Why is the bridge (WDS) throughput in fat AP mode of the AP620-H low?

Why is the bridge (WDS) throughput in fat AP mode ofthe AP620-H low?

Analysis methods:
1. Check whether the antenna interface is consistent with the connected radio interface.
2. Check whether directions of both antennas are aligned.
3. Check whether the signal RSSI reaches 50 or higher.
4. Check whether the bridging frequency band is 40 MHz.
5. Check whether the connection rate is 300 Mbit/s.
6. Check whether the MIMO antenna is correctly placed.

Solution:
1. Use the confirmed latest version.
2. Check the RSSI to determine whether the antenna is connected to the proper radio interface.
On the root-bridge, run show dot11 ass all to check whether the RSSI is increased.
3. Launch a throughput speed testing as adjusting the antenna direction until it reaches the best performance.
4. If the co-frequency interference exists and the channel needs to be changed, use the 802.11na channels 149, 153, 157, and 161.
5. Set the frequency band of the 802.11na channels to 40 MHz.

On the non-root-bridge, configure the corresponding radio interface.

interface dot11radio 1/0
radio-mode 11na_ht40plus
chan-width 40
channel 149

On the non-root-bridge, run show dot11 wireless 1/0 to check whether the frequency band is 40 MHz.

non-root#show dot11 wireless 1/0
WLAN ID: 0
Network Name (SSID): <NULL>
Interface.................... Dot11radio 1/0(intfcb 0x8fae800, wlan 0x8faec00)
VID.......................... 1
Mac Address.................. 001b.b120.3d0e
Operation Mode............... Access Point
802.11 State................. Associated
Beacon Period................ 100
RTS Threshold................ 2347
Fragement Threshold.......... 2346
Radio Mode................... 11na_ht40minus
Channel...................... 5765(153)
Noise Floor.................. -101 dBm
Channel width................ 40Mhz
Maximum Regulatory Tx Power.. 30 dBm
Maximum Tx Power............. 15 dBm
Minimum Tx Power............. 15 dBm
Tx power limit............... 60 dBm
Current Tx Power Level....... 17 dBm(Auto)
Protection Mode.............. 1(1-CTS/S, 2-RTS/CTS)
A-MPDU Max Length............ 0
Subframe Max Length.......... 0
A-MSDU Max Length............ 0

On the root-bridge, run show dot11 ass all to check whether the RSSI and rate are within the normal range.
root#show dot11 associations all
INTF-IDX ADDR              AID  CHAN RATE   RSSI IDLE TXSEQ  RXSEQ  ERP  STATE  CAPS HTCAPS
0        00:1b:b1:20:3d:0e 1    153    300M 66   120  10     27824  0x0  0x22b  Es   WPS

6. On the same AP, the antenna placement direction and the antenna polarization direction should be on the contrary. Otherwise, the MIMO antennas mutually interference each other. Three antennas of the same AP should be separated with a minimum distance of 20 cm. For example, when the outdoor pot antenna is polarized vertically, the antenna should be placed horizontally.