A NOVEL PLANAR FILTERING MAGIC-T

This paper presents a planar filtering magic-T with a simple structure. It consists of four half-wavelength microstrip resonators with one loaded with a shorted microstrip stub at its central location. The planar filtering magic-T has four ports, which all adopt a tapped line structure. Its novelty lies in the simple structure. Compared with previous works in the literature, its inter-resonator coupling zones are apart away and have no influence on each other, which means a simple design. Furthermore, a different-properties coupling is not needed, and its filtering response can be easily extended to the high-order case. The operational mechanism and design method are introduced in details. A planar filtering magic-T with center frequency of 920 MHz was designed and fabricated. The measured results show that, at the center frequency, the return loss ([S.sub.11]/[S.sub.44]) is less than 20/12 dB; an isolation degree of 25dB ([S.sub.41]) can be observed; the insertion losses of the difference port ([S.sub.21]/[S.sub.31]) and sumport ([S.sub.24]/[S.sub.34]) are 4.5/4.7dB and 4.3/4.6dB; the phase unbalance is 8[degrees]/7[degrees]([SIGMA]/[DELTA]). Totally, these results can verify the effectiveness of the proposed novel planar filtering magic-T.