High Dynamic Range Receiver System Designed for High …iaiest.com/dl/journals/8- IAJ of Innovative...

International

Academic

Journal

of

Innovative Research International Academic Journal of Innovative Research Vol. 2, No. 9, 2015, pp. 1-20.

ISSN 2454-390X

1

www.iaiest.com

International Academic Institute for Science and Technology

High Dynamic Range Receiver System Designed for High

Pulse Repetition Frequency Pulse Radar

Behrouz Kalate Meymaria, Reza Fatemi Mofrad

b, Morteza Shahidi Nasab

c

aMaster Student of electrical engineering of malek ashtar University, Tehran, Iran.

b Department of Electrical and Electronic Engineering, Malek Ashtar University of Technology, Tehran, Iran.

c Master Student of electrical engineering of malek ashtar University, Tehran, Iran.

Abstract

Microwave receivers play a critical role in Pulse Doppler radars, particularly in airborne radars and air

surveillance; and are extremely versatile; therefore their analysis and conceptual design is an important

issue. The receiver should have high dynamic range given that it is linked with a wide range of signals in

Pulse repetition frequency Pulse radars in term of input power; but we cannot use Sensitivity Time

Control (STC) or Automatic Gain Control (AGC). Therefore, the current paper provides a new conceptual

structure that yields high dynamic range (over 100 dB).

Keywords: Dynamic range, Noise figure, Sensitivity, Phase noise

Introduction:

Receivers are an integral part of radars receiving return signal echo. The receiver receives return signal

echo in the radio band and converting it to a digital baseband signal delivers it to signal and data

processing unit to be processed for detection, range and speed extraction, target tracking, and so. In Pulse

radar, the same antenna is used to send and receive signals, so low-loss Duplexer that switches between

the receiver and transmitter to keep them isolated is used to prevent the receiver saturation from the

transmitter with high power signals. In modern receivers input, a Low Noise Amplifier (LNA) is used to

reduce receiver noise figure sufficiently; and then the received signal is passed from a band pass filter to

prevent the arrival of signals outside the frequency band of mixer. Modern radar receivers do other tasks

such as switching frequency, bandwidth, and signals gain control for different radar modes, in addition

more sophisticated receivers have digital control networks to provide best efficacy of radar in different

working modes and meet different modes requirements. Moreover, sophisticated receivers include a

section that is usually used in automatic detection to test the receiver and prevent errors.

International Academic Journal of Innovative Research,

Vol. 2, No. 9, pp. 1-20.

2

The first section of the current paper (parts 1 to 3) describes basic concepts that are essential for receiver

design. Section 4 provides the receiver parameters calculation, and Section 5 is about phase noise

calculation. Section 6 shows analogue to digital converters considerations and Section 7 provides the final

structure of the receiver.

2- Radar receiver’s components and parameters

2-1 RF Pre selection As previously explained, Duplexer is used to protect receiver from strong signals leaking from

transmitter. In addition, we know many return signals that reach the receiver are not signals echo returned

from the target ; but are outcomes of jammers, environment clutter, and disturbing signals from other

radars at a different frequency with echo returning from the target and are placed outside radar band, for

example in the operation of a noise barrage jammer only a part of the jammer signal has the same

frequency of returned target echo. Therefore, the signals radio frequency pre selection is crucial in the

design of the radar receiver to minimize or prevent nuisance signals to the receiver.

Given two signals that are both in receiver passing band and show desired signal with the letter “S” and

jammer signal with the letter “J”, both signals are converted to baseband when passing from the mixer

with a local oscillator; thus jammer signal is on the desired signal and radar is not able to detect target. A

band pass filter is applied to the radio frequency (RF) after low noise amplifier and before the mixer to

prevent this, thus just a desired signal is seen at the mixer input and interfering signals in the baseband

greatly reduced. The presence of low noise amplifier at the beginning of the receiver enhances receiver

sensitivity and overcomes filters losses before mixer. A significant portion of jammer signal effect on the

target signal is neutralized by combining the RF signal and the frequency produced by local oscillator and

filtering its output at baseband. It does not only undermine jammer signal effect but other unwanted

signals, as well. [1]

2-2 Convert the radio frequency signal to an intermediate frequency band

A signal to be processed and detected in a processor must be converted from a radio frequency to the

baseband frequency.For example, assume that the radio frequency signal is 10 GHz received and it should

be 200 MHz in order to be processed, thus frequency conversion should occur in receiver . Mixers and

local oscillators do this.

Figure 1 shows that local oscillator frequency must be chosen very close to radio frequency, this causes

unwanted frequency components due to oscillator phase noise in base band and this prevents (or makes

difficult) designing narrow-band RF filter to remove unwanted signals caused by local oscillator

frequency offset, and locate image frequencies within the band, and if we can remove image frequency

components using only one mixer there will remain sidelobe surfaces; therefore, frequency conversion is

done in several steps to prevent producing troublesome harmonics[1].


Vol. 2, No. 9, pp. 1-20.

3

Figure 1: 10 GHz Radio frequency conversion to 200 MHz baseband, stage 1

2-3 Mixer Mixer is a non-linear plot that converts a primary frequency signal to a secondary frequency signal in

radar receiver. In fact, the mixer output is not the only desirable signal but there will be unwanted signals

at the output produced by harmonics and is not desirable. Assuming that the output voltage can be

described in terms of a mixer, in that case, only the second order power can produce the desired signal

and other orders produce unwanted signals or the so-called spurious signal (spurs).

Where, V is the sum of the radio bands signal voltage ( ) and local oscillator signal voltage (

)

1 1 2 2sin sin (2)V t v t v t

Where, and are the baseband and local oscillator signal angular frequency, respectively .

Therefore, the desired frequency in baseband will be ( ) and spurs that are unwanted frequency

will appear as ( ) [1].

2-4 Local oscillator and baseband frequency selection

Local oscillator and baseband frequency selection depends on the need for video signal bandwidth and the

signal effects caused by mixer inter modulation (spurs) which must be minimized. It should be noted that

different harmonics frequencies and local oscillator frequency should not be placed in the receiver pass

band to avoid or minimize spurious signals [1].

If we show radio frequency band signal with H and local oscillator frequency with, then H-L will be

desired frequency in baseband.

2-5 Receiver gain

The components of the receiver, in the simplest definition, can be assumed as a block that a signal with a

specified power will enter it and exit with a different specified power. Therefore, the receiver has

weakened or strengthened input signal.

The weakening or strengthening based on the design parameters of the radar receiver is known as receiver

gain. Weakening or strengthening of the input signal to the receiver is of the important when the receiver

1

0 0 1 (1)n

nI a aV a V


Vol. 2, No. 9, pp. 1-20.

4

output signal reaches from the analog to digital converter ; it can saturate the converter and actually

disable the radar receiver if it is with a power higher than converter input power tolerance [5], [20].

Figure 2: Schematic view of a receiver representing its gain

2-6 Thermal noise and receiver noise figure

The thermal noise power at the receiver input is where K is Boltzmann's constant

( , T is ambient temperature usually considered a standard temperature of 290 degrees

Kelvin and B is the receiver bandwidth in Hertz.

Power level in radar receiver is expressed in milliwatts, because it is usually low and is shown as dBm for

ease of calculation . The ratio of the noise output of a receiver to an ideal receiver noise output at the

temperature T is defined as the noise figure, showed as the signal-to- receiver input noise signal to signal-

to- receiver output noise ratio. Noise figure can be shown as (dB) using .

If we have N pieces of the series with the gain , and noise figure numerically; be total noise figure

is calculated as follows:

321

1 1 2 1 1

1 11... (3)

...

N

N

f fff f

g g g g g

2.7. Receiver sensitivity

Typical receiver sensitivity required minimum input signal in order to achieve a certain output signal and

is determined by the amount of signal-to-noise ratio (Equation 4). Antenna gain should be effective in

sensitivity for a receiver that binds to the antenna, thus the minimum operational sensitivity is defined in

the operating environment for the receiver (Equation 5).

0( ) ( ) (4)min minSS KT B NF dB

N

0( ) ( ) (5)

minS KT B NF

NMOS dBLiG

Where, in equation (4) and (5) is the minimum required signal-to-noise ratio for signal

processing, is the Boltzmann constant, is the absolute temperature in receiver input in Kelvin

usually assumed to be 290 degrees Kelvin, is the receiver bandwidth in Hertz, is the receiver

noise figure and is the antenna gain, respectively.

2-8 Dynamic range


Vol. 2, No. 9, pp. 1-20.

5

Dynamic range is the power range that the receiver can receive and process the signals. Usually the lower

limit of signal power for dynamic range is considered noise level and the mixer or limiter is considered to

be the upper limit based on the saturation level of the amplifier [1], [4].

Receiver dynamic range is entirely dependent on the components that are used in the receiver; particularly

analog components such as ADC.

Mixers and amplifiers are the most effective analog components in receiver that play a role in limiting the

dynamic range [1].

2-9 Receiver Bandwidth

The receiver bandwidth ( is one of the most important factors in radar design that is determined

according to the sent pulse bandwidth using the equation . [5], [21]. It is understood that

the broader bandwidth leads to more noise into the system.

2-10 Pulse Repetition Frequency (PRF)

The number of pulses sent by radar in a second is known as Pulse Repetition Frequency. This parameter

is important because it determines the rate of data sent and received, and its maximum depends on radar's

unambiguous range , as the receiver in mono static radar can receive reversed between two consecutive

pulses of a target in the maximum unambiguous range of , thus the maximum amount of PRF

is [3].

3 .Phase noise problem

In coherent radar where phase signal is measured target can be isolated from clutter in frequency by

analyzing the echoes received phase. The accuracy of this operation depends on oscillator stability that

produces a transmitter signal and used as a reference signal in RF to IF conversion in the local oscillator,

known as exciter. In fact, the target of exciter is to produce coherent signals to provide send and coherent

reference signal to the radar receiver.

Usually the received signal is processed and in the same phase (I) and orthogonal (Q) the each of these

two is a function of the range (R) and wavelength ( ).

Ideally, I and Q components are analyzed in processing with regard to the sustainability of sent reference

signal phase at the time of the sent signals production and received the returned echo. However, certainly

reference phase will not be sustainable in the operation and is with fluctuations; thus two components

I and Q occurs with respect to the phase difference in achieve the results are not, but are in turn a

consequence. Attempts of organizations are to improve performance and discover hidden talents among

staffs. They can also deal with the problems raised in crisis and prepare for the administration.

4πRI A cos( δ ) (6)

λ


Vol. 2, No. 9, pp. 1-20.

6

practice, although ideally ( ) is considered zero, and is as follows [12].

The minimum thermal noise that is causing volatility in phase and known as phase noise

is not white as noise in spectral characteristics and its power spectral density is not

uniform.

3-1 The effect of phase noise on Pulse Doppler processing

Radars designed to detect small targets at the presence of clutter is one of the things that make radar

systems performance phase noise facing difficulty . Assuming that the amount of signal that reaches the

noise to receiver is sufficient for processing, the important issue that significantly affects on radar

performance will be the amount of clutter signal with the phase noise also playing a role . Target echo and

clutter are shown in a range in the pulse Doppler radars faced with the problem of ambiguity in range,

however , there is different ranges given the main clutter echo results from close ranges to radar and the

target echo that is far.

Furthermore the problem of echoes accumulation in different ranges because of the ambiguity of the

range should also be considered. Therefore, in measuring the signal-to-clutter ratio, although target and

clutter appear at the same range of range, different ranges need to be considered. This is because that

clutter is usually in the first range and target is at a distance . Range in the signal-to-clutter ratio is

inversely by the power of 4, that leads to substantial decrease in the signal-to-clutter ratio.The next factor

that reduces the signal-to-clutter ratio is the target to clutter radar cross section that is always smaller than

one due to the larger radar cross section ratio.

Figure 3: Competition of target signal in distance range with clutter signal at close range in an ambiguous

system [12]

Figure 3 shows a distance range target and the clutter cells in different ambiguous ranges in the

competition with the target echo. Surface that radar clear s from clutter is proportional to non modulated

pulse width, 3dB bandwidth and clutter cells range.

3 (8)2

c c dB

cA R

Therefore, the signal-to-clutter that appears at first range ( ) will be:

4 21

0( ) ( ) (9)t c t

c t c

R GSCR

A R G

4πR

Q A sin( δ ) (7)λ


Vol. 2, No. 9, pp. 1-20.

7

Where and are antenna gain in the direction of the target and in the direction of clutter,

respectively .We face with an uncertainty in range in the pulse Doppler radar; thus we should consider the

folded effect of

multi-echo clutter in signal-to-clutter ratio. Thus, the total ambiguous range clutter in range between the

target and the closest clutter is calculated (n) . Given the clutter folded effect of we have:

2 4

0 4 21

(10)n

t t ci

it ci ci

G RSCR

R A G

Ideally, remaining Doppler power in clutter bin is zero after pulse Doppler processing (FFT), but clutter

spectrum will spread in all Doppler bins with phase noise.

The remaining amount of clutter in any Doppler bin is depending on the clutter power and inherent clutter

spectrum, phase noise power spectral density and Doppler bin bandwidth.

The remaining authorized amount of clutter in each Doppler bin depends on the probability of detection

and the system false alarm and is a function of the clutter probability density. Phase noise power spectral

density (PSD) requirements in each frequency offset are:

( ) ( ) (11)req d reqS f SCR dB B dBHz SIR dB

Where, is Doppler filter 3dB bandwidth that is inversely proportional to the radar Deauville time and

is and signal-to-interference ratio.

Power spectral density of phase noise should not exceed -110 dBc / Hz in each Doppler frequency in

pulse Doppler radar in detection mode and power spectral density of phase noise should not exceed -140 dBc / Hz if we want to design a radar system that detects targets with very low radar cross section and

Stealth.

Oscillator phase noise spectrum for each offset frequency is considered 2S f

f

and the desirable

amount for can be calculated. Also, normalized phase noise power ( ) to interference signal ( )

in the frequency range ( ) is calculated as follows [13]:

2

(12)H

L

f

PN

int f

Pdf

P f

4- Calculate of the receiver parameters

In this section, we explain and calculate the basic parameter of a pulse Doppler radar receiver design

process.

4-1 IF signal frequency calculation

We select the first IF and oscillator frequency in X-band frequency given the input signal bandwidth

(frequency range 9.25 to 9.75 GHz). We try to go into the area with the smallest IF signal while at the

same time give us the greater spur harmonic content because it is much more weakened at these


Vol. 2, No. 9, pp. 1-20.

8

frequencies. That's why we select the area with [0.21,0.24]H L

H

f f

f

frequency ratio. This area is

between two sections of harmonic content.

If we select and for and based on the preceding explanations, thus,

and therefore, 0.22IF

RF

f

f , as a result, the first intermediate frequency of, 2062.5

MHz is obtained. So if we take the second oscillator frequency of 2 GHz, the second IF frequency is

equal to 62.5 MHz.

4-2 Receiver bandwidth calculation

As mentioned above, the receiver bandwidth is inversely related to the pulse width and it can be estimated

according to equation0.886 1

rB

, but the receiver bandwidth is multiplied further since we must

have sufficient bandwidth for FFT processing, here it is assumed to be four times higher. Since the length

of some air targets is 100 meters, so resolution should be considered about 150 meters for separation in

the range thus:

R (13)2

c

Therefore, given that is equal to 100 m, the pulse width will be equal to:

150 (14)2

c

1 (15)sec

So, this IF bandwidth can be considered 4 MHz.

4-3 Minimum and maximum input signal to a receiver calculation

4-3-1 radar antenna gain calculation

One of the important parameters in the radar equation that should be measured is radar antenna gain. The

higher this value returning echoes will come with more power to the receiver greater [14]. Considering

the types of antennas used in different radars, we will discuss parabolic antenna gain.

4-3-2 Parabolic antenna gain

Assuming antenna diameter is equal to two and a half meters and have 60 percent efficiency [5] gain will

be equal to [14]:

(16)


Vol. 2, No. 9, pp. 1-20.

9

(17)

Where, in Eq.(16) is the area of antenna that is equal to and d is diameter of the antenna

opening. In practice, antenna gain of 43 dB is obtained.

4-3-3 The radar data

Pulse Doppler radar to the authors of the paper includes:

Value parameter

75 KW

4-3-4 Targets RCS

One of the factors that determine the strength of the RCS returns signal is targets and objects that return

signal to the radar. In fact, bodies and different targets depending on the size and direction of the radar

reflectivity are different and that makes radar with different cross sections.

RCS can be obtained based on two types of targets, i.e., distributive target and point target. The current

paper uses point target for the ease

.

4-3-5 Minimum target return signal calculation

Returning echoes power to the receiver from various targets can be modeled by the following equation

[15]:

2 2

3 4[ ] (18)

(4 )

Tx trx

S

P GP W

R L

In equation (18) represents the losses that occur in Duplexer and transceiver modules.

The minimum signal is obtained at the maximum distance, in a 200 km range for a target with a 4 square

meters radar cross section, we have:


Vol. 2, No. 9, pp. 1-20.

10

Table 2: receiver received power from a target with a 4 square meters cross section in band X in 200

kilometers distance

dBm 78.8 dB 86

29.8-

6 dB 33

212- dB 10

dBm 114

4-3-6 Clutter power with the upward main lobe calculation

Figure 4: the radar main lobe is upward and clutter enters sidelobe level

Assuming that the radar main lobe is upward without dealing with the ground complications and only

sidelobe level have return of complications of ground (Figure 4) and given that block range created for

radar is 100 meters, therefore the clutter surface at a distance of 100 meters by sidelobe level (as the

shortest distance) is intended to calculate the level of clutter by antenna sidelobe level, we have: Thus, on the basis of radar data and the equation, for input clutter echo power to receiver at a range of 100

meters, assuming that return clutter echo intensity factor is we have:

sec (19)2

csl B

cA R

100 ( 1) 150 sec0 (20)180

cslA

2 2 261.8 24.2 (21)cslA m dBm


Vol. 2, No. 9, pp. 1-20.

11

Table 3: clutter echo power in the range of 100 meters that reaches the receiver from radar antenna

sidelobe level

dBm(75KW) 78.8 dB 46 (X band) 29.9-

20

24.2 dB 33

80 dB 7 L

20.9- Clutter

4-3-7 the clutter main lobe power toward the horizon calculation When the radar antenna main lobe is on the horizon, given 3 dB lobe width of antenna lobe width collide

with the ground complications in a calculated distance, therefore, clutter echo is received not only from

sidelobe level but main lobe (Figure 5).

Therefore, received clutter power for side lobe and main lobe must be calculated based on the range.

So we should first know at what range the main lobe collision with the ground complication begins, so we

have:

3

(22)sin(0.5 )

RSMlobe

dB offset

hR

4 1 146 (23)

sin(0.5 0.3)SMlobeR m

Figure 5 clutter enters receiver from the sidelobe and main lobe [16]


Vol. 2, No. 9, pp. 1-20.

12

So from the moment the echo clutter of the main lobe began to enter the clutter should be calculated for

the total sidelobe and main lobe that given the main lobe impact on input clutter power to the receiver, the

echo clutter in the range of 1146 meters will be -12.67 dbm.

Figure 6 input clutter power to receiver for one pulse

We face with ambiguity in pulse Doppler radars and clutter that enters each cell range is in a state of

ambiguity the total clutter entering receiver is accumulated in different distances (Fig. 7) and is obtained

using the following equation [16]:

1

1

0 0

( ) (24)N

c folded c

n

t nTP P Rect

Where, N is the number of pulses per coherent processing interval, T is inverted pulse repetition

frequency, is pulse width, and t is calculated in corresponding time delay due to the switching on or

off the transmitter and receiver and will be 0 0{ 2 1 ;0 1}nT t n T n N .

Figure 7: the input clutter to the radar from the side and main lobe piled of different ranges [16].

So, the amount of clutter obtained from pilled different pulse should be higher than clutter that arises

from a pulse.This problem is studied using MATLABF and shows the highest received clutter of -

11.22 dBm in 10 consecutive pulses. So, the highest received clutter in a total of two scenarios will be the

same amount.


Vol. 2, No. 9, pp. 1-20.

13

Figure 8: a) input clutter pilled from 10-pulses

.

Figure 9: echo Received from pilled received clutter for 10 consecutive pulses.

Thus, maximum and minimum input signal to the receiver are -11 dBm and -114 dBm.

The minimum input signal to the receiver is considered the minimum detectable signal that, according to

equation (25) and taking into account the bandwidth of 4 MHz for the receiver, the minimum signal to

noise of12 dB and noise figure of 4 dB, -90 dB is obtained. Here, noise level is considered the minimum

signal that is -102dBm.

4-4 Dynamic range receiver

As previously explained, the extent to which the receiver can do signal processing operation to the input

signal power to receivers is known as receiver dynamic range. The dynamic range of 103 dB for the

receiver will be necessary, with regard to the equation and the maximum and minimum receiver input

signal.

4-5 Receiver structure and gain to achieve high dynamic range

The receiver gain is adjusted according to the minimum receiver input signal, so as to reach the level of

full scale analog to digital converter, receiver gain is determined considering peak to peak voltage of

analog to digital converter that is 2 volts. However, since the noise system level of -102 dBm is

calculated, so this amount is considered as a minimum signal to gain.Therefore, an appropriate level for

the signal to reach analog to digital converter is a gain equal to 102 dB. However, since the maximum

signal is -11.2dB, the receiver is saturated in the primary classes and breaks. On the other hand, we face

with ambiguity in pulse Doppler radar; therefore we cannot use STC that is based on range, because the


Vol. 2, No. 9, pp. 1-20.

14

gain controlling maximum dynamic range is ultimately 60 dB, so we cannot use gain controllers, and thus

the best thing to Downconvert signals with the appropriate gain is switching.

We need a high dynamic range to receive the signal and convert it to baseband, and as described we

cannot use the conventional methods, so we have to divide signals using microwave switching between

the received signals divide receiver into two. Thus, we use a path for weak signals and another path for

strong signals that reach us to an ideal signal.

Thus, when low power signal is received over long distances and

this requires that high sensitivity receiver , we use a path with low noise amplifier (LNA), and a

restriction is placed before LNA to prevent saturation in case a strong signal to enter this path.

Signal that comes from close range is certainly high, which is calculated so we pass it from the path with

voltage variable attenuator (VVA) where a voltage controlled attenuator (VCA) is used. In this case,

P1dB will increase and we can achieve high dynamic range over 100 dB, but surely half or one dB will be

added to the receiver noise figure due to some increased receiver components that is predicted [17].

Figure 10: The proposed structure for a high dynamic range receiver with high gain

Thus, we consider the LNA gain amount of+ 25dB given the maximum input signal (-11dBm) and the

minimum noise (-102dBm) for the signal range of -102 to -70dBm and undermine the VCA from 0 to

35dB and take the total gains n other levels of 50dB, we will have the maximum and minimum IF signal

range between -30 to + 5dBm

.

5. phase noise requirements for receiver oscillator

As we explained earlier, phase noise originated from oscillators can have a devastating impact on the

receiver so that makes the clutter spectrum wide and prevent the discovery of the targets. We can be

considered six channels as Fig 11 indicates, if we consider 4 channels for the receiver with 500 MHz

bandwidth and assuming that the center frequency of each channel with adjacent channel is

approximately 167 MHz.


Vol. 2, No. 9, pp. 1-20.

15

Figure 11: Receiver channel

As explained, the presence of phase noise in oscillator signal leads to mutual mix. Considering the worst

case, i.e., we're going to work on mutual mix effect on channel 4 and the mixer output that the received

signal contains all 4 channels and the desirable channel is number 4 with minimal input signal with input

signals received in other channels the maximum amount. To simplify the calculations, each of the

interference signals is assumed to be hit and channel 4 bandwidth is considered to be 4 MHz, also, we

assume the ideal mixer and nonlinear effects are ignored and Let us examine only the effect of phase

noise .So, Figure 12 shows Mixer output after being transferred to the lower band signal, where an

amount of the spectrum of the each of the adjacent channels is within the channel 4 band and the noise

level will increase.

Figure 12: Effect of phase noise on the fourth channel reduced signal value -to-noise.

We're going to calculate the sum of the effects of interference signals that have been created due to the

phase noise. Oscillator phase noise spectrum can be considered as 2S f

f

and calculate the

appropriate value of .

Phase noise normalized power ( to be interference signal ( ) in the frequency range ( ) is

calculated as follows:

2(25)

H

L

f

PN

int f

Pdf

P f

Also, interference signal can be considered k times of desirable signal, i.e., int sigP k P that Equation

26 is rewritten as:

1 1[ ] (26)PN

sig L H

Pk

P f f

So we can write the whole phase noise power to signal ratio for all interfaces as follows:


Vol. 2, No. 9, pp. 1-20.

16

1 2 3 4 5 6

( ) 1 1 1 1 1 1[ ] (27)PN

sig

P totalk

P f f f f f f

Frequency values are given below according to Figure 12. Also considering the problem assumptions 10.310 ( 103 )int sigk P P dB and for the amount of distortion created is minimal and ineffective, it

should be 27 dB below the desired signal power so the Eq. (28) is as follows:

2.7 10.3 1 1 1 1 1 110 10 [ ] (28)

165 169 332 336 499 503MHz MHz MHz MHz MHz MHz

Where, α value equals to . So now we can calculate receiver oscillator phase noise in any

given desired offset as follows

4

2 2

5.1 10(29)S f

f f

Thus, required phase noise for oscillator to offset 1KHz is:

PN@1 10log( (1 )) 93 (30)

dBckHz S KHz

Hz

Also we can add -20dBc / Hz to the obtained value and consider the value of phase noise in a kilo Hz

offset equal to -110 dBc/H z, taking into account other effects as well as approximation that we have in

our analysis.

6- Spur level required for the oscillator analysis

We should consider two issues to analyze Spur level required for the oscillator.The first thing is that

correct harmonics are usually generated from main harmonics in oscillators, that are unwanted and

attempts are made to remove them in design, because the presence of these harmonics also causes outside

the band interference signals Downconvert into the band. But in practice, It will not be very annoying in

receiver design because of interference signals outside the band, are attenuated to an acceptable level by

before the mixer RF filter also oscillator harmonic power is much less than its original harmonics. The second problem is that in some structures, especially structures of direct digital frequency synthesis

(DDS) with spurs in offsets near the oscillator frequency with problems in the oscillator signal due to the presence of the spur. The output signal from the mixer includes a combination of the original

frequency spectrum by shifting their findings If the spurs are present in an offset within the input channel

bandwidth and as a result, the signal-to-noise is affected [13].This is shown in Figure 12. In this figure,

for simplicity oscillator signal and its spur are shown as the hit.


Vol. 2, No. 9, pp. 1-20.

17

Figure 13: a) an input RF signal and the oscillator signal; b) output signals from the mixer

But we should assume another case that spurs are located in the offset higher than the bandwidth of the

original signal. Now, the spurs make unwanted interference signals downconvert into the band that this

case is much more important. The worst possible conditions should be considered to calculate the spur

level. First, we assume that the desired signal level is the minimum possible value (i.e., -114dBm) and

radar interference is the maximum possible value (i.e., -11dBm). Given the fact that the out of the filter

band weakening is considered to be 60dB, thus interference signals that reach the mixer will be -71dBm.

now, oscillator level of spur should be selected so that the interference signal are about 60 dB of lower

than the original signal after interference signals downconvert and transferred to the main band. The

oscillator spur level should be selected about 103dBc that we consider the value of -105dBc given that the

difference between the interference signal and the original signal is 43dB.

7- The analog to digital converter

According to Figure 14, we know that analog to digital convertor is used to convert IF analog signal to

digital signal in receiver structure. Generally in operation one or two bits should be added to the number

of effective bits based on theoretical calculations for analog to digital convertor to overcome constraints

such as quantization noise [18]. According to [19] the number of effective analog to digital converter bits

includes:

1.76 (31)

6.02

SINAD dBENOB

10 27 12 1.76 8 (32)

6.02

dBENOB

Therefore, we need a 10-bit digital converter given that we need to add two bits to the value obtained in

(32) for optimal performance, according to [18].


Vol. 2, No. 9, pp. 1-20.

18

8- Structure and receiver specifications table

Figure 1shows high dynamic range pulse Doppler radar receiver block diagram, based on the

calculations:

Figure 14: Structure of Pulse Doppler radar receiver with high dynamic range

According to our calculations X-band Pulse Doppler radar receiver characteristics is given in Table 4:

Table 4: Pulse Doppler radar receiver parameters

Parameter Value

Frequency band X-Band

RF bandwidth 500 MHz

Number of Channels 4

STALO Phase noise -110 dBc/Hz @

1KHz

STALO Spore levels -105dBc

The maximum and

minimum input power

-11.2~-114 dBm

Dynamic Range 103dB

Noise level -102 dBm

Noise figure 4~5 dB

Power

compression points 1dB

of output ( )

+20dB

The analog to digital

converter number of

effective bit

10bit یا 12bit

PRF changes and

received signal regime

Medium and high

Pulse repetition

frequency


Vol. 2, No. 9, pp. 1-20.

19

9- Conclusion In the current paper described the necessary concepts to receiver design and presented the receiver basic

parameters calculated values such as dynamic range, sensitivity, gain and phase noise analytically. A

new structure to achieve high dynamic range has also been suggested . This structure, as described in the

text, despite high dynamic range is very simple to implement. In addition, the analog to digital converter

was intended in term of dynamic range and the effective number of bits and as was observed we need up

to a 12-bit analog to digital converter despite receiver’s more than 100 dB dynamic range.

10- References

[1] M. A. Richards, J. Scheer, W. A. Holm, and others, Principles of modern radar: basic principles.

SciTech Pub., 2010.

[2] M. T. Safdar, K. Hanif, and S. A. Ghumman, “Super-Regenerative Receiver (SRR) for short-

range HF band applications,” H{ö}gskolan i Halmstad/Sektionen f{ö}r Informationsvetenskap, Data-och

Elektroteknik (IDE), 2009.

[3] I. S. Merrill, Introduction to radar systems. 2001.

[4] M. E. Yeomans, “Radar Receivers,” in Radar Handbook, McGraw Hill Professional, 2008.

[5] A. I. Mohungoo, “An airborne x-band synthetic aperture radar receiver design and

implementation,” University of Cape Town, 2004.

[6] J. Tsui, Microwave receivers with electronic warfare applications. The Institution of Engineering

and Technology, 2005.

[7] jim stiles, “Minimum Detectable Signal,” 2006, p. 4.

[8] D. O. Defense, “Electronic Warfare And Radar Systems Engineering Handbook,” Jeffrey Frank

Jones.

[9] K. Chang, RF and microwave wireless systems, vol. 161. John Wiley & Sons, 2004.

[10] R. V Alred and A. Reiss, “An anti-clutter radar receiver,” J. Inst. Electr. Eng. III Radio

Commun. Eng., vol. 95, no. 38, pp. 459–465, 1948.

[11] M. I. Skolnik, “Radar Clutter,” in introdution to radar systems, 3rd ed., McGraw Hill

Professional, 2002, pp. 402–482.

[12] M. A. Richards, “Radar Exciter,” in principles of modern radar:basic principles, 2010.

[13] M. E. Yeomans, “Radar Receivers,” in Radar Handbook, 3rd ed., McGraw Hill Professional,

2008, pp. 6.1–6.51.

[14] M. I. Skolnik, Radar Handbook, Vol. 1, 8. McGraw Hill Press, 2008.


Vol. 2, No. 9, pp. 1-20.

20

[15] B. R. Mahafza, Radar Systems Analysis and Design Using MATLAB Third Edition. CRC Press,

2013.

[16] B. R. Mahafza, “Radar Clutter,” in RADAR SYSTEMS ANALYSIS AND DESIGN USING

MATLAB, 3 rd., CRC Press Taylor & Francis Group, 2013.

[17] B. S. Rao, R. Das, and C. G. Balaji, “High Dynamic Range Monopulse Microwave Receiver

Front-end,” in 2007 Asia-Pacific Microwave Conference, 2007, pp. 1–3.

[18] M. I. Skolnik, “MTI and pulse doppler radar,” in introduction to radar systems, 3rd Ed., New

York: McGraw Hill Professional, 2001, pp. 104–209.

[19] W. Kester, “Understand SINAD, ENOB, SNR, THD, THD+ N, and SFDR so You Don’t Get

Lost in the Noise Floor,” MT-003 Tutorial, www. Analog. com/static/importedfiles/tutorials/MT-003.

pdf, 2009.

[20] S. Mousavi, R. De Roo, K. Sarabandi, A. England and H. Nejati, "Remote sensing using

coherent multipath interference of wideband planck radiation," 2016 IEEE International Symposium on

Antennas and Propagation (APSURSI), Fajardo, 2016, pp. 2051-2052.

[21] S. Mousavi, R. De Roo, K. Sarabandi, A. England and H. Nejati, "Dry snowpack and freshwater

icepack remote sensing using wideband Autocorrelation radiometry," 2016 IEEE International

Geoscience and Remote Sensing Symposium (IGARSS), Beijing, 2016, pp. 5288-5291

High Dynamic Range Receiver System Designed for High …iaiest.com/dl/journals/8- IAJ of Innovative...

Documents

Transcript of High Dynamic Range Receiver System Designed for High …iaiest.com/dl/journals/8- IAJ of Innovative...