4 Things You Need to Know About 4G/5G Smartphone Antenna Tuning

走马观花

4 Things You Need to Know About 4G/5G Smartphone Antenna Tuning [Copy link]

Antenna efficiency plays a critical role in the overall RF performance of a smartphone. However, current smartphone industrial design trends and RF requirements, especially with the upcoming transition to 5G, mean that smartphones must fit more antennas into 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 cover four key elements of antenna tuning in 4G and 5G mobile devices.

Background: Why is antenna tuning needed?

The RF front-end (RFFE) design of modern mobile phones is becoming increasingly complex due to the increasing number of frequency bands, features, and modes required for the phone to operate. The need for more antennas to deliver higher data rates using carrier aggregation (CA), 4x4 MIMO, Wi-Fi MIMO, and new wideband 5G bands has increased the number of antennas in smartphones from 4-6 to 8 or more. At the same time, the space available for mobile system antennas has shrunk, resulting in reduced antenna efficiency.
Some of the lost performance can be recovered through antenna tuning. Without tuning, antennas perform well over a limited frequency range, but adding antenna tuning can achieve more optimized performance over a wider frequency range.
Antenna tuning systems, such as impedance tuners and aperture tuners, enable the higher bandwidths and carrier aggregation required by LTE smartphones. They enable antennas to operate efficiently across the entire LTE and 5G frequency bands (from 600 MHz to 5 GHz), while also conserving battery power and enabling slim phone designs.
However, implementing antenna tuning requires a deep understanding of how to apply the technology for each application. Let’s look at the four essential elements:
Impedance vs. Aperture Tuning
Choosing the right components for your tuning application
On-state resistance (RON), off-state capacitance (COFF), and eliminating unwanted resonances
Aperture Tuning and CA

#1: Impedance or Aperture Tuning, which is the best approach?

The radiation pattern and efficiency of a T-antenna depends on the size, shape, housing, contact with metal, and shape and size of the ground plane. An untuned antenna is less efficient than a tuned antenna; in contrast, the higher efficiency of a tuned antenna means it has higher radiated power and greater range.
Smartphones can use two methods for antenna tuning - impedance tuning and aperture tuning - as shown in the figure below.
Aperture tuning optimizes the total antenna efficiency from the empty space at the antenna terminal, which can be optimized across multiple frequency bands. Aperture tuning has a significant impact on antenna efficiency for both transmit and receive communication applications, and total radiated power (TRP) and total isotropic sensitivity (TIS) can be improved by 3 dB or more, depending on the application.
Impedance tuning maximizes the power transfer between the RF front end and the antenna, and increases TRP and TIS by minimizing mismatch losses between the antenna and the antenna front end. Impedance tuning also helps compensate for environmental effects, such as the position of a person's hand on the smartphone.

(, downloads: 0)

上传

点击文件名下载附件

Currently, aperture tuning is the main method used in mobile phones to overcome the problems caused by reduced antenna area and efficiency. Mid-range and high-end smartphones use a combination of aperture and impedance tuning to support the ever-expanding frequency band range, especially 5G applications.

#2: How to choose the right tuning components

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

(, downloads: 0)

上传

点击文件名下载附件

It is important to select the aperture tuning switches, capacitors, and inductors for the best performance. Some guidelines include:

Tuner Switches:
Use switches with low RON and COFF to minimize system losses.
Use high linearity tuning switches to avoid impact on radiated spurious emissions (RSE) and TIS.
The switch must be multi-mode to tune the 2G/3G/4G/5G standard frequency ranges.
The switch should be able to handle high RF voltages for broadband antenna applications.

Tuning components:
Use capacitors with capacitance greater than 0.5 pF to avoid using high tolerance components.
Avoid using inductors with inductance greater than 36 nH.

#3: RON, COFF, and Eliminating Unwanted Resonances

Two key characteristics of an aperture tuning switch significantly affect the efficiency of the antenna: the on-state resistance (RON) and the 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 an inductor is connected to the RF port for tuning, the combination of COFF and the inductor will produce an unwanted resonance. In other words, a resonant mechanism must exist when the switch is in the off-state. To suppress this resonance, the tuner switch has an internal switch that can be connected in parallel to ground.
The figure below shows an SP4T tuner switch 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 in the off-state. The ON-state resistance between the antenna and the RF3 port is replaced by RON, and the OFF-state capacitance between the antenna and the RF1, RF2, and RF4 ports is simulated by COFF. This ground path feature helps to eliminate the resonance caused by the capacitance generated by the off-switch port. In the figure below, the black line in the lower right corner indicates the presence of resonance, and the orange line indicates the absence of resonance.

(, downloads: 0)

上传

点击文件名下载附件

Reducing RON can improve the efficiency of both inductively tuned and capacitively tuned antennas by several dB, which can have a large impact on the overall RF performance of the phone. Reducing COFF is equally important. However, the impact of RON and COFF varies depending on the location and voltage distribution of the antenna tuner. To learn more about RON and COFF, refer to our free guide How to Implement 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 on both bands simultaneously.
Using aperture tuning switches can help meet the CA requirements of smartphones:
Aperture tuning is used to support CA combinations of band 39 and band 41 (commonly used in China).
Placing a switch near the peak voltage point of each frequency allows each band to be tuned efficiently with minimal impact on the other band.
Placing the tuning switch near the peak voltage point of the resonant frequency will tune best to that frequency.

btty038

Intelligent tuning to match the best point Point-to-point matching