design
6. Folded Inverted Conformal Antenna (FICA)
PIFAs exhibit two resonant modes, which operate by sharing the same available
antenna volume, the FICA structure is synthesized in order to sustain three resonant
modes that better reuse the volume.

29. Some of antenna design
7. Parabolic Dish antenna
Dish diameter = 10 λ  50 λ (larger is better)
G = ε(πD)2/ λ , ε = Aperture area efficiency
Focal point, F = 0.35D 0.7D
Parabolic formula
x2= 4F (F-y), x<=D/2

30. Various antenna

31. Various antenna

32. Various antenna

33. Various antenna

34. Various antenna

35. Various antenna

36. Various antenna

37. Various antenna

38. Various antenna

39. Some research antenna
Nuclear fusion antenna
Metamaterial antenna

40. Measurements
1. Radiation pattern and gain
We are measuring the gain of antenna not the directivity.
The gain, G of an antenna is an actual or realized quantity which is less than the directivity, D due to
ohmic losses in the antenna or its radome (if it is enclosed). In transmitting, these losses involve
power fed to the antenna which is not radiated but heats the antenna structure
Measurement is done inside
Anechoic chamber
Equipment setting

41. Measurements
2. Polarization measurement
To perform the measurement, we will use our test antenna as the source. Then we will use a linearly
polarized antenna (typically a half-wave dipole antenna) as the receive antenna. The linearly polarized
receive antenna will be rotated, and the received power recorded as a function of the angle of the
receive antenna. In this manner, we can gain information on the polarization of the test antenna. This
received information only applies to the polarization of the test antenna for the direction in which the
power is received. For a complete description of the polarization of the test antenna, the test antenna
must be rotated so that the polarization can be determined for each direction of interest.

42. Measurements
2. Polarization
Figure shows the example result of
polarization measurement
Horizontal
Vertical
Elliptical
Circular

43. Measurements
3. Impedance
Impedance measurements are pretty easy if you have the right equipment. In this case,
the right equipment is a Vector Network Analyzer (VNA). This is a measuring tool that
can be used to measure the input impedance as a function of frequency. First
calibration is needed.
Typically VNA will be supplied with a "cal kit" which contains a matched load (50 Ohms),
an open circuit load and a short circuit load.
If the circuit matched to 50 Ohm then we will get low value of S11(Return loss).

44. Measurements
3. Impedance
Figure shows S11 measurement result using VNA
So this measurement typically measures how close to 50 Ohms the antenna
impedance is.

45. Measurements
4. Specific Absorption Rate (SAR)
Specific Absorption Rate (SAR) is a measure of how transmitted RF energy is absorbed
by human tissue.
SAR is a function of conductivity (ς), induced E-field (E) and the mass density of the tissue (ρ)
SAR measure in W/kg = mW/g
The SAR limit in the US for mobile phones is 1.6 W/kg, averaged over 1 gram of tissue. In
Europe, the SAR limit is 2.0 W/kg averaged over 10 grams of tissue. It is typically harder to
achieve the US specification than the Europe spec, so if the phone meets the US spec it will
typically also meet the European spec.
The SAR values quoted for a mobile phone are the highest value of SAR
measured for any frequency the phone operates in, from both the left and
right side of the head.The antennas for mobile phones are typically on the
bottom of the phone, to keep the radiating part of the phone as far as
possible from the brain region.

46. Measurements
4. Specific Absorption Rate (SAR)
Picture shows the SAR Measurement system
To simulate the conductivity and density correctly, the tub is filled with a fluid that
has similar properties to human tissue.