In wide-band microwave systems there is a tendency for the gain to roll-off at higher frequencies, reducing the overall gain-flatness of the system due to the negative gain slope of signal chain components. Active devices, such as amplifiers tend to exhibit a negative gain slope, as well as passive components, such as connectors, adapters, coaxial cables, microstrip\/stripline transmission lines, and waveguide interconnect. This can be problematic for communications and sensing systems that rely on a high level of gain flatness for performance.<\/p>\n
On the other hand, there are also microwave systems that experience positive gain slope, where the roll off happens at lower frequencies. This is often due to the loss through low pass filters, wideband filters, and waveguide transmission lines where there is greater loss at the lower frequency parts of the spectrum. To correct for this, positive gain slope equalization aids in equalizing the gain slope by applying a gain at lower frequencies that reduces as a function of increasing frequency.<\/p>\n
In order for a positive gain slope equalizer to perform well, the equalizer needs to exhibit flat insertion loss over the desired bandwidth, and relatively linear equalizing value. It is also important for the input return loss to also present a flat response over the bandwidth of interest.<\/p>\n
Positive Slope Equalizers are commonly packaged in coaxial packages with field replaceable coaxial connectors. The coaxial connectors typically range from SMA to 2.92mm sizes corresponding to the frequency of the module, which can range from hundreds of megahertz to tens of gigahertz. The equalizing value is generally specified in dB and is a measure of the gain difference between the specified low frequency and high frequency points of the component. For upper microwave and millimeter wave positive slope equalizers, it is common for the equalizing value to be several dB higher than lower frequency equalizers. This is due to the typically greater losses at higher frequency regimes and the need for greater gain compensation.<\/p>\n
Other important specifications for positive gain slopped equalizers include maximum RF input power, VSWR, impedance, hermiticity\/environmental ruggedness, and operating temperature range. Given that the equalization performance of a positive slope equalizer will likely change as a function of temperature, exceeding the specific temperature of the device will likely degrade its equalizing performance.<\/p>\n