under-the-radar       
adjective [ before noun ] uk/ˌʌn.də.ðəˈreɪ.dɑːr/ us/ˌʌn.dɚ.ðəˈreɪ.dɑːr/ (also below-the-radar, beneath-the radar)
 无人知晓的|低调的
ignored or not noticed much by people in general
  The boutique specializes in trendy and under-the-radar brands. 这家流行服饰店专营时尚小众品牌。 
 The couple's wedding ceremony was very much a below-the-radar affair. 这对夫妻的婚礼几乎无人知晓。 
 See also: radar
 - More examples
 - This under-the-radar Sri Lankan-inspired restaurant is truly a hidden gem.
 - To fully appreciate her as an artist, you have to see one of the low-key, under-the-radar cabaret gigs in her native New York.
 - The Democratic contest has been largely an under-the-radar race.
 - It took a delicate, below-the-radar diplomatic mission by Lott to end the stalemate.
 - He has, until recently, been a somewhat beneath-the-radar figure.