Cloverleaf possibly blew out transmitter?
It's possible that the transmitter was damaged by reflected power from a poorly matched antenna. That's the scenario the manufacturer is warning about with running the transmitter with no antenna. Without a well-matched load on the transmitter output, the RF power reflects from wherever the discontinuity is and back into the output of the amplifier. This can cause the amplifier to operate incorrectly or even destroy it.

Antennas look simple, but there's a lot going on electrically, and matching an antenna's impedance to the system impedance at the operating frequency can be a bit of a challenge. Although impedance is measured in Ohms, it is not a resistance, and can't be measured with a DMM. Instead, impedance is the relationship between voltage and current through a circuit, and it depends not only on the resistances in the circuit, but also the capacitances, inducatances, and the measurement frequency.

An RF network analyzer could do the job, but those instruments are indeed quite expensive. You may be able to make friends with someone who has access to one and could help you tune your antenna. For an idea of what's involved, read The Dropout's Guide to PCB Trace Antenna Design.

Amateur radio operators use SWR meters to measure the ratio of the power going towards the antenna to the power reflecting back from it, and make adjustments to minimize the reflected power. While those SWR meters aren't extremely expensive, they are designed for much lower frequencies than 2.4 Ghz, and it is useless to match an antenna at a frequency other than its operating frequency. I've never seen an SWR meter in the microwave range that could reasonably be bought or built by the casual hobbyist.

Other options:


Buy an antenna that's already well-matched
Buy a transmitter that is more robust against poorly matched loads.