Power dividers/combiners provide the essential functions of splitting or combining high-frequency signals with as little degradation as possible to those signals. Especially when the number of signal divisions is high, such as in 12-way or 16-way power dividers, it is critical to minimize insertion loss through the divider/combiner to ensure that usable output levels remain from such a high division ratio. And in military electronics applications, which often include multiple-channel receivers and transmitters, good amplitude and phase balance among the many output ports of a power divider can have a significant impact on final system performance.

Fortunately, some new power dividers/combiners from Synergy Microwave Corp. are designed and constructed for high-reliability applications in ground, airborne, and naval military systems. The first two models in the line cover frequencies from 50 to 300 MHz and 50 to 500 MHz, both with input power ratings of 50 W CW as power dividers. The 500-MHz unit is a 16-way divider/combiner, while the 300-MHz model is a 12-way divider/combiner.

As a quick refresher course in specifying RF/microwave power dividers and combiners, these passive components are usually categorized by the number of outputs for a divider, such as a four-way or eight-way divider, and the number of inputs for a combiner. Components designed to be a combination combiner/divider typically provide near-equivalent electrical performance in both directions.

Ideally, a power divider provides an equal-amplitude division of power at its output ports, within a relatively tight amplitude tolerance. An in-phase power divider should also provide outputs that are at the same relative phase, within a few degrees.

Power dividers and combiners are characterized by a number of parameters, including insertion loss, isolation between ports, amplitude unbalance, phase unbalance, power-handling capability, return loss, and package style. Insertion loss refers to the power dissipated through the divider or combiner above and beyond the normal coupling losses. For example, coupling loss for a two-way power divider is 3 dB, so that a 4-W signal applied at the input will result in a pair of 2-W output signals. For a four-way power divider, the coupling loss doubles to 6 dB, so that the same 4-W signal at the input port now produces for 1-W output signals. For an eight-way power divider, coupling losses double again, to 9 dB, and for a 12-way power divider, coupling losses are 12 dB.

Insertion losses are in addition to these coupling losses. Because the power levels of output signals will be so much less than the input signal due to coupling, the best power divider/combiner designs minimize insertion loss as much as possible.

Power dividers and combiners are typically designed to achieve high isolation between ports, so that a signal applied at one output port does not appear at the adjacent output port when all other ports are matched to the systems characteristic impedance (usually 50 Ω). Isolation of 15 dB or higher is considered very good performance, with final isolation usually dependent upon other performance parameters. For example, high isolation is harder to achieve as the bandwidth of a power divider or combiner increases. Amplitude balance or unbalance refers to the peak-to-peak difference in amplitude (in dB) between the output ports over a specified frequency range, while phase balance or unbalance is the peak-to-peak difference in phase (in deg.) between the output ports over a specified frequency range.

In terms of power-handling capability, power dividers and combiners are resistive or passive components that are limited by the power ratings of their internal resistances. When operating a unit as a power combiner at relatively high power levels, for example, all signal phase and impedance-mismatch conditions must be considered, as these can affect the amount of power seen by the combiner. One key to achieving good power-handling capability in a power divider/combiner is to eliminate thermal hotspotsareas where excess power dissipation can turn into circuit-damaging heatthroughout the component.

A power divider/combiners return loss is a measure of how well the components source and load impedances are matched to the characteristic impedance of the system. A good impedance match helps to minimize signal reflections and those unwanted variations in power level mentioned in the power-handling discussion. In most cases, it is difficult to achieve good insertion-loss performance in a power divider/combiner without also having good return-loss performance.

RF/microwave power dividers/combiners are available in a variety of different packages, including with coaxial connectors. Synergy, for example, offers rugged coaxial packages as well as smaller hermetic surface-mount packages with slightly lower power-handling capabilities.

Synergys model DPK50500S 16-way power divider/combiner (Fig. 1) can handle 50 W CW maximum input power as a power divider and 4.15 W maximum power per port as a power combiner. As a 16-way power divider, it exhibits the normal 12-dB coupling loss from input port to output ports. But it also succeeds in minimizing insertion loss to typically just 0.35 dB from 100 to 350 MHz and typically just 0.50 dB across the full operating frequency range of 50 to 500 MHz (Fig. 2). The low insertion loss limits the thermal hotspot in the ferrite core to less than 15C when in operation. As Fig. 2 shows, the power divider/combiner also delivers very tight amplitude balance among its signal paths. The typical amplitude unbalance is specified as typically 0.05 dB from 100 to 350 MHz (a maximum level of 0.2 dB) and 0.13 dB from 50 to 500 MHz (a maximum level of 0.3 dB).

The phase unbalance between signal paths is similarly well controlled (Fig. 3). The typical phase unbalance for the model DPK50500S 16-way power divider/combiner is 5.0 deg. from 100 to 350 MHz (a maximum of 8 deg. over that frequency range) and 6.5 deg. across the full operating frequency range from 50 to 500 MHz (a maximum of 10 deg. over that frequency range). Model DPK50500S achieves typical isolation between output ports (Fig. 4) of 22 dB from 100 to 350 MHz (with a minimum of 18 dB isolation over that frequency range). It provides typical isolation of 18 dB across the full operating frequency range of 50 to 500 MHz (with a minimum of 15 dB isolation across the full frequency range).

Model DPK50500S exhibits maximum VSWR at its input port (port J1) of 1.35:1 from 100 to 350 MHz and 1.55:1 from 50 to 500 MHz. The maximum VSWR at the output ports (J2 J17, when used as a divider) is 1.55:1 from 100 to 350 MHz and 1.80:1 from 50 to 500 MHz. This performance is also reflected in the components well-behaved return loss (Fig. 5), which is typically better than 15 dB though 500 MHz.

With regard to the lower-frequency model DLK50300S 12-way power divider/combiner: It covers a frequency range from 50 to 300 MHz with a maximum input power rating of 50 W as a power divider and 4.15 W maximum at each port as a combiner. It has typical insertion loss of 0.5 dB from 50 to 100 MHz (maximum of 0.9 dB through 100 MHz) and typical loss of 1.6 dB from 100 to 300 MHz (with maximum loss of 1.8 dB through 300 MHz).

Isolation is at least 15 dB from 50 to 100 MHz (and typically 20 dB through 100 MHz) and at least 20 dB from 100 to 300 MHz (and typically 28 dB through 300 MHz). The amplitude unbalance is typically 0.18 dB from 50 to 100 MHz (and no worse than 0.3 dB across that frequency range) and typically 0.80 dB from 100 to 300 MHz (and no worse than 1.1 dB through 300 MHz). The phase unbalance is typically 1.5 deg. to 100 MHz (and no worse than 4 deg. from 100 to 300 MHz) and typically 4 deg. from 100 to 300 MHz (and no worse than 6 deg. through 300 MHz).

Model DLK50300S exhibits maximum VSWR at its common (input) port (J1, when used as a divider) of 1.50:1 from 50 to 100 MHz and 1.35:1 from 100 to 300 MHz. The maximum VSWR at the output ports (J2 through J13, when used as a divider) is 1.80:1 from 50 to 100 MHz and 1.35:1 from 100 to 300 MHz.

Both power dividers/combiners are crafted from materials and with practices specified by pertinent military standards, including MIL-STD-1639A, MIL-P-23971, MIL-E-5400, MIL-STD-883, and even MIL-DTL-23971 from the Defense Logistics Agency (DLA) for maritime use of power dividers/combiners. The 50-Ω power dividers/combiners are designed for operating temperatures from −55 to +85C.

Synergy Microwave Corp.
201 McLean Blvd.
Paterson, NJ 07504
(973) 881-8800
FAX: (973) 881-8361
e-mail: sales@synergymwave.com