Multilayer substrate and antenna element

An antenna element, comprising:

• a multilayer substrate comprising;
• a multilayer body including a plurality of dielectric layers being layered;
• a wire conductor in the multilayer body and through which a radio frequency signal passes;
• a first ground electrode that is in or on the multilayer body and that includes a first surface facing a first main surface of the wire conductor;
• a radiation electrode on the multilayer body and that has a main surface facing the first surface of the first ground electrode;
• and
• a via conductor that extends in the direction normal to the first surface of the first ground electrode and that connects the wire conductor to the radiation electrode, wherein
• the radiation electrode is electrically connected to the wire conductor,
• the first surface includes a first region and a second region,
• a surface roughness of the first region is lower than a surface roughness of the second region,
• the first region overlaps at least part of the first main surface of the wire conductor in plan view in a direction normal to the first surface of the first ground electrode
• the first ground electrode includes a third surface that faces the main surface of the radiation electrode,
• the third surface includes a fifth region and a sixth region,
• a surface roughness of the fifth region is lower than a surface roughness of the sixth region, and
• the fifth region overlaps at least part of the main surface of the radiation electrode in plan view in the direction normal to the first surface of the first ground electrode.

An antenna element, comprising:

• a multilayer substrate;
• and
• a radiation electrode on the multilayer substrate and that radiates a radio frequency signal, wherein
• the multilayer substrate includes
• a multilayer body including a plurality of dielectric layers being layered and
• a first ground electrode in or on the multilayer body and that includes a first surface facing a main surface of the radiation electrode,
• a wire conductor in the multilayer body and through which the radio frequency signal passes, and
• a via conductor that extends in the direction normal to the first surface of the first ground electrode and that connects the wire conductor to the radiation electrode,
• the first surface includes a first region and a second region,
• a surface roughness of the first region is lower than a surface roughness of the second region,
• the first region overlaps at least part of the main surface of the radiation electrode in plan view in a direction normal to the first surface of the first ground electrode,
• the first ground electrode is between the radiation electrode and the wire conductor,
• the first ground electrode further includes a second surface that faces a main surface of the wire conductor,
• the second surface includes a third region and a fourth region,
• a surface roughness of the third region is lower than a surface roughness of the fourth region, and
• the third region overlaps at least part of the main surface of the wire conductor in plan view in the direction normal to the first surface of the first ground electrode.