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Antenna Design Lab. 02 – A Half-Wave Wire Dipole

2.1 Purpose

- Learn how to use the antenna simulation software.

- Learn to check results of the simulation.

2.2 Theory

- A dipole is a two-piece metal component fed at the center.

- Its impedance changes with the frequency. Its first resonance is at the frequency where its total length is about a half wavelength. The resonant resistance is 72 ohms.

- 2.4 Materials definition

- Do it when a volume is made or you can do it later.

- Choose an object and right-click and change material

- Vacuum, new material, load from material library, PEC

2.5 Source definition: 'Solve'

- 'Waveguide port'

- 'Discrete port'

- 'New plane wave'

- 'Far-field source'

- 'Field source'

- 'Field import'

- 'Excitation signals': excitation signals for transient solver

2.6 Setting parameters to be calculated

- 'Field monitors': various fields at far distances. You have to choose what you want to calculate.

- 'Voltage monitor': You have to define a curve along which a voltage is calculated.

- 'Current monitor': You have to define a curve along which a current is calculated.

- 'Probe': various fields at any point.

2.7 Choose solvers (solution method): 'Solve'

- 'Transient solver': time-domain solver

- 'Frequency domain solver': we don't have a license. Tetrahedral mesh. MoM

- 'Eigenmode solver': we have a license

- 'Integral equation solver': we have a license. Surface mesh. MoM

- 'Multilayer solver': we don't have a license. Added from v.2011

- 'Asymptotical solver': we don't have a license. Added from v.2011. SBR, PO

- 'TLM solver': we have a license. Added from v.2011

- 'ADS co-simulation': we have a license. Added from v.2011

2.8 Choose mesh type: 'Mesh'

- 'Mesh types': hexahedral (for transient solver and frequency domain solver), hexahedral TLM (for

TLM solver), tetrahedral (for frequency domain solver), surface(for integral equation solver),

multiplayer (for multilayer solver)

2.9 Start simulation: 'Start'

2.10 Check the results: 'Result'

- 1D result: Port signals, S-parameter(in many forms including Smith chart), Balance, Egergy,

Material

- 2D: Port mode, E-field, H-field, Surface current; results of field monitors

- 3D:

Far-fields (Abs, Axial ratio, Theta, Theta phase, Phi, Phi phase, Theta/Phi, Phi/Theta)

Far-fields(Abs, Axial ratio, Left pol., Left pol. phase, Right pol., Right pol. phase, Left/Right,

Right/Left)

- Tables: all of the results can be made in tabular forms.

2.11 Improving solution accuracy:

- Adjust transient solver parameters: many parameters to be set

- Mesh: many parameters to be set. Mesh density

2.3 Simulation

1) Draw the geometry.

- Draw the following geometry of a dipole with dimensions:

d = 0.5mm (You will fabricate the dipole using a thin wire used for wiring components on the breadboard)

L = λ/2 @ 1.575GHz = 95.2mm

g = 0.1 mm

- Be sure to make the dipole axis be in the z direction. In this case, the E-plane is zx- or yz-plane and the H- plane is the xy-plane.

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2) Simulate and tune the antenna.

- Use a discrete port (a delta-gap source) for the excitation.

- Frequency range: 0.2 to 3.2GHz.

- With the initial dimension, your antenna will resonate at 1.46GHz. Using the following formula based on

the theory of frequency scaling, we find the dipole length for a resonance at 1.575GHz.

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- Now adjust the dipole length to 88.2mm and do the simulation again.

3) Analyze the result and write a report.

- Analyze the result, that is, see simulation results and form your opinions on them.

- In making graphs, make sure that sizes of axis labels, scale values are big enough.

○ Near field at 1.575GHz:

- Observe the electric field around the dipole using stationary and animated views.

- Observe the magnetic field (or the equivalent electric current) around the dipole. The surface electric current density on a conductor is related to the magnetic field

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- Plot the magnitude and phase of Jz along the surface of the dipole on the same graph.

○ Input impedance:

- |S11|(dB) from 0.2 to 3.2GHz. Find the impedance bandwidth (|S11| < -10dB) with two vertical cursors.

- Plot the impedance locus on the Smith chart from 1.0 to 2.0GHz.

- Plot Rin and Xin from 0.2 to 3.2GHz on the same graph. Mark Rin and Xin at 1.575GHz with a vertical

cursor.

○ Gain and directivity:

- G(dB) and D(dB) from 0.2 to 3.2GHz by 0.2GHz step on the same plot.

○ Gain pattern at 1.575GHz:

- Gabs: 3D, E-plane polar pattern, H-plane polar pattern

- Gθ: 3D, E-plane polar pattern, H-plane polar. Mark the 3dB beamwidth on the polar plot.

- Gφ: 3D, E-plane polar pattern, H-plane polar pattern

- Write a full report using graphs from the simulation software.

- Give the antenna geometry, dimensions and the method of excitation. Include the coordinate axis.

- Present graphs described in the above and give your assessment of the results.

- Make a hand-written report on the spot as follows.

- Describe the antenna geometry, dimensions and the feeding method. Include the coordinate axis.

- Plot the magnitude of Jz along the surface of the dipole. Give your analysis of the result.

- Input impedance:

- |S11|(dB) = ( ) @ 1.575GHz

- Impedance bandwidth (-10dB reflection)

- Zin = ( ) + j( ) ohms @ 0.2, 1.0, 1.575, and 2.0GHz

- Gain and directivity:

- Gθ(dB) = ( ) @ 0.2, 1.0, 1.575, 2.0GHz. Give your analysis of the result.

- Dθ(dB) = ( ) @ 0.2, 1.0, 1.575, 2.0GHz. Give your analysis of the result.

- Gain patterns at 1.575GHz:

- Plot Gθ(dB), Gφ(dB) on E-plane. Give your analysis.

- Plot Gθ(dB), Gφ(dB) on H-plane. Give your analysis.

- E-plane beamwidth = ( ) deg.

4) Simulation results.

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Fig. 2.1 Electric field distribution

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Fig. 2.2 Magnetic field distribution

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Fig. 2. 3 Surface current distribution

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Fig. 3.1 Magnitude and phase of Jz along the surface of the dipole

(Question) In a discrete port, what is the terminal voltage or current?

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Fig. 3. 2 Monitor current and voltage of the discrete port

(Answer)

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Fig. 3.3 Reflection coefficient

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Fig. 3.4 Smith chart from 1.0 to 2.0GHz.

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(a) Real and Imaginary impedance inaccurate below 1GHz.[pic]

(b) Accurate for 0.2-3.2GHzRin and Xin from 0.2 to 3.2GHz

Fig. 2. 4 Input Impedance

(Question) Why is the accuracy below 1GHz poor?

(Answer) We have to increase the accuracy setting in the 'Solve' - 'Transient Solver Parameters' menu. Increase the accuracy from -30dB to -60dB for example.

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(a) Gain Inaccurate below 1GHz

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(b) Gain and Directivity inaccurate at 0.2GHz (Increase the accuracy from -30dB to -60dB)

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c. Accurate 0.2-3.2GHz (accuracy -60dB, boundary size at 0.2GHz)

Fig. 2. .. Broadband G(dB) and D(dB) pattern

(Question) Why does the result below 1GHz seem to be incrorrect?

(Answer) The absorbing boundary is too close to the antenna. We have to increase the distance from the dipole to the absorbing surfaces of the rectangular box enclosing the dipole.

(Try to get an accurate solution of the same dipole at 1kHz). Simulate the antenna from 0 to 2kHz.

D=1575000 m, l=1.39*108 m, f=1KHz, g=157500 m

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Fig. 7.1 Electric field distribution

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Fig. 7.2 Magnetic field distribution

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Fig 8.1 Surface current distribution

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Fig. 8.2 Reflection coefficient

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Fig. 8.3 Smith chart from 1.0 to 2.0GHz.

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Fig9.1(a) Real and Imaginary impedance inaccurate below 1GHz.

[pic] Fig 9.1 (b) Accurate for 0.2-2.0GHz Rin and Xin from 0.2 to 2.0GHz

[pic][pic]

Fig. 3.6a 3D Gabs pattern Fig 3.6b Gabs 2D pattern

[pic] [pic]

Fig. 3.7a 2D Gabs H-plane Fig. 3.7b 2D Gabs E-plane

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Fig 3.8a 3D (Gθ) Fig 3.8b 2D (Gθ)

Fig 3.9a plane (Gθ) Fig 3.9b H-plane (Gθ)

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Fig3.10a 3D (phi) Fig3.10b 2D (phi)

Fig3.11a E-plane (phi) Fig3.11b H-plane (phi)

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