RF InductorProposal of the Loss Reduction in the RF Circuit

The loss in RF circuits is also influenced by the level of the inductor Q used for matching circuits. Murata offers a lineup of numerous High Q products, and proposes a reduction of loss in RF circuits. In this lineup, we recommend the best High Q characteristics wound structure"LQW Series Open in New Window ".

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Comparison of Loss in Various RF Inductors

The reason why we recommend the LQW series is described in the following using a SAW filter as an example.
Murata's SAW filter (pass band 800 MHz) and RF inductor were used, and an RF inductor with a different Q was replaced on the matching circuit, in order to measure and compare the insertion loss of the SAW filter.

The circuit diagram is shown in Figure 1. In the case of this circuit, only 1 RF inductor was used in the matching circuit.

Figure 1: SAW Filter and Matching Circuit

Figure 1: SAW Filter and Matching Circuit

Figure 2 shows the frequency characteristics of the RF inductor Q compared in this test, and Table 1 shows the structure, size and Q (Typ. value at 800 MHz) .

Figure 2: Comparison of RF Inductor Q (both 7.5 nH)

Figure 2: Comparison of RF Inductor Q (both 7.5 nH)

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Table 1 Comparison of RF Inductors
Part Number Structure Size (mm) Q
LQW15AN7N5H00 Wire Wound 1.0×0.5 59
LQW04AN7N5D00 Wire Wound 0.8×0.4 48
LQG15HN7N5J02 Wire Wound 1.0×0.5 33
LQP03TN7N5H02 Film 0.6×0.3 27

Figure 3 shows the overall characteristics of the SAW filter when the RF inductor was replaced in the matching circuit, and Figure 4 shows the pass band characteristics.

  • Figure 3: Overall Characteristics of SAW Filter

    Figure 3: Overall Characteristics of SAW Filter

  • Figure 4: Pass Band Characteristics of SAW Filter

    Figure 4: Pass Band Characteristics of SAW Filter

When looking at the pass band in Figure 4, it can be confirmed that the insertion loss of the SAW filter differs by the RF inductor used.
In high frequency circuits, the difference in the level of loss becomes important.

From these test results, it can be understood that the insertion loss of the SAW filter is lower when the RF inductor Q is higher (lower loss) .
Accordingly, the level of inductor loss becomes the level of the SAW filter loss including the matching circuit.

In addition, keep in mind that the loss will change according to the RF component (SAW filter in this test) , the matching circuit, frequency band and etc. to be used.

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