How to choose PCB antenna in wireless design
As consumer demand for the latest and greatest wireless technologies grows in wireless design, the need for PCB antennas that can be easily installed in wireless communication products is growing.
Antennas are a key component of many wireless systems, and printed circuit board (PCB) antennas are widely used in the industry due to their small size and ease of integration with other high frequency circuits. The performance and consistency of a PCB antenna depends to a large extent on the quality of its base circuit laminate, the size of which depends to a large extent on the target frequency and wavelength of the antenna.
Whether it's from personal communication systems (PCS), Internet of Things (IoT) applications, to automotive electronic control and security systems, the demand for wireless applications is undoubtedly very strong. As operating frequencies become higher and higher, antennas are needed everywhere from the 2.4 GHz band of PCS applications to the millimeter wave (mmWave) frequency of automotive advanced driver assistance systems (ADAS). That's where PCB antennas work – designers often use them as a practical solution to their growing wireless applications.
A high frequency PCB antenna can be as simple as a microstrip patch fabricated on one side of a circuit laminate, requiring only a slightly larger ground plane on the other side of the underlying dielectric layer. This low profile antenna is ideal for installation in systems with any available flat surface.
Of course, the antenna radiation pattern of such a simple microstrip patch will be limited. PCB antennas using microstrip patches typically combine multiple patches on a single PCB to achieve higher gain at a given operating frequency. The size of the patch depends on the wavelength of the target operating frequency, typically half the wavelength, to achieve the best resonant antenna characteristics at the target frequency.
Of course, RF/microwave PCB antennas can be composed of many different transmission lines, such as stripline and coplanar waveguide transmission lines. They can even combine multiple different transmission lines in the same PCB antenna design.
Many suppliers offer PCB antennas as manufacturing components that can be added to system design; some manufacturers also offer services for building PCB antennas based on computer-aided engineering (CAE) design documents or custom mechanical requirements. For example, Advanced Circuitry International (ACI) can make large antennas (for lower frequencies) or large small antennas on large boards, such as 12 x 18 inches and 18 x 24 inches, using single-sided, double-sided and multi-layer PCBs. Antenna configuration (Figure 1).
Figure 1. Some manufacturers offer extended functionality to fabricate PCB antennas on a variety of circuit materials based on customer precise requirements. (available from Advanced Circuitry InternaTIonal)
ACI manufactures antennas on a variety of substrate materials, including DuPont's high-performance flexible circuit materials and RF/microwave circuit laminates from leading circuit material suppliers such as Yalong, Isola, Rogers and Taconics.
PCB antennas are often equipped with an adhesive to simplify installation in the intended application. Choosing such circuit materials as the basis for PCB antennas is critical to their performance, especially when PCB antennas are used for higher mmWave frequencies and harsher operating environments (eg, ADAS applications).
In some cases, PCB antennas are provided as "components" with connected coaxial cables and connectors for quick and easy interconnection with internal boards. One of the PCB antenna suppliers, TE ConnecTIvity, has developed a wide range of PCB antennas with cables and connectors for various frequency bands for personal communication system applications.
Specifically, TE ConnecTIvity's Model 2118060-1 PCB Antenna Assembly (Figure 2). It provides operating frequencies of approximately 2.4 to 2.5 GHz for Bluetooth, Wi-Fi and Wireless Local Area Network (WLAN). The cable length is 13.78 inches (350 mm) and different types of connectors are available, such as MCIS and MHF connectors; the PCB antenna includes an adhesive for mounting on a flat surface.
Figure 2. The PCB antenna is considered a component with interconnecting cables and connectors and adhesives for easy integration and installation in different applications. The antenna assembly (model 2118060-1) is designed for 2.4 to 2.5 GHz. (provided by TE ConnecTIvity)
Similarly, Taoglas Antenna Solutions' FXP07.07.0100A is a thin flexible PCB antenna with a shorter cable length and IPEX connector and tape for easy attachment on a flat surface (Figure 3). Compliant with the RoHS standard for “five-frequency” frequency antenna designs, the frequency bands include AMPS from 824 to 896 MHz, GSM from 880 to 960 MHz, DCS from 1710 to 1880 MHz, PCS from 1850 to 1990 MHz, and UMTS from 1710 to 2170 MHz. The compact 50Ω antenna measures 41 x 24 mm and features linear polarization and omnidirectional radiation.
Figure 3. This thin PCB antenna assembly supports multiple frequencies from 824 to 2170 MHz. (provided by Taoglas Antenna Solutions)
One growing trend in PCB antenna design is multi-band coverage to accommodate systems with wideband frequency ranges or multiple applications. For example, Pulse Electronics' CW3315B0100 series flexible PCB antennas use dual-band Wi-Fi antennas designed to cover WLAN bands from 2.4 to 2.5 GHz and 4.90 to 5.85 GHz (Figure 4).
Figure 4. This miniature flexible PCB antenna assembly is designed to cover WLAN bands from 2.4 to 2.5 GHz and 4.90 to 5.85 GHz. (provided by Pulse Electronics)
This is also a PCB antenna assembly with a 100 mm cable and a standard IPEX connector for easy connection to the application. The miniature antenna assembly provides antenna efficiency above 50% and is designed for internal installation of Wi-Fi products. The dual-band/broadband coverage of the CW3315B0100 is a representative example of the practical application of industrial applications and IoT devices as well as public safety devices.
Although the use of adhesives to mount such miniature PCB antennas is very easy, it can sometimes result in the absence of any type of ground plane, which reduces antenna efficiency. While the underside of the PCB antenna laminate is typically a ground plane, the larger ground plane required for higher efficiency may increase the physical size of the PCB antenna, which must be considered when the antenna is installed in an application.