Need help regarding Coaxial feed line length in printed LPDA antenna

Hello fellow members

I am new on this forum and find it very helpful. I wanted to post query. Is there any rule of thumb for the length of coaxial feed line in printed antennas. Actually i wanted to know if the length of coaxial feed would effect the performance of my printed log-periodic dipole array antenna. Need some details. kindly help me out in this regard,

Coax lines have a dominant mode with zero cut-off frequency and theoretically if the coaxial cable is good quality, and its impedance is the same as the source and load impedances at its ends, the cable do not affect the connected circuits and its length is meaningless. Only the insertion loss will change with the length.
Sometime, if the source or load impedance are different than the coax impedance, in this situation the coax length should be multiples of 1/2 wavelength to improve VSWR.
On the other hand, the length of the coax cable should be lower as possible as the system permits, to prevent greater insertion loss.

@ vfone thank you for your detailed response. so basically if the coax line has good quality and matching with the antenna then there is no problem for length consideration. you stated that insertion loss will be effected by length. is there any equation or relation comparaing insertion loss value to length increased/decreased

http://www.microwaves101.com/encyclopedia/coaxloss.cfm