AN548A Datasheet, PDF (1/8 Pages) Motorola, Inc – MICROSTRIP DESIGN TECHNIQUES FOR UHF AMPLIFIERS

MOTOROLA
SEMICONDUCTOR APPLICATION NOTE
Order this document
by AN548A/D
NOTE: The theory in this application note is still applicable,
but some of the products referenced may be discontinued.
Microstrip Design Techniques for
UHF Amplifiers
AN548A
Prepared by: Glenn Young
INTRODUCTION
This note uses a 25 watt UHF amplifier design as a vehicle
to discuss microstrip design techniques. The design
concentrates on impedance matching and microstrip
construction considerations. A basic knowledge of Smith
chart techniques is helpful in understanding this note.¹
The amplifier itself, as shown in Figure 1, provides 25
watts of output power in the 450 – 512 MHz UHF band. It
is designed for 12.5 volt operation which makes it useful for
mobile transmitting equipment. A variety of police, taxi,
trucking and utility maintenance communication systems
operate in this band.
A summary of the performance of the completed amplifier
operating with a 12.5 volt supply at 512 MHz indicates a
L7
power gain of 16 dB and a bandwidth (– 1 dB) of 8 MHz.
Overall efficiency is 48.5% and all harmonics are a minimum
of 20 dB below the fundamental output.
Sections on construction and device handling
considerations are also presented.
MICROSTRIP DESIGN CONSIDERATIONS
Microstrip design was used for this amplifier due to its
inherent superiority over other methods at this frequency.
These techniques not only offer good compatibility with the
Motorola “stripline” package but they also offer very good
reproducibility. Microstrip construction is more efficient than
lumped constant equivalents since microstrip lines are less
lossy than lumped constant components.
+ 12.5 Vdc
L8
50 Ω C10
C4
MICROSTRIP
LINE
L4
C11
C5
C1
C7
L1
C12
MICROSTRIP
LINE
2N5945
L5
C13
C2
C6
C8
L2
MICROSTRIP
C14
LINE
2N5946
L6
C15
C3
C9
L3 MICROSTRIP
LINE
C17 ^{50 Ω}
2N6136
C16
All Microstrip lines 5.72 mm wide 2.5 cm long
C1,2,3
470 pF feedthru
C4,5,6
1.0 µF Tantalum
C7,8,9
0.1 µF Ceramic
C10,11,13,15,16,17 1.5-20 pF Compression Trimmer ARCO 420
C12,14
10 pF Microwave capacitor ATC type
100-B-10-M-MS or equivalent
FERRITE BEADS
L1, L2, L3 – 5 turns #20 Closewound 3/16” I.D.
L4, L5, L6 – 0.15 µh molded choke
L7, L8 – Ferroxcube VK 200 20/4B or equivalent
Ferrite beads are Ferroxcube 56 590 65/3B
or equivalent
Figure 1. Schematic Diagram of 25 W UHF Amplifier
REV 0
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