1

CASE STUDY 2

RF WIRELESS TRANCEIVER –

SIMULATION AND ANALYSIS

AKOMA, CHIEMELE OGECHUKWU (11065981)

MODULE CODE: CTP 149N MODULE NAME: MICROWAVES AND OPTICAL COMMUNICATIONS

FACULTY OF COMPUTING

LONDON METROPOLITAN UNIVERSITY

166-220 HOLLOWAY ROAD N7 8DB

LONDON, UK

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ABSTRACT

An RF wireless transceiver system is designed in this case study. The transmitter system is a one

stage Intermediate frequency (IF) superheterodyne transmitter, with a baseband frequency of

300MHz. The receiver uses a two stage IF downconverter, downconverting the RF first to

1000MHz and finally to 300MHz. The received power at PORT2 is 10.402dBm. Analyses

showed that as the link distance increased from 0.5-2.5Km, the received power decreased from

16.054-2.538 dBm; the decrease is almost linear. Also, a linear increase in Transmitter antenna

gain (TxGain) with received power (IFout). From budget power gain analysis, link1 showed the

highest loss in power while amp2 showed the highest gain. Link1 and Amp2 showed a high

contribution in noise figure (6.380 and 19.015) to the system.

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OBJECTIVES OF THE EXPERIMENT

Create a system project for an RF transmitter using behavioral models (filter, amplifier,

mixer)

Use an RF source, LO with phase noise, and a noise controller

Perform a Harmonic Balance simulation

Analyze the system spectra

Perform System Budget analysis

Analyze the effect of the line-of-sight parameters on the system performance

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BACKGROUND THEORY

RF WIRELESS TRANSCEIVER

A transceiver is any device comprising both a transmitter and a receiver which are combined and

share common circuitry or a single housing. The figure below shows the block diagram of an RF

wireless Transceiver, showing the transmitter, wireless link and the receiver. Transceivers enable

duplex communication modes (half or full). Various applications of transceivers include

WLANs, GPS, RF-Identification systems (RF-IDs), Home Satellite Networks, GSM, Satellite

Phones, Bluetooth devices, pagers, etc. Transceiver circuits are been implemented with IC chips,

in a drive towards miniaturization, cost and linearity [1-2].

Figure 1: A wireless transceiver system

Figure 2: A communication system

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TRANSMITTER

The transmitter must produce a signal that has enough power, have generally a very accurate

frequency, and has a clean enough spectrum so that the transmitter does not disturb users of other

radio systems. Information to be transmitted, the baseband signal, is attached to a sinusoidal

carrier signal by modulating the carrier amplitude, frequency, or phase either analogically or

digitally [3]. There two basic types of transmitters, these are direct conversion (homodyne)

transmitter and superheterodyne (two or more steps) transmitter.

a. Direct conversion (homodyne) transmitter

Figure 3: Block diagram of a Direct conversion transmitter with phase-locked loop

Figure 2 presents a direct-conversion transmitter. A digital baseband signal (fref)

modulates the carrier in an IQ-modulator. The modulated signal is then filtered and

amplified [3].

b. Superheterodyne transmitter

Figure 4: block diagram of a superheterodyne transmitter

Superheterodyne transmitters are more complex than direct conversion transmitters. The

information signal modulates an intermediate frequency (IF) signal then converted to the

transmit relative frequency by a mixer. An IF filter is needed to eliminate the local

oscillator harmonics after the modulation. An RF filter is required at the mixer output to

move out the undesirable sideband. After stages for correction, equalization and

sometimes amplification, the IF signal is converted to an RF signal by a stage

named frequency mixer or frequency converter [4-5]. The superheterodyne transmitter is

based on the heterodyne principle.

CHANNEL

The channel in the communication system refers to the medium through which the information

transmitted from the transmitter sub-system to the receiver sub-system. This could either be air

medium, optical fibre, twisted pair, copper wire, coaxial cable, wave guide, etc [3].

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Factors affecting radio range include antenna (gain, sensitivity to body effects, etc), sensitivity,

output power, radio pollution (selectivity, blocking, IP3) and environment (line-of-sight,

obstruction, reflections, multipath fading. The following can increase the range of the transceiver

systems, increasing the output power (eg adding an external power amplifier), increasing the

sensitivity, increasing both output power and sensitivity, and using high gain antennas [11].

Signal strength: A strong source signal allows for better reception over long distances than a

weak source signal. But the FCC limits unlicensed signal transmission strength to one watt

maximum and six dB watts of EIRP. Effectively, this allows for a maximum signal gain

equivalent to four watts. A signal conditioner at the receiving end can be used to enhance the

signal-to-noise performance by an order of magnitude [12].

Distance: RF signal strength decreases with distance. Also, the potential interference and signal

fading increases with distance [12].

Interference: sources of atmospheric interference can be rain, snow, hail or lightening in the

signal path. RF interference normally results from other nearby RF activity in the same band (in-

band interference). Only very strong out-of-band activity can interfere with a 2.4 GHz signal

[12].

Line of sight: RF line of sight requires a wider band of free-space signal path than visual line of

sight. Signal clarity is best when the line of sight between antennas is precisely focused and free

of all obstructions. Obstructions within the RF line of sight can absorb the signal and sap it of

strength or deflect the signal and cause multiple copies of the same signal to arrive at the receiver

out of phase. The success of an RF link depends on a clear line of sight. An unobstructed line of

sight is called a free space path. An acceptable line-of-sight for an RF signal is defined as at least

.6 clearance in the first Fresnel zone. This means that for successful RF transmission, at least 60

percent of the area between the center lobe and the bottom of the first Fresnel zone must be a

free-space path. A large obstruction can reduce or totally block the signal. The bending of signals

as they pass around obstructions or are deflected by them is known as diffraction. A reduction of

the strength of a signal is known as attenuation . Factors affecting line-of-sight include free space

loss, attenuation and scattering, atmospheric absorption, ducting, multipath and fading, refraction

and reflection [11-12].

Equation for free space path loss is given by

Free space path loss (dB) = 27.6(dB) – 20log[frequency(MHz)] – 20log[distance(m)]

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Figure 5: Graph of Attenuation against Frequency showing attenuation by various components

for different frequencies.

RECEIVER

The receiver subsystem receives the signal and converts it back to usable form, either visual (as

in television), audio (as in FM or AM), or data (for computers, etc). A receiver should be able to

select the desired signal, and distinguish very weak signals from noise and other unwanted

signals lying in the band [8].

Frii’s transmission equation for free space propagation is given by

Where Pt is the transmitted power, Pr is the received power, Gt and Gr is the transmitter and

receiver antenna gain respectively, λ is the wavelength and d is the distance between transmitter

and receiver or the range. [11].

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Figure 6: Simulated Operation of a receiver

Most popular architectures for receivers are Heterodyne, Homodyne, Wideband-IF and Low-IF

[8].

Heterodyne Architecture

Super-heterodyne is the most widely used architecture in wireless transceivers so far. It is a dual

conversion architecture, in which, at the first state RF is down-converted to IF and then, in

second stage it is from IF to baseband signal. The block diagram of super-heterodyne receiver

architecture is shown in Figure 3. From the incoming RF signal preselection filter removes out of

band signal energy as well as partially reject image band signals. It is then amplified by LNA to

supress the contribution of noise from the succeeding stages. Image Reject filter attenuates the

signals at image band frequencies coming from LNA. Mixer-I downconverts the signal coming

out of the IR filter from RF frequency to IF frequency with the output of a Local Oscillator. The

channel selection is normally achieved through IF filter: It is a BP filter to allow the IF band of

interest and other band is rejected. This filter is critical in determining the sensitivity and

selectivity of a receiver [9-10].

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Figure 7: Block diagram of a typical Heterodyne Receiver

Since channel selection is done at IF1, the LO requires an external tank for good phase noise

performance. In case of phase or frequency modulation, downconversion to the baseband

requires both in-phase(I) and quadrature(Q) components of the signal. Mixer-II does the second

down conversion of IF signal into I and Q components for digital signal processing. The LP filter

acts as a channel reject filter along with job of anti-aliasing functionality [9-10].

Trade-offs

IR filter and channel selection.

Good sensitivity and selectivity [9-10].

Drawbacks

High Q filter

High performance oscillator or LO

LNA output impedance matched to 50 ohm is difficult.

Integration of HF image reject filter is a major problem [9-10].

Homodyne Architecture

Homodyne receivers translates the channel of interest directly from RF to baseband (ωIF=0) in a

single stage. Hence these architectures are called Direct IF architectures or Zero-IF architectures.

For frequency and phase modulated signals, down conversion must provide quadrature outputs

so as to avoid loss of information [9-10]. The block diagram of heterodyne architecture is

illustrated in Figure 4.

Figure 8: Block diagram of Homodyne Receiver Architecture

Merits of Zero-IF architecture are

Less hardware

No image problem. So image filter not required.

Because of no IF stage, LPF is sufficient for filtering.

Amplification at BB stage. Hence power saving.

In integrated circuits LNA need not to match to 50 ohm. Because no image reject filter

between LNA and mixer [9-10].

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De-merits of Zero-IF architecture are

LO Leakage: Generally there will be an imperfect isolation between LO port and input

port of mixer and LNA, due to capacitve and substrate coupling. Because of this there

will be LO feed though from LO port to the input port of the mixer and LNA. This LO

leakage mixes with original LO, called self-mixing, produces DC offsets in the mixer

output and causes saturation of following stages in the receiver chain.

DC offset errors: It is the most serious problem in the baseband section of the homodyne

receivers. The cause of it is self mixing of LO leakage which is due to LO feed through to

mixer input port and LNA and insufficient isolation between LO port to mixer input port

and LNA input.

Since LO frequency is same as carrier frequency, it leaks from receiver to antenna which

interferes with same frequency-band receivers.

Flicker noise from an active device contaminate the BB signal.

I/Q mis-match

Even order distortion [9-10]

Wideband-IF Architecture

Wideband-IF receiver is a dual conversion architecture in which data is downconverted from RF

to IF in the 1st stage, and in the 2nd stage it is from IF to Baseband [9-10]. The block diagram of

Wideband-IF receiver architecture is shown in Figure 5.

Figure 9: Block diagram of Wideband-IF Receiver Architecture

In this architecture all the RF channels are complex mixed and downconverted to fixed IF after

preselection filtering and amplification. In second stage an Image Reject (IR) mixer does

complex mixing and translate IF to BB using a tunable channel select frequency synthesizer. All

the image frequencies are cancelled by IR mixer. If the IF is chosen high enough, additional

image rejection may be obtained from the RF front-end preselection filter. Channel selection is

performed at baseband by using programmable integrated channel select filter. Since LO-1 is

fixed frequency synthesizer generated by crystal controlled oscillator good phase noise

performance is obtained. Channel tuning is achieved by using programmable frequency

synthesizer at IF [9-10].

Low-IF Architecture

In Low-IF receiver architecture all the RF signals are translated to low-IF frequency which is

then down-converted to BB signal in digital domain. Low-IF architecture comprises the

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advantages of both heterodyne and homodyne receivers [9-10]. The block diagram of Low-IF

receiver architecture is shown in Figure 6.

Figure 10: Block diagram of Low-IF Receiver Architecture

After preselection filtering and amplification, all the RF channels are quadrature mixed and

downconverted to low IF containing both wanted and unwanted signals. The IF frequency is just

one or two channels bandwidth away from DC, which is just enough to overcome DC offset

problems. It is then amplified and filtered before sampled by ADC. Since the ADC samples both

wanted and unwanted signals, there will be higher demand on ADC dynamic range requirements.

The ac-coupled signal path to ADC eliminates the need of DC offset compensation circuitry. The

sampled digital data is fed to image reject mixer which is implemented in digital domain [9-10].

HETERODYNING

Heterodyning technique was invented in 1901 by Reginald Fessenden. In heterodyning, two

frequencies are mixed or combined to create a new frequency range. It is used in shifting a

frequency into a new frequency range. The two frequencies, f1 and f2, are combined using a non-

linear device called a mixer (which could be a diode or transistor). The new frequencies

generated from the non-linear mixing consist of two frequencies, that is, the sum (f1 + f2) and the

difference (f1 – f2). These frequencies are call heterodynes or beat frequencies. The analysis of

the frequency spectrum from the mixer output shows the f1+f2, f1-f2, harmonics of f1, harmonics

of f2, beat frequencies of the interactions of the various harmonics. In most situations, one of the

two frequencies is desired; the other is filtered out at the output of the mixer [4, 13].

Mathematically, heterodyning can be expressed thus,

When two sine wave signals, sin (2πf1t) and sin (2πf2t), are multiplied, using trigonometric

identity,

This is result shows the two intermediate frequencies (the sum and difference of the two original

frequencies).

Three reasons for the use of Intermediate frequency (IF) in RF circuits include:

1. At very high (gigahertz) frequencies, signal processing circuitry performs poorly. Active

devices such as transistors cannot deliver much amplification (gain) without becoming

unstable. Ordinary circuits using capacitors and inductors must be replaced with

cumbersome high frequency techniques such as striplines and waveguides. So a high

frequency signal is converted to a lower IF for processing.

2. A second reason to use an IF, in receivers that can be tuned to different stations, is to

convert the various different frequencies of the stations to a common frequency for

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processing. It is difficult to build amplifiers, filters, and detectors that can be tuned to

different frequencies, but easy to build tunable oscillators. Superheterodyne receivers tune

in different stations simply by adjusting the frequency of the local oscillator on the input

stage, and all processing after that is done at the same frequency, the IF. Without using an

IF, all the complicated filters and detectors in a radio or television would have to be tuned in

unison each time the station was changed, as was necessary in the early tuned radio

frequency receivers.

3. An important use of intermediate frequency is to improve frequency selectivity. In

communication circuits, a very common task is to separate out or extract signals or

components of a signal that are close together in frequency. This is called filtering. Some

examples are, picking up a radio station among several that are close in frequency, or

extracting the chrominance subcarrier from a TV signal. With all known filtering techniques

the filter's bandwidth increases proportionately with the frequency. So a narrower bandwidth

and more selectivity can be achieved by converting the signal to a lower IF and performing

the filtering at that frequency [11].

Applications of IF (heterodyning)

Heterodyning is used very widely in communications engineering to generate new frequencies

and move information from one frequency channel to another. it is used in radio transmitters,

modems, satellite communications and set-top boxes, radar, radio telescopes, telemetry systems,

cell phones, cable television converter boxes and headends, microwave relays, metal detectors,

atomic clocks, and military electronic countermeasures (jamming) systems, analog tape recorder

and music synthesis [4].

Advantages of superheterodyne includes

In transmitters several correction and equalization stages are used after modulation. In direct

modulation these stages must be developed separately for each output RF (so called

channel). On the other hand, in superheterodyne transmitters since a single intermediate

frequency signal is used, only one type of stage for IF is developed. Thus the said stages are

more reliable in superheterodyne. Also R&D is much easier for the designer.

Operators may change the RF output of the transmitter. In direct modulation, it is very

difficult to change the RF output. Because in this case, practically all stages need to be

retuned for the new RF. On the other hand in superheterodyne only the output stages need to

be retuned [4].

COMPONENTS OF TRANSMITTER/RECEIVER SUBSYTEM

RF MIXERS

An RF mixer is a 3-port non-linear device. It is any passive or active device that converts a

frequency to another. A mixer can be used to modulate, demodulate a signal or even as a phase

detector [11-12]. Figure 5 shows an ideal mixer.

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Figure 11: An ideal mixer

The mixer takes an RF signal at RF input, combines it with the signal from the local oscillator

(LO) at LO input, to produce an intermediate frequency (IF) at the IF output port. It is at the

mixer that heterodyning (as explained above) is done [11-12].

When the sum of the LO and RF is required, the mixer is called an upconverter (this is used in

transmitter circuits); but when the difference of LO and R Fir required, the mixer is called a

downconverter (this is used in receiver circuits). Low-side injection occurs when the LO

frequency is less than the RF frequency; the reverse is called high-side injection. Another

important to note in an RF is that each output is half (½) of the individual inputs. Therefore,

there would a loss of 6dB in an ideal mixer [12]

Figure 12: Output spectrum of an up-conversion mixer system

Important Mixer properties are: Conversion Gain or Loss, Intercept point, Isolation, Noise

Figure, High-order spurious response rejection and Image noise suppression [14].

1. Conversion Gain or Loss of the RF Mixer is dependent by the type of the mixer (active or

passive), load of the input RF circuit, output impedance at the RF port, the level of the

LO. The typical conversion gain of an active Mixer is approximately +10dB when the

conversion loss of a typical diode mixer is approximately -6dB. The Conversion Gain or

Loss of the RF Mixer measured in dB is given by:

Conversion (dB) = Output IF power delivered to the load (dBm) – Available RF input signal power (dBm)

2. Input Intercept Point (IIP3) is the RF input power at which the output power levels of the

unwanted intermodulation products and the desired IF output would be equal. The Third-

Order intercept point (IP3) in a Mixer is defined by the extrapolated intersection of the

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primary IF response with the two-tone third-order intermodulation IF product that results

when two RF signals are applied to the RF port of the Mixer.

3. Spurious products in a Mixer are problematic, and Mixer vendors frequently provide

tables showing the relative amplitudes of each response under given LO drive conditions.

4. Isolation is the amount of local oscillator power that leaks into either the IF or the RF

ports. There are multiple types of isolation: LO-to-RF, LO-to-IF and RF-to-IF isolation.

5. Noise Figure is a measure of the noise added by the Mixer itself, noise as it gets

converted to the IF output or is a measure of how much the signal-to-noise ratio (SNR)

degrades as the signal passes through the block. It is defined as

where PO is the total output noise power, PL is the output noise power that results from

noise generated by the load at the output frequency, and PS is the output noise power that

results from noise generated by the source at the input frequency.

For a passive Mixer which has no gain and only loss, the Noise Figure is almost

equal with the loss.

In a mixer noise is replicated and translated by each harmonic of the LO that is

referred to as Noise Folding [14].

Present also in the mixer frequency spectrum is the image frequency. This is given by the

formula,

fimage = frf + 2(I.F)

A good choice of LO and IF frequencies would help to reduce the effect of image frequency as it

can negatively affect the RF frequency [14].

FILTER Filter circuits can be used to separate or combine different frequencies, reject unwanted frequencies while permitting the transmission of a wanted frequency. Filters are used to select or confine specific

frequencies within the allotted Spectruml limits. Example of such circuits where a filter can be found

includes multiplexers, demultiplexers, transmitter and receiver circuits, etc. Filters can be classified into low pass filter (LPF), high pass filter (HPF), band pass filter (BPF) and band stop filter (BSF) [14-15].

Figure 7(a) shows the idealized filter responses of filters, with the shaded region indicating the

allowed (or pass band) frequencies. Since it is almost impossible to realize such an ideal filter

response with an infinite stopband attenuation and instantaneous transition from pass band to

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stopband, figure 7(b) shows a typical response of a lowpass filter. Five practical filter parameters

are shown in figure 7(b)

(a) (b)

Figure 13: (a) Idealized filter responses; (b) Realistic low pass filter response showing key filter parameters

There various standard filter responses. This varies with filter transfer functions and could affect

filter complexity and cost [14]. They are as follows:

Butterworth

It is also known as the maximally flat filter as it has no ripple in the pass band or stopband. It has

the best compromise between attenuation and phase response. It has a relatively wide transition

region with average transient characteristics [14]. The equation for the pole positions is

(Where k is the pole pair number and n is the number of poles)

Chebyshev

The chebyshev filter for the same order butterworth filter, has a smaller transition region, but at

the expense of ripples in its pass band. The number of ripples equals the order of the filter [14].

Bessel The Bessel filter is optimized for better transient response of linear phase in the pass band. This

implies a relatively poor frequency response. The poles are determined by locating the poles on a

circle and then separate the imaginary parts by ; where n is the number of poles [14].

Elliptical

The presence of ripples in both pass band and stopband of the elliptical filter gives it a shorter

transition region than the chebyshev filter (since zeros are in the stopband) [14].

Other response types include Gaussian and inverse chebyshev filter responses [14].

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Figure 14: Comparison of amplitude response of Bessel, butterworth and chebyshev filters.

POWER AMPLIFIER (OP AMP)

An RF power amplifier is an example of an electronic amplifier. It is used in converting a low-

power radio-frequency signal into a larger signal of significant power, typically for driving the

antenna of a transmitter. It is optimized to have high efficiency, high output Power (P1dB)

compression, good return loss on the input and output, good gain, and optimum heat dissipation.

Applications of RF power amplifier include Wireless Communication, TV transmissions, Radar,

and RF heating, and exciting resonant cavity structures [15-16].

RF power can be classified in classes A, B, AB, C, D, E and F. Important parameters that defines

an RF Power Amplifier include: Output Power, Gain, Linearity, Stability, supply voltage,

Efficiency, and Ruggedness. The level of performance of an rf power amplifier can be

determined by choosing the bias points. By comparing PA bias approaches, one can evaluate the

trade-offs for: Output Power, Efficiency, Linearity, or other parameters for different applications

[16].

The Power Class of the amplification determines the type of bias applied to an RF power

transistor. The Power Amplifier’s Efficiency is a measure of its ability to convert the DC power

of the supply into the signal power delivered to the load.

The definition of the efficiency can be represented in an equation form as:

Power that is not converted to useful signal is dissipated as heat. Power Amplifiers that has low

efficiency have high levels of heat dissipation, which could be a limiting factor in particular

design. Other factors affecting Power Amplifier output include dielectric and conductor losses

[16].

When two or more signals are input to an amplifier simultaneously, the second, third, and higher-

order intermodulation components (IM) are caused by the sum and difference products of each of

the fundamental input signals and their associated harmonics [16]. These are

Fundamental: f1, f2

Second order: 2f1, 2f2, f1 + f2, f1 - f2

Third order: 3f1, 3f2, 2f1 ± f2, 2f2 ± f1,

Fourth order: 4f1, 4f2, 2f2 ± 2f1,

Fifth order: 5f1, 5f2, 3f1 ± 2f2, 3f2 ± 2f1, + Higher order terms

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Of these intermodulation frequencies, the odd order intermodulation products (2f1-f2, 2f2-f1,

3f1-2f2, 3f2-2f1, etc) are close to the two fundamental tone frequencies f1 and f2. The order of

non-linearity of a power amplifier is equal to the amplitude change in dB of the intermodulation

components against the fundamental level [16]. A typical frequency spectrum of a non-linear

power amplifier is shown in figure 9.

Figure 15: Frequency spectrum from a non-linear power amplifier, showing intermodulation

frequencies

The gain of the Power Amplifier approaches zero for sufficiently high input levels. In RF circuits

this effect is quantified by the “1dB compression point”. This is defined as the input signal level

that causes the small-signal gain to drop by 1dB [16].

Figure 16: 1dB compression point

RF ANALYSES AND MEASUREMENTS

HARMONIC BALANCE

Harmonic balance formulates the circuit equations and their solution in the frequency domain.

The solution is written as a Fourier series that cannot represent transient behavior, and so

harmonic balance directly finds the steady-state solution [18-19]. Consider

(1)

This equation is capable of modeling any lumped time-invariant nonlinear system, however it is

convenient to think of it as being generated from nodal analysis, and so representing a statement

of Kirchhoff’s Current Law for a circuit containing nonlinear conductors, nonlinear capacitors,

and current sources. In this case, v(t)ϵRN is the vector of node voltages, i(v(t))ϵRN represents the

current out of the node from the conductors, q(v(t)) represents the charge out of the node from

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the capacitors, and u(t) represents the current out of the node from the sources. To formulate the

harmonic balance equations, assume that v(t) and u(t) are T-periodic and reformulate the terms

of (1) as a Fourier series [18].

It is in general impossible to directly formulate models for nonlinear components in the

frequency domain. To overcome this problem, nonlinear components are usually evaluated in the

time domain. Thus, the frequency domain voltage is converted into the time domain using the

inverse Fourier transform, the nonlinear component (i and q) is evaluated in the time domain,

and the current or charge is converted back into the frequency domain using the Fourier

transform [18].

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METHODOLOGY

Figure 17: RF wireless Transceiver schematic in ADSTM

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The schematic diagram shown above is for an RF wireless transceiver system, consisting of a

direct conversion transmitter system, link (channel) and a 2-stage heterodyne receiver. The

transmitter subsystem consists of the BaseBand (PORT1), a baseband up-converter mixer

(b1_MIX1), an RF bandpass butterworth filter (b2_BPF1), and an RF power amplifier

(b3_AMP1). The receiver subsystem consists of an RF bandpass butterworth filter (b5_BPF2),

two IF bandpass butterworth filters (b8_BPF3 and b9_2_BPF4), Low noise amplifier

(b6_AMP2), 2 IF – downconverter mixers (b7_MIX2 and b9_1_MIX3), and an IF Power

amplifier (b9_0_AMP3).

PART 1

The schematic components are connected as shown in figure 11 from the various libraries in the

ADSTM

component library palette.

PART 2

The baseband frequency of the system is given as 300MHz while the RF output frequency of the

system is given to be 19.5GHz. The chosen frequency for the three oscillators (LOfreq1,

LOfreq2 and LOfreq3) and centre frequency of the four bandpass filters (RFfreq, IFfreq1 and

IFfreq2) are shown in table 1 of Results and Analyses section.

PART 3

The following simulation tools where added to the schematic, HarmonicBalance, Options,

BudGain, BudFdeg, BudNF, BudPwrInc and Var, to test and analyze the performance of the

system. The Var component sets the variables in the system.

For Part 4 and Part 5 please see Results and Analyses

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RESULTS AND ANALYSIS

Table 1: Frequency selection for LOfreq1, LOfreq2, IFfreq and RFfreq

Component Variable Value (MHz)

OSC1 LOfreq1 19200

OSC2 LOfreq2 18500

OSC3 LOfreq3 700

b2_BPF1 RFfreq 19500

b5_BPF2 RFfreq 19500

b8_BPF3 IFfreq1 1000

b9_2_BPF4 IFfreq2 700

Figure 18: Spectrum of Baseband signal in dBm

The spectrum of the Baseband signal from PORT1 shows a power value of -2dBm at the

baseband frequency of 300MHz.

Figure 19: Mixer Spectrum

From figure 19, the spectrum of the mixer shows the rf frequency, 19500 MHz (19200 + 300

MHz), from the up-conversion of both LOfreq1 and baseband. The power (in dBm) of the IF is -

1.054dBm. The spectrum also shows other spurious (or undesired harmonics) products from the

1 2 3 4 5 6 7 8 90 10

-2.10

-2.08

-2.06

-2.04

-2.02

-2.12

-2.00

freq, GHz

dB

m(B

ase

ba

nd

)

Readout

m1

m1freq=dBm(Baseband)=-2.000

300.0MHz

5 10 15 20 25 30 350 40

-600

-400

-200

-800

0

freq, GHz

dB

m(m

ixe

r1)

Readout

m2

Readout

m3

m2freq=dBm(mixer1)=-1.054

19.50GHzm3freq=dBm(mixer1)=-222.060

18.90GHz

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mixing. Among the undesired harmonics is downconversion of LOfreq1 and baseband, (19200-

300MHz), 18900MHz; its power in dBm is -222.060

Figure 20: Filter1 spectrum

After the upconversion, a filter with a narrow bandwidth is needed to suppress all wanted

(spurious) frequencies and prevent them from being transmitted through the antenna, allowing

only the upconverted frequency to pass through. The spectrum of filter1 is shown in figure 20

above.

Figure 21: Amp1 spectrum

After filtering, the signal is then amplified to ensure that sufficient power is transmitted to the

antenna and subsequently through the antenna to the receiver. The signal received at the receiver

has to have sufficient power levels above the sensitivity of the receiver to ensure proper

reception of the transmitted signal.

5 10 15 20 25 30 35 40 45 50 550 60

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

-200

20

freq, GHz

dB

m(f

ilte

r1)

Readout

m8

m8freq=dBm(filter1)=-1.054

19.50GHz

5 10 15 20 25 30 35 40 45 50 550 60

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

20

-200

40

freq, GHz

dB

m(a

mp

1)

Readout

m11

m11freq=dBm(amp1)=27.763Max

19.50GHz

23

The amplifier (AMP1) amplifies the filter RF from -1.054dBm to 27.763dBm. Figure 21 shows

the spectrum from AMP1. Spurious signals are also noticed in the spectrum

Figure 22: Spectrum of Link1 at 1km range

After transmission, through space, the signal is attenuated due to travelling through space. As a

there is loss in power levels from 27.763dBm to -28.731dBm, giving a -56.494dBm loss. This is

shown in figure 22. Spurious signals are also noticed in the spectrum.

Figure 23: Filter 2 frequency spectrum in dBm

The signals from the received RF signal is filtered to attenuate all undesired signals in the

transmitted spectrum before amplification is done. The spectrum from filter2 is shown above.

4 8 12 16 20 24 28 32 360 40

-550

-500

-450

-400

-350

-300

-250

-200

-150

-100

-50

-600

0

freq, GHz

dB

m(l

ink)

Readout

m5

m5freq=dBm(link)=-28.731

19.50GHz

10 20 30 40 50 60 700 80

-360

-320

-280

-240

-200

-160

-120

-80

-40

-400

0

freq, GHz

dB

m(f

ilter2

)

Readout

m17

Readout

m18

m17freq=dBm(filter2)=-28.731

19.50GHz m18freq=dBm(filter2)=-363.291

18.90GHz

24

Figure 24: Amp2 frequency Spectrum

After the received signal is filtered, the signal is ready for amplification, due to the heavy

attenuation in transmission. Amp2 is a Low Noise Amplifier (LNA), whose function is to

amplify possible very weak signals received by the receiver’s antenna.

The received RF is amplified by Amp2 from -27.731dBm to -2.487dBm. The spectrum of Amp2

is shown in figure 24 above.

Figure 25: Mixer2 frequency spectrum in dBm

An IF is generated to the downconversion of mix2 of the RF, from 19500MHz to 1000MHz.

This is to enable the processing of the signal in the receiver. The desired IF generated has a

power level of -1.784dBm. The presence of spurious signals and intermodulation frequencies

noise is also seen in the spectrum shown in figure 25.

The Image frequency generated is

fimage = frf + 2(IF)

= 19500 + 2(1000) MHz

= 19500 + 2000 MHZ

= 21500 MHz (21.5 GHz)

5 10 15 20 25 30 350 40

-450

-400

-350

-300

-250

-200

-150

-100

-50

-500

0

freq, GHz

dB

m(a

mp

2)

Readout

m19

m19freq=dBm(amp2)=-2.487

19.50GHz

5 10 15 20 25 30 350 40

-700

-600

-500

-400

-300

-200

-100

-800

0

freq, GHz

dB

m(m

ixe

r2)

Readout

m20

Readout

m21

m20freq=dBm(mixer2)=-1.784

1.000GHzm21freq=dBm(mixer2)=-206.534

38.00GHz

25

Figure 26: Frequency spectrum of filter3 in dBm

Filter3 further attenuates all unwanted signals from the mixed frequency spectrum. The output of

filter3 spectrum is shown in figure 26 above.

Figure 27: frequency spectrum of Amp3 in dBm

Amp3 amplifies the filtered signal, attenuating all undesired frequencies present in the spectrum.

This is shown in figure 27 above.

5 10 15 20 25 30 350 40

-1400

-1300

-1200

-1100

-1000

-900

-800

-700

-600

-500

-400

-300

-200

-100

-1500

0

freq, GHz

dB

m(f

ilte

r3)

Readout

m22

20.20G-343.4

m23

m22freq=dBm(filter3)=-1.732

1.000GHzm23freq=dBm(filter3)=-1046.669

38.00GHz

5 10 15 20 25 30 350 40

-1400

-1300

-1200

-1100

-1000

-900

-800

-700

-600

-500

-400

-300

-200

-100

0

-1500

100

freq, GHz

dB

m(a

mp

3)

Readout

m24

m24freq=dBm(amp3)=17.402

1.000GHz

26

Figure 28: Frequency spectrum of mixer3 in dBm

In this final stage of downconversion, the IF is downconverted from 1000MHz to 300MHz, the

baseband frequency. The presence of intermodulation noise generated by this downconversion is

attenuated by filter4 before the signal is reconverted back the original form at port2. This is

shown in figure 29 below.

Figure 29: Frequency spectrum of IFout in dBm

FURTHER ANALYSIS

The effect of the link distance (range) on IFout was investigated and the result is shown in figure

30 below.

2 4 6 8 10

12

14

16

18

20

22

24

0 25

-1400

-1300

-1200

-1100

-1000

-900

-800

-700

-600

-500

-400

-300

-200

-100

0

-1500

50

freq, GHz

dB

m(m

ixe

r3)

Readout

m6

m6freq=dBm(mixer3)=10.402

300.0MHz

5 10 15 20 25 30 350 40

-1900-1800-1700-1600-1500-1400-1300-1200-1100-1000-900-800-700-600-500-400-300-200-100

-2000

0

freq, GHz

dB

m(I

Fo

ut)

Readout

m7

m7freq=dBm(IFout)=10.402

300.0MHz

27

Figure 30: A plot of Power received at receiver antenna (dBm) and IFout (dBm) against Link

distance (Km).

From the above graph, it is observed that as the link distance increases, the power received at the

antenna and at the PORT2 decreases. This indicates that attenuation increases with distance and

consequently reduces the power received at the receiver antenna.

Secondly, the effect of varying the received power, IFout as a function of transmitter antenna

gain TxGain was investigated, and this is shown in figure 31 below.

Figure 31: A plot of IFout (dBm) against TxGain (dB)

-22.711

-28.731

-32.253 -34.752 -34.752

16.054

10.402

6.943

4.466

2.538

0

2

4

6

8

10

12

14

16

18

-40

-36

-32

-28

-24

-20

-16

-12

-8

-4

0

0 0.5 1 1.5 2 2.5 3 P

ow

er (d

Bm

)

Link distance (Km)

Power received at receiver antenna (dBm)

IFout (dBm)

-9.487

0.503

10.402

19.138

-15

-10

-5

0

5

10

15

20

25

0 10 20 30 40 50

Ifo

ut

(dB

m)

TxGain (dB)

IFout (dBm)

I…

28

The plot above shows an increase in received power (IFout) as the gain in transmitter antenna

(TxGain) increases.

Factors affecting the transmitter antenna gain include the antenna’s directivity, antenna

efficiency, antenna effective area, and its electrical efficiency. Antenna efficiency is a measure of

the electrical losses that occur in the antenna (this losses include ground loss, ohmic and

capacitive loss). The directivity of an antenna is a measure of the power density the antenna

radiates in the direction of its strongest emission compared to the power radiated by an isotropic

radiator, radiating the same power. The antenna effective area is a measure of how effective an

antenna is at receiving or radiating the power of radio waves. Directional antennas are best suited

for such transmission as they radiate greater power in one or more directions, allowing for

increased performance and reduced interference from unwanted sources. Such antennas include

yagi-uda, log-periodic antenna, parabolic antenna, helical antenna, etc [20].

Thirdly, the values of the three oscillators and centre frequencies for the bandpass filters was

changed to observe the effect of different IF frequencies on the system. The new values are

shown in table 2.

Table 2: New Frequency selection for LOfreq1, LOfreq2, IFfreq and RFfreq

Component Variable Value (MHz)

OSC1 LOfreq1 19200

OSC2 LOfreq2 9500

OSC3 LOfreq3 9700

b2_BPF1 RFfreq 19500

b5_BPF2 RFfreq 19500

b8_BPF3 IFfreq1 10000

b9_2_BPF4 IFfreq2 300

It was observed that the new set of frequencies did not affect the system. The received power

(IFout), budget gain, budget noise figure and budget noise figure degradation were not affected.

29

AC SIMULATION

figure 32: Budget Gain Analysis

Figure 32 above shows the budget power gain in the RF wireless transceiver system above. From

the plot above, a heavy attenuation or loss in signal power was noticed at link (-27.472dBm).

This is due to the attenuation of the signal by ions in free space. The plot also shows the

amplification by the LNA, amp2 on the received power.

Figure 33: Budget Incident Power

Eqn x=sweep_size(our_bgain[0])-6

Component

b1_MIX1b2_BPF1b3_AMP1b4_LINK1b5_BPF2b6_AMP2b7_MIX2b8_BPF3

b9_1_MIX3b9_2_BPF4

b9_AMP3OSC1OSC2

our_bgain

freq=300000000.000

9.643E-16-1.283-1.283

-21.472-21.472-21.472

6.7525.528

26.75219.752

5.528-3040.000-3040.000

b2_B

PF

1

b3_A

MP

1

b4_LIN

K1

b5_B

PF

2

b6_A

MP

2

b7_M

IX2

b8_B

PF

3

b9_1_M

IX3

b9_2_B

PF

4

b1_M

IX1

b9_A

MP

3

-20

-10

0

10

20

-30

30

Component

ou

r_b

ga

in[0

::x,0

]

Eqn x2=sweep_size(our_bpwri[0])-6

Component

b1_MIX1.t1b1_MIX1.t2b1_MIX1.t3b2_BPF1.t1b2_BPF1.t2b3_AMP1.t1b3_AMP1.t2b4_LINK1.t1b4_LINK1.t2b5_BPF2.t1b5_BPF2.t2b6_AMP2.t1b6_AMP2.t2

our_bpwri

freq=300000000.000

-7.105E-15-13.000

-3010.000-13.000

-1.000-1.000

-92.497-34.24837.000

-34.248-21.248-21.248

-3010.000

b1_M

IX1.t2

b1_M

IX1.t3

b2_B

PF

1.t1

b2_B

PF

1.t2

b3_A

MP

1.t1

b3_A

MP

1.t2

b4_LIN

K1.t1

b4_LIN

K1.t2

b5_B

PF

2.t1

b1_M

IX1.t1

b5_B

PF

2.t2

-3000

-2500

-2000

-1500

-1000

-500

0

-3500

500

Component

ou

r_b

pw

ri[0

::x,0

]

30

Figure 34: Budget Noise figure

The figure above shows the budget noise figure by each component in the RF wireless

transmitter system. It shows an increase in the noise figure at the link (from 0.130 to 6.380).

Noticeable also is the intermodulation frequency noise in Amp2 which reflects in the plot (from

6.380 to 19.015).

Various sources of noise in the system include thermal noise from vibrations of conduction

electrons and holes due to temperature; shot noise from quantized nature of current flow, etc

[20].

Eqn x3=sweep_size(our_bnf[0])-6

Component

b1_MIX1b2_BPF1b3_AMP1b4_LINK1b5_BPF2b6_AMP2b7_MIX2b8_BPF3

b9_1_MIX3b9_2_BPF4

b9_AMP3OSC1OSC2

our_bnf

freq=300000000.000

0.0000.1300.1306.3806.3806.380

19.01519.01519.02319.02419.015

0.0000.000

b2_B

PF

1

b3_A

MP

1

b4_LIN

K1

b5_B

PF

2

b6_A

MP

2

b7_M

IX2

b8_B

PF

3

b9_1_M

IX3

b9_2_B

PF

4

b1_M

IX1

b9_A

MP

3

5

10

15

0

20

Component

ou

r_b

nf[0

::x,0

]

31

REFERENCES

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N.pdf on the 18/04/2012.

11. Wikipedia, “Intermediate Frequency,” retrieved on 18/04/2012, from

http://en.wikipedia.org/wiki/intermediate_frequency

12. H. Zumbahlenas and Analog Devices, “Linear circuit design handbook”. Amsterdam;

Boston: Elsevier/Newnes Press, 2008, pp 4.1-4.60

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14. S. Hong and M. J. Lancaster, “Microstrip filters for RF/Microwave applications,” John

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Boston: Elsevier/Newnes Press, 2008.

16. Wikipedia, “RF Power Amplifier,” retrieved on 18/04/2012, from

http://en.wikipedia.org/wiki/rf_power_amplifier I. Rosu, “RF Mixers,” retrieved from

http://www.qsl.net/va3iul on 18/04/2012

17. I. Rosu, “RF Power Amplifiers,” retrieved from http://www.qsl.net/va3iul on 18/04/2012

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