Aug 15, 2010, 05:06 PM
Engineer for Christ
Amherst, VA
Joined Jun 2006
11,058 Posts
Mini-HowTo
Fast Patch - IBCrazy's easy DIY patch antenna

By request, here is a tutorial on how to build your own patch antenna. As you can see, it's really quite simple and almost anyone can make a good antenna with some basic soldering skills.

If you haven't made your own TX antenna yet, I recommend you build my inverted Vee antenna as in this tutorial: http://www.rcgroups.com/forums/showthread.php?t=1159968 The combination of these two antennas will suit most people's FPV requirements.

In this tutorial I will be building a dynamic patch antenna. I will discuss the basic principals governing the patch and how it works as well as how to adjust and tune it to meet your specific needs. This is different from RC Cam’s Goof Proof Patch, which is also an excellent antenna.
I am constructing this out of 26 gauge galvanized steel, but any conductive metal will work well. Thin galvanized steel (22-30 AWG) works well and can be found for \$5-6 at most hardware stores. I bought mine at Lowes in a 12”X24” sheet for \$6.

For the bolts and spacers I am using ¼-20 nylon bolts and 1/2 “ spacers. You can use any non conductive bolt or even wooden blocks as spacers.

I will update this thread periodically with more theory and principals later. I will also see if I can model the radiation patterns.

So without further delay, on to the tutorial

-Alex

# Images

Last edited by IBCrazy; Aug 15, 2010 at 05:17 PM.
Aug 15, 2010, 05:16 PM
Engineer for Christ
Amherst, VA
Joined Jun 2006
11,058 Posts
Calculations: Calculating your length and width

The ½ wavelength measurement:

The first thing you need to do is calculate your ½ wavelength for your frequency. The formula is:

½ Wave in inches = 5124/f in MHz
Or for you metric folks:
½ Wavelength in mm = 130150/f in MHz

This measurement will be the length of your active element. For my 1280 MHz patch, my element is 4-1/16” long.
The length of you element is you ½ wavelength measurement. Now we need to get the width. As the width of the antenna increases, it lowers the impedance of the antenna. However this also changes the radiation pattern. For the patch your width can be anywhere from 3/2 to 4/3 of your length. 3/2 will yield a 50 ohm impedance. 4/3 will yield 75 ohm impedance in theory, but in actuality, it still hits close to 50 ohms. In fact, you can almost make it square. The width affects the radiation pattern more than anything.

So for 50 ohms:
Width in inches = 7686/F in MHz
Or
Width in mm = 195227/f in MHz

For 75 Ohms:
Width in inches = 6832/f in MHz
OR
Width in mm = 173535/f in MHz

Which do you use? It’s up to you. You can pick any value in between those two widths and the antenna will work well. A wider panel will give you a wider beam width but reduce gain slightly. A 50 ohm antenna will have a beam of ~ 90 degrees and a 75 ohm will have a beam of ~75 degrees. Both will work well with your RX. For my 1280MHz I made mine 6 - 1/8” which will give me a wide beam width and an impedance of about 50 ohms.

-Alex

# Images

Last edited by IBCrazy; Apr 04, 2011 at 12:17 PM.
Aug 15, 2010, 05:19 PM
Engineer for Christ
Amherst, VA
Joined Jun 2006
11,058 Posts

Determining you height:

The height of the antenna is entirely up to you. It should be between 1/5" and ½” for 2.4 GHz, between 3/8" and 5/8” for 1.2-1.3 GHz and between 5/8” and 3/4” for 900 MHz.

For my 1280 MHz antenna I chose ½”. Why? Because the hardware store sold ½” nylon spacers which make this really easy

-Alex

# Images

Last edited by IBCrazy; Mar 03, 2011 at 05:23 PM.
 Aug 15, 2010, 05:20 PM Engineer for Christ Amherst, VA Joined Jun 2006 11,058 Posts The ground panel The Ground Panel: The ground panel is not critical. I recommend you make it square and wider than your width by 4X you height. So for me, I made mine 8” Simple as that -Alex Last edited by IBCrazy; Mar 03, 2011 at 05:24 PM.
Aug 15, 2010, 05:23 PM
Engineer for Christ
Amherst, VA
Joined Jun 2006
11,058 Posts

Now that you have cut out your elements, now it is time to build your antenna. First you need to drill out a small hole in the active element where you plan to connect your coaxial line. This should be dead center width wise and the same distance from the edge as your height. So for my 1280 MHz patch, this is located at 3-1/16” from either side and ½” from the bottom.

Now you need to drill the holes for your nylon bolts. Where you place them is entirely up to you. I put mine 1” from the corners. Place your active element in the center of your ground panel and tape them together and drill them as one plate. This will ensure proper alignment. Once done, mark your active element hole and drill that such that you can pass the center element of your coaxial line through it.

-Alex

# Images

Aug 15, 2010, 05:26 PM
Engineer for Christ
Amherst, VA
Joined Jun 2006
11,058 Posts
Assembly: Constructing the antenna

Assembly – Constructing the panels:

Place your spacers (you can use spacers, washers, or even wood) between your panels, pass your bolts through and secure them. Now make a small solder bead around the coaxial line holes.

Strip your coaxial line and flare out the shield. Strip the insulation off of the top of the center element. Now pass your cable through the backside of the ground panel. Solder the shield to the ground panel and the center element to the active panel.

No go out and try it! The best results will be achieved when the edge of your active element is about ½ wavelength off of the ground. Experiment with this height to achieve best results.

Good luck and have fun! Feel free to post questions and your results.

-Alex

# Images

 Aug 15, 2010, 05:56 PM Registered User Joined Mar 2001 2,626 Posts Still learning here. What is the purpose of a patch antenna? I regret I never took the time to learn much about electronics. At age 50+ and working to learn about FPV, I may be at a bit of a disadvantage. Tony
Aug 15, 2010, 06:21 PM
Praying for better weather
Joined Dec 2007
4,318 Posts
This will teach you loads, very long but shows you the principles of how different antenna works

 Antennas 101 - Polarization, Diversity & Gain Patterns (27 min 56 sec)
 Aug 15, 2010, 07:14 PM Registered User Joined Mar 2001 2,626 Posts Thanks C. Tony
Aug 15, 2010, 08:49 PM
Registered User
Benicia, CA
Joined Jan 2010
26 Posts
Quote:
 Originally Posted by IBCrazy The best results will be achieved when the edge of your active element is about ½ wavelength off of the ground.
I think there was another thread which someone posted this suggestion, quoting you as the source. Is it that the ground acts like another reflector? is this only with patch types? Will it still be a general improvement if the terrain is such that the LOS might be slightly less at the ground instead on on a tripod?
 Aug 15, 2010, 10:49 PM Registered User Ånge Sweden Joined Dec 2006 133 Posts I bought a patch antenna that I tried yesterday and it,s crap, itsa 1,2-1,3Ghz patch from rceletronica, my standard wip is alot better.. dont know y?
Aug 15, 2010, 11:03 PM
400' ..... NOT
Joined Jan 2009
4,267 Posts
Quote:
 Originally Posted by Unpoor I bought a patch antenna that I tried yesterday and it,s crap, itsa 1,2-1,3Ghz patch from rceletronica, my standard wip is alot better.. dont know y?
What type of connector? Sma or rp-sma? If you have a multimeter test the connector from the pin to ground. Should be infinite resistance
Aug 15, 2010, 11:25 PM
Flying FPV from the lab.
Joined Jun 2008
2,183 Posts
Quote:
 Originally Posted by Unpoor I bought a patch antenna that I tried yesterday and it,s crap, itsa 1,2-1,3Ghz patch from rceletronica, my standard wip is alot better.. dont know y?
1000's of reasons. could be the center pin on the connector, the element might be damaged, etc etc...

you are aware that patch antennas are directional? Polarization is important unless you have a circular polarized patch antenna.
 Aug 16, 2010, 02:09 AM Registered User France Joined May 2010 537 Posts Wow thanks IBcrazy ! I'll do it soon, just need to find a galvanized steel. All my antennas will be from IBcrazy, do you have some stickers ??
 Aug 16, 2010, 02:38 AM Registered User Romania, Dolj, Craiova Joined Sep 2007 17,364 Posts Any changes if using raw PCB board instead ?