Precision PCB Fabrication, High-Frequency PCB, High-Speed PCB, Standard PCB, Multilayer PCB and PCB Assembly.
The most reliable PCB & PCBA custom service factory.
Material source: "Microwave Magazine" March/April 2019 Issue Entry Time: 2019/3/25 11:02:56
Antenna booster-Antenna Tuner Combo Cover LTE Bands
Aurora Andújar, José L. Leiva, Fractus Antennas, Jaume Anguera, Fractus Antennas and Universitat Ramon Llull, and Cor Schepens and Roberto Gaddi, Cavendish Kinetics
Due to the large number of LTE frequency bands, wireless devices require many complex multi-frequency antenna designs 1-12. Compared with 2G and 3G, which only use 824 to 960 and 1710 to 2170 MHz, one of the biggest challenges of 4G is the large operating bandwidth: 698 to 960 and 1710 to 2690 MHz. The lower frequencies in the low-frequency region, especially the frequencies between 698 and 960 MHz, exacerbate the challenge because the antenna must be small compared to the operating wavelength.
This article describes how to combine Fractus Antennas' 86.4 mm3 small antenna booster and Cavendish Kinetics's small antenna tuner with an area of only 2 mm2 to implement an antenna system that covers the LTE frequency band in the frequency range of 698 to 2690 MHz.
Booster + Tuner
Virtual AntennaTM technology 13-18 relies on very small antenna elements, called antenna boosters, which makes it a good way to meet LTE bandwidth requirements. Using a matching network, instead of adjusting the operating frequency band by designing a complex antenna geometry, but only adjusting an appropriate matching network, this is faster and more cost-effective. The same antenna booster can be adapted to different platform sizes because only the matching network changes from one design to another18. This is different from the traditional antenna design, which has to be designed separately for different geometrical shapes in different situations. In addition to its small size, antenna boosters are also surface-mounted components, simplifying their integration in wireless devices.
The antenna booster, with a size of 12 mm*3 mm*2.4 mm, is installed in a corner of the smartphone PCB.
Antenna tuners are precise, low-loss, variable capacitors that can withstand high RF voltages. They are ideal for tunable antennas, dynamic load tuners, tunable filters, and analog RF applications that require high-voltage operation. Cavendish Kinetics antenna tuners use patented RF MEMS technology to eliminate the high insertion loss and RF voltage processing limitations of traditional silicon-on-insulator (SOI) or GaAs RF front-ends.
The combined design of Fractus antenna booster and Cavendish Kinetics antenna tuner supports all communication frequency bands 19-20 in the frequency range of 698 to 2690 MHz. The main advantage of this enhancer and tuner combination is that wireless devices can dynamically optimize the performance of a specific bandwidth over the entire frequency range, and provide the platform with maximum radiation to support each coverage and user usage scenario.
The devices produced using Cavendish Kinetics' RF MEMS technology and manufacturing process have high accuracy and reliability, and can still meet all specifications 21-22 even after 100 billion cycles of use. 32CK301R SmarTune™ antenna tuner (see Table 1) Used to demonstrate the design concepts in this article. Products with a wider capacitance range are available. Cavendish Kinetics' tuner series provide various capacitance ranges from 0.4 to 3 pF. All SmarTune antenna tuners are controlled through the MIPI RFFE interface (see Figure 2). The function of the tuner is independent and managed by the logic circuit in the controller.
The reconfigurable matching network proposed in this paper includes a MEMS adjustable capacitor (Z2) and seven lumped capacitors and inductors In this design, all passive components from Murata are SMD 0402 type with high Q value and strict tolerances. The tunable capacitor has 32 states, digitally controlled, and each state corresponds to a capacitance value of 0.4 to 1 pF. In this design, the corresponding relationship between value and state is 0.40 (S00), 0.44 (S02), 0.55 (S08) and 0.92 pF (S27).
The impedance characteristic of the antenna booster without matching network is very poor, especially at low frequencies, from 698 to 960 MHz, where |S11| is lower than -1 dB17. However, through a multi-band matching network, performance can be easily adjusted without changing the antenna geometry. The position of the antenna booster is important to excite the effective radiation pattern on the ground plane. In this design, a corner 16-17 of the ground plane was selected.
The state of the tunable capacitor is controlled by software through the parallel interface at the end of the ground plane. This interface connects the evaluation board to a PC running Cavendish Kinetics' SkyWalker software, which is used to set the impedance tuner to any of 32 states.
Since the ground plane is an important contributor to radiation, in order to avoid adverse effects on the interface connection when measuring the antenna performance, the following procedure is used: select the desired state of the impedance tuner through the connection interface. After setting the state, the interface connection is removed, and the battery on the ground plane provides a DC voltage to the tuner to maintain the state. This makes the antenna efficiency and S11 measurements unaffected by the interface connection.
The evaluation board is designed for carrier aggregation (CA), which can simultaneously use multiple LTE frequency bands to increase the data rate. Table 4 shows the recommended antenna tuner status for each inter-band CA pair.
