1. Field of the Invention
Apparatuses consistent with the present invention relate to a loop antenna having a matching circuit integrally formed. More particularly, the present invention relates to a loop antenna having a matching circuit integrally formed thereon to facilitate design and modification of the matching circuit and reduce the antenna size.
2. Description of the Related Art
Mostly, loop antennas are formed in a loop shape such as quadrangle and circle, and utilized in various fields according to the antenna length.
The loop antenna features low input resistance. The design of the loop antenna should take account of its length to match to input resistance 50Ω of the general antenna.
As for the square loop antenna, the input resistance approximates 50Ω and the input reactance approximates zero when the loop length is close to one wavelength in the impedance curve. That is, only when the length of the loop antenna is designed to one wavelength, resonance is generated to the loop antenna.
Also, a radiation pattern of the loop antenna differs depending on the length of the loop antenna. For instance, when the length of the loop antenna is shorter than one wavelength, the radiation is produced along the plane of the loop antenna. When the length of the loop antenna is longer than one wavelength, the radiation is generated perpendicular to the plane of the loop antenna. Thus, in order to regulate the radiation pattern of the loop antenna, the length of the loop antenna is adjusted.
Yet, in adjusting the radiation pattern by making the length of the loop antenna shorter or longer than one wavelength, it is hard to match the input resistance and the input reactance because of the properties of the loop antenna. Accordingly, when the length of the loop antenna is shorter or longer than one wavelength, a separate matching circuit is required for the matching of the input resistance and the input reactance.
However, space is required for the installation of the separate matching circuit. Additionally, after mounting the matching circuit on the device, it is not easy to change the design of the matching circuit because of the interaction with other circuit elements.
Therefore, it is desirable to reduce the size of the device having the loop antenna and facilitate the design of the matching circuit by minimizing the space occupied by the matching circuit at the design phase of the loop antenna.