ALTERNATIVE MILLIMETER-WAVE COMMUNICATION RECEIVERS

IN SIX-PORT TECHNOLOGY

Serioja O. Tatu Institut National de la Recherche Scientifique Energie, Matériaux, Télécommunications, 800 de la Gauchetière O., R 6900, Montréal, H5A 1 K6,

email: tatu@emt.inrs.ca

Emilia Moldovan Poly–Grames Research Center,, École

Polytechnique de Montréal, Pavillon Lassonde, 2500 Chemin Polytechnique, Montréal, H3T 1J4,

email: emilia.moldovan@polymtl.ca

Abstract The six-port technology, originally used to perform

complex reflection coefficient measurements of a microwave device, is an excellent candidate for the future millimeter-wave wireless communication systems.

The millimeter-wave frequency conversion is performed using a passive circuit, the six-port, avoiding the conventional millimeter-wave active costly mixers. Basically, the six-port circuit is an additive mixer in which the resulting sum of millimeter-wave signals is nonlinearly processed using millimeter-wave detectors.

A new V-band six-port circuit designed in MHMIC technology is presented in this paper. The operating principle of the proposed heterodyne receiver and demodulation results of V-band high-speed MPSK/QAM signals are presented and discussed. According to high-speed requirements of the IEEE 802.15.3.c wireless standard (100 - 400 Mb/s), the IF of this receiver was chosen at 900 MHz. A second frequency conversion using conventional means is used. Initial results show more that 70 dB of overall gain of the six-port heterodyne receiver.

Keywords: Six-port technology, heterodyne, MPSK, QAM.

1. Introduction

The modern communication receivers are more and more exigent in terms of wide-band, data rates, size and costs [1]. The millimeter-wave based technology has received increased attention in both academia and industry for very high-data-rate wireless personal area network (WPAN) applications such as wireless data bus for cable replacement, high-speed wireless Internet access, wireless direct communication between notebooks and related devices, wireless high-resolution TV and videoconferencing. The IEEE 802.15.3.c industrial standard based on millimeter-wave technology has been recently introduced for WPAN.

The use of millimeter-wave frequencies enables the design of compact and low-cost wireless millimeter-wave communication front-ends, which can offer convenient terminal mobility and high-capacity channels. This wide range of applications requires low-cost equipment operating at hundreds of megabits per second. In the last decade some initial research has been made, especially in terms of designing

new millimeter wave components operating over the V-band [2]-[5].

In order to improve overall performances of a communication receiver, alternative wide-band architectures for high-speed wireless communication systems have been explored in the past years [6]-[9].

This paper presents MPSK/QAM demodulation results of a V-band six-port heterodyne receiver suitable for very high-data-rate WPAN applications.

2. Six-Port Mixer

The equivalence between the front-end conventional mixer architecture and the six-port mixer is presented in Figure 1. The purpose of this paper is to demonstrate that the six-port circuit together with related power detectors and two differential amplifiers can successfully replace a conventional mixer.

Fig. 1. Equivalence between conventional and six-port mixer.

The RF input MPSK/QAM modulated signal and the local oscillator signal are expressed as follows:

( ) ( ) ( )[ ]tttatxRF θω +⋅= cos (1) ( ) ( )[ ]tttxLO 00cos θω += (2)

In practice, for a six-port heterodyne receiver, the carrier frequency ω is close to the local oscillator frequency ω0.Therefore, these receivers are low IF receivers.

Using the conventional mixer architecture of a heterodyne receiver with complex frequency conversion (see Figure 1) and low-pass filtering we obtain the well known equations:

π/2

LO

RF

i

q

3

1

4

2

+

-

+

-

LO

RF

i

q5

6

π/2

LO

RF

i

q

π/2

LO

RF

i

q

3

1

4

2

+

-

+

-

LO

RF

i

q5

6

3

1

4

2

+

-

+

-

LO

RF

i

q5

6

1-4244-0038-4 2006IEEE CCECE/CCGEI, Ottawa, May 2006

2337

( ) ( ) ( )[ ]tttaKtxi θω Δ+⋅Δ⋅⋅= cos1 (3) ( ) ( ) ( )[ ]tttaKtxq θω Δ+⋅Δ⋅⋅= sin1 (4)

The six-port equivalent circuit of the low IF heterodyne receiver uses four power detectors and two differential amplifiers operating at IF frequency. Considering the six-port architecture presented in [8], the IF signals can be expressed as:

( ) ( ) ( ) ( ) ( )[ ]tttaKtvtvtxi θω Δ+⋅Δ⋅⋅=−= cos213 (5)

( ) ( ) ( ) ( ) ( )[ ]tttaKtvtvtxq θω Δ+⋅Δ⋅⋅=−= sin224 (6)

Equivalent equations are obtained for the IF signals using the conventional or the six-port mixer. We note that a homodyne receiver is obtained if ω0 = ω. In previous equations, constants K1 and K2 are function of electrical parameters of circuits. Therefore, the six-port mixer can successfully replace the conventional one in a low-cost millimeter-wave heterodyne or homodyne architecture.

A V-band six-port circuit was designed in MHMIC technology using a 125 μm ceramic substrate having a relative permittivity of 9.9. Figure 2 shows the layout of the circuit having a size of approximately 3 by 3 mm. The circuit is composed of four 90° hybrid couplers connected by 50 Ωmicrostrip transmission lines. In order to avoid reflections at two unused ports of the multi-port circuit, two 50 Ω loads are connected to open circuited quarter-wave transmission lines (virtual RF short-circuits). The hybrid coupler connected to LO port together with the 90° phase shifter (made using an additional quarter-wave transmission line on curved branch) is equivalent to an in-phase 3 dB power divider.

Fig. 2. Layout of the V-band six-port circuit.

The circuit was optimized to operate at 60 GHz central frequency with a maximal bandwidth using ADS Momentum software. Figure 3 shows simulation results of S parameters at RF input ports over the unlicensed V-band, for the proposed six-port circuit. Excellent return losses and isolation between

input RF ports were obtained in a 2 GHz bandwidth centered at the 60 GHz operating frequency. The phase and the magnitude of the transmission S-parameters are also of main interest to obtain the requested four “qi point” six-port circuit (see the block diagram in [8]).

Fig. 3. Simulation results of S parameters magnitude at RF inputs.

In order to demonstrate that the six-port is a four “qi point” circuit having all points spaced by 90º, a harmonic balance simulation was performed at 60 GHz using a six-port model based on ADS Momentum S-parameter results. The phase shift between RF inputs was swept in a 360º range and the RF input signal power was set to 0 dBm. The RF six-port output magnitudes versus this phase shift are shown in Figure 4. As seen, the minimum magnitude values are shifted by 90º multiples as requested for this six-port architecture.

Fig. 4. Simulation results of Vout magnitude versus RF input phase shift.

3. Demodulation results

Demodulation results of the V-band six-port heterodyne receiver are presented in this section. The six-port heterodyne receiver simulation block diagram using ADS software is presented in Figure 5. Simulations are performed using a 60 GHz carrier frequency of MPSK/QAM modulated signal. According to high-speed requirements (100 - 400 Mb/s for the IEEE 802.15.3.c wireless standard), the IF of the heterodyne receiver was chosen at 900 MHz. A second frequency conversion using conventional mixers is also implemented.

4

2

1

36

5

50 Ω

50 Ω

RF

LO

4

2

1

36

5

50 Ω

50 Ω

RF

LO

S65

S55S66

60 61 62 6359 64

-40

-30

-20

-10

-50

0

Frequency (GHz)

Mag

.S p

aram

(dB

)

90 180 2700 360

0.1

0.2

0.3

0.0

0.4

V1 V2 V3 V4

Phase shift (deg)

Mag

. Vou

t (V

)

2338

The six-port heterodyne receiver is composed of a low noise amplifier AMP1, the V-band six-port module (including power detectors), two IF differential amplifiers (AMP2, AMP3) and a conventional IF demodulator (MIX2, MIX3, LPF1, LPF2). The I/Q output demodulated signals are obtained at the outputs of the sample and hold circuits SAMP1 and SAMP2.

As known, a millimeter-wave oscillator does not have excellent frequency stability and is difficult to be controlled. If the difference between the carrier and the local oscillator is not exactly equal to IF, the demodulated constellation turns clockwise or anti-clockwise, depending on the sign of this difference [9]. However, this frequency/phase error can be compensated using signal processing techniques. The second LO must be dynamically adjusted by a control loop. A millimeter-wave local oscillator frequency error (5 MHz in simulation diagram of Fig.5.) was successfully compensated.

The heterodyne architecture will allow an increased gain of the receiver for relatively long range applications comparing to the homodyne architecture. Simulation results show more than 70 dB of the six-port heterodyne receiver overall gain, compared to 50 dB of gain, reported for the homodyne receivers [6]-[7].

Figure 6 shows a typical IF spectrum (IF_I or IF_Q on the simulation block diagram) considering a 100 Mb/s QPSK

signal. We note that a 400 Mb/s can be successfully demodulated using the 900 MHz IF value.

Fig. 6. Spectrum of the IF signal.

Supposing a perfect synchronism and no additional noise, Figure 7 shows various simulation results of demodulated constellations using the proposed heterodyne architecture for high-speed MPSK/QAM signals: 100 Mb/s for QPSK, 200 Mb/s for 8PSK and 16 QAM, and 400 Mb/s for 16PSK. As seen, all clusters of demodulated constellations are very well positioned and individualized.

Fig. 5. Simulation block diagram of the six-port heterodyne receiver using ADS.

in_I in_Q

V1

IF_I

V3

clock

V4

V2IF_Q

SP_module_SYMX1

2

4

3

1

5

6

SampleHoldSMLSAMP2

SampleHoldSMLSAMP1

LOS_LinkLINK1

PathLength=10 meterRxGain=10 dBTxGain=10 dBBW=1000 MHzCenterFreq=fr

VARVAR1

def=0delta_fr=900 MHzerror=5 MHzph=360*error*timefr=60 GHz

EqnVar

EnvelopeEnv1

Step=0.000025 usecStop=1.5 usecOrder[1]=3Freq[1]=fr

ENVELOPE

VtLFSR_DTSRC2

Rate=50 MHzVhigh=1 VVlow=-1VDT

VtLFSR_DTSRC1

Rate=50 MHzVhigh=1 VVlow=-1VDT

IQ_ModTunedMOD1

Rout=50 OhmFnom=fr

P_1TonePORT1

Freq=frP=polar(dbmtow(5),0)Z=50 OhmNum=1

Vf_SquareSRC6

Delay=0 nsecFreq=100 MHz

RR4R=50 Ohm

RR3R=50 Ohm

P_1TonePORT2

Freq=fr+delta_frP=polar(dbmtow(-10),ph)Z=50 OhmNum=2

P_1TonePORT3

Freq=delta_frP=polar(dbmtow(0),ph)Z=50 OhmNum=3

RR1R=50 Ohm

LPF_ChebyshevLPF2

Astop=20 dBFstop=400 MHzRipple=1 dBFpass=150 MHz

LPF_ChebyshevLPF1

Astop=20 dBFstop=400 MHzRipple=1 dBFpass=150 MHzMixer2

MIX2

ConvGain=dbpolar(30,0)SideBand=

OpAmpIdealAMP3

Freq3db=delta_frGain=20

OpAmpIdealAMP2

Freq3db=delta_frGain=20

AmplifierAMP1S21=dbpolar(20,0)

Mixer2MIX3

ConvGain=dbpolar(30,0)SideBand=

PwrSplit2PWR1

S31=0.707S21=0.707

RR2R=50 Ohm

PhaseShiftSMLPS1

ZRef=50. OhmPhase=275.

Q

I

Frequency (GHz)

IF s

igna

l (dB

m)

-0.9 -0.6 -0.3 0.0 0.3 0.6 0.9-1.2 1.2

-70

-60

-50

-40

-80

-30

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Fig. 7. Demodulated high-speed MPSK/QAM signals.

Figure 8 shows the bit error rate (BER) versus the energy per bit to the spectral noise density Eb/No for various LO frequency errors (no error, 5 MHz and 25 MHz) using the frequency/phase error compensation in the case of a 100 Mb/s QPSK modulated signal. Simulation shows an excellent result: the BER is less than 10-6 for Eb/No equal to 12 dB, in the case of considered errors of synchronism of the millimeter-wave oscillator.

Fig. 8. BER simulation results for various errors of synchronism of the millimeter-wave oscillator.

4. Conclusions Simulation results of a V-band millimeter wave six-port

heterodyne receiver have been presented in this paper. The millimeter-wave frequency conversion is obtained using the specific properties of the six-port circuit, avoiding the use of a conventional active mixer.

Excellent demodulation results were obtained using high-speed V-band MPSK/QAM modulated signals. Simulated BER results, in the case of an important millimeter-wave LO frequency error from synchronism (dynamically compensated at the second LO), are excellent. Comparing to the direct conversion, due to the heterodyne architecture, an improved overall gain was obtained.

The proposed six-port heterodyne architecture enables the design of compact and low-cost wireless millimeter-wave communication receivers for future high-speed wireless communication systems, according to the IEEE 802.15.3.c wireless standard.

References

[1] C.A. P. Smulders, “Exploiting the 60 GHz Band for Local Wireless Multimedia Access: Prospects and Future Directions, IEEE Comm. Magazine, pp. 140-147, January 2002.

[2] J. Wenger, J. Splettstober, “Ka-band and V-band MMIC Components for Personal Communication Networks”, 1996 IEEE MTT-s Digest, pp.491-494, San Francisco, California.

[3] A. Nesic, I. Radnovic, V. Brankovic, “Ultra-wide band Printed Antenna Array for 60 GHz Frequency Range”, 1997 Antennas and Propagation Society International Symposium, pp.1272-1275.

[4] K.S. Ang and I.D. Robertson, “Monolithic resistive mixers for 60 GHz Direct Conversion receivers”, 2000 IEEE RFIC Symposium, pp. 35-39, Boston, Massachusetts.

[5] T. Brabetz, V. Fusco, “Six-Port Receiver MMIC for V-band MBS Applications”, 11th GaAs Symposium, pp. 97-99, Munich 2003.

[6] S.O. Tatu, E. Moldovan, Ke Wu, R.G. Bosisio, “A New Direct Millimeter-Wave Six-Port Receiver”, IEEE Trans on MTT, vol.49, no.12, pp. 2517-2522, December 2001.

[7] S.O. Tatu, E. Moldovan, G. Brehm, Ke Wu, R.G. Bosisio, “Ka Band Direct Digital Receiver”, IEEE Trans. on MTT,vol.50, no.11, pp. 2436-2442, Nov. 2002.

[8] S.O. Tatu, E. Moldovan, Ke Wu, R.G. Bosisio, T. Denidni, “Ka-Band Analog Front-end for Software Defined Direct Conversion Receiver”, IEEE Trans on MTT , vol.53, no.9, pp. 2768-2776, September 2005.

[9] S.O. Tatu, T.A. Denidni, “Millimeter-Wave Six-Port Heterodyne Receiver Concept”, 2006 IEEE MTT International Microwave Symposium, San Francisco, California, June 11-16, in press.

BE

R

0 2 4 6 8 10 12 14 16 18-2 20

1E-151E-141E-131E-121E-111E-101E-91E-81E-71E-61E-51E-41E-31E-21E-1

1E-16

1

Eb/ No (dB)

No error

5 MHz

25 MHz

I (V)

Q (V

)-0.5 0.0 0.5-1.0 1.0

-0.5

0.0

0.5

-1.0

1.0

-0.5 0.0 0.5-1.0 1.0

-0.5

0.0

0.5

-1.0

1.0

-1.0 -0.5 0.0 0.5 1.0-1.5 1.5

-1.0

-0.5

0.0

0.5

1.0

-1.5

1.5

-0.5 0.0 0.5-1.0 1.0

-0.5

0.0

0.5

-1.0

1.0

I (V)

I (V) I (V) Q

(V)

Q (V

)Q

(V)

QPSK 8PSK

16PSK 16QAM

2340