How to Design PCB Small Loop Antenna for Remote Control – Part III

In the beginning of post, we should note that the conclusion in blog series is only suitable for sub-GHz remote control loop antenna design – mainly in 290 – 915 Mhz range, having the most popular ISM range included.

In previous second part of this blog series, we have concluded that the remote control PCB loop antenna should cover as large area as possible to achieve the best antenna efficiency, thus the best output transmitting power.

Simply put, there are two main factors in remote control antenna design, one is resistor, the other is inductor, the above step – design as large loop antenna as possible – is to solve the resistor problem, and following steps is to solve inductor problem.

And the next step is to determine one key component’s value – the capacitor value to cancel loop antenna’s inductance, the calculation formula and process can be found on previous post, or you can just use our excel spreadsheet calculator to simplify the process.

The reason why to cancel loop antenna’s inductance is simple, inductance as resistance to high frequency circuit, will weaken the power from being transmitted, so should ideally be reduced to zero, making the current in loop antenna flow without obstacle.

In remote control mass production, we can either use SMD capacitor or use PCB track capacitor, the later can be considered easy to adjust value in small steps, but require some testing to achieve the best results, while the SMD capacitor maybe easier to use, if aiming mainstream market, which means SMD capacitor’s precision is enough.

Also you will notice we have used two 0603 SMD pad positions on each arm of Si4010 power output pin, the positions can be mounted with inductor, zero value resistor or even capacitor depending on different output frequency requirement, these positions is to make sure our PCB board has maximum output frequency capacity, enabling our board to be used from 433 to 868 frequency range.

In this way, we can use several external components to adjust on board capacitors and inductors in a wider range, this is good for production, as we can reuse one hardware design on different RF remote control products, to reduce cost as much as possible.

Conclusion, in the three post blog series, we have described certain way to design PCB loop antenna in practice, which doesn’t require sophisticated instrument, and only require some basic math and one spectrum analyzer, and is suitable for most circumstances in practice.