Radar performance starts with the power amplifier. Learn how PA design supports signal transmission, system range and reliable detection in demanding environments. White Paper Amplifiers DigiKey-Knowles, capacitors, radar, RF, amplification, power, coupling, bypassing, tuning, impedance, ceramic, microwave, reliability, high-frequency, semiconductors, defense
While many amplifier monolithic microwave integrated circuits (MMICs) come equipped with
matching capabilities, these networks of discrete and distributed elements support finer
performance optimizations.
Coupling
Coupling describes the linking between different stages of a circuit to ensure effective signal
transfer and strong system performance. In radar systems, the way components are coupled can
significantly impact signal integrity and power efficiency. With capacitors in series, AC coupling
(i.e., DC blocking) connects circuit stages such that only AC signals, like RF or microwave
signals, pass from one stage to the next. By extension, this removes any DC offset and protects
components by allowing chips with different common mode voltages to interface with each
other. Amplifier MMICs can also come with their own coupling, but circuit designers are largely
responsible for coupling in high-performance systems.
Bias Networks
Biasing ensures that the right amount of DC voltage and current goes to an active device (e.g.,
field-effect transistor (FET)) to keep it operating in an optimal region.
An active device can also connect to a gate, drain, or source bias network. Gate bias networks
control voltage at the gate terminal of an FET, relative to its source, to act as a switch in digital
applications or a set point for analog applications. Drain bias networks set and control voltage
at the drain terminal of an FET, which influences the output characteristics. Source bias networks
adjust voltage and current at the source terminal for added stability. Bias networks are critical
for setting the quiescent current to optimize amplifier performance metrics like linearity and
efficiency.
Bypass capacitors and storage capacitors connect to bias networks and contribute to the stability
and efficiency of the amplifier circuit. Bypass capacitors act as lowpass filters, allowing DC signal
through while removing low- and high-frequency RF noise and interference that could negatively
impact the amplifier. Larger capacitance is helpful for low-frequency filtering and smaller
capacitance is best suited for higher-frequency RF signals.
Figure 3. Example of a bypass capacitor that provides an efficient
path to ground for RF energy
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Large charge storage capacitors can maintain power levels during pulsed operation. Aluminum
electrolytic capacitors, for example, make great storage capacitors because of their high
capacitance density. They’re often found in or near the T/R module and the pulse driver circuitry
in a radar system.
From signal conditioning to stability and noise reduction, capacitors support a variety of critical
functions in power amplification within radar systems. As these systems grow more and more
complex, component-level decisions have a more significant impact on performance. For more
information on our offerings and full specs, see our Mil / Aero industry page.
Input/Output Matching and Coupling
Matching ensures that the input and output impedance of an amplifier aligns with the rest of the
circuit. In LC matching, inductors (L) and capacitors (C) form networks that facilitate impedance
matching between different parts of a circuit to maximize power transfer and minimize echoes in
radio frequency (RF) applications.
Depending on your application requirements, LC matching networks can be configured a few
different ways (Figure 2) to accommodate various operating frequencies and impedance levels:
• L-Network: Includes an inductor and a capacitor in series or in parallel, depending on
whether the impedance needs to be stepped up or down. L-networks are most effective in
narrow frequency bands as they don’t allow for much adjustment.
• Pi-Networks: Form the Greek letter “Pi” with two capacitors and one inductor. They’re
designed to transform a low source impedance to a high load impedance or vice versa, so
they’re particularly useful in power amplifiers and RF amplifiers.
• T-Network: Includes two inductors and one capacitor (or two capacitors and one inductor)
to form a T-shaped configuration. With greater versatility, T-networks can manage a wider