Emerson Estridge admitted four counts of corruption while he was working for the force, at a court hearing on December 4 last year.
The 45-year-old resigned from the force in June 2019 after the allegations came to light. A hearing held on July 2, 2019 found that he would have been dismissed had he not resigned.
He had served as a response constable in Solihull but moved to the operational support unit shortly before he was arrested for misconduct in a public office in March last year.
Estridge was originally charged with six counts of improper use of his police powers and privileges and one count of sexual assault.
He preyed on victims of crime he met while on duty, to develop personal and sexual relationships. He admitted sending flirtatious texts and photos and having sex on one occasion, while on duty.
Estridge, from Highland Road, Leamington Spa, was sentenced to 18 months in jail at Birmingham Crown Court.
Deputy Chief Constable Vanessa Jardine said: “Estridge took advantage of his position as a member of West Midlands Police to pursue improper relationships for sexual and emotional gain. This was completely unacceptable and a clear breach of the standards of professional behaviour.
“A proactive investigation by our Counter Corruption Unit identified the gravity of offending and led to Estridge pleading guilty.
“It is disappointing we’ve recently seen two ex-colleagues convicted after developing inappropriate relationships with people they’ve met while at work. There is no place for this type of behaviour in our organisation.
“Estridge abused his position, his actions were appalling and my thoughts are with the people affected by them.
“Serving and protecting the public is paramount and it is vital that our communities have the utmost trust and confidence in everything that we do."