High-frequency transmission line and antenna device
An antenna is connected to a first end of a high-frequency transmission line, and a connector is connected to a second end of the high-frequency transmission line. A characteristic impedance of a microstrip line is higher than characteristic impedances of first and second strip lines, and a characteristic impedance of a coplanar line is higher than a characteristic impedance of the second strip line. Thus, at a certain frequency, a standing wave develops in which the position of the microstrip line and the position of the coplanar line are maximum voltage points and three-quarter-wavelength resonance is a fundamental wave mode. Thus, the cutoff frequency of the high-frequency transmission line is high, and an insertion loss of a signal is significantly reduced to be low over a wide band.
1. A high-frequency transmission line comprising:
a first end that is a low-impedance end;
a second end that is a high-impedance end;
a low-impedance portion including a strip line; and
a high-impedance portion having a characteristic impedance higher than the low-impedance portion and including a microstrip line or a coplanar line; wherein
the high-frequency transmission line is bent at the high-impedance portion and is not bent at the low-impedance portion.
2. The high-frequency transmission line according to claim 1 , wherein
the strip line includes ground electrodes; and
at least one of the ground electrodes is not located in the high-impedance portion.
3. The high-frequency transmission line according to claim 1 , wherein a total length of the low-impedance portion is larger than a total length of the high-impedance portion.
4. The high-frequency transmission line according to claim 1 , wherein the low-impedance end is an antenna connection end, and the high-impedance end is a connector connection end.
5. The high-frequency transmission line according to claim 1 , wherein
the low-impedance portion and the high-impedance portion include a multilayer body including a plurality of dielectric layers and a plurality of line conductors; and
the high-impedance portion has a smaller number of dielectric layers than the low-impedance portion.
6. An antenna device comprising:
a high-frequency transmission line including:
a first end that is a low-impedance end;
a second end that is a high-impedance end;
a low-impedance portion including a strip line; and
a high-impedance portion having a characteristic impedance higher than the low-impedance portion and including a microstrip line or a coplanar line; and
an antenna element connected to the low-impedance end; wherein
the high-frequency transmission line is bent at the high-impedance portion and is not bent at the low-impedance portion;
the high-frequency transmission line further includes a multilayer body including a plurality of dielectric layers and a plurality of line conductors; and
the antenna element is provided in the multilayer body integrally with the high-frequency transmission line.
7. The antenna device according to claim 6 , wherein
the strip line includes ground electrodes; and
at least one of the ground electrodes is not located in the high-impedance portion.
8. The antenna device according to claim 6 , wherein a total length of the low-impedance portion is larger than a total length of the high-impedance portion.
9. The antenna device according to claim 6 , wherein the low-impedance end is an antenna connection end, and the high-impedance end is a connector connection end.
10. The antenna device according to claim 6 , wherein the high-impedance portion has a smaller number of dielectric layers than the low-impedance portion.