  Context. Aalto University Mets\"ahovi Radio Observatory has collected solar
intensity maps for over 45 years. Most data coverage is on the 37 GHz frequency
band, tracking emissions primarily at the chromosphere and coronal transition
region. The data spans four sunspot cycles or two solar magnetic cycles. Aims.
We present solar maps, including recently restored data prior to 1989, spanning
1978 to 2020 after correcting for observational and temporal bias. Methods. The
solar maps consist of radio intensity sampled along scanlines of the antenna
sweep. We fit a circular disk to the set of intensity samples, neglecting any
exceptional features in the fitting process to improve accuracy. Applying a
simple astronomical model of Sun and Earth, we assign each radio specimen its
heliographic coordinates at the time of observation. We bin the sample data by
time and heliographic latitude to construct a diagram analoguous to the classic
butterfly diagram of sunspot activity. Results. Radio butterfly diagram at 37
GHz, spanning solar cycles 21 to 24 and extending near to the poles.
Conclusions. We have developed a method for compensating for seasonal and
atmospheric bias in the radio data, as well as correcting for the effects of
limb brightening and beamwidth convolution to isolate physical features. Our
observations are consistent with observations in nearby bandwidths and indicate
the possibility of polar cyclic behaviour with a period exceeding the solar 11
year cycle. Key words. Solar physics, radioastronomy, butterfly diagram, solar
cycle
