Ask for recommends for selecting a proper gain antennas for wearable device with XBee Wi-Fi

We plan to using XBee Wi-Fi to implement an high speed (3.2 Mbps @10 Meter indoor and 20 Meter outdoor) wireless data acquisition system wearable, which mean two points:
1- the distance from device to human being is less than 20cm;
2- gain antenna should be used to maintain a stable wireless link.

We read page 75~77 of XBee W-Fi Module Guide @90002124_F, and found that too many options to make a proper selection.

1- Dipole Antennas;
2- Omi-directional Antennas;
3- Panel class Antennas;
4- Yagi class Antennas for channel 11~15

All with diversified gain [:((] and range from 2.1 dBi to 19 dBi.

Please kindly indicate any standard to select a proper antenna.

P.S. Is there anyone implement an SPI TO TCP/UDP interface with XBee Wi-Fi in a high data rate (like 3.5 M bit/second)?
Digital data are collected by SPI interface and transmit to Access point or Android smartphone through Wi-Fi.
Hope some suggestion from practical implementation.

Hi William_torino

That will depend on your requirement. As you are using it for data acquisition, then Omi-directional Antennas will give you equal range in all direction while rest all will not give you equal range in all direction.

Thanks a lot for your suggestion. Omi-directional Antennas should be an good option, and the available options from digi are as follow attachment:

From A24-F2NF Omin-Directional (Fiberglass base station) 2.1 dBi
to A24-F15NF Omin-Directional (Fiberglass base station) 15 dBi.

Any suggestion for wearable device ?
From a website keywords with Antenna Gain A Simplified Explanation:
in very simple terms a 3 dBi gain antenna is equivalent to raising transmit power from 10 mW to 20 mW, 5 dBi ~ 33 mW, 8 dBi ~ 66 mW, 12 dBi ~ 160 mW, 15 dBi ~ 320 mW, 18 dBi ~ 640 mW, 21 dBi ~ 1.28 Watts, 24 dBi ~ 2.56 Watts.

Usually, a cellphone has a limitation of 100mW.

I hope that these formulas are correct:
1- from page 8 of the datasheet of XBee Wi-Fi RF Modules version 90002124, the RF transmit power output is >15 dBm, and 15dBm equals to 31.6 mW;
2-while select a gain antenna, consider that in very simple terms a 3 dBi gain antenna is equivalent to raising transmit power from 10 mW to 20 mW, 5 dBi ~ 33 mW, 8 dBi ~ 66 mW. According to the FCC standard (FCC Part 15 ), as following:

Maximum transmitter power versus largest antenna table for PTP (Point-to-Point)
Transmitter RF power Antenna GainM EIRP in watts
30dBm 1W 6dBi 3.98
29dBm 800mW 9dBi 6.35
28dBm 630mW 12dBi 10.14
27dBm 500mW 15dBi 15.81
26dBm 398mW 18dBi 25.23
25dBm 316mW 21dBi 40.28
24dBm 250mW 24dBi 62.79
23dBm 200mW 27dBi 100.2

We could select the gain of antenna higher than 27 dBi.

Which cover all the available antenna by digi, since the highest one is only 19 dBi. Every 3 dBi, will increase the value to 2 times, while 19 dBi means increase the value around 15 dBm into 65 times.

31.6 mW *65 = 2.054 Watt.