Improving the Standing Wave Ratio (SWR) and matching the impedance of a Yagi antenna involves optimizing its design and tuning its elements to achieve resonance and efficient signal transmission. Here are some steps you can take to achieve better SWR and impedance matching for your Yagi antenna:

Choose the Right Frequency: Ensure that the frequency you want to operate at is within the design frequency range of your Yagi antenna. Mismatched frequency can lead to poor SWR and impedance mismatch.

Calculate Element Lengths: Use Yagi design software or calculators to determine the correct element lengths based on the frequency of operation and the design specifications.

Element Spacing: Spacing between the elements also affects the antenna's performance. Refer to Yagi design guidelines to determine the optimal spacing for your antenna.

Balun: A balun (balanced to unbalanced transformer) can help with impedance matching between the antenna and the transmission line. It ensures that the balanced antenna's impedance is transformed to the unbalanced impedance of the coaxial cable. A properly designed balun can help reduce SWR and improve impedance matching.

Adjust Element Lengths: Fine-tune the lengths of the elements to achieve resonance at the desired frequency.

Use an Antenna Analyzer: An antenna analyzer is a valuable tool for measuring SWR and impedance. It helps you visualize how the antenna performs at different frequencies and can guide you in making adjustments for better matching.

Test and Iteration: Testing your Yagi antenna in real-world conditions is crucial. Set up the antenna and use an SWR meter to measure the SWR across the desired frequency range.

_Make adjustments based on the readings to improve SWR and impedance matching_

Antenna Design Software: There are various Yagi antenna design software tools available that can help you simulate and optimize the antenna's performance before building it. These tools can assist you in achieving better SWR and impedance matching by providing insights into the antenna's behavior.

Keep in mind that environmental factors such as wind, moisture, and temperature can affect the performance of your Yagi antenna over time. Regular maintenance and re-tuning might be necessary to maintain optimal performance.