In recent years, technological advances in the field of mobile communications, as well as the shift of mobile phones from business tools to handheld devices, have prompted manufacturers to constantly look for new ways to integrate increasingly complex antennas.
Mobile phones can only work at a single frequency initially. Adopted in Europe and Asia is usually one of the two frequencies of 900 MHz or 1800 MHz specified by the European GSM Commission. However, the economies of scale of developing and manufacturing handsets that support both frequencies, and the considerable profit that roaming capabilities bring to network operators, have led to the birth of dual-band GSM handsets that can simultaneously support two frequencies. . Due to the lack of uniform standards in the fairly fragmented US mobile phone market, the 1900MHz GSM frequency application in the United States started very slowly. However, as operators begin to see the benefits of global roaming with unified technology, the US GSM network has made great efforts in recent months to expand across the United States. Although many new mobile phones still use dual-band mode, in the next 12-18 months, tri-band mobile phones will gradually become the de facto GSM standard, that is, a single mobile phone can support all three GSM frequencies currently used in the world. The recently announced fourth major GSM frequency allows certain operators to transition from other technologies to GSM, but this further complicates the situation faced by handset manufacturers and antenna providers if they want a single handset to support all GSM frequencies. .
As the 3G network is scheduled to be officially launched in the second half of 2002, it is extremely urgent to design more challenges with 3G mobile phones that are backward compatible with existing technologies and frequencies. More importantly, in addition to communicating with mobile phone networks, future mobile phones must be able to communicate with many other devices and networks, including technologies such as Bluetooth, IEEE 802.11b (wireless LAN) and GPS. More requirements are placed on the antenna design of next-generation communication devices, including PDAs, networking products, new Internet appliances, and many other devices.
Built-in antenna designIn mobile phone designs, external antennas are gradually being replaced by built-in antennas. Initial concerns about built-in antenna performance are now largely absent. It turns out that a well-designed internal antenna provides the same performance as an external antenna in terms of antenna efficiency, the most critical electrical parameter for mobile applications. Consumer demand for a more stylish look further motivates handset manufacturers to integrate antennas inside the device. SAR (SAR) has previously been considered the biggest problem with built-in antenna phones. However, the test results show that quite good SAR performance can be achieved in mobile phones with built-in antennas. The built-in antenna has the same performance, better appearance characteristics and more robustness than the external antenna, so the transition from the external to the built-in antenna has become an irreversible trend.
Antenna performance standardNearly all of the main types of devices with built-in antennas use a PIFA (Planar Inverted F Antenna) structure. The performance of such antennas mainly includes the following aspects:
â— Physical size
â— Electrical design quality
â— Radio frequency (RF) material characteristics (dielectric constant and loss tangent) of dielectric substrate and case
â— Packaging and design of the entire device
It is important for system designers to fully understand the features and functions of different internal antenna technologies early in the product design process. An overly optimistic assumption about the size of the antenna will result in a compromise between package and antenna performance.
The built-in antenna of most wireless handheld devices is located above the system ground plane and uses a PIFA structure. A key physical parameter of the mobile phone PIFA is the height of the radiator above the ground plane. Most commercial solutions currently use heights from 7mm to 9mm. However, it should be noted that smart packaging offers the opportunity to minimize this height while maintaining antenna performance (an example of such an application is a single-sided board, although it can be used in some imaginative designs) More ways).
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