For an good efficacity and directivity on radio spectrum it's necessary to use an YAGI antenna.
This antenna is very adapted at VHF and UHF domain inside 30 MHZ to 900 MHZ.
The dimension of the antenna below is in function of the frequency.
For know the length of the "element's" , choice
your frequency of work.
For exemple in FM broadcasting band choice 100 MHZ it's easy for calculate
!
The dimension is in meters !.
EXAMPLE : the first director is 120 / F if F = 88 MHZ then 120 / 88 = 1,36 Meters.
1 
director 1  120 / frequency  A 
interval betwen 1 et 2  60 / frequency  
2 
director 2  125 / frequency  B 
interval betwen 2 et 3  45 / frequency  
3 
director 3  130 / frequency  C 
interval betwen 3 et 4  30 / frequency  
4 
director 4  138 / frequency  D 
interval betwen 4 et 5  30 / frequency  
5 
Dipôle  143 / frequency  E 
interval betwen 5 et 6  48 / frequency  
6 
reflector  150 / frequency 

the dipole is an essential element of the YAGI antenna. He receive the wave. the impédance ( résistance in function of the frequency ) is one parameter very important. for the most popular FM TUNER receive the impédance is 75 ohms. For respect this condition, the dimension of the dipole is accurate. In this exemple is constituted of too pipe of different diameter. The first pipe N°1 diamter 15 mm and the N°2 is 10mm. Joint the pipe at the extremity .
TUBE in French = PIPE