Antenna Design

Lab 07 - Friis Transmission Equation

Dipole dimensions:

Feeding: Center-fed with a discrete port with source impedance of 50 W

Design frequency: f ₀= (1000 + PIN/1000) MHz=1GHz

실습조교 PIN = 0000

Dipole end-to-end length: L = 0.40 λ=120mm

Dipole diameter: d = L/15=8mm

Dipole feed gap at the dipole center: g = d/2=4

Dipole material: PEC

Frequency range: 0.5f₀ to 1.5f₀

Use Dipole #1 and Dipole #2 with dimensions as above.

Dipole #1 arm: Direction = z, dipole center at y = 0 and x = 0

Dipole #2 arm: Direction = z, dipole center at y = R and x = 0

ㅇ 프로젝트 template 생성

ㅇ 다이폴 #1 구조 그리기: 다이폴 원통 전체를 만든 후, 급전 간극 (feed gap)을 제거한다.

(1) Make a Dipole 1

Modeling, Cylinder 아이콘 선택, ESC 키, Name: solid1, Orientation: Z

(2) Make a feed gap

Modeling, Cylinder 아이콘 선택, ESC 키, Name: solid1, Orientation: Z

Shape intersection: Cut away highlighted shape

(3) Make a Dipole 2

ㅇ 다이폴 #2 구조 그리기: 다이폴 #1을 복사한다.

Use Dipole #1 and Dipole #2 with dimensions as above.

Dipole #1 arm: Direction = y, dipole center at z = 0 and x = 0

Dipole #2 arm: Direction = y, dipole center at z = R and x = 0

a) Select the dipole1

b) Make dipole 2 wire using Transform

For R = 0.25 λ=0.25*300=75 mm

Modelling, Components, component1

Click the dipole 1, the right mouse button, Transform

X: 0

Y:75

Z: 0

ㅇ 다이폴 급전 포트 설정

Modeling, Pick Points, Pick Face Center, gap 한면에 마우스 위치후 더블클릭

Pick Points, Pick Face Center, gap 한면에 마우스 위치후 더블클릭

Simulation, Discrete Port

키보드 A를 누르고 중앙 선택

- 아래와 같이 점이 생성됨

- 위와 같은 방식으로 반대쪽에도 점 생성

- [Simulation]-[Discrete Port] Click

- 아래와 같은 창이 생성됨

- OK Click

- 반대쪽도 똑같이 생성해주면 된다.

- 유의할 점은 포트의 방향은 같아야 한다는 것.

Repeat a discrete port2 same the discrete port1.

ㅇ 시뮬레이션 설정

주파수 설정:

Simulation, Frequency, Min. frequency: 0.5, Max. frequency: 1.5

필드 모니터 설정:

Simulation, Field Monitor, E-field, Frequency, Frequency:1, Apply

Simulation, Field Monitor, H-field and Surface current, Frequency, Frequency:1, Apply

Simulation, Field Monitor, Far field/RCS, Frequency, Frequency:1, Apply

Simulate

Simulation, Setup Solver, Start

1-1. Plot the antenna structure.

1-2. Plot Plot |S11|, |S21| in dB.

1-3. Find |S21| (dB) at f₀.

|S21| = -8.87 dB @ 1GHz

1-4. Plot the co-polarized gain Gtheta at f₀ of a dipole toward the other dipole on a polar plot in θ= 90° plane. Find the Gtheta (dB) in the direction of the other dipole. The presence of the other dipole may change the omnidirection pattern of an isolated dipole.

- Navigation Tree,

2D/3D Results, Farfileds, Theta

a) Polar

- 3D pattern에서 마우스 우클릭 후 [Farfield Plot Properties] 클릭

- 아래 화면과 같이 지정

(Theta->Phi, OK)

Gtheta = 2.55 dBi @ phi = 90° (in the direction of the other antenna)

For Y=R = 0.5 λ=150 mm, repeat the above.

Double click the dipole1_1

Then double click the Transform component (translate)

Change the distance (Y=R = 0.5 λ=150 mm)

Simulate

Simulation, Setup Solver, Start

2-1.Plot the antenna structure.

2-2. Plot Plot |S11|, |S21| in dB.

2-3. Find |S21| (dB) at f₀.

|S21| = -13.91 dB @ 1GHz

2-4. Plot the co-polarized gain Gtheta at f₀ of a dipole toward the other dipole on a polar plot in θ= 90° plane. Find the Gtheta (dB) in the direction of the other dipole. The presence of the other dipole may change the omnidirection pattern of an isolated dipole.

a) Polar

Gtheta = 1.79 dBi @ 1 GHz in the direction of the other antenna

For Y= R = 1.0 λ=300 mm, repeat the above.

Double click the dipole1_1

Then double click the Transform component (translate)

Change the distance (Y = R = 1.0 λ=300 mm)

Simulate

Simulation, Setup Solver, Start

3-1.Plot the antenna structure.

3-2. Plot Plot |S11|, |S21| in dB.

3-3. Find |S21| (dB) at f₀.

|S21| = -18.46 dB @ 1GHz

3-4. Plot the co-polarized gain Gtheta at f₀ of a dipole toward the other dipole on a polar plot in θ= 90° plane. Find the Gtheta (dB) in the direction of the other dipole. The presence of the other dipole may change the omnidirection pattern of an isolated dipole.

a) Polar

Gtheta = 2.07 dBi @ 1 GHz in the direction of the other antenna

II. Discussions

1. Compare |S21| (dB) by CST Studio with |S21| (dB) by Friis equation.

	R = 0.25 λ	R = 0.5 λ	R = 1.0 λ
1. \|S21\| (dB), CST Studio	-8.87	-13.91	-18.46
2. Antenna gain Gtheta (dB) in the other dipole direction	2.55	1.79	2.07
3. Path loss: (λ/4πR)² (dB)	1/(4π×0.25)² = -9.94	1/(4π×0.5)² = -15.94	1/(4π×1.0)² = -21.94
4. \|S21\| (dB), Friis equation	-4.84	-12.36	-17.80
5. \|S21\| difference (dB) (1-4)	-4.03	-1.55	-0.66

2. Find the minimum distance where the Friis equation is accurate within ±1 dB. Note the Friis equation is accurate when both antennas lie in the far-field region of the other antenna.

R = 0.5, delta = -1.55

R = 1.0, delta = -0.66

R = x, delta = -1.0

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Use a linear approximation (비례식)

x = 1.0 - (1.0-0.66)*(1.0-0.5)/(1.55-0.66) = 0.809 λ