Mobile 5G device antenna tuning knowledge

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Mobile 5G device antenna tuning knowledge [Copy link]

Every antenna has a natural resonant frequency at which maximum antenna efficiency is achieved. Placing a shunt capacitor (to lower the resonant frequency) or a shunt inductor (to raise the resonant frequency) across the antenna allows aperture tuning. Using multiple capacitors and inductors, the antenna can be tuned to multiple frequencies using an antenna tuner switch, as shown in the figure below.

Aperture tuning is primarily done with tuner switches and tunable capacitors. The main quality factors for these switches are on-state resistance (RON) and off-state capacitance (COFF), as shown in the figure below. For tunable capacitors, it is critical to have a wide range of tuning capacitance and a good Q factor (quality factor). RON and COFF can significantly affect antenna efficiency. RON has a greater impact at low voltages, while COFF has a greater impact at high voltages; a switch layout strategy with low RON or low COFF can optimize tuning for different frequencies.

In the off state, the aperture tuner's COFF affects the capacitive loading on the antenna, lowering the resonant frequency. The higher the tuner's COFF, the further this frequency will deviate from the antenna's natural resonant frequency.

Figure 1 below shows the effect of the COFF of a single-pole double-throw (SPDT) switch on the simulated efficiency of an inverted-F antenna (IFA). The baseline measurements shown were taken without the SPDT placed in the tuning position. After adding the SPDT, the COFF of each port was set to 100 fF and 200 fF, respectively.

Figure 1.

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