실습 07a – GPS L1 세라믹 패치 안테나 설계

Purpose

- Learn how to design a patch antenna.

- Learn how to design a circularly-polarized ceramic patch antenna.

1. Theory

1) 인쇄회로 기판의 구조

The structure of a printed circuit board (PCB): ground plane, dielectric, circuit patterns

Metal: copper, thickness 0.017mm, 0.034mm, 0.068mm, etc.

Dielectric: dielectric constant (ε_r = 2.5, 4.4, 10, 20, 45, 90, etc.), loss tangent (tanδ = 0.02, 0.005, 0.002, 0.0002)

2) 사각패치 안테나 구조 및 동작원리

A patch antenna: a wide and thin dipole in a printed form with a metal backing.

3) 사각패치 안테나의 전류, 패치 아래 공동의 전기장, 급전위치에 따른 입력 임피던스

Feeding of a patch: by a coaxial probe or a microstrip line. Feed position changes the antenna input impedance.

4) 패치의 방사패턴

Radiation patterns of a patch: E-plane pattern is broader than H-plane pattern. Pattern shapes are affected by the ground plane size.

(보충) 접지판 크기에 따른 방사패턴

5) 원편파 생성원리

(수정) y축 방향 반대로

RHCP(right-hand circular polarization):

LHCP(left-hand circular polarization):

LP(linear polarization):

EP(elliptic polarization: none of the above cases.

6) 우원편파, 좌원편파, 축비

평면파가 +z 방향(오른손 엄지)으로 진행할 경우 전기장의 회전방향(오른손 나머지 손가락): RHCP(우원편파)\

축비(AR; axial ratio)

Axial ratio bandwidth: frequency for AR < 3dB

7) 자가 원편파 생성원리

Method of phasing: length adjustment

a) Crossed dipoles:

(보완) 그림 수정

b) Rectangular patch: for RHCP

(보완) 그림 수정

8) 패치 안테나 설계

Design of a patch antenna:

- Length L is determined by the center (resonant) frequency. Use the following formula for the initial dimension.

Adjust the length (after initial simulation) by frequency scaling.

- Width W is determined for high efficiency. Efficiency is proportional to W for . For simplicity make W same as L.

- Dielectric substrate thickness h determines the bandwidth(BW). Increase h if BW is too small.

- Ceramic patch: use a high dielectric constant ceramic material to reduce the patch size. Dielectric constants (ε_r) used = 10, 20, 45, 90. Reduction ratio is proportional toaccording to the formula

- Patch efficiency and bandwidth:

- Probe (microstrip) feed position adjust along the center line according to the formula

If the resistant is too large, move the probe toward the patch center.

- Circular polarization: for RHCP, remove upper right and lower left corners until a good axial ratio is obtained.

- Probe design: use the following formula for a 50-ohm cable.

2. Simulation

1) Draw the geometry

3D View:

Top view and dimensions:

접지판( t = 0.035mm ), 세라믹( t = 6mm ), 패치( t = 0.035mm )

동축선 내심 직경( 0.8mm ), 외심 유전체 직경( 1.85mm ), 유전율 ( 1 ), 외부도체 직경( 2.25mm )

동축선의 내심은 패치중심에서 아래 방향으로 1.7mm 이격되어 패치에 연결됨.

Side view:

2) Simulate the antenna.

○ Setting

- 'Solve'-'Frequencies': Fmin =1GHz, Fmax = 2GHz

- 'Mesh'-'Global Mesh Properties': Lower mesh limit = 10.0

- 'Solve'-'Field Monitor': E-field at 1.575GHz, H-field at 1.575GHz, Far-field at 1.575GHz

3) Analyze the antenna.

a) Antenna 3D geometry with the rectangular coordinate axis.

b) Near fields

○ Electric field with animation: see if you got RHCP.

- on the patch surface

- at 1cm above the patch.

○ Magnetic field (or electric surface current density):

- on the patch surface

- at 1cm above the patch.

c) Input impedance

- |S₁₁|(dB) from 1.5 to 1.7GHz. Find the impedance bandwidth (|S₁₁| < -10dB) with two vertical

cursors.

- Plot the impedance locus on the Smith chart from 1.5 to 1.7GHz. Move the reference plane to

the top surface of the ground plane.

- Plot R_in and X_in from 1.5 to 1.7GHz on the same graph. Move the reference plane to the top

surface of the ground plane. Find R_in and X_in at 1.575GHz with a vertical cursor.

d) Far-field patterns

○ RHCP gain(dB) patterns at 1.575GHz:

- 3D, polar patterns of xy-plane, yz-plane and zx-plane.

- 2D

○ LHCP gain(dB) patterns at 1.575GHz:

- 3D, polar patterns of xy-plane, yz-plane and zx-plane.

- 2D

○ Axial ratio(dB) patterns at 1.575GHz:

- 3D, polar patterns of xy-plane, yz-plane and zx-plane.

- 2D

4) Simulation result

a) Antenna 3D geometry with the rectangular coordinate axis.

b) Near fields

○ Electric field with animation: see if you got RHCP.

- on the patch surface

- at 1cm above the patch.

○ Magnetic field (or electric surface current density):

- on the patch surface

- at 1cm above the patch.

c) Input impedance

- |S₁₁|(dB) from 1.5 to 1.7GHz. Find the impedance bandwidth (|S₁₁| < -10dB) with two vertical cursors.

- Plot the impedance locus on the Smith chart from 1.5 to 1.7GHz. Move the reference plane to the top surface of the ground plane.

- Plot R_in and X_in from 1.5 to 1.7GHz on the same graph. Move the reference plane to the top surface of the ground plane. Find R_in and X_in at 1.575GHz with a vertical cursor.

d) Far-field patterns

○ RHCP gain(dB) patterns at 1.575GHz:

- 3D RHCP gain pattern

- 2D RHCP gain pattern

- 1D RHCP gain pattern on the xy plane

- 1D RHCP gain pattern on the yz plane

- 1D RHCP gain pattern on the zx plane

○ LHCP gain(dB) patterns at 1.575GHz:

- 3D LHCP gain pattern

- 2D LHCP gain pattern

- 1D LHCP gain pattern on the xy plane

- 1D LHCP gain pattern on the yz plane

- 1D LHCP gain pattern on the zx plane

○ Axial ratio(dB) patterns at 1.575GHz:

- 3D axial ration pattern

- 2D axial ratio pattern

- 1D axial ratio pattern on the xy plane

- 1D axial ratio pattern on the yz plane

- 1D axial ratio pattern on the zx plane

3. Measurements

1) Make two dipole antennas with a center frequency of 1.6GHz.

2) Calibrate the network analyzer in the full 2-port calibration mode over 1-2GHz. Store the calibration data.

3) Measure and plot S₁₁ and S₂₂ of two dipole antennas over 1-2GHz.

Dipole 1 connected to the port 1. Dipole 2 connected to the port 2.

4) Place two dipole antennas parallel to each other with a distance of 10cm. And measure S₂₁ over 1-2GHz. Store the result in the memory.

5) Set the network analyzer to display the stored S₂₁ and measured S₂₁. Replace dipole 1 with a 25x25x6mm ceramic patch antenna. Use a rotary joint to rotate dipole 2.

With a distance of 10cm between the ceramic patch and dipole 2, rotate dipole 2 and observe S₂₁ at 1.575GHz (GPS) and 1.602GHz (GLONASS). Record the maximum and minimum values of S21 at 1.575GHz and 1.602GHz. Adjust the vertical scale value per division (like 2dB/div, 4dB/div, 6dB/div) to increase the readability of the displayed curves.

6) Calculate the gain and the axial ratio of the ceramic patch.

안테나의 이득 측정: 이득이 정확하게 알려진 표준 안테나 (예: 다이폴, 이득 2.15dBi)와의 전달계수를 측정하여 비교

축비: 피측정 안테나와 다이폴 안테나 사이의 전달계수를 다이폴 안테나를 회전시키면서 측정하여 전달계수의 최대값과 최소값의 차이를 측정

P₁: power coming out of the port 1 into the antenna 1

P₂: power entering into the port 2 from the antenna 2

S₂₁: transmission coefficient between two antennas

S₁₁: reflection coefficient of the antenna at the port 1

S₂₂: reflection coefficient of the antenna at the port 2

d: distance between two antennas

G₁, G₂: gain of the antenna 1 and 2