PCB patch antenna have received massive acceptance in wireless industries especially after its success and adaptance to impedance match properties. These antennas include applications for wireless applications like Global Positioning System (GPS) receivers, wireless local area network (WLAN) routers, GSM communications, Bluetooth and RF networks, etc.
A patch antenna, which is also known as a micro strip antenna, can be fabricated with standard printed wiring board (PCB) processes using high-frequency laminate materials. An antenna can be as simple as a retangular patch above a ground plane or as elegant as a complex array of patches, customized for a specific radiation pattern. As with other printed circuits, the choice of circuit material can greatly impact the performance possible from the final antenna design. That choice should be guided by a clear understanding of how a circuit material’s electrical and mechanical properties relate to the performance of a patch antenna.
In most of the cases, where PCB patch is placed on PCB itself in a fixed manner, it is really difficult to have impedance matching as feed point is fixed. The concept of VSWR (Voltage Standing Wave Ratio) is introduced as a measure of how well-matched an antenna is to the transmission line. If the impedance of the antenna does not match the impedance of the cable, a part of the signal will reflect from the antenna – back to the source. Standard patch antennas are manufactured by matching to 50Ω input & output impedance on a well-defined Ground plane; on the PCB manufacturers test fixture, in a controlled environment. In real world application when this antenna is placed on the final PCB production, optimization is required. This optimization involves impedance matching in the final product electronic circuit board to optimize the reflection coefficients this website. Further, if the final product is encapsulated or has a metal cover, etc., this optimization accounts for the frequency shift of the patch in the end-product PCB.
From PCB material perspective as well, it is important to have proper dielectric properties to have signal integrity. dielectric circuit material has a part in determining the physical dimensions of a patch antenna needed for resonance at a particular wavelength and, thus, frequency.with higher dielectric constant values resulting in smaller physical dimensions for a given wavelength or frequency for both the feed lines and the antenna patch. The consistency or doel tolerance of a circuit material is also important to consider because variability in the Dielectric constant value results in variability of the canter frequency of a patch antenna formed on that material. In general, a tight dielectric constant of PCB material tolerance is to be preferred for consistent patch antenna centre-frequency performance. A micro strip antenna with smaller patch on higher-Dielectric constant material will provide less gain and less efficiency than a larger patch antenna on lower-Dielectric constant material, with both operating at the same centre frequency. So, the savings in size with the higher-Dielectric constant material can result in a sacrifice in performance. Weight is another factor while deciding PCB for patch antennas.
In case device is being designed for high temperature variant mode, temperature co-efficient of laminate is important to observe. In general, following are three attributes which are altogether responsible for a high performing PCB antenna:
1. Low di-electric constant
2. Low dissipation factor
3. Good thermal conduction