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4 things to know about 4G/5G smart phone antenna tuning

  • Categories:News Center
  • Time of issue:2021-02-02 15:17
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(Summary description)Antenna efficiency plays a vital role in the overall RF performance of smartphones . However, the current industrial design trends and RF requirements of smartphones (especially the transition to 5G ) mean that smartphones must install more antennas in a smaller space and / or increase the bandwidth of existing antennas.

4 things to know about 4G/5G smart phone antenna tuning

(Summary description)Antenna efficiency plays a vital role in the overall RF performance of smartphones . However, the current industrial design trends and RF requirements of smartphones (especially the transition to 5G ) mean that smartphones must install more antennas in a smaller space and / or increase the bandwidth of existing antennas.

  • Categories:News Center
  • Author:
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  • Time of issue:2021-02-02 15:17
  • Views:
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Antenna efficiency plays a vital role in the overall RF performance of smartphones . However, the current industrial design trends and RF requirements of smartphones (especially the transition to 5G ) mean that smartphones must install more antennas in a smaller space and / or increase the bandwidth of existing antennas.

In short, antenna tuning is more important than ever. In this blog, we will introduce the four key elements of antenna tuning in 4G and 5G mobile devices.


Background: Why is antenna tuning required?
As the number of frequency bands, functions and modes required for mobile phone operation continues to increase, the RF front-end (RFFE) design of modern mobile phones is also becoming increasingly complex. We need more antennas, using carrier aggregation (the CA) , 4x4 the MIMO , the Wi-Fi the MIMO and new broadband 5G band to provide higher data rates, the number of antennas in the smartphone from 4-6 months increased . 8 months Or more. At the same time, the space available for mobile system antennas has shrunk, resulting in reduced antenna efficiency.

Some lost performance can be recovered by antenna tuning . If tuning is not implemented, the antenna can achieve excellent performance in a limited frequency range, but increasing antenna tuning can achieve more optimized performance in a wider frequency range.

Antenna tuning systems, such as impedance tuners and aperture tuners, can support the higher bandwidth and carrier aggregation required by LTE smart phones. They enable antennas to work efficiently across the entire LTE and 5G frequency bands (from 600 Mhz to 5 Ghz ), while also saving battery power and enabling slim mobile phone designs.

However, achieving antenna tuning requires a deep understanding of how to apply the technology for each application. Let's take a look at these four basic elements:

Impedance and aperture tuning
Choose the right components for your tuning application
On-state resistance (RON) , off-state capacitance (COFF) , and eliminate unnecessary resonance
Aperture tuning and CA

 

#1: Impedance or aperture tuning, which is the best method?
The radiation pattern and efficiency of the T antenna depend on the size, shape, housing, degree of contact with metal, and the shape and size of the ground layer. The efficiency of an untuned antenna is lower than that of a tuned antenna; in contrast, the higher the efficiency of a tuned antenna, it means that it has a higher radiation power and a larger range.

Smart phones can use two methods for antenna tuning - impedance tuning and aperture tuning - as shown in the figure below.

Aperture tuningOptimizing the total antenna efficiency from the free space of the antenna terminal can optimize antenna efficiency across multiple frequency bands. Aperture tuning has a great impact on the antenna efficiency of transmitting and receiving communication applications. According to different applications, the total radiated power (TRP) and total omnidirectional sensitivity (TIS) can be increased by 3 dB or more.
Impedance tuningMaximize the power transmission between the RF front end and the antenna, and increase TRP and TIS by minimizing the mismatch loss between the antenna and the antenna front end . Impedance tuning also helps to compensate for environmental influences, such as the position of a person's hand on a smartphone.


Aperture Versus Impedance Tuning

At present, in order to overcome the problems caused by the reduction of antenna area and efficiency, the aperture tuning method is mainly used in mobile phones. Mid- to high-end smartphones use a combination of aperture and impedance tuning methods to support the ever-expanding frequency range, especially for 5G applications.
 

#2: how to choose the right tuning component
Adding a tuning component (capacitor or inductor) between the switch and the radiating element can further adjust the resonance frequency to support LTE and 5G frequency bands. The figure below shows the resonant frequency of the antenna when the switch is off, on, and when an inductor or capacitor is added to the circuit.

Aperture Tuning Component Responses

It is important to choose the best-performing aperture tuning switch, capacitor, and inductor. Some guidelines include:

Tuner switch:

Use switches with low RON and COFF to minimize system losses.
Use high linearity tuning switch to avoid affecting radiated spurious emission (RSE) and TIS .
The switch must be multi-mode to adjust the 2G/3G/4G/5G standard frequency range.
The switch should be able to handle the high RF voltage for broadband antenna applications.
Tuning components:

Use capacitors with a capacitance greater than 0.5 pF to avoid using high tolerance components.
Avoid using inductors with inductance values ​​greater than 36 nH .
 
#3: RON , COFF and eliminate unnecessary resonance
Two key characteristics of the aperture tuning switch will significantly affect the efficiency of the antenna: on-state resistance (RON) and off-state capacitance (COFF) . The aperture switch is a capacitive switch in the off state (COFF) and a resistive switch in the on state (RON) . If the inductor is connected to the RF port for tuning, the combination of COFF and the inductor will produce unnecessary resonance. In other words, when the switch is off, there must be a resonance mechanism. In order to suppress this resonance, the tuner switch is equipped with an internal switch, which can be connected in parallel to the ground.

The figure below shows that an SP4T tuner switch is connected between the antenna and the tuning component to tune the antenna to different frequency bands. The antenna is connected to a tuning capacitor through the RF3 port, while the other three ports are disconnected. Replace the ON state resistance between the antenna and the RF3 port with RON , and use COFF to simulate the OFF state capacitance between the antenna and the RF1 , RF2, and RF4 ports . This ground path function helps to eliminate resonance caused by the capacitance generated by turning off the switch port. In the figure below, the black line in the lower right corner indicates that there is resonance, and the orange line indicates that there is no resonance.

Removing Resonance Using Grounded “Off” Ports

Reducing RON can increase the antenna efficiency of inductance tuning and capacitance tuning by several dB , which has a greater impact on the overall RF performance of the mobile phone . Lowering COFF is equally important. However, depending on the position and voltage distribution of the antenna tuner, the effects of RON and COFF are different. For more information about RON and COFF , please refer to our free - guide How to Achieve Aperture Tuning: Best Practices for 4G/5G Smartphones .
 

#4: aperture tuning and carrier aggregation
CA combines two or more LTE carriers (usually in different frequency bands) to increase bandwidth and achieve higher data rates. Due to the limited number of antennas in mobile phones, this usually means that a single antenna must communicate simultaneously on two frequency bands.

The use of aperture tuning switches helps to meet the requirements of smart phones for CA :

Aperture tuning is used to support the CA combination of band 39 and band 41 (usually used in China).
Placing a switch near the peak voltage point of each frequency can efficiently tune each frequency band with minimal impact on the other frequency band.
Placing the tuning switch near the peak voltage point of the resonance frequency has the best tuning effect on this frequency.

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