Patent ID: 7619578

Claim:
A wideband slot antenna comprising: a dielectric substrate having a front face and a rear face; a ground conductor provided on a rear face of the dielectric substrate, the ground conductor having a finite area; a slot recessing into the ground conductor, in a depth direction from an open point along an outer edge of the ground conductor, one end of the slot being an open end; and a feed line for feeding a high-frequency signal to the slot, the feed line being formed on the front face of the dielectric substrate and at least partially intersecting the slot, wherein, on the front face of the dielectric substrate, an antenna feed point for connecting an external unbalanced feed circuit to the feed line is provided at a position facing an outer edge of the ground conductor opposite from the open point; the feed line is bent by at least 90° within a plane of the dielectric substrate so as to reach the antenna feed point; the slot and the antenna feed point are each disposed at a center of the ground conductor along a width direction which is orthogonal to the depth direction; in an inductive region spanning a length of a ¼ effective wavelength at a resonant frequency fs of the slot from the open end point, a characteristic impedance of the feed line is prescribed to be higher than 50 Ω; the feed line and the slot intersect each other at a center of the inductive region; at a first point near the slot, the feed line branches into a group of branch lines including at least two branch lines, and at least branch line pair in the group of branch lines is connected at a second point near the slot, thus forming at least one loop line in the feed line; the loop line at least partially intersects a border line between the slot and the ground conductor, and the slot is excited at two or more feed points which are at different distances from the open point along the depth direction; a maximum value of a loop length of the entire loop line is prescribed to be a length less than 1× effective wavelength at an upper limit frequency of an operating band; in the group of branch lines, any branch line that does not constitute a part of the loop line but is left open-ended at a leading end has a branch length which is less than ¼ effective wavelength at an upper limit frequency of the operating band; and a distance from the open point to each outer edge at an end of the ground conductor along the width direction is prescribed to a length equal to or less than a ¼ effective wavelength at the frequency fs, and the ground conductor has a lowest-order resonant frequency at a frequency which is lower than fs.