Antennas are sensitive to their surroundings. Therefore, when there is an antenna on the PCB, the design layout should take the antenna requirements into account, as this can greatly affect the wireless performance of the device. Great care should be taken when integrating antennas into new designs. Even the material, number of layers and thickness of the PCB can affect the performance of the antenna.

Position the antenna to improve performance

Antennas operate in different modes, and depending on how individual antennas radiate, they may need to be placed in specific positions – along the short side, long side, or corner of the PCB.

In general, the corner of the PCB is a good place to place the antenna. This is because the corner position allows the antenna to have gaps in five spatial directions, and the antenna feed is located in the sixth direction

Antenna manufacturers offer antenna design options for different positions, so product designers can choose the antenna that best fits their layout. Typically, the manufacturer’s data sheet shows a reference design that, if followed, provides very good performance.

Product designs for 4G and LTE typically use multiple antennas to build MIMO systems. In such designs, when multiple antennas are used at the same time, the antennas are usually placed at different corners of the PCB

It is important not to place any components in the near field near the antenna as they may interfere with its performance. Therefore, the antenna specification will specify the size of the reserved area, which is the area near and around the antenna that must be kept away from metallic objects. This will apply to each layer in the PCB. In addition, do not place any components or even install screws in this area on any layer of the board.

The antenna radiates to the ground plane, and the ground plane is related to the frequency at which the antenna operates. Therefore, it is urgent to provide the correct size and space for the ground plane of the selected antenna.

Ground plane

The size of the ground plane should also take into account any wires used to communicate with the device and the batteries or power cords used to power the device. If the grounding plane is of the right size, ensure that cables and batteries connected to the device have less impact on the antenna

Some antennas are related to the grounding plane, which means that the PCB itself becomes the grounding part of the antenna to balance the antenna current, and the lower layer of the PCB may affect the performance of the antenna. In this case, it is important not to place batteries or LCDS near the antenna.

The manufacturer’s data sheet should always specify whether the antenna requires grounding plane radiation and, if so, the size of the grounding plane required. This may mean that the gap area should surround the antenna.

Close to other PCB components

It is crucial to keep the antenna away from other components that might interfere with the way the antenna radiates. One thing to watch out for is batteries; LCD metal components, such as USB, HDMI and Ethernet connectors; And noisy or high-speed switching components related to switching power supplies.

The ideal distance between an antenna and another component varies according to the height of the component. In general, if a line is drawn at an 8 degree Angle to the bottom of the antenna, the safe distance between the component and the antenna if it is below the line.

If there are other antennas operating at similar frequencies in the vicinity, it may cause the two antennas to detune, as they affect each other’s radiation. We recommend that this be mitigated by isolating at least -10 dB antennas at frequencies up to 1 GHz and at least -20 dB antennas at 20 GHz. This can be done by leaving more space between the antennas or by rotating them so that they are placed 90 or 180 degrees apart from each other.

Design transmission lines

Transmission lines are rf cables that transmit RF energy to and from the antenna to transmit signals to the radio. Transmission lines need to be designed to be 50, otherwise they may reflect signals back to the radio and cause a drop in the signal-to-noise ratio (SNR), which can render radio receivers meaningless. Reflection is measured as voltage standing wave ratio (VSWR). A good PCB design will exhibit suitable VSWR measurements that can be taken when testing the antenna.

We recommend careful design of transmission lines. First, the transmission line should be straight, because if it has corners or bends, it may cause losses. By placing perforations evenly on both sides of the wire, noise and signal losses that may affect antenna performance can be kept to a low level, as performance can be improved by isolating noise propagating along nearby wires or ground layers.

Thinner transmission lines may cause greater losses. The RF matching component and the width of the transmission line are used to adjust the antenna to operate at a characteristic impedance of 50 ω. The size of the transmission line affects performance, and the transmission line should be as short as possible for good antenna performance.

How to get better performance?

If you allow the right grounding plane and place the antenna in a very good position, you’ve got a good start, but there’s a lot more you can do to improve antenna performance. You can use a matched network to tune the antenna – this will compensate to some extent for any factors that may affect the antenna performance.

The key RF component is the antenna, which matches the network and its RF output. A configuration that places these components nearby minimizes signal loss. Similarly, if your design includes a matching network, the antenna will perform very well if its wiring length matches that specified in the manufacturer’s product specifications.

The casing around the PCB may also vary. Antenna signals cannot travel through metal, so placing an antenna in a metal housing or housing with metal properties will not be successful.

Also, be careful when placing antennas near plastic surfaces, as this can cause significant damage to antenna performance. Some plastics (for example, fiberglass filled nylon) are lossy and can decay into the ANTENNA’s RF signal. Plastic has a higher dielectric constant than air, which can seriously affect the signal. This means that the antenna will record a higher dielectric constant, increasing the electrical length of the antenna and reducing the frequency of antenna radiation.