1. Technical Field
The present invention relates to an array antenna having a structure in which a plurality of antenna elements is arranged in a predetermined fashion. More particularly, the present invention relates to a series-fed phased array antenna which can electronically steer an antenna beam through variation in frequency.
2. Description of the Related Art
Generally, in a radio communication system, an antenna is used to send and receive signals and the length of an antenna depends on the frequency to be transceived. Such antennas have developed into various forms as technology evolves. Recently, many studies have been made to develop a method of using multiple antennas.
Particularly, array antennas having a structure in which multiple antennas are arranged in a predetermined fashion are widely used. Such an array antenna is a device that uses a large number of radiating elements to acquire a narrow beam width and transmit a signal. When using the array antenna at broadband frequency, beam direction, efficiency, unit cost, and the like may vary depending on the type of feed network.
Generally, when a parallel feed network is used, the beam direction is fixed even when the frequency to be transmitted changes. However, as the overall length of the feed network increases, signal loss along a transmission line increases and transmission efficiency drops when the transmission line is constructed using a dielectric substrate. In addition, when a transmission line of a parallel feed network is constructed using a waveguide, the feed network becomes complicated, thereby making it difficult to manufacture the network while increasing manufacturing costs.
Conversely, a series feed network can reduce efficiency loss and manufacturing difficulty as mentioned above and can solve increase in unit price. However, when the series feed network is used, a transmission signal fed to a radiating element, that is, the phase of electromagnetic waves, also changes according to frequency change, and the direction of a main beam also changes. As a result, gain according to frequency changes dramatically to affect transmission and reception. Especially, in the case of a high gain array antenna, this effect is even larger due to very narrow beam width. Therefore, there is a need for a solution to this problem.