How do I make a Yagi-Uda antenna smaller?

  • Thread starter tackyattack
  • Start date
  • Tags
    Antenna
In summary, at 900mhz, a Yagi antenna with a reflector length of 0.495 x wavelength would use a director length of 0.440 x wavelength.
  • #1
tackyattack
56
0
How do I make a Yagi-Uda antenna smaller?

I am trying to build a Yagi antenna for 900mhz and I am using this formula:

http://www.skyscan.ca/Antennas.htm

Length:

Reflector length = 0.495 x wavelength

Dipole radiator = 0.473 x wavelength

Director D1 = 0.440 x wavelength

Director D2 = 0.435 x wavelength

Director D3 = 0.430 x wavelength

----------------------------------------------

Spacing:

R-DR = 0.125 x wavelength

DR - D1 = 0.125 x wavelength

D1 - D2 = 0.250 x wavelength

D2 - D3 etc = 0.250 x wavelength

--------------------------------------------------------------------------------------------

But the problem is, when I use this formula with 900mhz the antenna ends up being huge. What I need to do is make it smaller. Would it work if I took all of the lengths and spacings then divide it by, say four?
 
Engineering news on Phys.org
  • #2


tackyattack said:
I am trying to build a Yagi antenna for 900mhz and I am using this formula:

http://www.skyscan.ca/Antennas.htm

Length:

Reflector length = 0.495 x wavelength

Dipole radiator = 0.473 x wavelength

Director D1 = 0.440 x wavelength

Director D2 = 0.435 x wavelength

Director D3 = 0.430 x wavelength

----------------------------------------------

Spacing:

R-DR = 0.125 x wavelength

DR - D1 = 0.125 x wavelength

D1 - D2 = 0.250 x wavelength

D2 - D3 etc = 0.250 x wavelength

--------------------------------------------------------------------------------------------

But the problem is, when I use this formula with 900mhz the antenna ends up being huge. What I need to do is make it smaller. Would it work if I took all of the lengths and spacings then divide it by, say four?

Nope. The size of the antenna is what makes it efficient. And since you are talking about a Yagi antenna, it sounds like you are aiming for high gain, correct?
 
  • #3


berkeman said:
Nope. The size of the antenna is what makes it efficient. And since you are talking about a Yagi antenna, it sounds like you are aiming for high gain, correct?

Yes for high gain.

I found a small Yagi for 800mhz:

https://www.amazon.com/dp/B0006H4FVM/?tag=pfamazon01-20

This is a small antenna and it works. How did they get it to be small and still work?
 
Last edited by a moderator:
  • #4
Last edited by a moderator:
  • #5


berkeman said:
Is is smaller than the one you calculated?

Way, way, way smaller. The reflector ended up being about 12 feet long, that is wwwaaayyyy to big.
 
  • #6


tackyattack said:
Way, way, way smaller. The reflector ended up being about 12 feet long, that is wwwaaayyyy to big.

Nah, there must be a typo in your math. A wavelength in free space at 900MHz is 1/3 of a meter, so a half wavelength is 1/6 of a meter. That is the basic size of each of your elements.

Can you show your math where you plugged in numbers into the formulas in your original post (OP)?
 
  • #7


berkeman said:
Nah, there must be a typo in your math. A wavelength in free space at 900MHz is 1/3 of a meter, so a half wavelength is 1/6 of a meter. That is the basic size of each of your elements.

Can you show your math where you plugged in numbers into the formulas in your original post (OP)?

Reflector length = 0.495 x wavelength
wavelength = 900mhz
0.495 x 900 = 445.5
there is 37.125 feet in 445.5 inches
 
  • #8


tackyattack said:
Reflector length = 0.495 x wavelength
wavelength = 900mhz
0.495 x 900 = 445.5
there is 37.125 feet in 445.5 inches

900MHz is the frequency, and the speed of light c is the velocity (300*10^6 m/s)

Wavelength = velocity/frequency.

So what is the wavelength at 900MHz? Should be about 1/3 of a meter.

http://en.wikipedia.org/wiki/Wavelength

.
 
  • #9


berkeman said:
900MHz is the frequency, and the speed of light c is the velocity (300*10^6 m/s)

Wavelength = velocity/frequency.

So what is the wavelength at 900MHz? Should be about 1/3 of a meter.

http://en.wikipedia.org/wiki/Wavelength

.

Ahh I see! So at 900mhz the reflector would be 6.48956682 inches or 0.164835 meters long?

Thanks!
 

1. How does the size of a Yagi-Uda antenna affect its performance?

The size of a Yagi-Uda antenna directly affects its performance by determining its gain, directivity, and bandwidth. Generally, a larger antenna will have a higher gain and directivity, but a smaller bandwidth. Conversely, a smaller antenna will have a lower gain and directivity, but a wider bandwidth.

2. What are the key factors in reducing the size of a Yagi-Uda antenna?

The key factors in reducing the size of a Yagi-Uda antenna are the number and length of the elements, the spacing between the elements, and the type of reflector and director used. To reduce the size, the number of elements can be reduced, the length of the elements can be shortened, and the spacing between the elements can be increased. Additionally, using a folded dipole as the driven element can also help reduce the overall size.

3. How does the use of a folded dipole help make a Yagi-Uda antenna smaller?

A folded dipole, also known as a folded dipole reflector, is a type of reflector that is folded back on itself to reduce its physical length. This allows for a smaller overall antenna size while still maintaining a good level of gain and directivity. This type of reflector is commonly used in smaller Yagi-Uda antennas.

4. Can the length of a Yagi-Uda antenna be reduced without compromising its performance?

Yes, the length of a Yagi-Uda antenna can be reduced without compromising its performance by using loading coils or capacitive loading. Loading coils are inductors placed along the elements to electrically lengthen them, while capacitive loading involves adding capacitance to the elements to effectively shorten them. Both methods can help reduce the physical length of the antenna while maintaining its performance.

5. Are there any trade-offs when making a Yagi-Uda antenna smaller?

Yes, there are trade-offs when making a Yagi-Uda antenna smaller. As mentioned earlier, a smaller antenna will have a lower gain and directivity compared to a larger antenna. Additionally, reducing the size may also result in a narrower bandwidth and potentially a lower power handling capability. It is important to carefully consider these trade-offs when designing a smaller Yagi-Uda antenna for a specific application.

Similar threads

How do I make more smaller sidelobelevel value of patch antenna?
    • Electrical Engineering
Replies
1
Views
4K

Hot Threads

Recent Insights

Back
Top