WE PRESENT A NOVEL DESIGN OF A UMTS DIPLEXER USING A COMBINED CO-PLANAR WAVEGUIDE (CPW) AND MICROSTRIP STRUCTURE. THE DIPLEXER IS COMPOSED OF TWO BANDPASS FILTERS (BPFS) WHICH ARE TERMED THE TRANSMITTING (TX) AND RECEIVING (RX) FILTERS. A TRANSMISSION ZERO IS IMPLANTED FOR EACH FILTER TO REJECT THE SIGNAL OF THE OTHER FIL-TER’S BAND. THE TWO FILTERS ARE IN A PARALLEL-CASCADE LAYOUT AND A MICROSTRIP IS USED TO COUPLE THE I/O SIGNALS FROM/TO THE FILTERS. THE MUTUAL LOADING EFFECT BETWEEN THE TWO BANDPASS FILTERS IS MINIMIZED BY FINE DESIGN THE CONNECTING MICROSTRIP.

In this patent documentation, we propose a novel design of a UMTS diplexer using a combined coplanar waveguide (CPW) and microstrip structure. The diplexer is composed of two bandpass filters (BPFs) which are termed the transmitting (Tx) and receiving (Rx) filters. These two band pass filters are in parallel circuit layout with the two units connected by a suitable designed connecting microstrip line. The usage of this microwave diplexer is initially aimed for the UMTS system. However, it can be modified to be suitable for other band, such as the ones for WIFI and LTE systems.  The filter’s characteristics analyzed by a circuit model of the LC lumped elements are implemented using the CPW and microstrip. A transmission zero is carefully implanted for each filter to reject the signal of the other filter’s band. The two filters are in a parallel-cascade layout and a microstrip is used to couple the I/O signals from/to the filters. The mutual loading effect between the two bandpass filters is minimized by fine design the connecting microstrip.  The planar PCB structure of this diplexer makes itself having a very low fabrication cost and suitable for massive production. It is believed that it is good for modern commercial application in wireless communication systems. It has the properties of
1.The transmitting band of MHz ~ 1980 MHz, and the receiving band of 2110 ～2170 MHz.。
2.The planar structure of coplanar waveguide and the microstrip line are very easily fabricated by printed circuit board technology.
3.Two independent passband filters in parallel topology has made a minimum interference between these two filters, results in an excellent isolation between the TX and RX ports.
4.This diplexer design is very unique which is rarely seen in the literature and has been documented by a prestigious international journal.

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