New-Tech Europe Magazine | May 2016

Expanding Frequency Range in High-Power Splitter/ Combiners by Minimizing Resistor Capacitance

WeiPing Zheng and Brandon Kaplan, Mini-Circuits

M

resistor creates a capacitance to the PCB which can be expressed by the equation for the capacitance between two parallel plates:

ini-Circuits’ ZACS242-100W+ is a coaxial high-power,

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

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

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-

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