Design Of An Air Stripline Four-in-four-out Hybrid

With the development of wireless communication, competition between these carriers is becoming more and more intense. Now the indoor distribution system which can make different communication systems be compatible with each other has appeared. In the present indoor distribution system, the way to realize the combination of more than two-way same-frequency signals is to connect several 3d B hybrid together. This implementation has many disadvantages. First, we take cable to realize the connection and need several cables to link four 3dB hybrids together to realize four-way signals’ combination. It makes the structure complex. Then, beside the complicated structure, connection leads to poor indicators、difficult debugging、hard fitting and inconvenient system check.This paper proposes the design of an air stripline four-in-four-out hybrid to solve these problems. The design uses stripline with TEM mode as the transmission line to ensure the device can sustain larger power. Based on the design and optimizing of the 3dB hybrid, this paper completed the design and processing of an air stripline four-in-four-out hybrid. The main work of this paper is as follows:1.Based on the odd-even mode analytical method of the two ports plane symmetry network, the scattering matrix expression of the four ports plane symmetry network corresponding to the 3dB hybrid is obtained. On this basis, utilizing the transmission line equation and the circuit equation, we can deduce the relationship between the even-odd impedance and the characteristic impedance、voltage coupling coefficient and the even-odd impedance, as well as the phase relationship between input port and coupling port of the 3dB hybrid.2. Using the equivalent relationship between the n sections symmetric coupled line and a quarter of a wavelength stepped impedance filter with n sections, we can make a synthesis to three sections symmetric coupled line. Then Z0 e and Z0 o of every section can be worked out. Based on this, the width and the width of the dislocation can be easily calculated out.3. The next step is to build the model of the 3dB hybrid and make simulation. With the method of adding matched branches, we can optimize the index obtained in the previous step to receive a set of perfect design parameters of 3dB hybrid and build the circuit and electromagnetic model of the four-in-four-out hybrid. In order to ensure the return loss meeting the index, making a special electromagnetic simulation to the joints is also significant.The frequency range of this air stripline four-in-four-out hybrid is 700-2700 MHz which can cover all the frequency bands of mobile communication. This device is able to accomplish the combination of four same band frequency signals.