Multilateration and

Start with a quarter wave so you have a comparison when building the colinear.
At least then you notice if the colinear didn’t quite work and has bad performance.

These two should be an easy build:
Three Easy DIY Antennas for Beginners - #2 by abcd567
QUICK SPIDER - No Soldering, No Connector

If you already have such an antenna, try tuning the whip a bit (changing whip length for example by cutting the whip and then attaching another part that can be moved up / down by soldering).
I personally ended up with a whip at 65 mm instead of 68 mm and it made a difference.

Instead of the typical coax colinears also take a look at this colinear: G7RGQ Antenna 1090MHz

When comparing antennas or tuning it a bit there are a quite a few tools that can be helpful in regards to judging ADS-B reception.
Due to obvious bias i’ll list some stuff i maintain: graphs1090
Also useful in my opinion: tar1090 pTracks feature and displaying the heywhatsthat range outline, see the tar1090 github page for installation and how to use those features.
You’ll find links to tar1090 and graphs1090 here:
Raspbian Lite: ADS B receiver · wiedehopf/adsb-wiki Wiki · GitHub

(graphs1090 and tar1090 will work fine with dump1090-fa and won’t disrupt any feed client you might have)

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