5G Antenna Design for mobile Devices
Antenna design for mobile phones has always been a challenging topic for engineers, and designing antennas to support the new 5G frequency bands will raise the bar further. Two frequency ranges are of most interest: frequency range 1 for sub 6 GHz bands communication and frequency range 2 for communication at the millimeter (mm) wave frequencies above 24 GHz. Some of the bands are still under discussion, and the exact frequency designations will vary geographically. Initial phone integration has focused on sub 6 GHz antennas, and millions of subscribers around the world already have 5G mobile phone contracts. mm-Wave support has initially been used for providing broadband links to homes or other fixed infrastructure, but is gradually finding its way into mobile phones too.
Simulation plays a fundamental role in designing antennas in general, and especially for designing the highly customized, individually tailored, antennas found in compact mobile devices. The challenges in the two frequency ranges are different, though.
Sub 6 GHz Antennas
These antennas don’t need to be at a specific location within the phone. They can fit in to whatever space is available among the other components which are densely packed by the design team. However, only 5G antennas are not sufficient for the phones. An efficient phone requires connectivity with 4G, 3G and Wi-Fi communication channels as well. This increases number of antennas to be integrated in phone and most of the standards also include support for MIMO multi antenna operations. So a well connected mobile device would require half a dozens or more antennas.
With multiple antennas comes the problem of resonance. The overlap in operating frequencies ranges combined with close proximity can cause noise in received and transmitted signals. These resonant behaviors depend on configuration of internal structure that changes with every version of the phone. It is thus crucial to design antennas in context of full phone including all its components and use simulation for every design change to compute resonance.
The increasing demand in mobile data traffic will require mm-wave communication to complement sub 6 GHz massive. The small physical size of antennas at or above 28 GHz makes the use of chip-integrated arrays – often containing four elements – an interesting option. These antennas have a high gain and support multiple beams, thus addressing the design goals of providing a high-quality data link in all directions around the phone. The antenna design in this case is not tightly coupled to the overall phone as the location is usually superficial just behind the cover. The material and thickness of the cover has substantial impact on the performance of the antenna. Antennas can be efficiently integrated behind plastic or glass covers by engineering the cover geometry to act locally as a lens, and even behind metal covers by including electromagnetic windows, perhaps based on Frequency Selective Surfaces (FSS) design principles.
Performance vs. Safety
As these devices are used by humans, safety regulations and standards should be met before these devices can have access to people. The frequency bands play a role in defining these standards. The sub 6 Hz band is more concerning as these waves can penetrate in human tissues. The existing specific absorption rates standard applies in this case. The mm-wave frequencies do not penetrate more than 3mm into the tissues. Majority of energy is rather reflected from the surface. The maximum power flow on a surface at a given distance from the device is rather the standard followed.
Electromagnetic performance and safety are the key indices that define the electromagnetic aspects of a mobile device. But that is not enough to make a competitive phone. The structural aspects such as drop test and light weight should be considered as well. The thermal and CFD aspects should be considered as well to prevent overheating of circuits. It is a multi disciplinary design scenario in which one physics often interacts with the other. The efficient design requires a unified multi physical design and simulation platform in which a single source of design data can integrate with multiple physics and their experts. A disconnected point tools architecture would rather be a less competitive approach.