Help with λ/4 monopole antenna.

[manos87]

Hello to all,
I am working on a project for channel measurements in an indoor environment and my part of this project is to design and
construt 2 quarter-wave monopoles for 2 different operating frequencies( one for 900MHz and the other for 2.4GHz).
The antennas will be made with a PCB(which is not my responsibility) and a ground plane.
I have found some information about the design but I would appreciate any additional info that you can give me.
Thanks in advance

 

[manos87]

Any help please?

 

[enjunear]

How do you intend to make quarterwave monopoles on a PCB? Generally, whip monopole (quaterwave monopole) antennas are mounted orthogonal to the ground plane. For an example, think about the FM whip antenna mounted into the sheet metal of a car.... the antenna is installed at right angles to the surface. On a PCB, you generally design microstrip patch antennas, which are approximately a quarter-wave long, and wide.

 

[davenn]

Hello to all,
I am working on a project for channel measurements in an indoor environment and my part of this project is to design and
construt 2 quarter-wave monopoles for 2 different operating frequencies( one for 900MHz and the other for 2.4GHz).
The antennas will be made with a PCB(which is not my responsibility) and a ground plane.
I have found some information about the design but I would appreciate any additional info that you can give me.
Thanks in advance

what additional help do you need? ask a specific question
is there something in what you have been reading that you dont understand ?

A monopole antenna on a PCB ground plane is about as basic an antenna as you can get

You could use semi rigid coax like UT-141 bring it up through a hole in the centre of the PCB ground plane, solder the upper side of the ground plane to the solid outer conductor of the coax and use the centre conductor as the radiator. You could leave on the teflon dielectric for added protection or strip it off. Being on or off will affect the tuning slightly, either way ensure that you cut the length of the radiator a bit longer than needed and then trim it down to get a good return loss.


Cheers
Dave

 

[SU-4]

i think u can made an antenna monopole on pcb like microstrip antenna

 

[enjunear]

i think u can made an antenna monopole on pcb like microstrip antenna

I'm aware of the many forms of planar antennas designs, but don't know about making a monopole on PCB, other than Dave's mention of a basic coax monopole (which just uses the back-side metal of the PCB to form a large ground plane). Can you send us a link?

 

[FvM]

There are various planar antennas comprised of a copper pour and a straight or folded/bended trace, that can be analyzed as a kind of monopole. Like the below one from a TI application note. But these antennas are compromise designs and don't implement a straightforward design principle. In so far, I don't hear a clear question from the original post, or at least can't give a simple answer.

 

[enjunear]

There are various planar antennas comprised of a copper pour and a straight or folded/bended trace, that can be analyzed as a kind of monopole. Like the below one from a TI application note. But these antennas are compromise designs and don't implement a straightforward design principle. In so far, I don't hear a clear question from the original post, or at least can't give a simple answer.

Is there copper on the back side of the PCB, directly below the monopole, or is the only ground the flooded metal surrounding the chip? I could see the latter working as a monopole, just not a very good one :???:

 

[FvM]

Is there copper on the back side of the PCB, directly below the monopole, or is the only ground the flooded metal surrounding the chip?

Of course no copper on the back side.

I could see the latter working as a monopole, just not a very good one.

Yes, you can read "compromise design" as another word for "not a very good one". Nevertheless, similar designs serve their purpose. I also did one for a wireless product.

The bended monpole as well as the small ground plane involve typical "electrical small antenna" properties like small bandwidth and low radiation resistance. You may want to analyze the geometry as asymmetrical dipole rather than a monopole, in any case the antenna is rather sensitive to cable and "hand" effects. A simple impedance measurements requires RF craftmanship and the performance of the final product, including enclosure and mounting, is hard to predict.

 

[davenn]

........... In so far, I don't hear a clear question from the original post, or at least can't give a simple answer.

yup a bit difficult when the OP doesnt bother to check back and respond to the comments and questions

Dave

 

[plasma]

you can use this Ultra Wide band monopole

 

[manos87]

what additional help do you need? ask a specific question
is there something in what you have been reading that you dont understand ?

A monopole antenna on a PCB ground plane is about as basic an antenna as you can get

You could use semi rigid coax like UT-141 bring it up through a hole in the centre of the PCB ground plane, solder the upper side of the ground plane to the solid outer conductor of the coax and use the centre conductor as the radiator. You could leave on the teflon dielectric for added protection or strip it off. Being on or off will affect the tuning slightly, either way ensure that you cut the length of the radiator a bit longer than needed and then trim it down to get a good return loss.


Cheers
Dave

First of all, thank you for your precious help.

What I was thinking is that I will use a pcb laminate(with fiber glass) which will have copper sheet at the bottom side and there we will solder a right angle sma connector.
I will connect to the connector a sma rf cable.
Also, I will drill a hole in this part to place the antenna.
Do you have any papers to read for that type of design?
Finally, I would like to learn about the cost of such a design, ie the pcb laminate, the connector, the brass rod and the sma cable.

Thanks in advance

 

[enjunear]

First of all, thank you for your precious help.

What I was thinking is that I will use a pcb laminate(with fiber glass) which will have copper sheet at the bottom side and there we will solder a right angle sma connector.
I will connect to the connector a sma rf cable.
Also, I will drill a hole in this part to place the antenna.
Do you have any papers to read for that type of design?
Finally, I would like to learn about the cost of such a design, ie the pcb laminate, the connector, the brass rod and the sma cable.

Thanks in advance

That design sounds very straightforward. Find an SMA connector with a "solder-pot" end (the center conductor will have a hole milled out of the center, so you can stick a wire in and solder it in place). Then drill 3 holes (center conductor + 2 holes for screws to hold the connector onto the PCB), install the connector, solder the body of the connector to the groundplane copper, remove the two screws (if desired), and solder your wire element into the center conductor.

The cost will be a sheet of PCB (make it's dimensions at least 2x the length of your quaarterwave element), price of a right-angle solder-pot SMA connector, and a piece of wire. Check out Allied, Newark, and Digikey for the cost of the connector... calls Rogers, Taconic, etc for PCB prices, and you can probably find the wire at your local hardware store.

This is an example of a solder pot termination. Your wire antenna would fit into the hole in the center conductor and solder in place.

 

[davenn]

thanks for responding to the OP, enjunear, I havent had a chance to visit for a couple of days. great advice

cost --- less than US$15, probably less than $10 per antenna, if you shop around .... the most expensive part is the straight or right angled SMA connector


Dave

 

[manos87]

Dave, I want to thank you for your advice too.
One more question to you and enjunear.
I have read that the are of the ground plane should be λ/4*λ/4.
Why do you propose the PCB sheet to be 2Xλ/4?
Is this for performance reasons?
Thanks in advance,
Manos

---------- Post added at 19:38 ---------- Previous post was at 19:07 ----------

Also if we finally use a double sided PCB, does anything in our change?

---------- Post added at 19:44 ---------- Previous post was at 19:38 ----------

One more thing, about the thickness. In the labs university I have access to a PCB with 0.8mm thickness and one of 1.6mm thickness?
Does it make any difference if I use the thinner one?

PS. Are you aware of any books specifically for antenna design with information like those that you gave me?

Regards,
Manos

 

[davenn]

Dave, I want to thank you for your advice too.
One more question to you and enjunear.
I have read that the are of the ground plane should be λ/4*λ/4.
Why do you propose the PCB sheet to be 2Xλ/4?
Is this for performance reasons?
Thanks in advance,
Manos

Practically the ground plane can be as big as you want, a λ/4*λ/4 will be ok if you dont have much space to mount these antennas
Also the groundplane doesnt have to be square, it can be circular. whatever is practical for your situation

---------- Post added at 19:38 ---------- Previous post was at 19:07 ----------

[/COLOR]Also if we finally use a double sided PCB, does anything in our change?

Personally I have always used double sided board and would prefer to just make sure the top side of the board is well bonded to the lower side
especially around the SMA connector. Shouldnt be a problem with the small nut and bolts used to mount the connector

One more thing, about the thickness. In the labs university I have access to a PCB with 0.8mm thickness and one of 1.6mm thickness?
Does it make any difference if I use the thinner one?

for these frequencies and the way the board is being used ... thickness isnt an issue, as it would be if you were producing transmission (strip) lines on a board at 2GHz and up in freq.
you can happily use standard double sided PCB that you would use at much lower freqs

PS. Are you aware of any books specifically for antenna design with information like those that you gave me?
Regards,
Manos

Specifically ... No.... ummm mainly comes from personal experience. maybe others can suggest some reading material

Dave

 

[enjunear]

I have read that the are of the ground plane should be λ/4*λ/4.
Why do you propose the PCB sheet to be 2Xλ/4?
Is this for performance reasons?

When dealing with antennas of most kinds, they are traditionally analyzed assuming an infinite ground plane. When you limit the size of the ground plane (less than infinite), you introduce mechanisms that degrade the performance from the ideal case. By making the ground plane below your monopole antenna as large as possible/reasonable, you get closer to the ideal case. I'd consider a λ/4 square plane to be an absolute minimum to get a reasonable approximation, so double it to gain some margin, and avoid odd effects like the ground plane being a near-resonant size at your frequency of interest (it's nearly the same dimensions as a patch antenna for the same center frequency!).

Also if we finally use a double sided PCB, does anything in our change?

The easiest way to use a two-layer PCB is to just etch off (or peel off) the top layer copper and simply use the bottom layer metal to install your SMA connector.

If you use both layers of copper (I wouldn't mess with it), you'll want to completely connect the top copper to the backside, so all of the metal is a uniform potential ground. You'll have to isolate the center conductor from both layers (just make the hole in the PCB large enough). To ensure that you have short ground return paths and a "stiff" ground plane, I'd stitch the top and bottom together with vias spaced every λ/10, or less.

One more thing, about the thickness. In the labs university I have access to a PCB with 0.8mm thickness and one of 1.6mm thickness?
Does it make any difference if I use the thinner one?

Since you aren't using the substrate to support a transmission line structure (like microstrip or stripline), the thickness is not a concern, other than determining the rigidity of the flat ground plane. Thin boards are more likely to bend when they get bumped/dropped, etc.

PS. Are you aware of any books specifically for antenna design with information like those that you gave me?

My favorite text book is Antenna Theory by C.A. Balanis. It's very math intensive and theory-based, so not for beginners. For entry-level antenna design, look at the ARRL Antenna Book. ARRL is the amateur radio group (HAM radio enthusiasts), so most of their documents/books are based more in practice than theory.

 

[manos87]

Thanks guys!
Your advices are great.
Tons of knowledge here!
Regards,
Manos

 

[gkkashyap]

a similar lambda/4 monopole antenna design i am trying to simulate in hfss but stuck with excitation.please help me how to excite it.i have attahced the pdf i working out for my project.

thanks well in advance!

 

[ferdows]

whats the problem ????pls send your simulation