Patch antenna

Patch antenna

1. Patch antenna
Jay Chang
1

2. 2
Patch Antennas

3. 3
1. A patch antenna basically is a metal patch suspen ded over a ground plane. Simple to fabricate, easy t o modify
and customize and closely related to microstrip ante nnas. These are constructed on a dielectric substra te,
usually employing the same sort of lithographic pat terning as used to fabricate PCBs.
2. A microstrip patch antenna consists of a radiating patch, a dielectric substrate which has a ground p lane on the
other side. The simplest patch antenna uses a half- wavelength-long patch with a larger ground plane to give
better performance but cost of larger size. The cur rent flow is along the direction of the feed wire, so the vector
potential and the electric field follows the curren t. Such a simple patch antenna radiates a linearly polarized
wave. The radiation can be regarded as being produc ed by the “radiating slots” at top and bottom (H-pl ane), or
equivalently as a result of the current flowing on the patch and the ground plane.
3. A patch antenna is a narrowband, wide-beam antenn a fabricated by etching the antenna element pattern in
metal trace bonded to an insulating dielectric subs trate. Continuous metal layer which forms a ground p lane.
4. One of the key
drawbacks
of patch is their
narrow bandwidth
. In order to achieve wider bandwidth, a relatively
thick substrate is used
. However, the antenna substrate supports tightly b ound surface-wave modes which
represent a loss mechanism in the antenna. The
loss due to surface wave modes increases with the s ubstrate
thickness
(Also the question to QTI).
•Develop conformal microstrip antennas which enjoy wi de bandwidth, yet do not suffer from the loss of at tractive
features of the conventional microstrip patch antenn a.
•Some patch antennas
eschew a dielectric substrate
and suspend a metal patch in air above a ground pla ne using
dielectric spacers; the resulting structure is
less robust but provides better bandwidth
.
•Patch antennas have a
very low profile
, are mechanically rugged and conformable, they are often mounted on
the exterior of aircraft or spacecraft, or are inco rporated into mobile radio communications devices.
5. The
primary limitation
of this type of antenna is the
bandwidth
, which is
less than 5% for most single-substrate
designs. However, a second substrate can be added t o create a dual band design or a broadband design w ith a
bandwidth of up to 35%.
6. The two most common geometries, rectangular and c ircular, are widely employed.
Square patches
are used to
generate a
pencil beam
and
rectangular patches for a fan beam
.
Salient Features of Patch Antennas

4. 4
Microstrippatch antennas: structure
0
100
t
λ
≈
0
2
r
L
λ
ε
≈
0
r
W
λε
≈
ˆ
radiation pattern -dir
z
ˆ
-field in -dir
x E
single
polarization
The fields are linearly polarized, and in the horiz ontal direction ( x)

5. 5
Microstrippatch antennas: radiation pattern
broadside
-field pattern
E
The normalized E-field pattern is:
x

6. 6
Microstrippatch antennas: resonant frequency
/ 2
e.g. A patch antenna (with dimensions 1.56 cm and 1.25 cm) is mounted on a subst
rate with
2.2 and 0.795 mm having critical frequency of 4.37 GHz.
r
L
L W
h
λ
ε
≈
= =
= =
適用
are the incremental length and width which account for
the fringing of field at the respective edges.

7. 7
Microstrippatch antennas: characteristic impedance and slot impedance

8. 8
Microstrippatch antennas: radiation resistance and impedance bandwidth
patch is moved closer to the ground plane ,
less energy is radiated and more energy is stored i n the patch capacitance and i
nductance,
the antenna quality factor a
impedance bandwidth .
nd
t
Q
↓
↑ ↓
https://www.lsr.com/white-papers/understanding-ante nna-design http://ieeexplore.ieee.org/document/1417209/

9. 9
Microstrippatch antennas: feed in 1Techniques for feeding/matching patches
•Directly feed
•Electromagnetically coupled
•Aperture coupled
0
4
r
λ
ε

10. 10
Microstrippatch antennas: feed in

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Booker’s relation

12. 12
Booker’s relation

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Ex:
( ) 91.3 0 ( ) 0.019
r
a Z j b BW
= + Ω
=

14. 14
0
0
0.49
( ) In the -plane, parallel to , the pattern approxi mates that of 2 equal in-phas
e point sources 0.325 .
2.27
use octave code to find HPBW 180 .
In the -plane, parallel to , the pattern app
c E Ld
H W
λ
λ
= =
=
1
roximates that of complementary full-wave dipole.
use octave code to find HPBW 47 .
40000
4.7 or 6.7 dBi.
180 47
D
=
= =
×
1
1 1
P.S.

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Ex:
0
0
( ) 365 0
( ) 0.01
0.49
( ) In the -plane, parallel to , the pattern approxi mates that of 2 equal in-phas
e point sources 0.325 .
2.27
use octave code to find HPBW 180 .
In the -plane, para
r
a Z j
b BW
c E Ld
H
λ
λ
= + Ω
=
= =
=
1
llel to , the pattern approximates that of compleme ntary / 2 dipole.
use octave code to find HPBW 78 .
40000
2.85 or 4.5 dBi.
180 78
( ) To match patch to a 50 microstrip requires a / 4 section
of i
W
D
d
λ
λ
=
= =
×
Ω
1
1 1
0
0
mpedance 50 365 135.1 that has a length of 0.166 .
4 2.27
λ
λ
× = Ω =
P.S.

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P.S. Thin linear antenna
[ ( / )]
0 0
[ ]
j t r c
I I e
ω
−
=
2The currents are in phase over each λ/2 section and
in opposite phase over the next.

17. 17
Basic thin linear antenna

18. 18
2
2
h
λ
∴ =
h
Directivity and radiation resistance of n λ/2 dipole using numerical calculation

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https://gist.github.com/oklachumi/046fea1ab10720e24 8808262d371f1db
Square patch field pattern using HPBW to calculate the approximate gain
0
0
In the , parallel to ,
0.49
2 equal in-phase point so
-plane(red field patt
urces 0.325 ,
2
e
.27
HPBW 1
n
8 .
r )
0
L
E
d
λ
λ
= =
=
1
In the , parallel to , full
-plane(blue field
-wave dipole
patte
, HPBW 47
rn)
.
W
d
H
λ
= =
1
40000
4.7 or 6.7 dBi.
180 47
D= =
×
1 1

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Why patch antenna usually use differential fed ? 1.用differential方式饋入有一部分也是因為系統端的需求.
2. Differential line 通常用來抑制common mode noise.
3.用differential方式饋入patch結構也更對稱, E-plane場型才對稱, 因為傳統饋入方式, E-plane 場型會受饋入結
構的影響而不太對稱, 嚴重時main beam會偏掉, HPBW偏掉<180, broadside gain下降.
4.而結構對稱時, 造成cross pol (y-dir)的電流分量也會比較對稱(應該叫反對稱), 所以互相抵銷狀況會更好.
5. Cross polarization (sometimes written X-pol, in a ntenna slang) is the polarization orthogonal to the polarization
being discussed.
•Because an antenna is never 100% polarized in a sin gle mode (linear, circular, etc).
•Two radiation patterns of an antenna are sometimes presented, the co-pol (or desired polarization
component) radiation pattern and the cross-polariza tion radiation pattern.
•Level in negative dB, indicating how many decibels below the desired polarization.
For red field pattern:
6. wide BW(impedance bandwidth).
7. stable and good radiation pattern.
Summery:
1. wide BW.
2. stable and good radiation pattern.
3. broadside gain higher.
4. X-polarization level lower.
5. Less susceptible to common mode noise.

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Polarization review…

22. 22
Back to QTM050 simulation configuration
9
0
assume center frequency: 28 GHz
0.49
2.84 mm
3.4 28 10
QTI didn't offer these important param
one patch dimensio
eters
n and should between 2.5 ~ 2.8 mm.
0.
BUT we can roughly calculate:
11 mm
100
c
L
L W
t
λ
⋅
= ≈
⋅ ×
∴
≈ =.

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QTM050 Antenna Array Configuration

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QTM050 simulation port assignment
1 2
ˆˆ
if sin( ) sin( )
xE t z yE t z
ω β ω β δ
= − + − +
E
H-pol
V-pol
then for Tx point of view,
we can write all the components that fro
m SDR051 MMIC feed-in.

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How the beamforming work ? (array parameters relate d to beam parameters)

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Further study: patch antenna design and HFSS simula tion by ourself
http://www.oldfriend.url.tw/HFSS/51_patch_antenna.h tm

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Thank you for yourattention