CPWF stands for Circularly Polarized Wire-Frame Antenna. This is not a shorten to the ground antenna but it has circular polarization. This advantage brings new gains regardless the initial polarization of the arriving signal. In order the CP to occurs two different source points are feeding the antenna with 90 degrees out of phase signal. This required the use of a special device to shift and to split in two the Tx signal. The CP antenna mitigate succesfully the short term fading which is much annoying in VHF radio bands. As a real expert in the matter, Grant Bingeman - KM5KG has written in his book how any ham operator can built at home such a divice. If someone builds a quarter wave hybrid coupler as the phase shifter then the switching between 90 or -90 degrees can change between RHCP or LHCP (Right or Left Handed Circular Polarization).
Antenna Array vol. 1 – Chapter 12 – Control Interaction in a Phased Array by Grant Bingeman, KM5KG, pp 233-288
CM Design by Nicolae Crisan - YO5OUC
CM 15 February 2016
CM Resonance at 52.35 MHz
CM More details at http://antennex.com (antenneX Issue No. 228 - April 2016)