Gain disrtibution in receiver system

1.what is the optimum way to distribute the gain in superhetrodyne receiver system? We are planning for ku-band superhetrodyne .

2.what is basic steps for the design of non coherent receiver system??

1. The gain distribution in a receiver means giving particular stages gains and losses so that from the input signal-level range we get an equal range at the detector or demodulator. The best method is described by the Friis' equation for receiver gain and noise figure. The "dynamic" range , the difference between the input noise figure and a maximum signal input, should be transferred to the receiver output. This means the gain should be adjusted for each stage with an attention to gain compression in latter stages.

2. The non-coherent receivers are called radiometers; most often they amplify and process input noise power without a coherent signal. The design is similar to "communication" receivers but most important are the low noise figure, wide predetector bandwidth (usually defined to 0.5 or 1 dB instead of 3 dB), and gain stability.

abhijitrc said:

1.what is the optimum way to distribute the gain in superhetrodyne receiver system? We are planning for ku-band superhetrodyne .

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It depends on what you are trying optimize. Optimal noise figure involves more gain upfront, whereas optimal linearity will put more of the gain at the back end. Distributing the gain stages so that the cascade gain stays at least slightly positive throughout the chain is a good starting point.

what is the best way to mount the HEMT device for best possible NF and gain? i am facing the problem of repeatability of getting back the same noise figure and gain in multiple fabrication! we are using alumina substrate ( 9.8) and the subtrate is fabricate on kovar plate and the device is mounted at the kovar between two substrate.

what may be the reason of nt getting the repeatability? what is the right way to mount the device(HEMT), IF possible provide me some references.

abhijitrc said:

what is the best way to mount the HEMT device for best possible NF and gain? i am facing the problem of repeatability of getting back the same noise figure and gain in multiple fabrication! we are using alumina substrate ( 9.8) and the subtrate is fabricate on kovar plate and the device is mounted at the kovar between two substrate.

what may be the reason of nt getting the repeatability? what is the right way to mount the device(HEMT), IF possible provide me some references.

Click to expand...

I think it is tricky if your HEMT device must be grounded while the "live" lines are on alumina. You do not mention your frequency band. I have used FR-4 for many designs starting from 1 GHz up to 110 GHz. It works well and I had no repeatability problem. Instead of grounding by vias I use a direct solder or conductive Epoxy for ground connections, and live 50-Ohm lines are on FR-4.

Using alumina makes only sense if you create filters or matching structures at < 3 GHz. Otherwise the rigid ceramic is rather problem for dilatation, etc.

---------- Post added at 18:37 ---------- Previous post was at 18:35 ----------

Try to look inside satellite LNBs; they use FR-4 or a similar substrate, and at 10-12 GHz, they are extremely good over temperature while the NF is excellent.

You need to know NF , Gain and 3rd order intercept for each stage. to calculate Gain in power and loss of NF
Noise dB√Hz for each stage
Margin to max 3rd order intercept from disturbance or interference
Noise rejection with resulting SNR improvement from BPF
All these require assumptions for signal range, noise range, peak interference profile. Efficiency goals, cost targets, physical contraints,
Sensitivity Analysis for all high tolerance uncontrolled parts
Consider piezo effects of materials (eg ceramic caps )
and aging analysis of components.

Consider active Polymer materials for dielectric. This is becoming very popular in China.

Before you do any design,

Write a detailed spec. including all environmental specs to be met. and submit .

jiripolivka said:

I think it is tricky if your HEMT device must be grounded while the "live" lines are on alumina. You do not mention your frequency band. I have used FR-4 for many designs starting from 1 GHz up to 110 GHz. It works well and I had no repeatability problem. Instead of grounding by vias I use a direct solder or conductive Epoxy for ground connections, and live 50-Ohm lines are on FR-4.

Using alumina makes only sense if you create filters or matching structures at < 3 GHz. Otherwise the rigid ceramic is rather problem for dilatation, etc.

---------- Post added at 18:37 ---------- Previous post was at 18:35 ----------

Try to look inside satellite LNBs; they use FR-4 or a similar substrate, and at 10-12 GHz, they are extremely good over temperature while the NF is excellent.

Click to expand...

our band of operation is 11 GHz to 16 GHz respectively. What is the best way to mount the device? device is cfy67 ( infenion make) package style is MICRO-X