Here is another DIY Yagi antenna design for 1200MHz and also suitable for 2400MHz:
Construction details from calculation:
VK5DJ's YAGI CALCULATOR Yagi design frequency =1200,00 MHz Wavelength =250 mm Parasitic elements fastened to a non-metallic or separated from boom Folded dipole fully insulated from boom Director/reflector diam =4 mm Radiator diam =3,5 mm REFLECTOR 121 mm long at boom position = 30 mm (IT = 54,5 mm) RADIATOR Single dipole 116 mm tip to tip, spaced 50 mm from reflector at boom posn 80 mm (IT = 52,0 mm) Folded dipole 118 mm tip to tip, spaced 50 mm from reflector at boom posn 80 mm (IT = 53,0 mm) DIRECTORS Dir Length Spaced Boom position IT Gain Gain (no.) (mm) (mm) (mm) (mm) (dBd) (dBi) 1 103 19 99 45,5 2,8 5,0 2 102 45 144 45,0 5,4 7,6 3 101 54 197 44,5 7,1 9,3 4 99 62 260 43,5 8,4 10,5 5 98 70 330 43,0 9,4 11,6 6 97 75 405 42,5 10,2 12,4 COMMENTS The abbreviation "IT" means "Insert To", it is the construction distance from the element tip to the edge of the boom for through boom mounting Spacings measured centre to centre from previous element Tolerance for element lengths is +/- 1 mm Boom position is the mounting point for each element as measured from the rear of the boom and includes the 30 mm overhang.The total boom length is 435 mm including two overhangs of 30 mm The beam's estimated 3dB beamwidth is 49 deg A half wave 4:1 balun uses 0,70 velocity factor coax and is 87 mm long plus leads FOLDED DIPOLE CONSTRUCTION Measurements are taken from the inside of bends Folded dipole length measured tip to tip = 118mm Total rod length =259mm Centre of rod=129mm Distance HI=GF=46mm Distance HA=GE=64mm Distance HB=GD=82mm Distance HC=GC=129mm Gap at HG=3mm Bend diameter BI=DF=23mm
The required balun is made from RG316 coax cable and calculated with a velocity factor of 0.7.
The dipole is made from 10mm² (diameter 3.5mm) copper wire .
And finaly the plot of the VSWR measurment to proof the construction:
This Yagi is also suitable for 2400Mhz where the VSWR is a bit worser but still below 2 which is still accetable.
Material costs <10€.