Dividers/Combiners Channel Power

Sept. 21, 2010
The industry offers a wide assortment of power dividers and combiners port configurations and package styles.

Power dividers/combiners are simple but essential components. Depending upon the design and the direction in which they are connected, they either combine two or more channels of signal power into one, or divide one channel into a pair of outputs or a number of outputs in multiples of two. Applications in which signals are split, such as for antenna arrays, or combined, such as in multiple-device power amplifiers, can often require as many as 16 or more divisions or combinations. As with many RF/microwave components, selecting the best power divider/combiner for the job comes down to tradeoffs, and deciding how much performance is needed for the price.

A basic two-way power divider splits a single input signal into two output signals. Depending upon the design, the phase relationship of the split signals may remain the same ( 0 deg.) or have some offset, such as 90 or 180 deg. Since the power level drops by at least one-half (3 dB) with every division, and often more because of circuit losses, practical dividers usually stop at about 32 splits of an input signal. Power dividers can also have an odd number of output ports, such as a three-way divider. These are called N-way power dividers, with N being an odd number.

In an ideal in-phase, two-way power divider, a 10-W input signal would yield a pair of 5-W output signals, with the same phase and amplitude characteristics versus frequency as the input signal. But insertion loss will occur through the most carefully designed power divider. Higher insertion loss at high input-power levels results in lost signal power, and also results in generation of heat due to the losses. Insertion loss is one of the key operating parameters for a power divider/ combiner, since the goal in any such component is to conserve as much of the available power as possible. Assuming that the component's bandwidth is sufficient to handle all the signals in an application of interest, additional specifications to compare among power dividers and combiners include isolation between ports, the voltage standing wave ratio (VSWR) at different ports, and the amplitude and phase balance between channels.

High isolation, such as 20 dB or more, can be achieved in practical designs. As with insertion loss, isolation is dependent upon frequency, decreasing as frequency increases.

Two more specifications that are important to power divider/combiner specifiers are amplitude balance and phase balance. Good amplitude balance is simpler to achieve in a two-way divider where there are only two output signal paths, with values of 0.2 or 0.3 dB, not unusual for well-made components. As the number of ports increases, the value of the amplitude balance tends to rise. It is not unusual for an eight-way power divider to exhibit amplitude balance of 10 dB.

Similarly, phase balance can be maintained within tightly controlled limits for simple two-way power dividers, but that control becomes more difficult to maintain for higher numbers of ports. The bandwidth of the power divider/ combiner will also have an impact on the achievable phase balance. For example, model D-0418-2 from ET Industries is a two-way power divider with total frequency range of 0.4 to 18.0 GHz. From 0.4 to 2.0 GHz, the maximum phase balance is 1 deg. Over the remainder of the frequency range, the phase balance is 3 deg.

For recent coaxial power divider/ combiner introductions, Marki Microwave unveiled a pair of Wilkinson two-way in-phase power dividers (with 0-deg. nominal phase shift). Model PD-0109 operates from 1 to 9 GHz while model PD-0R510 works from 0.5 to 10.0 GHz. Both exhibit insertion loss of 1.2 dB to 9 GHz with typical isolation of 22 dB and VSWR of 1.20:1. The typical amplitude balance is an impressive 0.1 dB while the phase balance is 1 deg. for both models. Each measures 1.8 x 0.8 x 0.410 in. not including SMA female connectors.

Response Microwave announced a family of compact coaxial power dividers/combiners for signal routing in 3GPP Long Term Evolution (LTE) fourth-generation (4G) wireless systems (Fig. 1). Based on classical Wilkinson designs, the family includes 2-, 4-, 6-, 8-, 16-, and 32-way components with frequency range of 700 to 3000 MHz and typical insertion loss of 0.45 dB. The isolation is at least 22 dB while the typical VSWR is 1.25:1. Rated for CW power level to 50 W per unit, the maximum amplitude balance is within 0.5 dB and the maximum phase balance is within 5 deg. The RoHS-compliant components are available with SMA or Type N female connectors.

As might be apparent from these specifications, manufacturers often present both amplitude unbalance and phase unbalance in several formats, including as a simple value representing a range, such as 0.5 dB or 6 deg., or as a deviation, such as 0.4 dB or 5 deg. It is important to recognize the format used by a given manufacturer and to "normalize" the specifications when performing a side-by-side comparison.

The model 4326B-4 from Narda Microwave is a four-way power divider for use from 5 to 18 GHz (Fig. 2). It has 0.5 dB maximum insertion loss over the full frequency range, with 18 dB minimum isolation between ports. It maintains amplitude balance within 0.3 dB to 18 GHz and phase balance within 6 deg. from 5 to 18 GHz.

As an example of a considerably more narrowband four-way power divider, model AM5400PD851 from Anatech Electronics, operates from 4.9 to 5.9 GHz with power-handling capability of 10 W and insertion loss of 2.4 dB.

Krytar's model 8010180 eight-way power divider is based on the firm's matched-line-directional- divider (MLDD) technology. It covers 1 to 18 GHz with 5.5-dB loss and 17-dB isolation, 1 dB amplitude balance and 1 deg. phase balance.

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ARRA offers broad lines of power dividers/combiners, including four-way units with SMA connectors in frequency bands from 0.005 to 18.0 GHz. One of the company's broadest-frequency components covers 8 to 18 GHz with insertion loss of 1 dB and minimum isolation of 17 dB.

Smaller power dividers/combiner for surface-mount applications are available from a number of manufacturers, including Merrimac Industries, Mini-Circuits, and Synergy Microwave. Synergy's model SPD-5-1000 is a fourway unit measuring just 0.8 x 0.3 x 0.2 in. and with a power rating of 1 W. It features an operating-frequency range of 5 to 1000 MHz with typical insertion loss of 0.7 dB from 5 to 50 MHz, 0.65 dB from 50 to 500 MHz, and 0.7 dB from 500 to 1000 MHz. Mini-Circuit's model SBB-2-23 is a two-way surface-mount power divider/combiner that covers 2000 to 2300 MHz and measures just 0.2 x 0.275 x 0.070 in. but can handle 10 W. It offers better than 20 dB isolation across its operating range with phase unbalance of better than 1 deg.

A recent addition to the ranks of miniature surface-mount power dividers comes from International Manufacturing Services, with its IPS series of resistive splitters for applications as wide as DC to 20 GHz for two-way models (Fig. 3). They are also available in three-way and four-way models from DC to 7 GHz. They are rated for power levels to 3 W. Additional suppliers of power dividers/ combiners can be found in the Microwaves & RF Product Data Directory.