Antenna 120 Deg

[RXTX]

Hi,

I need to design Antenna with a -3dB beamwidth of around 120 deg,Is anyone has ideas which antenna is compatible ?

The antenna need to be with High Gain as possible.

Please advice.

Doron

 

[Higgler]

Notch/Slot is easier than any other antenna. Bandwidth is so wide, dimensions are not critical. It also makes feeding it easy too and the center conductor is short circuited to ground and you will never have static damage to your transmitter or receiver with a grounded center conductor antenna. Patches are open circuited center conductors and not as safe as a shorted notch due to static.

Dimensions are easy, everything is 1/4 wavelength except the slot opening, make that 0.050" to 0.1" roughly.
1/4 wave dimensions are;
1) distance feedline crossing slot to short circuit in the back
2) distnace feed line crossing slot to open circuit in the front
3) distance from the slot to the top of the antenna
4) distance from the slot to the bottom of the antenna

essentially a square thin antenna. You can make the antenna much taller also, it just needs a half wavelength height for efficiency. If you don't have enough room, VSWR can be ok subsituting the 1/4 wave dimension with closer to 1/3 wavelength and still get 2:1 VSWR and super wide antenna patterns.

example, wavelength = 12 inches. Slot
Antenna becomes 6" tall x just over 6" deep x thickness. Cut slot in center. attach coax across center slot (ground on one side of slot, right in the center of the slot, center conductor of coax. is shorted to opposite side of short). Then for VSWR tuning, and wider bandwidth, on the front opening part of the slot, make it wider and V shaped, so the slot is small at the coax. connection and wide (up to 1/4 wavelength, 3" wide at the open end). If you keep the slot thin at the front opening, it's more challenging to get good VSWR and it's narrower band, but you can make it work with a narrow slot, not sure how well though.
It'll work, I've done it alot with a wide opening in the front of the slot. But the antenna pattern will only be very smooth if you add antenna foam absorber all around the antenna.

 

[RXTX]

Hi Higler,

For a mass production issue: do you have idea how i can not solder the coax manually to antenna ?

 

[Higgler]

Yes,
for short circuiting the center conductor; you can use printed circuit techniques, and use a via to ground. Using coax. though, you can use any mechanical screw into the circuit board and hold it down that way. Benefit of wide bandwidth is insensitivity to using imperfect mechanical assembly.
for open circuiting the center conductor; just pass the center conductor 1/4 wavelength across the slot, instead of shorting it on the far side of the slot. Spray coat the metal with an insulator and then glue the center conductor onto the spray coasted metal(proper length 1/4 Lambda) past the slot.

If it connects to a transceiver, marketing it as "static damage insensitive shorted center conductor" might help. It works either way though.

 

[RXTX]

Hi Higler,

See attached, Please review and let me that i drew it correct.

I am still do not understand how to connect the center conductor from the PCB, Please explain.

What about to use dipole antenna with the arms like a arrow - will it achieve beamwidth 120 degree ?

What about patch antenna with beamwidth expander above the patch ?

RXTX

 

[Higgler]

Search "vivaldi antenna" on Google and click on the top of the Google search for Images and you'll see a huge collection of photos and I think you'll understand the design alot better.

Vivaldi antenna is a notch antenna, use my "make everything one quarter wavelength" note above.

Get a piece of thin metal, cut with scissors the slot, add a coax. and you have an antenna.

your sketch has a cavity, I don't think I mentioned having a cavity.

good luck.
what application is this for that needs high volume?

 

[RXTX]

Hi Higler,

OK, I understand the feeding issue - see attched fo example.

By the way the vivaldi antenna beamwidth is not smoothing and there are a lot of ripple.

Is the Slot antenna has such of ripple ?

I need that the beamwidth will be 120 degree for Elevation & Azimuth.

RXTX

 

[RXTX]

Hi Higler,

OK, I understand the feeding issue - see attched for example.

By the way the vivaldi antenna beamwidth is not smoothing and there are a lot of ripple.

Is the Slot antenna that you present has such of ripple ?

I need a smoothing beamwidth at 120 degree for Elevation & Azimuth.

RXTX

 

[Higgler]

The notch antenna = The vivaldi antenna. They are the same, like calling something a car and automobile is the same. Vivaldi is a man's name, notch is a physical description.

The two feeding options are shorting the feed at the opposite side of the slot and leaving the feed open circuited, with a feed length of 1/4 wavelength (electrical length if in a dielectric) past the slot. Sometimes instead of a simple transmission line shape, an oval, round or other shape is used in place of a simple feed line for greater bandwidth.

Recall "The antenna pattern of a very wide beamwidth antenna (120 degrees is very wide) depends on what's around the antenna much more than it depends on the antenna itself".

You can make a vivaldi or notch antenna anywhere from 1/3 Lambda (air) square for a backwards beam (very low gain, very wide beamwidth), up to one wavelength square having about +6 dBi gain. I'd suggest making two antennas or three antennas, 1/2 wavelength and 3/4 and one wavelength square and you'll see the difference in beamwidths when you measure them.

These antennas can actually have ultra high gain too if you make them long enough.

good luck.

 

[IRstuff]

For the frequency specified (4.5GHz), the effective antenna aperture should be 3 inches or less, using Rayleigh criteria. However, too small an aperture will result in an even larger beamwidth and degrade its apparent gain.

TTFN
faq731-376