Digital Techniques for Wideband Receivers (2nd Edition)
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This newly updated, second edition of Digital Techniques for Wideband Receivers is a current, comprehensive design guide for your digital processing work with today's complex receiver systems. Brand new material brings you uptodate with the latest information on wideband electronic warfare receivers, the ADC testing procedure, frequency channelization and decoding schemes, and the operation of monobit receivers. The book shows you how to effectively evaluate ADCs, offers insight on building electronic warfare receivers, and describes zero crossing techniques that are critical to new receiver design. From fundamental concepts and procedures to recent technology advances in digital receivers, you get practical solutions to all your demanding wideband receiver problems. This handson reference is packed with 1,103 equations and 315 illustrations that support key topics covered throughout the book.
Inspec keywords: signal processing; electronic warfare; radio receivers
Other keywords: communication receivers; Matlab; computer programs; digital signal processing approach; wideband receivers; EW systems; electronic warfare system
Subjects: Signal processing and detection; Electronic warfare; Radio links and equipment
 Book DOI: 10.1049/SBRA005E
 Chapter DOI: 10.1049/SBRA005E
 ISBN: 9781891121265
 eISBN: 9781613531334
 Format: PDF

Front Matter
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1 Introduction
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This book discusses digital signal processing schemes that are potentially applicable to electronic warfare (EW) receivers. These receivers must have very wide instantaneous input bandwidth (about 1 GHz) to fulfill their operational. However, communication bandwidth is increasing because the wider the bandwidth, the more information per unit time can be transmitted from one point to another.

2 Requirements and Characteristics of Electronic Warfare Receivers
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In this chapter, the information contained in a radar pulse will be presented first. Then some of the difficulties encountered in receiver research will be stated. A very simple discussion on analog and digital receivers will then be presented and, finally, the characteristics of EW receivers will be discussed. If several definitions of one term are available, only the ones that have a direct impact on EW receivers will be discussed. All the characteristics presented here are measurable quantities and the measurements will be presented in Chapter 14. Finally, the research trend in EW receivers will be discussed. Readers with EW background can skip this chapter.

3 Fourier Transform and Convolution
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In this chapter, both the Fourier transform and Fourier series will be discussed. The properties of the Fourier transform will be presented and the concept of impulse function will be introduced. The definition of convolution and its relation with Fourier transform will be presented. Examples of some commonly used Fourier transforms are given and the results are presented in a table for quick reference. There are many good books on this subject. A few of the books are listed at the end of this chapter. Readers with a background in this area can skip this chapter. However, Examples 3.10 and 3.11 may be of interest, because the former one is related to the radar pulse train and the latter will be used in the Hilbert transform.

4 Discrete Fourier Transform
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In this chapter, the discrete Fourier transform (DFT) will be discussed. The Fourier transform discussed in the previous chapter is quite useful, but the applications will be limited for two reasons. First, the function in the time domain must be representable in closed form so that the Fourier integral can be performed. Thus, unless the input function can be written in closed form, it is impossible to evaluate the integral. Second, even if the time function can be written in closed form, it might also be difficult to find a closedform solution to the integral.

5 Fourier TransformRelated Operations
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In this chapter, the operations discussed will be related to the Fourier transform and especially to the discrete Fourier transform (DFT) or fast Fourier transform (FFT). Some of these operations are useful to receiver design and some of these techniques can improve the results of the FFT. The discussion includes zero padding, better localization of FFT peaks, digital convolution, parallel FFT operations to increase overall speed, performing real FFT by using complex FFT operations, and a phase sampling scheme to increase the bandwidth of the receiver.

6 AnalogtoDigital Converters
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In this chapter, the performance of analogtodigital converters (ADCs) will be discussed. The discussion will concentrate on the impact of ADCs on the performance of receivers; therefore, the discussion will be emphasized from a system point of view. The important parameters of the ADC related to receiver performance are number of bits, number of effective bits, maximum sampling frequency, and input bandwidth.

7 Amplifier and AnalogtoDigital Converter Interface
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The main purpose of this chapter is to present an optimum way to match the radio frequency (RF) amplifier with the ADC. The word optimum means to obtain a certain sensitivity and dynamic range, desired by the designer, within the limits of the amplifier performance and the ADC. The important parameters for the ADC are the number of bits, maximum sampling frequency, and input power level. It is assumed that the performance of the ADC is ideal. The lower limit of the dynamic range is the noise level rather than the spur levels because the spur levels are difficult to predict, as discussed in the Chapter 6. This same approach can be used to design with nonideal ADCs. For nonideal ADCs, the lower limit of the dynamic range should be considered as limited by the spur's response rather than the noise level.

8 Frequency Downconverters
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This chapter will discuss both schemes of frequency conversion, the onechannel and twochannel conversions. Both analog and digital frequency conversions will be discussed. Several digital approaches to create the I and Q channels will also be discussed. The impact of imbalance between the land Q channels on the receiver performance will be presented. Finally, a correction scheme to rectify the l and Q channels imbalance will be discussed.

9 Sensitivity and Detection Problems
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This chapter discusses different types of detection schemes. The difference between the detection schemes of analog and digital receivers will be emphasized. The possible advantages of a digital receiver from a detection point of view will be discussed. The detection based on one data sample will be discussed first. The one sample case will be extended to multiple samples. Finally, frequency domain detection, which can be applied to digital receivers, will be examined. Examples with computer programs are used to illustrate some of the detection schemes.

10 Phase Measurements and Zero Crossings
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In this chapter, a phase measurement method and a zero crossing method will be discussed. These methods are relatively simple, but they can operate only under limited conditions. If the input contains only one sinusoidal wave, these methods can provide very accurate frequency measurement. Theoretically, these methods can detect the existence of simultaneous signals. The phase measurement approach uses analog inphase and quadrature (IQ) channels as the front end. If the IQ channels are perfectly balanced, the phase measurement method can measure the frequencies of two input signals. The zero crossing method can measure the frequencies of multiple input signals. However, when multiple signals are present, the frequency accuracy measured by both these two methods will suffer compared with one input signal. Some of these methods need more investigation to determine their performances.

11 Frequency Channelization
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Channelization is one of the most important operations in building digital electronic warfare (EW) receivers. The equivalent analog operation is the filter bank. Therefore, digital channelization can be considered a digital filter bank. It can also be considered as an Nport network with one input and N1 outputs. An input signal will appear at a certain output according to its frequency. By measuring the outputs from the filter bank, the frequency of the input signal can be determined. The design of a specific digital filter bank will be presented. This specific example is used to illustrate the design procedure while avoiding the unnecessary mathematical complexity of a general design. In this example the concepts of polyphase filter and multirate operation will be introduced. In order to understand these concepts, decimation and interpolation are discussed first.

12 Monobit Receiver
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In this chapter the concept of the monobit receiver will be introduced. This technique can be considered as a digital channelized approach. The fast Fourier transform (FFT) is very simple and can be built on one chip. A simple frequency encoder is used after the FFT outputs to determine the number of input signals and their frequencies. The design of a candidate encoder will be presented. The encoder and the FFT can be built on one chip. The chip has been fabricated and the monobit receiver concept has been validated successfully in the laboratory.

13 Processing Methods After Frequency Channelization
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This chapter describes how, after the frequency channelization, further processing is performed to determine the number of frequencies and the frequencies themselves. The frequency data resolution (or frequency bin width) calculated through an FFT operation determines the frequency precision measured on the input signal. It is often desirable to obtain better frequency precision than the FFT operation can provide. Another problem with such a wide frequency bin is that when two signals fall into one frequency output channel, the receiver cannot effectively separate them.The traditional way to separate signals by frequency is through an analog filter bank. Although the main emphasis of this book is digital, one still can consider the analog filtering approach. In an analog channelized receiver, after the filter bank and amplifier, crystal video detectors are used to convert the radio frequency (RF) into video signals. The video signals are digitized by ADCs and are further processed to determine the number of signals and their frequencies. In converting RF into video signal, some information is lost. If two signals fall into one channel, it is difficult to separate them.

14 HighResolution Spectrum Estimation
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In this chapter, some spectrum estimation approaches have been introduced that has been referred to as highresolution spectrum estimations. Their major advantage is that they can provide higher frequency resolution than FFT, especially on simultaneous signals. In this chapter, seven highresolution methods have been discussed: linear predication (or autoregressive (AR)) method, Prony's method, the least squares Prony's method, the multiple signal classification (MUSIC) method, the estimation of signal parameters via rotational invariance techniques (ESPRIT) method, the minimum norm method, and the minimum norm with discrete Fourier transform (DFT) method.

15 Angle of Arrival Measurements
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The angle of arrival (AOA) is the most valuable information that can be obtained from an enemy radar because the radar cannot change its position drastically in a very short time frame (i.e., a few milliseconds). Unfortunately, the AOA information is also the most difficult information to obtain. It requires several antennas with receivers. The two common approaches to measure AOA are based on amplitude and phase comparisons. Another approach is to use the Doppler frequency shift generated by the aircraft movement. However, this approach is closely related to the phase measurement system. If the requirement is to measure AOA on simultaneous signals, the problem becomes even more complicated because receivers with multiple signal capability are needed.

16 Receiver Tests
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This chapter discusses the performance of a digital receiver and the procedures of testing it. The receiver performance is one of the most important aspects in receiver research. One of the main impasses in receiver research is that there are no universally acceptable standards in the performance of electronic warfare (EW) receivers. Because of this shortcoming, researchers do not know where to improve the EW receiver performance. If one claims to have made some improvements in receiver performance, but cannot report the result quantitatively, it will be rather difficult to be accepted. Worse yet, people can make claims on certain performances of an EW receiver that cannot even be used in a system at all. For example, if a receiver misses many signals or produces a large number of spurious responses, in general it cannot be used in any system. Under this condition, no matter how good other performances are, the result should not be reported. There should be some minimum requirements a receiver must be measured against in order to qualify as a functioning receiver.

Back Matter
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