9) Method of selecting chip inductors for optimized performance

1. Mounting initial value of chip inductors L1,L2 and L3
At first, check initial resonance frequency and impedance property (minimum VSWR value) after mounting initial values of chip inductors.
・As an initial set of chip inductors, the same value set of the standard antenna in section 1 is recommended. These are L1=24nH,L2=220nH and L3=27nH. Though antenna properties are depending on the various conditions of PCB and so on, antenna resonance will appear in the frequency range of 430±50MHz under most conditions with this inductor set. Here, be sure to check whether resonance frequency is higher or lower than the target and how much larger the minimum VSWR value becomes.


2. Frequency tuning with L1 and L2
In this stage, L1 and L2 will be optimized. The chip inductor L3 is fixed here, since it has very minimal influence on the frequency shift.
・If the resonance frequency is higher or lower than your target frequency, replace the initial L1 or L2 to higher or lower one, respectively. Here the result of Fig.8-4, which represents the resonance frequency dependence on L1+L2, will help you to select an optimal combination of L1 and L2.


3. Impedance tuning with L3
In this stage, optimization of chip inductors will be completed. After optimizing L1 and L2, VSWR property will have a minimum peak at target frequency. However minimum VSWR value will not be close to 1, in other words impedance is not tuned to 50 ohm yet. The chip inductor L3 can optimize this impedance characteristic.
・If the minimum peak value of VSWR is not small enough, L3 should be optimized. Please refer to the results of Fig. 8-2 in order to know how L3 value affects the VSWR properties.



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