On 3700 series, and probably some others, you can only have max two SSIDs on the same VLAN. One SSID per radio on the same VLAN. If you wan’t to have multiple SSIDs per radio, you’ll have to use different VLANs – this is the recommended option.

This is basic setup (wifi only) for home networks with only one VLAN (or access point connected to access port – untagged port). First SSID on 2.4 GHz radio and second SSID on 5 GHz radio, both in the same VLAN.

Setup 2.4 GHz:

3702-1N#conf t
3702-1N(config)#dot11 ssid HOMEWIFI2.4
3702-1N(config-ssid)#vlan 1
3702-1N(config-ssid)#authentication open
3702-1N(config-ssid)#authentication key-management wpa version 2
3702-1N(config-ssid)#wpa-psk ascii 0 YOUR_WIFI_PASSWORD
3702-1N(config-ssid)#mbssid guest-mode

3702-1N(config-ssid)#interface Dot11Radio0
3702-1N(config-if)#mbssid
3702-1N(config-if)#encryption vlan 1 mode ciphers aes-ccm
3702-1N(config-if)#ssid HOMEWIFI2.4
3702-1N(config-if)#no shut

3702-1N(config-if)#interface dot11radio 0.1
3702-1N(config-subif)#encapsulation dot1q 1 native
3702-1N(config-subif)#bridge-group 1
3702-1N(config-subif)#no shut

3702-1N(config-subif)#interface gigabitethernet0.1
3702-1N(config-if)#encapsulation dot1q 1 native
3702-1N(config-if)#bridge-group 1

Setup 5 GHz:

3702-1N#conf t
3702-1N(config)#dot11 ssid HOMEWIFI5
3702-1N(config-ssid)#vlan 1
Warning: Vlan 1 already mapped to SSID HOMEWIFI2.4. SSIDs with same 
vlan association cannot be attached to the same interface.
You can ignore this error, since you are going to use another interface for HOMEWIFI5.
3702-1N(config-ssid)#authentication open
3702-1N(config-ssid)#authentication key-management wpa version 2
3702-1N(config-ssid)#wpa-psk ascii 0 YOUR_WIFI_PASSWORD
3702-1N(config-ssid)#mbssid guest-mode

3702-1N(config-ssid)#interface Dot11Radio1
3702-1N(config-if)#mbssid
3702-1N(config-if)#encryption vlan 1 mode ciphers aes-ccm
3702-1N(config-if)#ssid HOMEWIFI5
3702-1N(config-if)#no shut

3702-1N(config-if)#interface dot11radio 1.1
3702-1N(config-subif)#encapsulation dot1q 1 native
3702-1N(config-subif)#bridge-group 1
3702-1N(config-subif)#no shut

The actual config (wifi only):

!
dot11 ssid HOMEWIFI2.4
   vlan 1
   authentication open
   authentication key-management wpa version 2
   mbssid guest-mode
   wpa-psk ascii 7 YOUR_HASHED_WIFI_PASSWORD
!
dot11 ssid HOMEWIFI5
   vlan 1
   authentication open
   authentication key-management wpa version 2
   mbssid guest-mode
   wpa-psk ascii 7 YOUR_HASHED_WIFI_PASSWORD
!
interface Dot11Radio0
 no ip address
 !
 encryption vlan 1 mode ciphers aes-ccm
 !
 ssid HOMEWIFI2.4
 !
 antenna gain 0
 mbssid
 station-role root
!
interface Dot11Radio0.1
 encapsulation dot1Q 1 native
 bridge-group 1
 bridge-group 1 subscriber-loop-control
 bridge-group 1 spanning-disabled
 bridge-group 1 block-unknown-source
 no bridge-group 1 source-learning
 no bridge-group 1 unicast-flooding
!
interface Dot11Radio1
 no ip address
 !
 encryption vlan 1 mode ciphers aes-ccm
 !
 ssid HOMEWIFI5
 !
 antenna gain 0
 peakdetect
 no dfs band block
 mbssid
 channel width 80
 channel dfs
 station-role root
!
interface Dot11Radio1.1
 encapsulation dot1Q 1 native
 bridge-group 1
 bridge-group 1 subscriber-loop-control
 bridge-group 1 spanning-disabled
 bridge-group 1 block-unknown-source
 no bridge-group 1 source-learning
 no bridge-group 1 unicast-flooding
!
interface GigabitEthernet0
 no ip address
 duplex auto
 speed auto
!
interface GigabitEthernet0.1
 encapsulation dot1Q 1 native
 bridge-group 1
 bridge-group 1 spanning-disabled
 no bridge-group 1 source-learning
!
interface BVI1
 mac-address 1a1a.1f1f.1c1c
 ip address dhcp client-id GigabitEthernet0
 ipv6 address dhcp
 ipv6 address autoconfig
 ipv6 enable

This AP support 80 MHz channel width on 5 GHz band. Enable it for maximum troughput, but do it only in non dense wifi areas, where there is less chance for radio interference. It’s recommended to keep it on 40 Mhz or even 20 Mhz in very dense wifi areas.

3702-1N#conf t
3702-1N(config)#interface dot11Radio 1
3702-1N(config-if)#channel width 80

Don’t forget to save the config:

3702-1N#wr
Building configuration...
[OK]

My WAN connection is maxed out during speed test on Google Pixel 3XL (wifi card specs: 802.11 a/b/g/n/ac 2×2 MIMO).