Stereo OR MONO microphone in Parabola?

Which type of microphone inside the parabolic dish: Stereo, Mono, or Twin Mono? As already stated by Wahlström (Sten Wahlström, Swedish Radio, Karlstad, Sweden, JAES Volume 33 Issue 6 pp. 418-429; June 1985), acquire a stereo effect using a parabolic microphone system is possible,…