  Trap antenna is well known method and has many applications. With this
method, trap(s) are used on antenna to block currents of some frequencies and
so electrically divide the antenna into multiple segments and thus one antenna
can work on multiple frequencies. In this paper, trap antenna method is used to
design a dual band Sub GHz printed F-antenna. The antenna is printed on FR4
board to achieve low cost solution. The two bands are 865-870 MHz and 902-928
MHz. The challenge of this design is that the frequency separation of the two
bands is very small. In this case, and also the extra section for low frequency
band is too small. Then, the influence of trap LC component variation due to
tolerance to the two resonant frequencies is big, and so it is difficult to
achieve good in band return loss within the LC tolerance. This is the main
difficulty of this design. The problem is solved by placing the low band
section away from the end of the antenna.
