จะเชื่อมต่อกับโปรแกรมปรับปรุงขับเคลื่อนผ่านช่องที่ reflectors ที่ reflectorsThe concept behind the mechanism of a printed microstrip Yagi array mirrors the idea of coupling energy to additional patches. The microstrip Yagi array is excited through the driven patch, D, and the main beam is tilted to a maximum angle between 33º-42º through capacitively coupling energy to the director1, D1, patches. The main beam angle is mainly controlled by the gap between the driven patch and D1 elements. The high F/B ratio is obtained through the use of two D1 and two director2, D2, patches. The D1 elements are used to establish the directionality of the beam as well as to increase the impedance bandwidth of the antenna due to the close proximity between the resonant modes of D1 and the driven element. (Note that since the resonant length of D1 is slightly shorter, than the driven element, around 5%, it will resonate at a slightly higher frequency, but the combination of these modes will produce an increase in bandwidth. If the length is too small, the resonant frequency will be too high and the two modes will be too far apart to produce a wider bandwidth.) The D2 patches are used to increase the gain of the design as well as assist in steering the main beam to larger elevation angles. It is important for the value of S1 to be small (<0.05 λeff where λeff=c/(fr*εeff½) and εeff, the effective dielectric constant, lies in the range of 1< εeff < εr) in order to achieve a sufficient coupling of the fields to the D1 elements. Conversely, the value of S2 has to be as large as possible (around 0.55 λeff, but too large to prevent coupling enough energy from the D1 elements to the D2 elements). This is associated with the role of the D2 patches to increase the gain of the antenna by maintaining a large effective aperture length between the elements. The decrease in the backside radiation allows the effect of the reflector patch to be minimal. Through simulation, the length, LR, of the reflector is designed to be about ¼ is total width, WR. A shorter length can result in increased backside radiation. A larger length is unnecessary for reducing the backside radiation (it will only increase the size of the design, while the radiation performance will stay the same). In addition, feeding through the reflector patches has negligible effect on the impedance mismatch between the microstrip-coplanar waveguide (CPW) transition because the impedance difference between the lines is less than 5 Ω and both lines have impedances above 100 Ω.
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