Figure 7: Shown is the frequency response of the FPC06078 directional coupler. The device exhibits a nominal coupling factor of -20 dB and a low insertion loss of 0.3 dB. Image source: Knowles DLI
range of 12 to 18 GHz. The FPC06078 directional coupler features an insertion loss of 0.3 dB and a minimum return loss of 15 dB. The device’s directivity is 14 dB (Figure 8). Conclusion Designers are responding to the demand for low SWaP-C in satcom applications by employing compact SMD passive components. Examples include the power dividers and directional couplers used in the fabrication of the satellite’s antenna arrays. By selecting good quality compact SMD passive devices – that promise superior performance through microstrip line construction and ceramic materials with high dielectric capabilities – designers can take advantage of higher frequency RF bands for satcom applications. Moreover, this new generation of SMD power dividers and directional couplers enables designers to come up with smaller and lighter antenna arrays, while simultaneously enhancing the antennas’ gain and beam forming capabilities.
is returned or reflected by the directional coupler ■ The insertion loss should also be minimized. This is the ratio of a signal level in a test configuration without the directional coupler present, compared to that when the component is present ■ Isolation should be maximized. This is the power level difference between the input port and the isolated port ■ The directivity should be maximized. This is the power level difference between Port 3 and Port 4 of the directional coupler and is related to isolation. It is a measure of the independence of the coupled and isolated ports
While RF directional couplers can be implemented using a variety of techniques, it is the microstrip line type that are finding favor in low SWaP-C satcom applications because of their small size. One example is Knowles’ FPC06078 directional coupler. The device is an SMD microstrip line device that measures 2.5 x 2.0 x 0.4 mm. It has an operating temperature range of -55°C to +125°C and a characteristic impedance of 50 Ω. While the coupling factor is frequency dependent, a high-quality directional coupler will exhibit a relatively flat coupling frequency response. From Figure 7 above, it can be seen that the Knowles device exhibits a nominal
coupling factor of 20 dB, which varies by only 2 dB across an operational
Figure 8: Shown is a graph of the FPC06078 directional coupler’s directivity. For higher antenna array performance, the directivity, which is related to isolation, should be maximized. Image source: Knowles DLI
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