A Research Of 8mm Quaci Elliptic Function Duplexer Components Based On Substrate Integrated Waveguide

Diplex technology is an essential part in modern communicating systems. Diplexer is a device which could make receiving system and transmitting system share one antenna. Doing research on diplexer is a work which have huge realistic meaning. A diplexer is made up of two part, a pair of band-pass filters and a ferrite circulator.The guided wave structures using by different diplexers can be divided into two classes. One is stereoscopic structures, for instance, rectangular waveguide. It exhibits some advantages such as low insert cost, high power capacity and high Q value. But there is also some drawbacks, such as its large size and hard to integration. The other kind of guide wave structure is planar structure, represented by microstrip line. On the contrary, microstrip line has characters like small size and easy to integration, but don’t give satisfactorily performance in cost, Q value or power capacity. This paper using a burgeoning planar structure, which is called substrate integrated waveguide(SIW), has both small size and excellent performance at the same time. Substrate integrated waveguide can be processed by PCB or LTCC technology. This paper introduced the propagation characteristic of SIW, and the design of a Ka band SIW transmission line and resonator. Then some work about the power capacity of SIW was done in this paper. It also introduced some matching methods between SIW and microstrip, including a new method called circular arc chamfering.The widely used band-pass filter in diplexer can be divided to two classes. One is called Chebyshev filter, the other is called elliptic function filter. Chebyshev filter has simple construction and can be realized easily, but it’s out-band restrain is not desirable. Elliptic function filter has outstanding out-band restrain, but its construction is very complicated and hard to realized in microwave engineering. This paper using a new-type filter called quaci-elliptic function filter. By using cross coupling constructions, this filter has excellent out-band restrain and easy to realize in SIW. This paper has designed a quaci-elliptic function filter which has small size as 7mm*1.0275mm*16.55 mm. The center frequency of the filter is 36.99 GHz, with 1GHz bandwidth. The insert loss in passband is less than-1dB, the return loss is less than-23 dB. In 500 MHz out of passband, the restrain is larger than-33.7dB. The squareness ratio of this filter is 1.56.This paper also designed a Y shape ferrite circulator. Due to a project’s requirements, the circulator was reformed to a T shape circulator with 50 ohm microstrip ports. Its pass band is from 33.6GHz to 37.17 GHz, with VSWR less than 1.09, insert loss less than-0.5dB, restrain larger than-25 dB.Aiming at the difficulty that in high frequency, microwave devices were hard to test, this paper designed a fixture which has characters such as high precision, three-dimension translational. Then the paper introduced the debugging work of this fixture. At last, the fixture was used to test the circulator, and got a satisfactory result.