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Diplexers & Multiplexers

Diplexers & Multiplexers

Frequency Range: 10 MHz TO 26 GHz


KW Microwave has designed and manufactured a wide variety of multiplexers using lumped element, combline, interdigital, suspended substrate, stripline, and wavelength guide filters. Dimensions range from 0.3 X 0.6 X 1.0 inches for an L-band lumped element diplexer, to 2 X 3 X 8 inches for a high power coaxial diplexer in the same frequency band.

Designs are obtained using analytical techniques implemented by proprietary computer programs, and basically are guaranteed to work with little or no empirical adjustments, apart from the usual tuning arrangements.

Multiplexers provide a passive, low-loss, means of splitting or combing two or more signals of different frequencies at a common port while providing isolation between the signal ports.

In addition to the standard filter parameters, the following specs are required when defining multiplexer performance.


The absolute insertion loss at the point of equal loss between adjacent channels of the multiplexer.


Fc refers to the frequency at the point of the crossover. This parameter is important to the systems designer and provides an easily identified reference point in the measurement of multiplexer performance.


Narrowband multiplexers (channel bandwidths less than 20%) are formed by combining bandpass filters Contiguous and non-contiguous multiplexers are available and, depending on the characteristics required of each channel, may be fabricated using lumped element, combline, interdigital or suspended substrate designs. In each case, the overall performance is close to the performance achievable from discrete bandpass filters in the particular technology.

If appropriate, hybrid solutions can be provided.


Broadband diplexers operating from 20-2000 MHz are formed by combining a highpass filter with a lowpass filter and modifying critical element values to ensure a good input and output match and improved rejection in the stopbands. More complex multiplexers are achieved by cascading diplexers.


Suspended substrate readily lends itself to broadband configurations and is widely used in systems where small size, high performance and lightweight are essential features.

Using this technology, broadband diplexers covering DC to 26.5 GHz are formed by combining a highpass filter with a lowpass filter with modifications to critical values to ensure good input and output match and improved rejection in the stopband.

More complex multiplexers are designed by cascading diplexers can achieve <5 dB crossover insertion loss, 60dB or rejection within 10-15 % of crossover while exhibiting less than 1 dB insertion loss within the passband. The passbands are the bands outside the crossover regions, which are within +/ -5% of the crossover frequencies.

Skirt characteristics can be supplied at both extreme band edges where 60 dB attenuation is achieved.

Typical performance of suspended substrate multiplexersFrequency Rangedc – 26.5 GHzCrossover Frequency Range0.5 – 16 GHzPass band Insertion Loss4.5 – 5.0 dBSelectivity (typical)>60 dB within 10 -15% of crossoverTemperature Range-55 to +125 ° C.