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CC-ANTENNA-DK2: 2.4 GHz PCB Trace Antenna Board #2

AB Singh
Prodigy 120 points
Part Number: CC-ANTENNA-DK2
Other Parts Discussed in Thread: CC2340R2, CC2511

Tool/software:

Hello Tech team,

I am planning to use the PCB Antenna designed in the Board #2 for one of my company's product. The item is a Remote Control unit based on the 2.4 GHz BLE signal. The DK2 has shown the dimensions of the Board 35 x44 mm, and the GND 26x34 mm. My goal is to keep the Remote size as small as possible. We don't need much bandwidth. The communication between the Remote and the main Device (under development) is minimal. Just like a car FOB, the user will push a button, and the device will respond if it is in the range. Only a few bytes of data will be transmitted - intermittently. After the Device receives the signal, it may send the Acknowledge signal approx. 10 times and then sit in the idle mode.

Q1) I want to use one AAA cell to power the Remote. Its length is 44.5mm. Can I place it vertically by the side of the PCB? looking at the board image, it appears the width of antenna is about 10mm less than the board. So, is the 5mm clear-out distance between the antenna and the cell is enough?

Q2 If I have to change the board size (make it wider and perhaps longer), how would it affect the performance? I am mostly concerned about the Range. We are planning to use TI's CC2340R2 Soc, which has a Link Budget of 110 dBm (shown in the datasheet).

Q3) The DK2 states that I would have to use matching components for changed board size. There are only 2 components - Z6 and Z7. How do I calculate the values of these?

Q4) Can I install SMT type electronic components on the PCB top layer? In that case, the metal layer won't be continuous. Would it affect the performance?

Q4) I read in section 2.6.1 of DK2 that the "Total Radiated Power" for board #2 is -1.96 dBm. This raised a question in my mind - What is the maximum power this antenna can radiate? Because we want to use the antenna with CC2340R2 which has max. output power of +8dBm, which would give us much higher transmission range. Please clarify.

Since I am new to RF design, sorry I had to ask these basic questions.

Thanks.

AB singh

 

  • 0
    TI__Expert 6520 points

    Hello,

    No worries, none of these questions is basic. RF design is quite a complex topic. Let’s look at each of the questions in turn:

    1) To achieve performance similar to what is shown in the design guide I recommend designing the board size to be as close as possible. Placing the battery as noted should be ok but may have an effect on the antenna which would need to be compensated for by adjusting the matching components.

    2) Generally speaking as long as you aren't making the board and ground reference plane for the antenna smaller then you won't have a significant negative effect on efficiency and range. You may change the directivity of the antenna though.

    3) a couple of points here, this antenna design only had two matching components. It may be beneficial to consider three matching components in a pi-network to give more flexibility to the antenna match. For determining the matching components there’s a process that’s described in this application note: https://www.ti.com/lit/an/swra726/swra726.pdf

    4) As far as I know the upper limit for power handling for this antenna hasn’t been evaluated. But it’s would be in far excess of the power levels we’re thinking about for these types of parts (i.e. maximum power output of 20dBm). For the value you’re quoting (-1.96dBm) this is the total power radiated as integrated from all directions around the device. This would be at an output power of 0dBm from the device. This is where the efficiency is derived from - 0dBm = 1mW and -1.96dBm = 0.63mW and Pin/Pout, 0.63mW/1mW = 0.63 or 63% efficiency. See 2.2.1 from the design guide. So if you’re transmitting at 8dBm then with this exact design you can expect to radiate around 6dBm at 2.40GHz on average. Somewhat less at 2.44GHz and 2.48GHz

     BR,

    Jake

  • 0 in reply to Jake Pulliam
    Prodigy 120 points

    Hello Jake,

    Thanks for ur reply. You have resolved some of my issues. I have downloaded the App Note about Impedance Matching, and will take my time to read and understand it. If I have questions, I may ask later. However, I made a mistake and used Q4 label twice. And one of my questioned was not answered. I am repeating that here:

    Q4) Can I install SMT type electronic components on the PCB top layer? In that case, the metal layer won't be continuous. Would it affect the performance?

    I have seen SMT electronic components installed near the antenna on the PCB, leaving a small distance between the antenna and the components; I think this distance is 5-10mm. But I don't know how it affects the antenna. So, I had to ask this question. 

    Thanks.

  • 0 in reply to AB Singh
    TI__Expert 6520 points

    Hello,

    Yes components can be installed on the top layer. There should still be a continuous (or as continuous as possible) ground layer on the bottom. You can review our reference designs for any of our SimpleLink CCxxxx product to see examples of how we've done this. If there's any concern please take advantage of our design review process via https://www.ti.com/tool/SIMPLELINK-2-4GHZ-DESIGN-REVIEWS

    BR,

    Jake

  • 0 in reply to Jake Pulliam
    Prodigy 120 points

    Hello Jake,

    Thanks for all your help. Reviewing TI's website, I found AN043. This antenna is smaller than the previous one I found, and also has a USB connection port. We are designing 4-5 BLE products. One of them needs to have a USB port for connection to a computer. The AN043 design is using CC2511, which has built-in USB. But we plan to use CC2340R which does not have. Can you suggest a suitable low cost way to create a USB port? So far, I have not been able to find any suitable IC on Digi-Key.

    Thanks.

  • 0 in reply to AB Singh
    TI__Expert 6520 points

    Hi AB,

    I'm not an expert in USB, but as far as I know TI doesn't offer a serial to USB IC any longer. There are some examples of using our low cost MSP430 MCUs for a USB to UART bridge, such as https://www.ti.com/lit/ab/slaae31/slaae31.pdf but you would need to reach out to that team on the forum for any questions regarding feasibility for your application.

    BR,

    Jake

  • 0 in reply to Jake Pulliam
    Prodigy 120 points

    Hello Jake, I have found a USB-UART part CY7C65213 by Cypress. Since USB connectors are evolving (Now USB-C is becoming popular), we decided not to use this I/F. So, now we are planning to use SPI to Ethernet chip W5500 by Wiznet. Wired This I/F should also be faster.

    Thanks.