Power dividers/combiners perform the essential functions of splitting and combining signals in high-frequency systems such as receivers and transmitters.
Signals must often be divided or combined within a system, a task usually handled at RF and microwave frequencies by power dividers and combiners. An ideal power divider would also be an ideal power combiner, but this is not always the case. The components are not always designed for reciprocal operation. In addition, all power dividers and combiners suffer some insertion loss, which will inevitably limit their power-handling capabilities. But, in spite of their flaws, power dividers and combiners are among the most important of passive RF/microwave components for their key roles in higher-level systems. This short report will first review some of the key performance parameters to consider when selecting a power divider or combiner. It will then examine a few examples from leading suppliers.
Rather than detail the various different design approaches to implementing power dividers and combiners, perhaps the simplest way to choose one of these components is by considering the function required (signal division or combination), the bandwidth of operation, the expected power levels, and the number of ways that a signal must be divided or the number of signals to be combined. Binary power dividers, for example, provide two output signals at essentially the same amplitude from a single input signal. By cascading multiple twoway dividers, higher-order (four-way, eight-way, etc.) power dividers can be realized. Similarly, power dividers can be formed with an odd number of outputs by combining several three-way power dividers.
How well a particular power divider serves as a power combiner is usually a function of the design approach and the internal components, such as resistors. Meca Electronics (www.e-meca.com) offers a free application note (Application Note MAP-801) on their web-site, "Why Most Power Dividers Are Not Suitable Power Combiners," which explains what to look for when selecting a power divider that must also be used as a power combiner.
For educational purposes, Micro-lab/FXR also offers an excellent application note on power dividers and combiners which reviews the basic differences among such types of components as resistive, reactive, Wilkinson, quadrature, branch-line, junction, and magic-T type power dividers/combiners. The application note is available for free from the Microlab/FXR website at www.microlab.fxr.com. Microlab/FXR also demonstrates that all dividers are not created equal. The company's new DX-N series of unequal splitters is designed to provide power division ratios as wide as 30:1 or as close as 2:1. Well suited for in-building wireless communications applications from 800 to 2500 MHz, the unequal splitters can handle 300 W average power and 1 kW peak power.
In general, selecting a power divider or combiner is a matter of comparing the specifications for key performance parameters, including insertion loss, isolation between ports, how close in amplitude the split signals are (output amplitude unbalance), and how close the signal phase for the split signals are (output phase unbalance). In addition, the power rating is usually critical and is specified in terms of the maximum input power (assuming impedance-matched conditions) and the maximum internal load dissipation (the power rating of the internal terminations). An additional key parameter is return loss or VSWR, a measure of how well the component is impedance matched to the characteristic impedance of the intended application.
Power dividers can impose phase differences on their output signals. A 0-deg. power divider, for example, will split an input signal into two or more output signals with equal amplitude and equal phase. In a 90-deg. hybrid divider, the output signals are 90- deg. out of phase from each other. In a 180-deg. hybrid, an input signal can be split into two output signals with equal amplitude and phase when the input is applied to sum input port. But when the input signal is applied to the difference input port, the resulting output signals are equal in amplitude but 180 deg. out of phase.
For example, the surface-mount model SP-2C1+ two-way power divider/combiner from Mini-Circuits (www.mini-circuits.com) is a 0-deg. component housed in a package measuring only 0.106 0.087 0.035 in. (2.69 2.21 0.89 mm). The RoHS-compliant power divider/combiner is designed for use from 640 to 1100 MHz and exhibits typical insertion loss of 0.4 dB and port-to-port isolation of 20 dB across the full frequency range. Suitable for cellular and other wireless applications, the power divider/combiner handles 1.5 W maximum input power as a divider with maximum internal power dissipation of 0.75 W.
For wider-bandwidth applications, the company also offers the model ZB4PD-232-50W+ coaxial four-way power divider/combiner with SMA connectors for applications from 600 to 2300 MHz. The 0-deg. component handles power levels to 50 W at each of the four ports. It features typical insertion loss of 0.9 dB from 1800 to 2000 MHz and typical isolation of 28 dB across the same frequency range. Typical isolation is 19 dB. The four-way power combiner/divider controls amplitude unbalance to typically 0.05 dB from 600 to 2300 MHz and phase unbalance to typically 0.9 deg. across that same frequency range. VSWR is 1.20:1 or better at all ports.
Mini-Circuits also offers Designer's Kits that provide numerous examples of power splitters/combiners for different frequency ranges. The model K1-QCN Designer's Kit, for example, contains two each of 10 different models at frequencies from 220 to 4500 MHz with power-handling capabilities to 15 W when used as splitters. These QCN power splitters/combiners feature low insertion loss of typically 0.4 dB and high isolation of typically 32 dB. They are supplied in miniature ceramic cases measuring just 0.012 0.60 0.35 in.
In terms of sheer power, few companies can match the component offerings of Werlatone (www.werlatone.com). The firm's model D5738 two-way power divider/combiner, for example, is rated for 12,500 W CW power from 1.5 to 30.0 MHz. The fan-cooled component exhibits low 0.2-dB insertion loss with 20-dB minimum isolation between ports and 1.25:1 maximum VSWR. The amplitude unbalance is 0.2 dB maximum and the phase unbalance is 5 deg. maximum. For higher-frequency applications, the company offers the model 3897 two-way power divider/combiner rated for 1000 W CW power from 500 to 1000 MHz. With 18-dB minimum isolation of mere 0.2-dB insertion loss, the component is available with a variety of connectors, including Type N, SMA, and BNC types.
The model 6005265 from Krytar (www.krytar.com) is a wideband two-way power divider with a frequency range of 0.5 to 26.5 GHz and maximum insertion loss of 1.9 across that range. Isolation is 19 dB with fullband amplitude unbalance of 0.5 dB and phase unbalance of 10 deg. The two-way power divider/combiner employs a unique matched-line configuration to achieve high directivity. It is supplied with 3.5-mm coaxial connectors and is rated for input power levels to 10 W.
Aeroflex/Weinschel (www.aeroflexweinschel.com) offers resistive power dividers and combiners for bands from DC to 40 GHz. Model 1575, for example, is a resistive two-way power divider that operates with 6-dB nominal insertion loss from DC to 40 GHz. Equipped with 2.92-mm connectors, the wideband power divider features better than 0.2 dB amplitude unbalance and 2 deg. phase unbalance with a 1-W CW input power rating.
Renaissance Electronics Corp. (www.rec-usa.com) features a series of 400-MHz power dividers/combiners in two- through 16-way configurations. Designed for use from 400 to 500 MHz, the high-performance versions achieve insertion loss of 0.15 dB with 21 dB isolation and 1.20:1 VSWR. The input power rating is 200 W CW.
Anaren Microwave provides extensive lines of miniature power dividers with total frequency coverage of 400 MHz to 8 GHz. The tiny power dividers measure just 0.79 0.49 in. (2.00 1.25 mm). For example, model PD0922J5050D2 is a miniature surface-mount Wilkinson power divider that is ideal for cellular applications. It exhibits 0.7 dB typical insertion loss and 12 dB typical isolation from 950 to 2150 MHz. It handles power levels to 2 W CW. The RoHS-compliant power divider is fabricated from ceramic-filled PTFE composite material for good thermal stability.
The list of suppliers for surface-mount, coaxial, and waveguide power dividers/combiners is long, but can be found in the online version of the Microwaves & RF Product Data Directory at www.mwrf.com.