Broadband Reconfigurable Matching Network of

Broadband Reconfigurable
Matching Network of Reduced
Dimensions for the UHF Military
Satellite Communication Band
Marc J. Franco, David Dening
Outline
• Motivation
• Network topology
• Implementation
• Experimental results
• Conclusion
Motivation
• Good impedance match between transmitter and antenna is needed
to maximize radiated power
• Antenna impedance varies significantly in portable equipment
• A reconfigurable matching network between the transmitter and the
antenna can overcome this problem
Design goals
• Convert 10:1 VSWR into 2:1 or better
• 220 to 450 MHz operating frequency range (~ 1 octave)
• Input power up to 35 dBm
• Harmonics below -60 dBm
• Very low insertion loss
• Small size and low power consumption
Network topology
TX LINE
TX LINE
INPUT
OUTPUT
TX LINE
TX LINE
• Network can be configured as PI, T or L, offering great flexibility and
bandwidth
• Transmission lines are paralleled to decrease their characteristic
impedance
• Insertion loss is minimized by avoiding series switches at low
impedance points
Alternative network
INPUT
OUTPUT
• For low frequency applications and size reduction, the transmission
lines can be replaced by inductors
• This is the approach followed in this design
Switching element
• 6 x 4 mm depletion mode RFMD GaAs pHEMTs stacked up to
withstand the off-state voltage swing
• Each branch was laid out as two triple gate transistors in series to
reduce size
• On-state resistance 0.8 ohms
• Off-state capacitance 0.3 pF
• GaAs switch can be replaced by SOI or RF MEMS
Implementation
• Size 1” x 1”, but easily reduced
• Passive elements: size 0603 capacitors (6 and 12 pF on each branch)
and 22 nH size 0908 inductors
Measurement setup
HARMONICS
IMPEDANCE MATCHING
MATLAB
(PC)
MATCHING
NETWORK
NETWORK
ANALYZER
SIGNAL
GENERATOR
POWER
AMP.
LOW
PASS
FILTER
MATCHING
NETWORK
SPECTRUM
ANALYZER
NOTCH
FILTER
TUNER/LOAD
HIGH
DIRECTIVITY
DIR. COUPLER
COUPLED
• S- parameters measured with a 2-port vector network analyzer for each
one of the 512 possible tuning patterns at different frequencies
• Matlab code used to control tuning and to record the data
• Harmonics measured by attenuating the fundamental frequency with a
notch filter
Evaluation setup
VSWR < 2:1
Insertion loss < 3 dB
Tuner S-parameters
Term
Term1
Num=1
Z=50 Ohm
Variable load
impedance
(optimized value)
S2P_Eqn
S2P1
Term
Term2
Num=2
Z=R+j*X
• The measured S-parameters were included in an Agilent ADS
simulation
• The load impedance was optimized for each tuning pattern to obtain a
VSWR of 2:1 or better at various frequencies
• All tuning patterns that did not provide an input VSWR better than 2:1
or an insertion loss of less than 3 dB were discarded
• A few tuning patterns were verified experimentally to confirm the
accuracy of the simulation
Impedance match capability
220 MHz
335 MHz
450 MHz
• Insertion loss
•
Green: < 0.5 dB Blue: 0.5 dB to 2 dB
Red: 2 dB to 3 dB
• Plots show single points that map into a 2:1 VSWR region
surrounding the 50 ohm system impedance
•
There is an area around each point which also maps into the desired
2:1 VSWR region, expanding the coverage of the matching network
• In regions where the density of tuning states is high the lowest
loss state should be chosen
System gain
220 MHz
335 MHz
450 MHz
• System gain is calculated by comparing the powered delivered to
the load before and after the insertion of the matching network
• Green: 1 dB to 2 dB
Blue: 0 dB to 1 dB
Red: loss up to 0.5
dB
• Small loss is expected when the load is perfectly matched
• Gain is obtained for mismatched loads
• The antenna impedance in portable equipment is usually
mismatched
Tuning methods
POWER
AMP.
RECONFIG.
MATCHING
NETWORK
3D LOOK UP
TABLE
(Z mag &
phase, freq)
IMPEDANCE
DETECTOR
IMPEDANCE &
FREQUENCY DATA
• The tuning algorithm for this reconfigurable matching network
depends on the particular requirements of the system where it
will be installed
• Several known methods could be employed, including look-uptable based solutions with appropriate search algorithms or load
impedance measurements
Summary
• Reconfigurable matching network can match up to 10:1 VSWR to
2:1 from 220 to 450 MHz
• Easily scalable to other frequencies using inductors or transmission lines
• Maximum input power of 35 dBm
• Can be increased by stacking up more transistors or using a different type of RF
switch
• Low insertion loss
• Typical 0.25 dB into a 50 ohm load
• Harmonics below -66 dBm
• Size 1” x 1”, easily reduced
• Based on GaAs FET switch technology
• Can be redesigned for SOI or MEMS
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