ADS BPF simulation problem/verification

Thread Starter

Natil

Joined Jan 15, 2019
7
Hi all,
I tried to convert a BPF from Lumped components to Transmission lines and the simulation result was different. I attached here doc file with relevant information.

Thanks in advanced
Nati
 

Attachments

cariban

Joined Aug 14, 2018
68
It is exactly the performance of distributed-filters based on transmission lines. After lamda/2 length, the impedance of a transmission line will end up with the same value. For example, your component connected to one open transmission line with length L. For all L + n*lamda/2, where lamda is the wavelength and n is an integer, the effective impedance is the same.

If the length keep the same, while the frequency increases, you will see the similar effect. That is why you see periodic transfer function of distributed-filters based on transmission lines.
 

Thread Starter

Natil

Joined Jan 15, 2019
7
@cariban thanks

according to the frequency response in addition to your explanation, can we conclude that the transmission lines filter is not a typical BPF but it is a kind of filter bank with response of filtering all the multiplications of the the initial planed frequency band?
 

cariban

Joined Aug 14, 2018
68
@cariban how can a filter like this be used?
Of course it is still useful. First you may not need good rejection at all out-of-band. You may just need good reject close to the in-band frequency. Secondly you can use another filter for extra filtering, for example a lowpass filter to obtain better rejection at out-of-band frequency.
 

Thread Starter

Natil

Joined Jan 15, 2019
7
@cariban so there are pros and cons for this transmission lines filter. I wonder, if I want to use this filter to be the first BPF in RX chain, before LNA which is broadband, should I add additional LPF between them? or maybe it will be better to design a different single BPF?
Is the advantage of using this filter over Lumped component one is only for higher frequencies?
 

cariban

Joined Aug 14, 2018
68
@cariban so there are pros and cons for this transmission lines filter. I wonder, if I want to use this filter to be the first BPF in RX chain, before LNA which is broadband, should I add additional LPF between them? or maybe it will be better to design a different single BPF?
Is the advantage of using this filter over Lumped component one is only for higher frequencies?
That is quite depending on your working frequency. What is the frequency of your signal? And what is bandwidth? How much out-of-band rejection do you need?
 

Thread Starter

Natil

Joined Jan 15, 2019
7
@cariban Can I GENERALLY say that considering 6GHz and above, distributed element filter is preferable than Lumped element filter regarding to out-of-band rejection parameter?
 

cariban

Joined Aug 14, 2018
68
@cariban Can I GENERALLY say that considering 6GHz and above, distributed element filter is preferable than Lumped element filter regarding to out-of-band rejection parameter?
6GHz leads to about 25 mm wave length (assume dielectric constant of 4). So the size of distributed filter has been reduced to the feasible range, while it still occupies more PCB area than lumped-filter. But lumped-filter at this frequency may be difficult to play with. The other option is to buy the filter in shelf, for example from mini-circuits:
https://ww2.minicircuits.com/WebStore/RF-Filters.html
 

Thread Starter

Natil

Joined Jan 15, 2019
7
@cariban Many Thanks Cariban,
Your explanations with this issue were very helpful.
Appreciated!!! All the best...
Nati
 
Top