This document discusses patch antennas. It describes the basic structure of a patch antenna, which consists of a radiating metallic patch on a dielectric substrate with a ground plane on the other side. Patch antennas radiate a linearly polarized wave and have a very low profile. Their primary limitation is narrow bandwidth, which is typically less than 5% for single-substrate designs. Common patch antenna geometries include rectangular and circular shapes to generate different beam patterns.

1. Patch antenna
Jay Chang
1

2. 2
Patch Antennas

3. 3
1. A patch antenna basically is a metal patch suspended over a ground plane. Simple to fabricate, easy to modify
and customize and closely related to microstrip antennas. These are constructed on a dielectric substrate,
usually employing the same sort of lithographic patterning as used to fabricate PCBs.
2. A microstrip patch antenna consists of a radiating patch, a dielectric substrate which has a ground plane 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 current flow is along the direction of the feed wire, so the vector
potential and the electric field follows the current. Such a simple patch antenna radiates a linearly polarized
wave. The radiation can be regarded as being produced by the “radiating slots” at top and bottom (H-plane), 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 antenna fabricated by etching the antenna element pattern in
metal trace bonded to an insulating dielectric substrate. Continuous metal layer which forms a ground plane.
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 bound surface-wave modes which
represent a loss mechanism in the antenna. The loss due to surface wave modes increases with the substrate
thickness (Also the question to QTI).
• Develop conformal microstrip antennas which enjoy wide bandwidth, yet do not suffer from the loss of attractive
features of the conventional microstrip patch antenna.
• Some patch antennas eschew a dielectric substrate and suspend a metal patch in air above a ground plane 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 incorporated 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 to create a dual band design or a broadband design with a
bandwidth of up to 35%.
6. The two most common geometries, rectangular and circular, 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
Microstrip patch antennas: structure
0
100
t
λ
≈
0
2 r
L
λ
ε
≈
0
r
W
λ
ε
≈
ˆradiation pattern -dirz
ˆ-field in -dirxE
single
polarization
The fields are linearly polarized, and in the horizontal direction (x)

5. 5
Microstrip patch antennas: radiation pattern
broadside
-field patternE
The normalized E-field pattern is:
x

6. 6
Microstrip patch antennas: resonant frequency
/ 2
e.g. A patch antenna (with dimensions 1.56 cm and 1.25 cm) is mounted on a substrate 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.

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Microstrip patch antennas: characteristic impedance and slot impedance

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

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Microstrip patch antennas: feed in
Techniques for feeding/matching patches
• Directly feed
• Electromagnetically coupled
• Aperture coupled
0
4 r
λ
ε

10. 10
Microstrip patch antennas: feed in

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Booker’s relation

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Booker’s relation

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

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

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Ex:
0
0
( ) 365 0
( ) 0.01
0.49
( ) In the -plane, parallel to , the pattern approximates that of 2 equal in-phase point sources 0.325 .
2.27
use octave code to find HPBW 180 .
In the -plane, para
ra Z j
b BW
c E L d
H
λ
λ
= + Ω
=
= =
=
llel to , the pattern approximates that of complementary / 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
0
0mpedance 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 −
=
The currents are in phase over each λ/2 section and
in opposite phase over the next.

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Basic thin linear antenna

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2
2
h
λ
∴ =
h
Directivity and radiation resistance of nλ/2 dipole using numerical calculation

19. 19https://gist.github.com/oklachumi/046fea1ab10720e248808262d371f1db
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
LE
d
λ
λ= =
=
In the , parallel to ,
full
-plane(blue field
-wave dipole
patte
, HPBW 47
rn)
.
W
d
H
λ= =
40000
4.7 or 6.7 dBi.
180 47
D = =
×

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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 antenna slang) is the polarization orthogonal to the polarization
being discussed.
• Because an antenna is never 100% polarized in a single 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-polarization 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
ˆ ˆif sin( ) sin( )xE t z yE t zω β ω β δ= − + − +E
H-pol V-pol
then for Tx point of view,
we can write all the components that from SDR051 MMIC feed-in.

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How the beamforming work ? (array parameters related to beam parameters)

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Further study: patch antenna design and HFSS simulation by ourself
http://www.oldfriend.url.tw/HFSS/51_patch_antenna.htm

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Thank you for your attention