Slot Array Base Station Antenna with
Electrical Control of Down-Tilt Beam
Presenter: George J. Chen
Author: Ming Hui Chen
Victory Microwave Corporation
Xizhi, Taiwan
Contents
§  Motivation for Beam Tilting
§  Theory
§  Propagation in Slab Loaded Waveguide
§  Downtilt
§  Measured Results
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Coverage Variation by Beam Tilting
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Beam A
Beam B
Beam C
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
Beam down tilt changes the coverage area
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Beam Tilting Options
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
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Expensive mechanical design
Electrical tilting using phase shifter


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Mechanical tilting


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Expensive electronic design (phase shifters) shifters
Electrical tilting using dielectric slab

Low cost motor attached to dielectric slab in waveguide
Propagation in Slab-Loaded Waveguide
b
Ey
equivalent to
b
Ey
a'
a
dielectric vertical
b
Ey
a
dielectric horizontal

Kx decreases => β larger"
equivalent to
b''
Ey
a
Kx same => β smaller"
Propagation constant β can be controlled through the
orientation of the dielectric.
Example Circular Polarizer
Ey ¡í
Ex ¡í+90¢X
Ey 0
Ex 0
Y
X
Application: Down Tilt

Slot array antenna has
alternating slanted
slots cut at intervals
of d = π/βH


Slot Array Antenna
Antenna
without down tilt
with down tilt
wavefront
wavefront
kd sinθ
Results in wavefront
without downtilt
d
When slot array
propagation is
lowered, wavefront is
downtilted at an angle
θ
βH
!Hd = !
d θ
βL
" Ld=!-kd sinθ
θ= down tilt angle
!H =
propagation constant for waveguide withα=90°
!L =
propagation constant for waveguide withα=0°
θ
Testing Setup
Electronic down tilt
Manual down tilt

Transmit + receive antennas, attached together to a
single structure.
Testing Setup
Offset 5°

In order to measure the downtilt, we raised the
antenna.
Testing Setup
TX
θ
TX

Radiation pattern measurement with downtilt angle
Results (1.95GHz, 0° DownTilt)

Elevation of peak a
function of slab
orientation


90° slab orientation
corresponds to a 10°
downtilt
Azimuth pattern at
0° for different
downtilts (slab
orientation) retains
relatively same
shape
slab rotation
Results (1.95GHz, 5° DownTilt)

Elevation of peak a
function of slab
orientation


90° slab orientation
corresponds to a 10°
downtilt
Azimuth pattern at
5° offset remains
relatively the same
across different
offsets.
slab rotation
Results (2.14GHz, 0° DownTilt)

Elevation of peak a
function of slab
orientation


90° slab orientation
corresponds to a 10°
downtilt
Azimuth pattern at
0° for different
downtilts (slab
orientation) retains
relatively same
shape
slab rotation
Results (2.14GHz, 5° DownTilt)

Elevation of peak a
function of slab
orientation


90° slab orientation
corresponds to a 10°
downtilt
Azimuth pattern at
5° offset relatively
constant for a given
slab orientation
slab rotation
Return Loss


Return loss varied
with the slab
orientation
Over all conditions,
the return loss was
under 10 db which is
acceptable for
antenna designs.
Isolation


Isolation is better than -25dB, indicating little
interference between the two antennas
If additional isolation is needed between Tx and Rx
bands, a band-pass filter can be used
Summary



Downtilt capability of antenna structures traditionally
relies on expensive mechanical design or expensive
phase shifters.
We noted dielectric slabs in waveguides change
propagation constant.
We’ve demonstrated a method to use this property to
design an electronically controlled downshift on a slot
array antenna.
Contact Information
Ming Hui Chen
Victory Microwave Corporation
396 Fude 1st Rd.
Xizhi City, Taipei County 22150
Taiwan (R.O.C.)
Tel. 886-2-8693-3799
Fax 886-2-8693-3798
Email: mchen@vicmic.com.tw
Web site: www.vicmic.com.tw