What is this type of radio fm antenna connector called?
Assuming the ruler is showing millimeters, I'd say that the connector is of JST-XH-2.5 mm type with two pins.  Sometimes, these connectors are sold and marked with 2.54 mm in their name, since that is a common spacing for inch-based measurements. Such connectors are commonly used for battery packs, so you might be able to find one, or a cable with one attached, in stores that sell equipment for radio-controlled planes/cars/boats etc.

My guess is that the radio was intended for use with a small loop antenna, such as one depicted in this photo from Wikipedia:



Most likely, two ends of such antenna would be connected to the appropriate female connector and then plugged into the radio.