As a design engineer at keyfobprog.com, I’m currently developing a key fob for a vehicle’s Remote Keyless Entry (RKE) system. My approach involves utilizing the RF430F5978 RF transceiver and implementing a PCB trace antenna operating at 434MHz. Given the handheld nature of key fobs and potential for antenna detuning due to user interaction, I believe a small magnetic loop antenna, also known as a Frame Antenna For Key Fob, is the most suitable choice.
Having limited prior experience in antenna or RF system design, I am seeking expert feedback on my current design to ensure its robustness and effectiveness before proceeding to the build phase.
My design is based on the Texas Instruments reference design for the RF430 family (https://www.ti.com/lit/an/slaa462a/slaa462a.pdf) for the fundamental RF output stage at 434 MHz. To minimize component count and PCB footprint, I’ve opted for an integrated filter and balun from Johanson Technology (https://www.johansontechnology.com/datasheets/0433BM15A0001E-AEC/0433BM15A0001E-AEC.pdf) as a replacement for the discrete LP filter and balun. For the frame antenna for key fob design itself and its matching network, I consulted a Microchip application note (http://ww1.microchip.com/downloads/en/appnotes/00868a.pdf). This resource aided in estimating component values and devising a tapped capacitor matching circuit for the loop antenna configuration. The resulting schematic is depicted below:
Schematic of the frame antenna for key fob design, detailing components and connections.
To facilitate testing and measurement, a UFL connector (J2) has been incorporated, along with provisions for removable components on either side. Additionally, resistors (RF10 and RF13) are included in parallel and series with the loop antenna, respectively, to provide flexibility for impedance tuning if necessary.
The PCB trace for the frame antenna for key fob is designed to follow the PCB outline edge, maximizing the loop area within the key fob’s form factor. The trace width is 2.032mm, and the total trace length is 12.89cm, enclosing an area of 11.68cm^2. Based on these dimensions, the estimated inductance is calculated to be 92.10nH, and the capacitance to be 1.467pF.
In light of this design approach for a frame antenna for key fob, I would greatly appreciate insights on the following:
- Does this overall design strategy appear to be a sound approach for a key fob application?
- Are there any critical considerations or potential oversights in this design that I should be aware of?
- Do the calculated component values for the matching network seem reasonable and appropriate for this frame antenna for key fob implementation?
Your expert feedback and guidance would be invaluable in ensuring the success of this key fob design. Thank you for your time and consideration.
