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ini-Circuits’ ZACS242-100W+
is a coaxial high-power,
2-way 0° splitter/combiner capable of
handling up to 100W RF input power
as a splitter. Its power handling
capability makes this model a useful
building block for signal distribution
in high-power systems from 500 to
2400 MHz. However, at frequencies
above 2400 MHz, the component’s
insertion loss performance degrades,
hampering the splitter’s usability in
higher-frequency applications.
This article will present a design
modification of ZACS242-100W, which
achieves a 50% bandwidth increase
by reducing signal loss due to the
capacitance of the chip resistors in
the circuit. The modification will be
shown in a new model, ZACS362-
100W+ which exhibits comparable
power handling capability to that
of its predecessor, but with low
insertion loss up to 3600 MHz. The
same technique has been used to
expand the frequency range of other
high-power splitter models in Mini-
Circuits line to support high-power
applications at higher frequencies.
Bandwidth Constraint:
Power Handling vs.
Resistor Capacitance
The power handling capability
of a power splitter is essentially
determined by the power handling
of the internal resistors. The power
handling of a resistor is proportional
to its size; the higher the power, the
larger the resistor. Therefore, the
resistors used in a 100W splitter/
combiner will be relatively large. This
is important to consider in regard to
the effect of resistor capacitance on
insertion loss.
ZACS242-100W+ utilizes four 100W
chip resistors configured in as
shown in Figure 1. The conductive
metallization the bottom of each
resistor creates a capacitance to the
PCB which can be expressed by the
equation for the capacitance between
two parallel plates:
Where
= the permeability of the
material between the two plates
A= the overlapping surface area of
the plates, and
d= the distance between the plates
In other words, assuming constant
and constant d, the greater the
area of conductive material on the
bottom of the resistor overlapping
the PCB, the greater the capacitance
from the resistor. The capacitance of
the resistors shown in Figure 1 adds
to the overall insertion loss through
the circuit, especially at higher
frequencies, and this is primarily what
constrains the bandwidth in ZACS242-
M
Expanding Frequency Range in High-Power Splitter/
Combiners by Minimizing Resistor Capacitance
WeiPing Zheng and Brandon Kaplan, Mini-Circuits
30 l New-Tech Magazine Europe