ZigBee On Windows Mobile--ZigBee Module Antenna Design

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ZigBee On Windows Mobile--ZigBee Module Antenna Design [Copy link]

For short range wireless communication devices (SRD), the design of antenna is related to the communication distance. Factors such as radiation model, gain, impedance matching, bandwidth, size and cost will affect our selection and design of antenna. At present, ordinary ZigBee chips in China all work in the 2.4G frequency band, which is the ISM frequency band. There are many wireless technologies working in this frequency band, and the common ones are Bluetooth, Wi-Fi (wireless LAN), etc. So, how to design the antenna we need? Let's discuss this issue here.

Generally speaking, in this frequency band, the antennas we can choose are PCB antenna, chip antenna and Whip antenna. The specific shapes are shown in Figure 1 below:

Figure 1: Schematic diagram of PCB antenna, chip antenna and whisk antenna

The advantages and disadvantages of these three antennas are as follows:

Antennas can be divided into two types: single-ended antennas and differential antennas. Single-ended antennas can also be called unbalanced antennas, and differential antennas can also be called balanced antennas. Single-ended antennas mainly rely on a ground-referenced signal, and their characteristic impedance is generally 50 ohms. However, many RF ICs have differential RF ports. Therefore, if a single-ended antenna is used, a circuit is required to change this characteristic. This circuit is called a balun (commonly known as a balanced/unbalanced transformer). Examples of single-ended and double-ended antennas are shown in Figure 2 below:

Figure 2: Single-ended antenna and double-ended antenna diagram

PCB antenna design is difficult and usually requires the support of simulation tools. In order to get an optimal design, simulation will take a lot of time and effort. Therefore, we usually follow the reference design provided by the chip manufacturer as is. Chip antennas can be used in scenarios where the antenna space is relatively small, even if the frequency is below 1GHz. Compared with PCB antennas, chip antennas increase the BOM (Bill of Material) and also increase the cost of the patch. Whip antennas have better performance, but compared to the previous PCB antennas and chip antennas, they are more expensive and larger in size, and usually require a connector. Generally speaking, this type of antenna is an omnidirectional antenna.

For CC2430, PCB antenna is a relatively economical choice. Moreover, the communication distance can also meet general requirements. Figure 3 below is the PCB diagram of the inverted F antenna of the CC2430 development board:

Figure 3: PCB diagram of F antenna

As can be seen from the figure, this inverted F antenna is a single-ended antenna, that is, an unbalanced antenna, and we need a balun. Similarly, TI also provides a design reference for a microstrip balun. Figure 4 below is the PCB of a microstrip balun:

Figure 4: PCB diagram of TI CC2430 microstrip balun

Freescale's MC13213 development board also uses a similar inverted F antenna, but the Freescale development board uses a balun device, which requires an increase in BOM.

We can choose the antenna according to the specific situation, mainly considering the three factors of performance, size and cost. This article mainly refers to TI's reference design:

swra088(SRD Antennas).pdf

swra161(Antenna Selection Guide).pdf

swru120b(2.4 GHz Inverted F Antenna).pdf

swra098d(Implementation of Microstrip Balun for CC2420, CC243x, and CC2480).pdf

Friends who need the above information can go directly to the TI website to download it.

alan000345

Thanks for sharing, the antenna design is great.

combat

I learned it, thank you.