dipole antenna design using ads momentum- mistake

hello, i have designed a dipole antenna in the frequency range 1 to 5GHz. Length of dipole is 2 inches i.e. length of one stub of dipole is 1 inch(=2.54 cm).
according to this, frequency at which it should resonate is 2.95 GHz but the simulation results are showing something different.
i have enclosed smith chart which is showing the real impedances at 1.194 GHz and 3.667 GHz.
can anybody tell me where i am doing the mistake.

Hello Pulkit,

Did you expect good VSWR over the full 1 to 5 GHz frequency range? The answer will be definitely NO.

Do some study on the behavior of thin wire dipoles or monopoles and you will see that you need a compete other approach to make something that has good VSWR/return loss over 1 to 5 GHz.

Regarding the center frequency (your expected 2.95 GHz): Due to capacitive fringing at the dipole ends, the resonant frequency goes down (depending on thickness or width of conductors). But it will not shift that much for thin dipoles (think of 5..20%). . Other thing can be the dielectric environment. What is the dielectric constant of the environment?

Do you feed the antenna directly (via localized port), or via some other circuit (balun?)?

thank you WimRFP. Is it so that ,i can make my resonant frequency close to the theoretical (calculated) by increasing the width of the conductor ?
i had feed the antenna directly (via loacalized port).

---------- Post added at 06:56 ---------- Previous post was at 06:54 ----------

thank you WimRFP. Is it so that ,i can make my resonant frequency close to the theoretical (calculated) by increasing the width of the conductor ?
i had feed the antenna directly (via loacalized port).

2.54 cm per stub would be exactly quarter wavelength at 2.95 GHz for an infinitely thin rod.

At 3 GHz your rods are likely thick in percentage of wavelength at 3 GHz. This would lower the frequency of resonance significantly, to something between 75% to 85% of actual quarter wavelength.

A 3 GHz dipole built with 0.062 inch diameter rods would be like 82% of half wavelenth.

Also, as the diameter of rods are increased, the termination impedance is lowered.

Make sure you are using a balancing balun to make measurements. See attachment.

can u provide a good tutorial on antenna design in ads ?

Reducing the thickness does bring the resonance frequency more close to the theoretical half wave frequency. As your actual resonant frequency is just 40% of the value for the infinite thin half wave dipole, there must be something else (probably a dielectrics issue). Did you check the meshing?.

I don't know ADS, but I assume that there is a tutorial provided with the package together with example files.

For simulation, you can place the port between the legs of the dipole. No need for a balun in this case.

Hey!
can any body give me the link for ADS software...

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