Planar antenna module, triple plate planar array antenna, and triple plate feeder - waveguide converter

The present invention provides inexpensively a planar antenna module that is able to realize a loss reduction, a reduction in characteristic variation caused by an assembling error, and an improved stability in frequency characteristics. A planar antenna module according to one preferred embodiment of the present invention comprises an antenna portion (101), a feeder portion (102), and a connection plate (18). The antenna portion (101) includes a first ground plate (11) having a first slot (21), a second ground plate (12) having dielectrics, an antenna substrate having a radiation element (41), a third ground plate (13) having dielectrics, a fourth ground plate (14). The feeder portion (102) includes the fourth ground plate (14), a fifth ground plate (15), a feed substrate (50), a sixth ground plate (16), a seventh ground plate (17). The connection plate (18) has a second waveguide opening portion (64). The connection plate (18) to be connected with a high frequency circuit, the seventh ground plate (17), the sixth ground plate (16), the feed substrate (50), the fifth ground plate (15), the fourth ground plate (14), the third ground plate (13) including the third dielectric (33) and the fourth dielectric (34), the antenna substrate (40), the second ground plate (12) including the first dielectric (31) and the second dielectric (32), and the first ground plate (11) are stacked in this order.