1. Field of the Invention
The present invention relates to a digital receiving antenna device and more particularly to a digital receiving antenna device for a digital television.
2. Description of Related Art
Digital televisions require a digital receiving antenna device to receive digital program signals so the televisions can display the video and play the audio. For portable digital televisions, the digital receiving antenna device is particularly important to provide good quality of the program video.
With reference to
The flat antenna (51) is mounted in the casing (50) and has a feed point (A) and a ground point (B). The feed point (A) and ground point (B) are respectively connected to a core conductor (61) and a braided layer (62) of the coaxial cable (60) respectively through the first and second transmission lines (522, 523). Since impedance of the flat antenna (51) and the impedance of an antenna signal processing circuit (not shown) must be matched, the antenna signal can be completely transmit to the antenna signal processing circuit. Therefor, in addition to the impedance of the flat antenna (51) and the antenna signal processing circuit, impedance of the first and second transmission line (522, 523) has to been considered.
Digital televisions have different sizes, and different sizes of digital receiving antenna devices are required. With further reference to
The flat antenna (50a) is a distance from the coaxial cable (60), which is longer than that of the smaller digital receiving antenna device (50). Consequently, a longer first transmission line (522a) is required to connect between the large flat antenna (511a) and the external coaxial cable (60). Therefore, a new impedance of the longer first transmission line (51a) is generated and the antenna signal processing circuit is not adapted to use the large antenna device since the impedance no longer matches. In brief, the large rectangular antenna needs to use a tailored antenna signal processing circuit.
Since different rectangular passive antenna devices do not use the same antenna signal processing circuit, fabricating cost of the passive digital antenna device will be increased.
The present invention provides a digital receiving antenna device that has a fixed impedance to overcome the problem with mismatched impedance with the antenna signal processing circuit in different size digital receiving antenna devices.
The main objective of the present invention is to provide a digital receiving antenna device with a fixed impedance to match the impedance of an antenna signal processing circuit.
A digital receiving antenna device is connected to a digital television through a coaxial cable and has a casing, a flat antenna, a coaxial cable connector and a coaxial transmission line. The flat antenna is mounted in the casing and connected electronically to the coaxial cable through the coaxial transmission line. Since the coaxial transmission line has a fixed capacitance without regard to the distance between the feed point and the coaxial cable connector, a fixed capacitor is connected between the flat antenna and the coaxial cable connector. Therefore, the coaxial transmission line can be used as a transmission line for different size flat antennas, and each coaxial transmission line will have the same impedance. These different size digital receiving antenna devices can use the same antenna signal processing circuit and still have an impedance match between the flat antenna and the antenna signal processing circuit.
Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
With reference to
With further reference to
The coaxial cable connector (11) is mounted through the casing (10), protrudes inside and outside the casing (10) and has an inner conductor (111) and multiple outer conductors (112). At least one outer conductor (112) is connected between the ground point (22) of the flat antenna (20) and the braided layer of the external coaxial cable (30).
With further reference to
Since the coaxial transmission line (23) mounted inside has a fixed capacitance, the capacitance is the same without regard to the distance between the feed point and the coaxial cable connector. When the feed point (21) of the flat antenna (20) is connected electronically to the external coaxial cable (30) through the coaxial transmission line (23) mounted inside the casing (20), a fixed capacitance (C) is connected between the feed point (21) and the external coaxial cable (30). Therefore, a large digital receiving antenna using a coaxial transmission line to connect between the large flat antenna and the external coaxial cable has the same impedance as different size digital receiving antenna using a coaxial transmission line because the coaxial transmission lines have the same capacitance. Therefore, different size digital receiving antenna devices can use the same antenna signal processing circuit because the impedance of the flat antenna matches the antenna signal processing circuit.
Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.