When designing filters for Yagi or log-periodic antennas, the focus is typically on achieving the desired frequency response characteristics and suppressing unwanted frequencies. Here are some techniques commonly used in filter design for these types of antennas:

Passive LC Filters: LC (inductor-capacitor) filters are widely used in antenna designs. They consist of inductors and capacitors arranged in specific configurations to create desired frequency responses. LC filters can be designed as low-pass, high-pass, bandpass, or band-stop filters to attenuate specific frequency ranges.

Stub Tuning: Stub tuning involves adding shorted or open-circuited stubs to the transmission line feeding the antenna elements. These stubs act as reactive elements, introducing additional impedance to modify the frequency response. By adjusting the length and position of the stubs, the frequency response of the antenna can be tailored.

Matching Networks: Matching networks are used to match the impedance of the antenna to the transmission line or the source impedance. They are often employed to optimize the antenna's performance across a specific frequency band. Techniques such as L-section matching networks or T-section matching networks can be employed to achieve impedance matching.

Baluns: Baluns are devices used to convert the unbalanced transmission line to a balanced feed or vice versa. They help in eliminating common-mode radiation and maintaining the antenna's desired radiation pattern. Properly designed baluns can improve the antenna's performance and impedance characteristics.

Optimization Techniques: Various optimization algorithms, such as genetic algorithms or particle swarm optimization, can be employed to fine-tune the filter design parameters for specific performance goals. These techniques help achieve desired frequency response characteristics, such as impedance matching, bandwidth, or rejection levels.

It's important to note that the specific techniques used in filter design for Yagi or log-periodic antennas may vary depending on the design requirements, desired performance, and the application context. Additionally, computer-aided design (CAD) tools and electromagnetic simulation software can greatly assist in the design and analysis of filters for these antennas.

Is there any possibilities to do filtering with directors or reflector size, distance or shape for introduce filtering. Currently I would not focus on any additional filtering in balun or on the later stages.

There are a number of techniques that can be used to design filters in Yagi or log-periodic antennas. Some of the most common techniques include:

• Dielectric loading: This technique involves inserting dielectric materials between the dipole elements of the antenna. This can help to reduce the antenna's size and improve its bandwidth.
• Sinusoidal dipoles: Instead of using straight dipole elements, sinusoidal dipoles can be used. This can help to improve the antenna's bandwidth and gain.
• Traps: Traps are small, resonant elements that can be inserted into the antenna's feed line. This can help to filter out unwanted frequencies and improve the antenna's selectivity.
• Phase shifters: Phase shifters can be used to control the phase of the signals that are fed to the antenna's dipole elements. This can be used to improve the antenna's beamwidth and directivity.

The choice of which technique to use will depend on the specific application and the desired performance characteristics of the antenna.

Here are some additional details about each of these techniques:

• Dielectric loading: Dielectric loading is a very effective way to reduce the size of a Yagi or log-periodic antenna. This is because the dielectric material has a lower electrical conductivity than air, which allows the antenna to be made smaller without affecting its performance.
• Sinusoidal dipoles: Sinusoidal dipoles are a type of dipole element that has a sinusoidal current distribution. This can help to improve the antenna's bandwidth and gain.
• Traps: Traps are small, resonant elements that can be inserted into the antenna's feed line. These traps can be used to filter out unwanted frequencies and improve the antenna's selectivity.
• Phase shifters: Phase shifters are devices that can be used to control the phase of the signals that are fed to the antenna's dipole elements. This can be used to improve the antenna's beamwidth and directivity.