Ku-Band Miniature Waveguide Low Pass Filter for Harmonic Suppression
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Solution Overview
Problem
Existing Waveguide Low Pass Filters struggle to effectively suppress harmonics and higher order waveguide modes in satellite OMUX channels, particularly in Ku-band applications, where high suppression levels and compact sizes are required, while avoiding power multipaction issues and numerical errors in filter synthesis.
Innovation Solution
A computer-aided design method that synthesizes Ku-Band Miniature Waveguide Low Pass Filters using a combination of filter synthesis software and electromagnetic optimization, allowing for the simultaneous optimization of all circuit elements to achieve high-order filter specifications with reduced size and improved selectivity, while controlling waveguide and cavity dimensions to prevent power multipaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional filter synthesis approaches are used, then filter specifications can be controlled, but numerical errors and difficulty in producing high-order filters occur
Solution Approach 1:
The patent transforms the filter design parameters from traditional circuit theory domain to electromagnetic field domain by using EM optimization techniques. This allows continuous adjustment of geometric parameters (waveguide dimensions, cavity sizes, iris positions) to achieve high-order filter specifications without suffering from numerical errors inherent in traditional synthesis methods. The EM optimization enables precise control of filter response by directly optimizing the electromagnetic fields rather than relying on approximate circuit models.
2Ease of manufacture
If EM optimization techniques are used, then realizable component values are obtained, but control over filter parameters is lost
Solution Approach 1:
The patent segments the filter design into distinct functional modules: waveguide sections with controllable dimensions, cavity resonators with adjustable sizes and positions, and iris couplings with variable geometries. Each module can be independently optimized using EM techniques while maintaining overall filter specification control. This modular approach allows both manufacturability (through realizable component values) and precision (through controlled parameter optimization).
Solution Approach 2:
The design methodology employs dynamic optimization where filter parameters are continuously adjusted during EM simulation and optimization processes. The system dynamically balances between manufacturability constraints (realizable component values) and performance requirements (filter specifications) by iteratively refining geometric parameters within physically realizable ranges while maintaining precise control over the final filter response.
3Speed
If waveguide width is increased to propagate TE10 mode, then basic mode propagation is enabled, but higher order modes and harmonics are generated
Solution Approach 1:
The patent intentionally designs the waveguide dimensions and cavity structures to generate higher order modes, then uses strategically positioned cavities and irises to create transmission zeros that suppress these harmful modes. The harmful higher order modes and harmonics are converted into useful transmission zeros in the stopband, which provide additional attenuation and shaping of the filter response. This transforms the problem of mode generation into a solution for enhanced stopband rejection.
4Volume of moving object
If filter size is reduced for compact applications, then space requirements are met, but suppression performance and selectivity deteriorate
Solution Approach 1:
The patent employs nested cavity structures where smaller cavities are positioned within or adjacent to larger cavities, and multiple functional elements are integrated within compact waveguide sections. This nesting approach allows high-order filter specifications to be achieved in a reduced overall volume by efficiently utilizing three-dimensional space and creating multiple transmission zeros within a compact footprint, thereby maintaining suppression performance while reducing filter size.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method achieves a filter size of 6.9 cm with over 60 dB rejection from 13.5 GHz to 40 GHz and 34 dB return loss, outperforming previous designs in terms of size and performance, with the ability to fine-tune for optimal results using EM optimization.
Implementation Method 1
Basic Mode is taken as TE10. For propagation of this Mode, wave frequency (f) should be higher than cutoff frequency (fc10) of this Mode.
Implementation Method 2
A typical module used in Waveguide Low Pass (LP) filter structures is shown in three dimensional in Figure 1a. The module shown in said figure consists of two cavity(C) resonators
Implementation Method 3
LP filter is expected to stop such Modes. In other words, filter is expected to propagate only TE10 Mode. In addition, even only TE10 Mode is propagated, the power amplifiers in the system may generate harmonics (nfo) of basic frequency (fo) and such harmonics may be generated by TE10 Mode.
Data Source
Figure 1(a)~1(c)
Figure 2~3
Figure 4~5
AI summary
The invention relates to a computer aided design method for designing a Ku-Band Miniature Waveguide Low Pass Filter suppressing harmonics and higher order mode signals generated at output multiplexer in satellites. With the method disclosed under the invention, both application circuits and stop circuits can be synthesized as one single part. Thus all of circuit elements contribute to both impedance matching and suppressing. This helps shortening filter size, enhancement of selectivity and increasing rejection level. In addition, both power, cavity (C) sizes and waveguide length (d) and waveguide height (b) can be taken under control by means of developed circuit transformations. Thus power issues can be eliminated.