Novel Canceller Diplexer for Future Mobile Handsets

When designing the front end of a two way single antenna communication system, the separation of the transmit power from the receiver components is of utmost importance. Without such separation many problems are encountered, for example the transmit signal causing feedback into the system or the transmit power saturating the receiver components possibly to the point of destroying them. High power into a sensitive low noise amplifier can be disastrous. The task is made all the more difficult when the communication system is full duplex. Generally filters are used to separate the transmit signal from the receiver port. However in small communication devices such as mobile handsets, where size is important, ceramic filters are very bulky and take up unwanted space. With the increasing consumer demand for smaller, neater, compact mobile phones the inclusion of a ceramic filter is undesirable to the designers especially the product designers of the façade. This paper looks at an alternative design for the diplexer which uses some of the inherent characteristics of a patch antenna, with transmission line cancellers, further increasing the isolation.