Badge size varies between 18 and 20 mm.
"Early" badges.
1st variation.
Reverse
賛助員會章 - Supporting Member of Association Badge
財團法人 - Foundation
大日本防空協會 - Dainippon Air Defense Association
Hot enamel + light metal alloy.
Original case.
Size 55 x 45 mm.
Another example of 1st...
dainippon air defense association
dainippon air defense association badge
great japan air defense association
great japan air defense association badge
greater japan air defense association badge
japanese air defense association badge
japanese air defense badge
japanese air defense maneuvers badge
supporting member badge
大日本防空協会大日本防空協会徽章
賛助会員章
The badge has the same design as special member badge https://asiamedals.info/threads/special-member-badge.23257/
Only suspension has reverse color scheme and reverse insciptions are different.
Suspension of regular member badge.
Suspension of special member badge.
Early "heavy" badges...
dainippon air defense association
full member badge
great japan air defense association
japanese air defense badge
regular member badge
大日本防空協会大日本防空協会正会員章
大日本防空協会章
正会員章