Transcript Miniature Antenna - A. James Clark School of Engineering

Miniature Antenna:
Results and Proposed Work
March 2008
Outline
• 916 MHz antenna prototypes and results
• 2.2 GHz, 2.4 GHz antenna prototypes and
results
• 433 MHz antenna prototypes and results
• Proposed New Research
916 MHz antenna,
prototype and test results
Simulation and
Measurement of S11
The volume of the antenna with its ground
plane is 0.024 λ  0.06 λ  0.076 λ,
where λ = 372.5 mm for 916 MHz antennas.
916 MHz antenna,
Gain measurements
Half wave dipoles
916 MHz FICA
Half wave dipoles
916 MHz FICA
S11 of 2.2 GHz & 2.45 GHz FICA
Total volume including ground plane:
0.09 λ x 0.09 λ x 0.025 λ
λ = 136.36 [email protected] GHz
λ = 122.44 [email protected] GHz
2.2 GHz FICA
Bandwidth = 14 MHz
2.2GHz FICA: 98% available
power transmitted
2.45 GHz FICA
Bandwidth = 3 MHz
2.45GHz FICA: 92%
available power transmitted
2.2 GHz FICA Gain Test (II)
0
68 mm
-5
Normalized Gain (dB), Theta = 90 degree
Calibrate using ½ wave dipole
Difference between FICA and ½
dipole is -7dB; Polarization
demonstrates functionality
Half wave dipole
-10
-15
-20
-25
-30
-50
0
50
100
150
200
Phi
0.09 λ x 0.09 λ x 0.025 λ
12 mm x 12 mm x 3.5 mm
250
300
350
400
433 MHz Dielectric Loaded
Miniature Antenna Results
BW=8MHz
At 433 MHz,
λ=693mm.
This antenna
can work with
a PCB board of
0.11λ x 0.037λ
77.2mm
Initial test:
-5dB
Bandwidth
is 8 MHz
Further design
needed for
10MHz
bandwidth
25.4mm
Commercial Chip Antennas (Antenna Factors, Co.)
need a ground plane to function properly
1
λ/8.84
2
λ/8.84
3
λ/8.84
4
λ/2.98
λ/3.64
λ/4.68
5
λ/9
λ/8
λ/9
λ= 32.75 cm ( 916 MHz )
Antenna 1~4, commercial chip antenna.
Antenna 5: Our FICA antenna
λ/8
SMA fed through a hole
FICA Outperforms Commercial
Resonance
frequency
-10dB bandwidth Received Power
Antenna 1
916 MHz
25 MHz
-42 dBm
Antenna 2
911 MHz
14 MHz
-39 dBm
Antenna 3
893 MHz
NA
-39 dBm (not sure)
Antenna 4
831 MHz
9 MHz
-55 dBm
Antenna 5
952 MHz
11 MHz
-32 dBm
1. Antenna 1-4 are commercial antennas. Antenna 5 is our FICA.
2. Antenna 1 is the exact design given by spec sheet,
3. Antennas 1-3: The feeding cable is along the same direction as the feeding
line, which helps antenna radiation, effectively increasing antenna size.
4. To eliminate this effect, feeding line is perpendicular to the ground plane.
This was done for Antenna 4, notice enormous performance drop.
5. Our FICA (Antenna 5) has substantially better performance than commercial
antennas, especially with when feed is not part of the system (4) where the
improvement is by more than 23dB (200 times).
Proposed Research for Ultra-Small Antennas
Task I: Design of Helical (FICA) Style Ultra-Small Antenna for
Requested Specifications (400MHz resonance, 10MHz BW)
• Ultimate optimization goal:
– Maximum achievable bandwidth (10 MHz or more Bandwidth
at 400 MHz with10 dB return loss )
– minimum antenna volume (2 parts)
• Part1: the component which we called “antenna”,
• Part2: the “virtual or image antenna”-----ground plane
(ground plane will be smaller than the current prototype
at 400 MHz)
– highest gain (-1 to -2 dBi)
– highest achievable efficiency (40%<efficiency<60%)
Proposed Research for Ultra-Small Antennas:
Realize Design Goals
•We will optimize the following parameters for FICA:
•Determine helix shapes for wire antenna families (i.e. FICA): pitch,
leaning angle, cross-section area of coils, helix length, tapping point.
•Determine geometry of ground plane: ground plane size, feeding
positions and FICA position on the ground plane.
•Optimize dielectric block: Use dielectric to increase capacitance to
ground, not the intercoil capacitance of FICA to minimize the coil length
These design goals will be realized with a synergistic approach using experiment
and theory:
•We will fabricate and test designs
•We will use finite element (HFSS) simulation to help guide experimental
program.
Proposed Research for Ultra-Small Antennas
We also propose to develop circuit models of FICA for antenna-RF circuit codesign, which will maximize performance on system level.
For example, for a FICA at 916 MHz (Fig a), we developed an equivaleng
circuit to represent the antenna’s impedance matching, radiation resistance,
and resonance. The circuit may look like the one in Fig. b. With the help of
circuit b, we could optimize system gain, and sensitivity for transceivers.
a
b
Proposed Research for Ultra-Small Antennas
•
Testing plan:
– Will have access to a world
class anechoic camber at
the FDA White Oaks Facility
– Antenna measurements at
the FDA will be very
accurate and help evaluate
with precision the gain
performance of the various
designs.
– We will regularly compare
our antenna prototypes with
commercially available
antennas.
– Comparisons will require
building test platforms for
commercial antennas, as
well as our own.
Anechoic Chamber
Half wave dipole
On fixed pole
FICA antenna
On rotating table
Receiver
Transmitter