Attested marriage certificate is a must.first u get a marriage certificate from ur country's relevant authority. then u have to get attestation from ur country's foriegn affairs and Qatar consulate.After that here u go to ur embassy and get attestation from there then go to Expatriate affairs and get attestation.now the end of the procedure, then u can use that marriage certificate to ur wife's visa.It is very easy to get a visit visa for wife. good luck