analog filtering - iucaf.org · analog filtering reinhard keller this ... tunable filters: ......

Folie 1

Analog Filtering

Reinhard Keller

This is a little overview of what is done and what is planned against RFI with analogfilters at the Effelsberg Telescope.

Folie 2

Bonn, 30. March 2001RFI Mitigation Workshop2

Analog Filters are everywhere

In the frontends:– at RF stages

– at IF stages

– at DC

In the backends– at IF level

– at DC

Besides many classical filters a lot of shielding is used to avoid RFI. That is whatindustry calls EMC, electro-magnetic compatibility. Filters are also incorporated in theDC connectors.

Folie 3


RFI at 21cm in Effelsberg:

The need of RFI mitigation is obvious! Small bands are reserved for astronomy butwideband observation are wanted. Only a few interferers are known. Most of themare changing with time and also in frequency. This delimits hardware filtering

Folie 4


Fixed Filters:

Frequency domain: – Bandpassfilter

– Bandstopfilter (Notch)

(Time domain)

Folie 5


Fixed Frequency Filters

Before LNA:1. Avoid saturation

(„robust receiver“)

2. Select desired frequencies

→ low loss → high gain stability

After LNA:1. Select desired

frequencies

2. Avoid saturation(„robust receiver“)

→ high selectivity → high gain stability

Folie 6


Fixed Frequency Filters

are

simple

Need no info about RFI

but

Seperation of RFI ⇔ signal in frequency domain

Folie 7


Example 1: 1.9cm Receiver

Realized at the Effelsberg telscope

Folie 8


13 GHz High Pass Filter

-80

-60

-40

-20

0

10 12 14 16 18 20

f/GHz

S/d

B

Folie 9



Insertion loss S21-Betrag

-0.5

-0.4

-0.3

-0.2

-0.1

0

10 12 14 16 18 20

f/GHz

S/d

B

Folie 10



waveguide realization:

Folie 11


„Adaptive“ analog filters

Switched filters:– Realized in Effelsberg

Prooved, but after LNA!

Tunable filters: – Waveguide filters;

Mecanicaly tuned in dewar

– HTSC-filters (Uni Wuppertal);Electr. Tuned by ferro elektric – magnetic material

Piezo electric tuning

Folie 12


Example 2: 21cm Receiver

Realized filter bank after the LNAFolie 13



Planned implementation of High Temperature Superconducting Filters. The filtersare realized.Folie 14


1st HTSC Filter: Notch at low end

Folie 15


1st HTSC Filter:

Folie 16



Folie 17


Corrugated bandpass filter

Folie 18


Corrugated bandpass filter

Fcenter=6.2GHz, RBW=21%; simulation results:

Folie 19


CMT + Bandpass integrated

Currently under developmentFolie 20


What will be realistic?

In the dewar:– low frequencies > 3 GHz:

1. (tuneable) HTSC filters

– medium frequencies :1. (tunable) waveguide filters

– high frequencies > 30 GHz: fixed waveguide filters

At room temperature:– filters of any kind

analog filtering - iucaf.org · analog filtering reinhard keller this ... tunable filters: ......

Documents