Delay Band-pass Filter

Microwave delay band-pass filters have always been the top difficulty of various filters. How to balance the rejection outside the pass-band and the delay inside is usually the focus of our RF engineers. With the rapid development of high quality microwave telecommunication system, we need such microwave filters, not only the amplitude responses of which meet the requirements, but also the delay within the pass-band be a constant. Therefore, it is quite important to research such delay filters in our engineering practice.In this thesis, according to the equidistant linear phase polynomial theory and the low-pass prototype network, an 8-cavity delay band-pass filter is produced with the pass-band as 1.910GHz~2.015GHz, the insertion loss as 0.4dB and its ripple as±0.1dB, the group delay as 9.5ns and its flatness as±0.1ns, the return loss as 24dB. On the basis of profound understanding of reflected group delay, the filter is tuned with the reflected group delay method. And it works well, lowering the difficulty of multi-cavity filter tuning, especially for early operators.Meanwhile, the use of coaxial cavity makes the introduction of cross coupling poles easier over the combline or waveguide structure, thus a more compact filter may be obtained. Advanced simulation software enable the circuit simulation to produce ideal curves and coupling coefficients, accordingly, the field simulation can give the physical size, greatly reducing the design cycle. It is benefited to batch production.For wide band-pass, the delay has a linear response when introducing a cross coupling pole. To eliminate such undesired response, another cross couple pole with opposite characteristic is creatively added to adjust the coupling strength and repeatedly test until the delay becomes flat.