Custom Search
More than 12,000 searchable pages indexed.

Your RF Cafe
Progenitor & Webmaster

Click here to read about RF CafeView the YouTube RF Cafe Intro VideoKirt Blattenberger ... single-handedly redefining what an engineering website should be.

Carpe Diem!
(Seize the Day!)

5th MOB:
My USAF radar shop

Airplanes and Rockets:
My personal hobby website

Equine Kingdom:
My daughter Sally's horse riding website

•−•  ••−•    −•−•  •−  ••−•  •
RF Cafe Morse Code >Hear It<

Job Board

About RF Cafe™


rejection of WLNA signal at input of colocated Wimax receive - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Please visit the new and improved RF Cafe Forums that were created in September of 2015. Unlike with the old forums where users registered individually, the new forums use a common User Name and Password so anyone can post without needing to create an account. Please find the current User Name and Password on the RF Cafe homepage. Thanks for your participation.

Below are all of the old forum threads, including all the responses to the original posts.

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews
-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

 Post subject: rejection of WLNA signal at input of colocated Wimax receive
Posted: Thu Nov 19, 2009 11:01 pm 
User avatar

Joined: Wed Aug 16, 2006 8:20 am
Posts: 31
Location: India
I am designing a transceiver where WLAN and WIMAX radios are colocated (on the same PCB).
consider an usage scenariuo when the WLAN (2.45 GHz) systems is transmitting and the WiMAX (2.51 GHz) is receiving. due to finite isolation between the antennas (<15 dB) of WLAN and Wimax, the WLAN signal will either saturate the WIMAX LNA or may produce some intermodulation product by mixing with other signals.
In the standard the minimum rejection requirements of WLAN signal at WIMAX receiver input is not specified.

I calculated that -40 dBm of any interferer signal would be desired to keep all IMD products at LNA input(IIP3=3) below the Noise Floor.

From this I found out the rejection required for WLAN signal. For example it the receiver antenan see a maximum of 5 dBm WLAN signal then the filter before LNA should attenuate the signal to -40 dBm so that any IMD generated by this signal is less than Noise floor.

However it seems that such filters are extremly difficult to realize.

I was wondering if this is the correct approach of finding the filter rejection requirements.

I would be grateful if anyone can share their views on this.


Ashish Bondia,
Design Engineer- RF

 Post subject: Re: rejection of WLNA signal at input of colocated Wimax receive
Posted: Fri Nov 20, 2009 9:36 am 
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 304
Location: London UK
Hi ashish
There are two separate issues here:
1) mutual interference that might be filtered
2) unacceptable high saturation of the non-linear devices
Regarding (1) I am not familiar with the relative relationship between mutual interferers in these particular systems, but in general with digital modulation, it is possible to operate even co-channel with interferers that are only -10dBc. Thus typically one obtains a Bit Error rate of say 1 in 10^-8 for a carrier to noise ratio of 10dB. This arises mainly because the modulation is quasi-synchronous, and the interferer signal clock will be out of phase coherence and thus appear as just noise.
Regarding (2) the resulting non-linearity products might be capable of being out-filtered using an elliptic function filter with the rapid roll-off side of the BPF placed between the two carriers.

At bottom, life is all about
Sucking in and blowing out.

Posted  11/12/2012