Coaxial Low Pass Filters to Improve SFB and SFU LO to IF Port Isolation

SAGE Millimeter offers complete balanced mixer and upconverter solutions under the product series of SFB and SFU based on GaAs Schottky beam-lead diode and balanced circuit configuration to offer the superior RF performance. For instance, the W Band balanced mixer with model SFB-10-N1 shown in Figure 1, supports the full waveguide band operation for both LO and RF frequencies from 75 to 110 GHz with an extremely broad IF output from DC to 35 GHz. The mixer offers a conversion loss of 9 dB and a high RF to LO port isolation of 30 dB typically. Due to the preferred compact mechanical package size, the integrated higher performance filter at IF port to reject the LO leaking is prohibited. Therefore, the desired high LO to IF port isolation is compromised to be settled around 10 dB for all models nominally.

Fig 1. SFB-10-N1

By considering the customers’ application requirements of high LO to IF port isolation, SAGE Millimeter had developed a series of coaxial lowpass filters to offer direct interface with the SFB and SFU series mixers and upconverters to improve the port isolation from 10 dB to 40 dB typically. For example, the figure 2 shows the model of SCF-55375330-KFKM-L1, which is developed for W Band mixer and upconverter applications.

Fig 2. SCF-55375330-KFKM-L1

The typical frequency response of the filter is shown in Figure 3, which displays 1.0 dB typical insertion loss in the frequency range of DC to 35 GHz and better than 30 dB rejection at 65 GHz.

Figure 3. Frequency Response of Model SCF-55375330-KFKM-L1

The table below shows the developed various lowpass filters for various band applications.

SCF-17327330-KFKM-L1Ka BandDC to 16.5 GHz/0.6 dB26.5 to 40 GHz/30 dB
SCF-21333330-KFKM-L1Q BandDC to 21 GHz/0.6 dB33 to 50 GHz/30 dB
SCF-25340330-KFKM-L1U BandDC to 25 GHz/0.6 dB40 to 60 GHz/30 dB
SCF-30350330-KFKM-L1V BandDC to 25 GHz/1.0 dB50 to 75 GHz/30 dB
SCF-36360330-KFKM-L1E Band DC to 30 GHz/1.0 dB60 to 90 GHz/30 dB
SCF-55375330-KFKM-L1W Band DC to 35 GHz/1.5 dB75 to 110 GHz/30 dB
SCF-77390330-KFKM-L1F Band DC to 40 GHz/2.0 dB90 to 140 GHz/30 dB
SCF-94311430-KFKM-L1D Band DC to 40 GHz/2.0 dB110 to 170 GHz/30 dB

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