Part2:  Why did I want to design such a small RF bandpass filter.The idea arose out of a problem encountered in my day job as a freelance RF Design Engineer.I was working on a radio transceiver at 868MHz and very late in the project I discovered there was a particular receiver blocking problem that could only be improved by using a higher performance saw filter at the front end. I investigated the available options,it was too late to change the PCB ,so the solution had to be a drop-in connectorized saw filter.There was a good choice of bandpass filters which would all improve the blocking problem but there was one major problem with all these possible filter solutions.The pcb's where typically about 1 inch (25.4mm) square and then they had edge mounted RF sma connectors added which needed even more room in any sort of enclosure.The bottom line for my problem was that none of the available connectorized filter solutions could be used since we had very little spare room inside the enclosure, and that's what made we think why much smaller connectorized filters are not available.I did an exhaustive search but I didn't find anything suitable.I already knew after being in the mobile phone design industry for a number of years that there where some great  saw filters available which are extremely tiny chips but very few people outside of the high volume Comms industry seems to have used these ultra small components in maker/hobbyist style projects.Typically,these mobile phone type saw filters are extremely small,roughly the size of an 0603 chip component but with 5 pads on the bottom side. Their size is described as 1411,which means that it is 1.4mm by 1.1mm and underneath the chip on the bottom face,there are 5 pads,3 of them ground pads and the other 2 are signal in and out.So you can imagine how big these pads are and they do not show on the edges of the device so when this filter is sat flat,no pads are visible.As you can imagine,this is not the sort of project you put together with your soldering iron on your bench.I had to learn lots of new techniques and skills to be able to take this project forward.I will tell you all about that in Part3 coming very soon