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CC2640R2F: Recommended integrated chip antennas for CC26xx BT wireless controllers

DMM
Intellectual 290 points
Part Number: CC2640R2F
Other Parts Discussed in Thread: CC2640, CC2650

Hello:

I wanted some help in finding a recommended RF chip antenna for the CC26xx BT wireless controllers. Due to severe space constraints, I plan to use "Johanson Technology Inc. 2450BM14G0011 balun optimized for Texas Instruments'  CC26xx Wireless MCUs Operating on Differential RF with INTERNAL BIAS". I will connect this balun to the chip antenna.

I have researched out a few chip antenna choices from Digikey but there are simply too many choices and my RF antenna expertise is close to none. The JTI balun has about a loss penalty or insertion loss (S21) of 2dB. I want an antenna that could potentially compensate for these losses without incurring other penalties, if possible. If not, that's ok.

What type of antennas would you recommend to use for the wireless micros (assume price is not much of a factor)? I also see that antenna lengths vary in length from 3mm to 7mm long, which affects some aspect of their performance(?). Is this something to worry about?

Assume a VSWR <= 2.0 .... What are some of the reasons and criteria are you using to select the appropriate chip antenna?

 

Thanks,

David

 

PS

The chip antenna you used in your BOOSTXL-CC2650MODA plug-in module is no longer available for purchase. Besides, it also seems a bit tall for my application. It seems to be 7mm long.

 

 

  • 0
    TI__Mastermind 33190 points

    Hi David,

    What is the area available for just the antenna ?

    Can you share your layout or a picture just for the antenna area ?

    Is the small 2.4 GHz PCB antenna AN043 an option ?

    For all types of antenna, chip pcb, wire etc. The antenna generally needs to be tuned especially when the size is small since this normally means that the antenna has a limited bandwidth as well. If you do choose a chip antenna, I would recommend to choose a vendor that can assist with tuning as well. Johanson Technology, Fractus and ProANT offer matching services and can recommend all these vendors. 

    When comparing performance it is important to compare the GND plane size as well. This is mostly valid for sub-1 GHz frequencies due to the wavelength. Many antenna chip vendors offer a large test board and show good efficiency. When the antenna is then ported into a small compact design, the efficiency will naturally drop and this has to be taken into account when choosing an antenna or calculating a link budget.

    Regards, Richard

  • 0 in reply to RGW
    Intellectual 290 points

    Richard,

    Thank you for answering my questions so quickly. I currently don't have a layout or picture of the antenna area since I'm in the beginning stages of my circuit design. But one thing I know is that board area is small. Imagine your favorite ballpoint pen ...and putting a BT PCB inside of it, with minimal changes to the pen's original design. I have wiggle room lengthwise (25mm) but my width is more constrained, probably 12 mm at best. I plan to use the 4mmx4mm sized CC2640 or CC2650 controllers.

    So my entire PCB would be 25mm(L) x 12mm(W) at best...which makes your excellent recommendation of the PCB antenna AN043 unfortunate as its width is too large for my specs.

    1.  Is there a way to design a similar PCB antenna in less than 12mm width but with a much longer meandering trace length?

    2.  If so, will it have comparable performance to a chip antenna?

    3. Using your recommended balun from JTI and a chip antenna, where is the tunability? The return loss specs might look good in free space but once the PCB is placed inside a structure, these specs become worse, so how do I compensate?

    4. Lastly, I don't understand the relationship between antenna frequency and PCB trace length. I know trace width, dielectric constant, ground planes overall PCB stack up determine the 50-ohm impedance. Ideally, if I could have a meandering snake line trace pattern that could fit my needs, that would be best as its free. If not, then a chip antenna will do (at extra cost).

    Any thoughts on the above? Sorry for the many questions... Thanks again!

    Regards,
    David

  • 0 in reply to DMM
    TI__Mastermind 33190 points
    Hi David,

    OK. Understand that the size is restricted considering the pen like layout.

    Have you considered to place a wire antenna inside the pen instead of a PCB antenna or chip antenna ?

    For this compact layout, the antenna basically needs to be as effectively large as possible. Using a wire to run inside the pen casing would allow for a larger antenna and you would achieve a higher antenna efficiency. The only drawbacks with wire antennas, is that the placement should be repeatable for each unit in production. Repeatability can be achieved by using a slightly thicker wire which is more rigid or using a thinner wire that is kept into a certain position by mechanical holders/clips.

    If a wire antenna is not an option, then a chip antenna sounds like it is the best option. I would choose a chip antenna that fits the available volume dedicated for the antenna so that the antenna "fills" the volume size (i.e. width, length and height) as much as possible.

    Even if chip antennas are used they still need to be matched. I would add a pi-network prior to the antenna for matching purposes. The exact match values can only be fixed once the final PCB, casing and choice of material is chosen.

    No worries with many questions. Antennas are tricky.

    Regards,
    Richard
  • 0 in reply to RGW
    Intellectual 290 points
    Thanks for the wire antenna suggestion. I hadn't thought of that option. So you recommend a pi-network match over the 2450BM14G0011 JTI balun optimized for TI processors? If thte latter, would the final tunability be implemented outside the balun, say with a cap in series with the balun and into the antenna or a cap to ground after the balun and connected to the antenna?