IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 9, 2010 413

Impact of Polarization Characteristics on 60-GHzIndoor Radio Communication Systems

Alexander Maltsev, Member, IEEE, Eldad Perahia, Member, IEEE, Roman Maslennikov, Member, IEEE,Alexey Sevastyanov, Member, IEEE, Artyom Lomayev, Member, IEEE, and Alexey Khoryaev, Member, IEEE

Abstract—This letter presents experimental results for the po-larization impact on 60-GHz indoor radio communication systems.Different transmit and receive antenna polarizations (linear polar-izations with different electrical field vector orientations and cir-cular polarizations with different handedness) were used to ana-lyze the degradation in the received signal power due to nonopti-mally matched polarization characteristics between the transmitantenna, the propagation channel, and the received antenna. Dif-ferent signal propagation paths including line-of-sight (LOS) prop-agation and first- and second-order reflections were investigated.It was found that the degradation due to polarization characteris-tics mismatch could be as large as 10–20 dB. Polarization charac-teristics of the transmit and receive antennas providing maximumreceived signal power were found to be dependent on the type ofthe signal propagation path. The most robust antenna polarizationconfiguration was identified as a configuration using linear polar-ization at one end of the communication link and circular polar-ization at the other end, giving the degradation relative to the op-timally matched case of 2–3 dB only.

Index Terms—60 GHz, polarization, wireless communications.

I. INTRODUCTION

I NDOOR radio communication systems operating in themillimeter-wave 60-GHz frequency band have the potential

to provide multi-Gb/s data throughput over radio channels todistances of up to 10–20 m. The small wavelength of the signalsin the 60-GHz band makes the propagation quasi-optical innature with most of the signal power received through theline-of-sight (LOS) and first- and second-order reflections [1].In addition, according to the Friis transmission equation, thesmall wavelength of the signal results in sizeable path loss.Highly directional antennas steered along the LOS path shouldbe used in order to establish a reliable communication link.First- and second-order reflected non-LOS paths should beused if the LOS path is unavailable [2].

Exploitation of a single signal propagation path for es-tablishing the communication link is different from wirelesscommunications systems operating in the traditional 2.4- and5-GHz bands where usually multiple reflected and diffracted

Manuscript received November 12, 2009; revised January 07, 2010 andMarch 09, 2010; accepted March 20, 2010. Date of publication April 19, 2010;date of current version May 17, 2010.

A. Maltsev, A. Sevastyanov, A. Lomayev, and A. Khoryaev are with the Wire-less Standards and Technology Group, Intel Corporation, Nizhny Novgorod603024, Russia (e-mail: alexander.maltsev@intel.com).

E. Perahia is with the Wireless Standards and Technology Group, Intel Cor-poration, Hillsboro, OR 97124 USA.

R. Maslennikov is with the Wireless Competence Center, N. I. LobachevskyState University, Nizhny Novgorod 603024, Russia.

Color versions of one or more of the figures in this letter are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/LAWP.2010.2048410

signal components contribute to the received signal. The natureof the signal propagation for indoor 60-GHz wireless systemsresults in much stronger susceptibility to the mismatch ofthe polarization characteristics of the transmit antenna, thepropagation channel, and the receive antenna than for the 2.4-and 5-GHz bands.

This work presents experimental results for the polarizationimpact on 60-GHz indoor wireless local communication sys-tems. A set of measurements was performed using differenttransmit and receive antenna polarizations and different typesof signal propagation paths to evaluate the impact of the polar-ization characteristics on the received signal power.

The remainder of the letter is organized as follows. Section IIgives a short description of the measurement setup and scenario.Section III presents experimental results. Section IV concludesthe letter.

II. MEASUREMENT SETUP AND SCENARIO

The measurement setup included an 800-MHz I/Q transmitsignal generator and receive signal digitizer connected tocustom RF components for up and down conversion to the60-GHz band. Switchable polarizers at the RF output allowedchanging of the polarization of the signals to four differenttypes: horizontal linear polarization (HLP), vertical linearpolarization (VLP), left-hand circular polarization (LHCP),and right-hand circular polarization (RHCP). The polarizationcould be changed independently at the transmitter and receiver.Circular horn antennas with 16 dBi gain, 25 half-powerbeamwidth, and dB sidelobe level were connected tothe switchable polarizers using a waveguide interface. Theantennas (with the RF components) could be mechanicallyrotated to perform scanning in the azimuth and elevation angleplanes. A wideband 800-MHz OFDM signal at 60 GHz carrierwas used for channel sounding.

The measurements were performed in a small conferenceroom with dimensions 3.0 4.5 3.0 m (W L H). Thefloor plan of the conference room and an example of theprototype placement are shown in Fig. 1.

III. EXPERIMENTAL RESULTS

We start with a description of the experimental results byshowing an example of the received power distributions for aprototype placed in a conference room as it is shown in Fig. 1.The distribution of the received power was measured as a func-tion of the receive and transmit antenna azimuth angles cal-culated relative to the LOS direction. The elevation angles forboth transmit and receive antennas were equal to 0 (i.e., in thisexperiment, the antennas were steered in the horizontal planeonly).

1536-1225/$26.00 © 2010 IEEE

414 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 9, 2010

Fig. 1. Conference room plan with quasi-optical signal propagation paths(LOS, first-order, and second-order reflections) marked by “A”–“E,” and anexample of the measurement setup placement.

The received power was measured relative to the noiselevel at the baseband of the experimental setup giving thesignal-to-noise ratio (SNR) characteristics. Parameters of themeasurement setup were approximately equal to those ofa typical 60-GHz indoor wireless system [2] (the transmitpower equal to 2 dBm, 16 dBi antenna gains, 800 MHz signalbandwidth, and the noise figure equal to 7 dB). Therefore, themeasured SNR values could be considered as an estimate ofthe SNR achievable by practical systems.

Experimental SNR distributions were measured for five dif-ferent configurations of the transmitter and receiver antenna po-larizations (TX-RX): LHCP-LHCP [Fig. 2(a)], LHCP-RHCP[Fig. 2(b)], LHCP-HLP [Fig. 2(c)], HLP-VLP [Fig. 2(d)], andHLP-HLP [Fig. 2(e)].

The main signal clusters that can be used to establish a reli-able communication link are illustrated in Fig. 2 and are markedwith letters “A” to “E.” These correspond to the signal propaga-tion paths predicted by ray tracing and are marked by matchingletters in Fig. 1. These clusters are the LOS path (“A”), twofirst-order reflections from the walls (“B” and “C”), and twodouble reflections from the walls (“D” and “E”). It can be seenfrom Fig. 2 that all the clusters are separated by more than 40in at least one of the two angular domains of the transmit andreceive azimuth angles. Since directional antennas with the 25beamwidth and dB sidelobe level were used at both thetransmitter and receiver, all the clusters in the two dimensionalangular domain were resolved (the power leakage between clus-ters was estimated to be not higher than dB). The receiveSNR for the five clusters “A”–“E” was measured for each ofthe transmit and receive antenna polarization pairs listed above.The results are summarized in Table I.

Fig. 2 shows that for the LOS path (“A” clusters), the max-imum gain (with an SNR of approximately 30 dB) is achievedwhen copolarized transmit and receive antennas are used. This isthe case when both antennas have LHCP or HLP polarizations.For the LOS case, if the transmit and receive antennas have or-thogonal polarizations (LHCP-RHCP or HLP-VLP configura-tions), the received power level is defined by the cross-polariza-tion discrimination of the antennas. For the given measurementsetup, this was about 18–20 dB.

The LOS power for the LHCP-HLP antenna polarization con-figuration (28.8 dB) should be 3 dB less than the copolarized

TABLE IRECEIVED SNR FOR DIFFERENT TYPES OF CLUSTERS AND ANTENNAS

POLARIZATIONS FROM FIG. 2

configuration. However for this experiment, the measured dif-ference was approximately 2 dB due to nonideality of the cir-cular polarization provided by the polarizer. The used polarizercould have up to 3 dB axial ratio resulting in the instrumentalerror of dB limiting the overall accuracy of the measure-ments with different antennas polarization configurations.

When considering the first-order reflected clusters (“B” and“C” clusters), it may be seen that polarization configurationsproviding the best received power are LHCP-RHCP and HLP-HLP. The handedness of a circular polarized electromagneticwave changes when reflected from a medium with higher re-fraction coefficient with the incident angle below the Brew-ster’s angle [3]. Hence, the LHCP-RHCP configuration is ex-pected to have larger gain than the LHCP-LHCP configurationfor the first-order reflected clusters. This is confirmed by themeasurement results where the LHCP-RHCP configuration has2.3 (“C” cluster) and 5.6 dB (“B” cluster) better SNR than theLHCP-LHCP configuration. The linear horizontal polarizationvector is parallel to the plane of incidence, and thus its orien-tation does not change after the reflection. It may appear thatthe HLP-HLP configuration is very effective for first-order re-flections (16.5 dB for “B” cluster and 12.4 dB for “C” cluster).However, a configuration with copolarized linear antennas re-quires similar orientation of the transmit and receive antennas,which may not always be achieved in a practical system. In theHLP-VLP configuration, the degradation of the first-order re-flected (“B” and “C”) clusters is more than 12 dB relative tothe matched polarizations as given by Table I. The receivedSNR was less than zero for most of the NLOS clusters with theHLP-VLP polarization configuration and could not be measuredwith this experimental setup.

For the second-order reflections (clusters “D” and “E”),the handedness of the circular polarization changes twice, sonear-optimal configurations are LHCP-LHCP and HLP-HLP.LHCP-HLP is also a robust configuration for double reflectedclusters.

This example of the experimental results demonstrates thatdegradation due to polarization mismatch can be significant, andthat establishing a communication link over different types ofsignal propagation paths requires different characteristics of thetransmit and receive antenna polarization.

MALTSEV et al.: IMPACT OF POLARIZATION CHARACTERISTICS ON 60-GHz INDOOR RADIO COMMUNICATION SYSTEMS 415

Fig. 2. Distributions of the received signal power for different combinations of the transmit and receive antennas polarizations: (a) LHCP-LHCP, (b) LHCP-RHCP,(c) LHCP-HLP, (d) HLP-VLP, and (e) HLP-HLP.

In addition to the experiment described, six other experimentswere carried out with different locations of the measurementsetup in the conference room. For each experiment, different po-larization configurations for the transmit and receive antennaswere used, as was done for the first experiment previously de-

scribed. Signal clusters were identified from the experimentaldata, and corresponding SNR values were calculated.

Then, for each cluster of every experiment, the polarizationconfiguration that provided the maximum received power wasfound and the relative degradation of other configurations

416 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 9, 2010

Fig. 3. CDF of degradation for different configurations of the transmit and re-ceive antenna polarizations relative to maximum received power.

TABLE IIAVERAGE SNR DEGRADATION FOR DIFFERENT ANTENNA POLARIZATION

CHARACTERISTICS AND DIFFERENT TYPES OF CLUSTERS

was calculated. The degradation values were divided into fivegroups depending on the type of the transmit and receiveantennas polarization configurations: circular copolarizedantennas (at the transmit and receive sides); circular cross-po-larized antennas; circular and linear polarized antennas; linearcopolarized antennas; linear cross-polarized antennas. For eachgroup, the degradation values (relative to the maximum powercase) were analyzed statistically by calculating the cumulativedistribution function (CDFs). Fig. 3 plots the CDFs for thefive groups of the antenna configurations. The curves shown inFig. 3 can be used for statistical analysis of performance effi-ciency for 60-GHz indoor communication system for differentantennas configurations.

The results given in Fig. 3 are calculated over all identifiedsignal clusters. However, as previously demonstrated, the po-larization mismatch degradation depends on the signal clustertype. To illustrate this dependence, the average degradation forevery group of antenna configurations and different types ofclusters (LOS, first-order reflections, and second-order reflec-tions) is presented in Table II.

It may be seen from Fig. 3 and Table II that linear copolar-ized antennas provide on average the maximum received powerand have the average (over all types of the clusters) degrada-tion relative to maximum received power of 0.9 dB only. How-ever, an accidental change of the mutual antennas orientation ina practical handheld or portable system can make the copolar-ized linear antennas to be cross-polarized, resulting in the worstaverage degradation of more than 11.6 dB.

Circular copolarized antennas do not have any restrictions onthe orientation of antenna polarization vectors and have goodperformance for the LOS and second-order reflected clusters.However, for the first-order reflected clusters, the degradationwas 5.7 dB, which is quite significant.

Conversely, circular cross-polarized antennas are effective forthe first-order reflections, but are not effective for the LOS andsecond-order reflections.

Cross-polarized linear antennas have large loss relative to theoptimally matched case, and such configuration is not appro-priate for the communication system.

The experimental results show that different polarization con-figurations provide maximum SNR for different types of clus-ters. Therefore, to achieve maximum efficiency and reliability,the 60-GHz communication system should be able to adaptivelychange polarization characteristics of antennas at the transmitterand receiver to exploit all possible cluster types.

Alternatively, the most robust nonadaptive (fixed) configura-tion providing moderate (2.3–2.9 dB) degradation for all typesof clusters is linear polarization at one antenna and circular po-larization at the other antenna.

IV. CONCLUSION

This work investigated polarization characteristics of the60-GHz wireless propagation channel and the impact thesecharacteristics may have on the design of a 60-GHz indoorradio system.

The experimental data demonstrated that mismatch of polar-ization characteristics of transmit and receive antennas can re-sult in a large degradation of the received signal power between10–20 dB. To mitigate the degradation, special measures haveto be considered at the system design stage. Two general ap-proaches to the design of reliable communication systems maybe applied. The robust approach consists of using a linear po-larized antenna at one end of the communication link and a cir-cular polarized antenna at the other end of the communicationlink. This approach minimizes the degradation due to polariza-tion mismatch to the moderate values of 2–3 dB. An alternativeway to mitigate polarization impact is to adaptively control thepolarization of the transmit and receive antennas. The adaptiveapproach may even eliminate the polarization mismatch, but atthe cost of higher implementation complexity.

REFERENCES

[1] H. Xu, V. Kukshya, and T. S. Rappaport, “Spatial and temporal char-acteristics of 60 GHz indoor channels,” IEEE J. Sel. Areas Commun.,vol. 20, no. 3, pp. 620–630, Apr. 2002.

[2] A. Maltsev, R. Maslennikov, A. Sevastyanov, A. Khoryaev, and A. Lo-mayev, “Experimental investigations of 60 GHz wireless systems inoffice environment,” IEEE J. Sel. Areas Commun., vol. 27, no. 8, pp.1488–1499, Oct. 2009.

[3] J. D. Jackson, Classical Electrodynamics, 3rd. ed. New York: Wiley,1998.