receiver system design 1

8/17/2019 Receiver System Design 1

http://slidepdf.com/reader/full/receiver-system-design-1 1/3

Receiver-System Design, Part 1- System Specifications Tuesday, June 1, 2004 - Dave Adamy

Receiver-System Design, Part 1— System Specifications

Dave AdamyJune 2004

Receiver systems for electronic warfare (EW) and reconnaissance (recon) are significantly

different from the receivers in communication systems and radars. In these other cases, each receiver isdesigned to optimally recover the information carried by only one type of signal, within a narrowfrequency range. More importantly, the receiver can be tuned to the known correct frequency and canusually make use of automatic gain control to optimize reception of the desired signal.

EW and recon receivers, on the other hand, typically must handle several different types ofsignals over a significant frequency range — and typically have very little information about the signalfrequency to be received. They are usually required to handle a range of different modulation types andparametric ranges, and they are often required to determine the emitter location as well. Thus, thespecifications for such a receiver system can be very challenging, requiring sometimes painfulperformance tradeoffs to be made.

In this series, we will cover the following subjects:

• Typical performance specifications that must be met by EW and recon receiver systems• Types of receivers used in EW and recon systems (review)• Calculation of receiver-system sensitivity and related design factors• Determination of dynamic range from component specifications and design procedures• The impact of various emitter-location approaches on receiver-system design• The general types of signal-flow paths within the receiver system• Design principles for radar-warning receivers• Design principles for reconnaissance receiver systems• The design of digital receiver systems

The Receiver System First, let’s consider the definition of a receiving system. As shown in Figure 1, it includes one ormore antennas, a signal-distribution network, one or more receivers, and usually some sort of signal-processing circuitry. Its output can be audio or video displays to one or more operators or data to one ormore computer or data-distribution systems. When emitter location is required, there is often significantpreprocessing before the receivers, as shown in Figure 2.

Table 1 lists the typical specifications for an EW or recon receiver system. All of thesespecifications are not required for all receiving systems. There will also be specifications having to dowith power-supply requirements, packaging limitations, and environmental conditions for storage andoperation, but we will concentrate only on performance specifications here.

Frequency Range The frequency range of the receiver system determines the range over which the receivers in thesystem can be tuned. If wideband receivers are included in the system, large portions of the frequencyrange may be continuously covered. Naturally, the antennas must provide adequate coverage of thefrequency range. If wide frequency ranges are covered, there may be several different receivers,connected to different antennas or antenna arrays. For example, in a typical ground-based emitter-location system, there are two or three antenna arrays, each covering a portion of the frequency rangeand connected to different preprocessors and receivers, as shown in Figure 3. This figure shows atypical wideband, ground-based, direction-finding system. Each array typically covers less than a five-to-one frequency range.

Modulations An EW/recon receiver system must be able to receive all of the expected types of modulations

for threat emitters. For radar signals, this includes pulse, continuous wave (CW), frequency-modulated(FM) CW, FM on pulse (chirp), or digital modulation on pulse.

For communications signals, this includes AM, FM, phase modulation, multichannel FM/FMsignals, single sideband (upper or lower sideband), and various digital modulations. For AM signals, thepercentage of amplitude modulation is normally specified, and for FM signals, the modulation index is

Pagina 1 di 3Naylor Publications

11/11/2008http://66.38.154.178/absolutenm/templates/default.aspx?a=1134&template=print-article.htm



commonly specified. Common digital modulations include pulse-amplitude modulation (PAM),frequency-shift keyed (FSK), binary-phase-shift keyed (BPSK), and quadrature-phase-shift keyed(QPSK). There are also spread-spectrum modulations, including frequency hopping, chirp, and directsequence. In manually operated receivers, there will typically be a control for modulation selection.

Automatic systems must typically determine the modulation and automatically select the properdemodulation circuitry.

Bandwidth The bandwidths specified are typically the effective bandwidths of the receivers, of which there

may be several types. In general, the bandwidth of any properly designed receiver narrows as the signalpath progresses. The front end is necessarily wide, and multiple intermediate frequency amplifiers arewider upstream and narrower downstream. A general rule of thumb for narrowband receivers is that theeffective bandwidth will be very close to the final predetection bandwidth. Manually operated receiversoften have selectable bandwidth. The narrower the bandwidth, the better the sensitivity, but thebandwidth must be wide enough to include the modulation spectrum of received signals.

The formula for the effective bandwidth when there is a wider radio-frequency bandwidth and asignificantly narrower video bandwidth (such as in radar-warning receivers) is as follows:BEff = sqrt (2 BRF x BVID)Where: BEff is the effective bandwidth

BRF = the predetection bandwidthBVID = the postdetection video bandwidth

What’s Next Next month we’ll complete this discussion of specifications and start our discussion of types of

receivers used in EW/recon receiver systems. For your comments and suggestions, Dave Adamy can bereached at [email protected].


11/11/2008http://66.38.154.178/absolutenm/templates/default.aspx?a=1134&template=print-article.htm



Naylor Publications

http://66.38.154.178/


11/11/2008http://66 38 154 178/absolutenm/templates/default aspx?a=1134&template=print-article htm

receiver system design 1

Documents