  We present the result of photo-ionizing modelling of the three planetary
nebulae (PNe) A 20, A 15 and MeWe 1-3. All three objects are roughly roundish,
highly excited and have a high galactic $z$. The PNe displayed low densities in
the shell, but relatively dense halos. A low metallicity and a relative high
electron temperature were found. Comparisons with radio observations confirmed
the obtained properties. The objects are very likely originating from thick
disk stellar progenitors. The distances found investigating the PNe shells are
somewhat lower than those derived spectroscopically with the central stars in
the past.
