Get tight specs at lower cost
Generally, engineering designs exist in a world of tradeoffs. Mixers, for example, can be
designed so that isolation can be improved at the expense of conversion loss; similarly, an
amplifier's noise figure can be improved if a reduction in dynamic range can be accepted in
exchange.
Not so, fortunately with power splitters. The key parameters are influenced
in the same direction
during the design stage. A well-designed power splitter/combiner will offer high isolation, low
insertion loss and good VSWR. You just don't encounter a power splitter/combiner with high
isolation and poor VSWR, nor high isolation with a poor insertion loss spec. Why? Because
poor insertion loss specs generally result from an improper matching transformer (winding not
exactly symmetrical) or slight variations in stray capacitances at each end of the transformer;
these effects, however, adversely affect insertion loss as well as isolation.
This raises a significant point. There is no need to specify a number
of tight spec parameters
when you need a power splitter/combiner for a particularly stringent requirement. Simply specify
a tight improved spec on the key parameter most critical to the task and you'll find the remaining
specs will also be upgraded. If you insist on writing tight specs on a number of parameters, you
may be paying extra money for a device you would have received anyway. Of course, you can
specify
one tight parameter, as suggested, and request support data on the other parameters to
monitor their characteristics.
In some applications, it is possible for several parameters to be important. In other applications,
only one parameter may be considerably significant while others are not. For example, in a
power combiner used to add
the outputs of two amplifiers, insertion loss is a critical factor while
isolation may not be deemed essential. On the other hand, consider a test setup for two-tone,
third-order IM measurement. Here it is common to operate two RF generators that are close to
each other in frequency, resulting in one generator "talking to the other" or "pulling".
To avoid
this measurement pitfall, a power combiner is placed between both RF generators; here the
isolation spec is very significant while other parameters, such as phase or amplitude unbalance,
have no importance at all.
You can lower your demands, and your cost, by analyzing what
parameters must be met while understanding others that can be ignored.
AN-10-006 Rev.: A M150261 (04/14/15) File:
AN10006.doc
This document and its contents are the property of Mini-Circuits.
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AN-10-006 Rev.: A M150261 (04/14/15) File:
AN10006.doc
This document and its contents are the property of Mini-Circuits.
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