Actually i am designing this whip antenna but getting problem in formula which i am using as usual general formula for antenna.please help me for designing
Dear Anil,
Is it lambda/2 or lambda/4 mono pole or any other kind design?
I think you are not getting exact resonance where you want....... try with 0.45*lambda or 0.47*lambda like that
He may get return loss below -10dB, but the resonance shift slightly due to improper meshing, wire radius effect. By trying with different dimensions as said, design will give fine results.
What formula are you using? In what way is it giving you a problem? You don't give us enough details for us to be very helpful. Note that the ground plane size, position and proximity is critical for good performance from a half-wave monopole. The picture you showed is for a broadcast receiver whip antenna, in which the antenna design or efficiency is not so critical, as it is being used to pick up quite strong signals. It is not exactly a DX-ing antenna!
As Nella stated, the wire radius also has an effect on the exact resonant frequency of the antenna.
The location of the monopole on the groundplane also influences the exact resonant frequency.
A dipole's first resonance occurs at the frequency where the length of the wire is around 0.5*lambda (at fc), while a monpole's first resonance occurs at a frequency when the wire length is around 0.25*lambda.
The second resonance of the monopole occurs at 3*fc (length of wire is 3/4*lambda).
The whip antenna is a monople, and the length of the wire should thus be 0.25*lamda
As I am using general formulae of antenna.that given in David M.Pozar book,but it was not sufficient design whip antenna @Nigel Berrie
I know that is a monopole antenna and consider as lambda/4 .it's shape is like helical,so how will find diameter ,length and width of whip antenna.which formula i can use@J. Maree
Usually the monopole antenna is a quarter wavelength. The frequency received usually from 88MHz to 108MHz for FM . Thus the wavelength are the range of 3.4m -2.7m respectively. A quarter of these length are in the range of 0.85m - 0.69 m. However the antenna can work even less than a quarter wavelength or a slightly more than a quarter wavelngth but not at half-wavelength.
It is said a monopole antenna since the antenna mounted on car body. The car body become grounding for the antenna. so monopole antenna tune at a quarter wavelength. If you lean the antenna , then it become a V antenna with the image on the ground plane. Then these antenna become broadband antenna if the length more than one lamda.
Dear Gupta
The analytical expressions give a first try - however the presence of the car chassis may shift the resonance (its not a perfect ground plane as theory suggests). You can try to model it inside some tool (e.g. CST) or make it longer than the analytical design and progressively cut small pieces to make it resonate in the right point.
The monopole antenna is a quarter wavelength (lamda/2). The car is ground plane for this antenna.
Dear MB Perotoni : default of media in CST usually can use air for simulation after real application.
In measurement antenna after applications is better than simulation can this happen? in my experience (laboratory).
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