Phased Array Antenna Design for 5G Applications
New antenna designs are the cornerstone of next-gen 5G devices
As the 5G rollout begins, designers have an important role to play in designing the technical infrastructure to support more connected devices and provide higher data rates. More component manufacturers are also providing a broader range of solutions for antennas in 5G systems.
Designers of 5G-capable mobile devices need to consider appropriate antenna designs for their systems. Two important requirements are tunability, where the response frequency of an antenna can be tuned, as well as beamforming, where the radiation pattern from an antenna can be directed. Patch or microstrip phased array antenna design for 5G applications is an easy area for any designer to begin implementing wireless capabilities in new 5G systems.
Phased Array Antennas in 5G
5G antennas operate in a number of bands that include the LTE bands, as well as higher frequency bands that exceed 5 GHz. The higher frequency bands include 24.25-27 GHz and 37-40 GHz with 50 to 400 MHz bandwidth in each channel. The U.S. FCC recently opened up higher bands extending to 64-71 GHz, and similar bands are in use in Europe, Japan, and China.
mmWave frequencies have always viewed as unsuitable for communication between mobile devices due to high losses. Scattering and absorption air attenuate signals to a greater degree than at lower frequencies, thus transmitters needed to operate at much higher power to compensate, making GHz wireless antennas impractical for long range communication in mobile devices.
Despite the attenuation of mmWave frequencies, beamforming techniques can be used to focus radiation emitted from an array of antennas. This type of antenna is called a phased array antenna, and they were originally used by the military in directional radar systems. This type of antenna consists of a number emitters that radiate in a spherical or dipole radiation pattern. Each antenna in the array must have particular spacing in order to provide the required interference that forms a beam with minimal side lobe generation.
The Russian Woodpecker: an early phased array antenna
The earliest type of phased array antenna was constructed in 1905 by Ferdinand Braun. This simple antenna array consisted of three separate monopole antennas placed in an equilateral triangle with a base station in the center. The signal sent to one of the antennas was delayed by a quarter wavelength, which enforced directionality in the radiation pattern through interference. This same idea is used in arrays of patch antennas, where the delay between signals on a board is controlled with a phase shifter.
PCBs for 5G Phased Array Antennas
On a PCB, a phased-array antenna contains multiple radiating elements placed in a particular geometry. Each element is connected to a delay line or phase shifter, and interference among the radiation patterns from each antenna forms a beam with low divergence. Monopole/dipole emitters be used in these applications can generate a beam directed along a specific angle. This is done by delaying the signal sent to each antenna in the array by a set amount.
Newer 5G-capable smartphones will need to include anywhere from 6 to 10 antennas in order to ensure the device can transmit no matter how it is held during operation. Each antenna in a 5G-capable array is normally placed as a printed patch antenna with a feeder line routed through the back of the board. Beamforming transceiver modules are available as ICs that can be used to control the beam steering angle in a phased array antenna.
These are normally connected to the mainboard with a coaxial line, and each patch antenna in the array can be connected to the module using a microstrip and via on the back layer. A good design choice may be to use a 4 layer board with an interior ground plane below the antenna array ground plane, as this will block radiation from propagating back into the module or mainboard circuitry. This is more important for analog beamforming modules as these are more prone to EMI problems than digital modules.
Placing these beamforming ICs on a PCB requires the following some standard RF design techniques, although the directionality of the beam emitted from each array helps reduce the possibility of self-jamming. Shielding and proper grounding around component sections and proper mixed signal ground plane arrangement will also help prevent susceptibility to EMI.
An important point regarding the construction of the antenna itself involves the spacing between neighboring elements in the array. The maximum spacing between the elements in the array depends on the wavelength of radiation emitted from the antenna and the maximum angle at which the array intends to emit. Most designers simply take emission along the normal direction just to be safe, thus the maximum spacing between elements would be equal to half a wavelength. The example below shows a 2x4 phased array antenna design for 5G applications.
Patch antenna design for 5G applications as a phased array
There are still many challenges for 5G PCB designers to consider, including thermal management, placement of pulsing ICs on the phone’s mainboard, accommodating the form factor of 5G phones, and much more. Working with a PCB design software package like Altium Designer allows you to design the antenna array you need for 5G devices. You’ll also have access to simulation tools that are invaluable for high frequency PCB design.
If you’re interested in learning more about Altium Designer, you can contact us or download a free trial and get access to the industry’s best layout, routing, and simulation tools. Talk to an Altium expert today to learn more.