FlightAware Discussions

Which one is the best antenna?

Alright, the PVC wasn’t even glued - LOL


Now dimensions:

XR-212 "Stamped side from SMA up (Ground side):
PCB width = 20mm
Thick strip = 68mm
Thin strip = 77mm x 3mm thick
Thick strip = 68mm
Thin strip = 77mm x 3mm

Other side from SMA up:
Thin strip = 14mm x 3mm (from base of SMA)
Medium strip = 18mm x 7mm
Thin strip = 40mm x 3mm
Thick strip = 72mm
Thin strip = 72mm x 3mm
Thick strip = 72mm
Wire = 75mm

Two sided PCB, Not shorted, looks like 1.5mm PCB width

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Thanks @Nitr0

Waiting for side by side performance test.

The configuration is a flattened CoCo.

Don’t hold your breath - it’s like 115F (~46c) outside for the next 45 or so days and it’s no fun crawling around an asphalt roof. Maybe if I get energetic I can pop up there one of these mornings after getting both rigs setup identical again. As it stands, I’m running a Pi4 on one rig and RockPi4 on the other with different gear on each, so will need to rekey for side-by-sides again.

I also need to pick up another FA antenna (to verify side by side and get a baseline), DPD and Jetvision since I want both of them in the test as well, but it’s my hope I can find someone selling either one of them since they get expensive. AirNav antenna won’t make the test (I wont even purchase) until they redesign and make it so the cable can be optional.

Come on, for every problem there’s a solution

image

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A quote from post #2 of this thread

 

This PCB antenna is a flattened CoCo.
The two sides of the PCB antenna are two limbs in column 3 of this sketch

The wide strips shield the thin strips, just like the shield of a Coax. The thin strips therefore do not radiate, and just act as connection between wide strip pieces. The actual radiators are wide strips. The top piece of thin strip projecting above pcb is un-shielded and is therefore a radiator.

This weekend I will prepare it’s computer model and run the simulation.

 

I can’t totally agree with that. Simple reason being -> look at the measurements again, 72mm sections, then there is a 75mm wire. The ground-plane side is 68mm/77mm alternating. Now if you take into account 1/4 wave for 1090Mhz @ 1.0 VF (who knows the actual VF through the substrate/material), you’d get approx 68mm elements with 77mm radials (1/4 wave ground-plane calcs). The active side is alternating 72mm sections with a 75mm wire. Way above my paygrade, but completely different element measurements for any coco I’ve built for 1090Mhz, VF aside. That said, I won’t pretend in the least to be an antenna design expert. More or less a moron on that front.

My first impression was based on configuration without paying attention to element lengths. Now that you have highlighted the measurements, i conclude you are right and it is not a CoCo, but some non conventional configuration.

I know nothing about PCB antenna (black-magic stuff) design. Collinear would most likely be 1/4 or 1/2 wave equal elements, at least conventionally and appropriately sized for the underlying cable velocity factor (VF). This on the other hand - intriguing, and the thing looks super solid on the VNA. Nothing beats real-world testing obviously. I have no clue what the maximum Dbi gain would be on a design like this, but I don’t think it would be above maybe 3-4Dbi (pure speculation, talking out my arse)

Who’s good at this stuff? Not even sure 4nec2 would be of help with this sort of a model?

The 4nec2 is good for wire antennas, but to model a pcb antenna seems beyond its capability. Let us concentrate on real world field testing.

No need to climb up the roof. Why not put both the pcb and benchmark antennas in a window and conduct side by side test? After all it is a comparison under same conditions, and not determination of maximum performance.

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Looking at the initial photos, the metallic label on the white PVC cover will have a small effect on the performance. this is from experience. I was using a transmitter at the time, and the adsorbed power blackened the PVC. Likely a similar impact for reception.

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Why would I take the time to perform tests under knowingly highly bottlenecked conditions?

I believe it would be unfair since antenna are affected differently by nearby spacial objects. Windows have metal frames and since I live in a single-story block home, signal is highly attenuated to begin with - move the antenna 2 feet in any direction and get totally different results - no thanks! Too many variables with indoor tests and if I’m going to spend the time (I have about 20 different antenna to benchmark so far), I want to eliminate as many of those variables as possible.

I also believe the tests should include maximum possible performance for my location or half of the reason for the tests in the first place would be eliminated. Performance is the point (to me)- so much that I’ll even be using Airspy R2’s to help eliminate some of the sensitivity bottlenecks and to lessen the effects of underlying tuner gain.

I guess in a nutshell, I’m stubborn? :crazy_face:

Excellent point - it shall be coming off.

Unless it is critical to the matching :wink:

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Prepration of PCB simulation model in progress.
Prepared model of copper strip on one side of pcb.
Took me 4 hours painstaking work to complete it. :tired_face:

Model of copper strip on other side of pcb will be prepared when I find time & energy to do it.

As 4nec2 has facility to create model using wires only, I made the strip as composed of mesh of very thin wires.

Full view:

image

 

Closeup:

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:+1: Looks like you got the ground side about nailed. No clue about the materials in use, the mill thickness, or about the substrate, but I assume there are PCB strip simulators somewhere out there?

If I missed any other measurements worth-while, please let me know and I’ll do my best to measure.

I may pop it up on the roof after running a quick baseline between my current setups and see what the percentage difference looks like as compared to the FA antenna. Maybe an hour or two test with VRS keyed up on both lines side by side. I think I can throw that much of a bone in the interim while I get setup for the full-blown shootout again. I’m more than curious myself…

YES, RF Engineers usually test an antenna in free space.

Here is an interesting article that describes how to simulate free space in an electromagnetic (henceforth EM) anechoic chamber

It shows what lengths RF Engineers go to.

I’m not suggesting that we need to go to that extreme or that we should understand the mathematics but it does suggest that indoor testing is not as good as free space.

Also look at how the first active element begins at the SMA connector. Any metal mast or clamp would clearly affect that part of the antenna.

S

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No idea about pcb strip simulators, never used these. As pcb material characteristics are unknown, I have decided to use a model with 3mm air gap between the two copper plates, and not a pcb.

You have given all the measurements I need to build a simulation model. Thanks.

It’s quite a while since I had to do any microstrip simulation but why have you decided on using a 3mm airgap?
The relative permittivity of FR4 PCB is about 4.4 and the thickness of the PCB is 1.5mm so would not 0.3mm (1.5/4.4) provide a closer simulation?


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It’s tough to say - I think the typical cheap 1oz PCB trace is .035mm (35um) thick, but that’s rated for copper. I have no clue what this stuff is…tin-something/nickel? The entire PCB is 1.5mm thick so far as I can tell, I didn’t actually mic it out