ELECO 2011 7th International Conference on Electrical and Electronics Engineering, 1-4 December, Bursa, TURKEY

Dielectric Resonator Oscillator Design and Realization at 4.25 GHz

Şebnem SEÇKİN UĞURLU

Department of Electrical and Electronics Engineering Dokuz Eylül University, Izmir, TURKEY [email protected]

Abstract device in our circuit. The negative resistance oscillator model is chosen for the design. In the following sections, the design In this paper design and realization of dielectric resonator procedure of the DRO will be considered. oscillator operating 4.25 GHz is explained. The oscillator is designed as a negative resistance oscillator where chip- 2.1 DRO Simulation amplifier is used as the negative resistance by adding feedback. The dielectric resonator is simulated using High The placement of the resonator is an important parameter. Frequency Structure Simulator. The simulation and The width and the length of the microstrip line, as well as the realization results are discussed. distance of the resonator to the microstrip line must be thoroughly analyzed. The resonator is modeled as parallel RLC 1. Introduction resonant circuit and RLC parameters as well as quality factors are calculated from the simulated S-parameter values. It was first presented by R.D. Richtymer [1] that cylindrical For the microstrip substrate, Taconic TLY 3 CH is used. The dielectric structure would act like a resonator. Many years after substrate has a relative dielectric constant of the 2.33 ±.02 and that discovery, such circuits containing dielectric resonators are substrate height of 0.76 mm. As the dielectric resonator, Trans- realized. Tech 8300 series dielectric resonator is used. The dielectric The dielectric resonator oscillators (DRO) are known as one constant of the resonator is 35.5. The unloaded quality factor of of the most suitable devices for generating low-cost microwave this resonator can be up to 15000. signals. Its properties of having low phase noise, small size, high It is calculated that for our substrate, at 4.25 GHz, the λ/2 quality factor, temperature and frequency stability, which allow microstrip line must have a width of 2.23 mm and length of it to have progressively extending area of usage in many 25.10 mm. S-parameters are obtained by high frequency applications [2] such as measuring the material properties [3], electromagnetic simulation program HFSS v.11. The S- oscillators [4], antennas [5], filters [6] that require low noise parameters of the simulated dielectric resonator configuration profile. Since the sizes of dielectric resonators are small they are can be seen in Fig.1 and the phases of S 11 and S 21 can be seen in mostly preferred in high frequency applications. Fig. 2. Due to the frequency in applications of electronics tends to increase, microwave oscillators have gained importance. Higher Magnitudes of S11 and S21 frequency causes lumped elements to gain different characteristics, thus usage of lumped elements are not preferable 1 in microwave frequencies. Distributed elements are used instead 0.9 of lumped elements. Furthermore, the rapid development in 0.8 semiconductor technology led the design of more stable and 0.7 low-noise microwave oscillators. 0.6

The important characteristics of the microwave resonators 0.5 are the resonant frequency f 0, the quality factor Q, which defines 0.4 the bandwidth of the resonance and the input impedance of the 0.3 resonator. [7] 0.2

0.1 2. DRO Design 0

Dielectric resonators can be used in both negative resistance 4.2000 4.2028 4.2056 4.2084 4.2112 4.2140 4.2168 4.2196 4.2224 4.2252 4.2280 4.2308 4.2336 4.2364 4.2392 4.2420 4.2448 4.2476 4.2504 4.2532 4.2560 4.2588 4.2616 4.2644 4.2672 4.2700 4.2728 4.2756 4.2784 (reflection) and feedback type oscillators [8]. The property of Frequency(Ghz) being easily coupled to a microstrip line is another reason to use S11 S21 dielectric resonators on integrated circuits [9]. Many types of active devices can be applied to the DRO design. GaAs technology is considered as one of the most Fig. 1. Magnitudes of S 11 an S 21 suitable transistor for microwave applications because of its temperature frequency stability and low noise characteristic [10]. On the other hand, GaAs MESFET is able to offer better performance than GaAs FET [11,12]. Considering the advantages of GaAs MESFET, an amplifier chip of GaAs MESFET, MGA72-543 is used as the active

185 ELECO 2011 7th International Conference on Electrical and Electronics Engineering, 1-4 December, Bursa, TURKEY

Phases of S11 and S21 (deg) 5.00

200 4.00 150 3.00 100

2.00 50

0 1.00 deg

-50 4.2000 4.2028 4.2056 4.2084 4.2112 4.2140 4.2168 4.2196 4.2224 4.2252 4.2280 4.2308 4.2336 4.2364 4.2392 4.2420 4.2448 4.2476 4.2504 4.2532 4.2560 4.2588 4.2616 4.2644 4.2672 4.2700 4.2728 4.2756 4.2784 0.00

-100 -1.00

-150

-200 4.000E+09 4.016E+09 4.032E+09 4.048E+09 4.064E+09 4.080E+09 4.096E+09 4.112E+09 4.128E+09 4.144E+09 4.160E+09 4.176E+09 4.192E+09 4.208E+09 4.224E+09 4.240E+09 4.256E+09 4.272E+09 4.288E+09 4.304E+09 4.320E+09 4.336E+09 4.352E+09 4.368E+09 4.384E+09 4.400E+09 4.416E+09 4.432E+09 4.448E+09 4.464E+09 4.480E+09 4.496E+09 Frequency(Hz) Frequency (deg)

mag(S(1,1)) mag(S(2,2)) StabFact1 S11(deg) S21(deg) Fig. 4. Magnitudes of S 11 , S 22 and stability factor.

Fig. 2. Angles of S 11 an S 21

The distance between the dielectric resonator and the 2.3 Harmonic Balance Analysis microstrip line is chosen as 1.5 mm. The resonant frequency is observed as 4.2384 GHz. It is clear that near resonant frequency, The harmonic balance simulation is a technique for analyzing frequency domain behaviors of non-linear systems. An oscillator S11 has its maximum value around 0 dB, indicating a full reflection. This means that the oscillator acts like an open circuit can be considered as a nonlinear system which may be near resonance. represented by a canonical set of differential equations. The harmonic balance method tries to find the solution to a steady- 2.2 Negative Resistance state non-linear design by iteratively solving for a set of variables, named as state variables [14]. The convergence of the iteration depends on choosing the initial values of state variables In order to achieve negative resistance, S and S 11 22 and oscillation frequency [15]. parameters of the active device must be greater than unity. The For validating our design, Advanced Design System S and S parameters are even desired to be at least 1.2 for 11 22 Harmonic Balance Simulation is used. The initial value of the start-up oscillation [13]. In order to achieve these conditions oscillation frequency is given as 4 GHz. The simulation is done positive feedback must be added. on a fast speed computer (Intel Core i7 2.93 GHz, 3 GB RAM, 1 The MGA 72543 is a single stage MESFET amplifier. At this TB HDD). The order of harmonics is chosen as 9 and the point, negative resistance by adding a positive feedback element simulation takes 3.49 seconds. The simulation also calculates is obtained by the active device property of the MESFET. The the phase noise of the oscillator system. The simulation results feedback element can be added to the source of the FET (Fig. 3). are shown in Fig. 5. Obtained S parameters and stability factor is seen in Fig. 4.

Oscillation Output Spectrum

15.00

10.00

5.00

0.00 dBm -5.00 4.24E+009 8.48E+009 1.27E+010 1.70E+010 2.12E+010 -10.00

Fig. 3. Source feedback FET configuration -15.00

-20.00

Frequency(Hz)

vs(dBm(Vout), freq) Fig. 5. Harmonic balance simulation results - spectrum components

186 ELECO 2011 7th International Conference on Electrical and Electronics Engineering, 1-4 December, Bursa, TURKEY

Oscillator Phase Noise dBm and -13.06 dBm which correspond to 0.26 μW and 49 μW, respectively (Fig. 8, Fig. 9, Fig. 10). Relative to the Fundamental Frequency

0.00

-20.00

-40.00

-60.00

-80.00

-100.00 dBc -120.00

-140.00

-160.00

-180.00

1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 Fig. 8. Output spectrum of the dielectric resonator oscillator Frequency(Hz)

VOUTPhaseNoise Fig. 6. Harmonic balance simulation results - phase noise relative to the fundamental frequency

The harmonic balance simulation shows (Fig.5. and Fig.6.) the oscillation frequency as 4.24 GHz and the first harmonic's power as 11.13 dBm. The phase noise relative to the fundamental frequency is about -29.283 dBc.

3. Realization of DRO

The layout of the circuit is drawn with Eagle free edition. The circuit is printed by LPKF ProtoMat S62 which is available Fig. 9. Power spectrum of the second harmonic of the oscillation in the Printed Circuit Board Laboratory. The capacitors and the frequency. inductors are the size of 0805 package. MGA 72543 is in SOT- 73 package. In Fig. 7. the final board layout is displayed.

Fig. 10. Power spectrum of the third harmonic of the oscillation frequency.

Fig. 7. Picture of the printed circuit board The spectrum analyzer can be used in noise measurements in a simple way. If linear approach is used, the single-sideband 4. Results noise ( in dBc/Hz) can be defined as:

The measurements of the final design are done with Hewlett (1) ேሺଵு௭஻ௐሻ Packard 8592B spectrum analyzer. DC source is connected to ௠ the DC bias block of the dielectric resonator oscillator. In equation (1), N ॎisሺ ݂theሻ powerൌ of஼ noise in 1Hz bandwidth at A serial multimeter is connected in order to measure the fm away from the carrier and C is the power of the carrier. Using current ID which is the device current. In order to prevent the a spectrum analyzer, one can calculate by reading the carrier pulling effect of the spectrum analyzer, the output is connected power which is the power of oscillation frequency, reading the to the isolator. power at fm away from the oscillation frequency and calculating Fig. 8 shows the observed output spectrum of the dielectric the ratio of those two. However, this technique has some resonator. The oscillation frequency is measured as 4.30 GHz. drawbacks because of the working principle of the spectrum The maximum measured output power is 6.5 dBm which analyzer [10]. The filters and amplifiers at the input of the corresponds to 4.47 mW. The second harmonic which is 8.60 spectrum analyzer must be taken into account as well as the non- GHz and the third harmonic at 12.90 GHz has a power of -45.92 existence of 1 Hz bandwidth band pass filters. According to equation (1), the noise power must be measured through

187 ELECO 2011 7th International Conference on Electrical and Electronics Engineering, 1-4 December, Bursa, TURKEY bandpass filter with a bandwidth of 1 Hz. So the measurements on Microwave Theory and Techniques, vol.29, no. 8, pp. must be corrected by reducing the noise power by 10 dB per 754-770. August 1981. decade if the internal filter of the spectrum analyzer has a [3] J. Krupka, J. Baker-Jarvis, R.G. Geyer, J.H. Grosvenor, bandwidth larger than 1 Hz. M.D. Janezic, C.A. Jones, et al, "Dielectric characterization Using these relations the phase noise of the realized DRO is of low-loss materials a comparison of techniques." IEEE found as in Fig.11. Transactions on Dielectrics and Electrical Insulation , vol. 5, no. 4, pp. 571-577. August, 1998. [4] H. Abe, Y. Takayama, A. Higashisaka and H. Takamizawa, 0 "A highly stabilized, low-noise GaAs FET integrated oscillator with a dielectric resonator at C-band." IEEE -10 Transactions on Microwave Theory and Techniques , vol.

-20 26, no. 3,pp. 156-162. March, 1978. [5] T.H. Huang, et al. "A simple design cylindrical dielectric -30 resonator antenna with wide aperture-coupled for broadband applications", Microwave and Optical -40 Technology Letters , vol. 49, no. 5,pp. 1064-1067. May,

-50 2007.

Phase Noise (dBc/Hz) [6] T.D. Iveland, "Dielectric Resonator Filters for Application in -60 Microwave Integrated Circuits", IEEE Transactions on Microwave Theory and Techniques , vol. 19, no. 7, pp. 643- -70 652.July, 2007. [7] A. Das and S. Das, "Microwave Engineering 8th ed.", Tata- -80 1 2 3 4 5 6 7 10 10 10 10 10 10 10 McGraw Hill, New Delhi, 2007 f(Hz) [8] S. Hamilton, "Microwave oscillator circuit", Microwave Journal , vol. 21, no. 4, pp. 63-66. April, 1978. Fig. 11. Measured phase noise of the realized DRO [9] W.R. Jr. Day, (1970). "Dielectric resonators as microstrip circuit elements." in G-MTT 1970 International Microwave 6. Conclusions Symposium , Newport Beach, CA, USA, pp. 24-28,1970. [10] O. Ishihara, T. Mori, H. Sawano and M. Nakatani, "A In this paper, design and realization of a dielectric resonator highly stabilized GaAs FET oscillator using a dielectric oscillator operating at 4.25 GHz is presented. The oscillator resonator feedback circuit in 9-14 GHz", IEEE Transactions operates at 4.30 GHz. The fundamental harmonic of the on Microwave Theory and Techniques, vol. 28, no. 8,pp. oscillator is 6.5 dBm. Total harmonic distortion is 376-378. August, 1980. approximately -20 dBm. [11] C. Tsironis and P. Lesartre, "X and Ku-band dual gate Stabilizing the bias conditions of the active device in MESFET oscillators stabilized using dielectric resonators" resonator circuits is an important issue. By using a single chip in 11th European Microwave Conference , Amsterdam, 1981. amplifier, this difficulty is overcome. Also, by using high [12] I Hilborn, A.P. Freundorfer, J. Show and M.G. Keller, frequency structure simulator through the design process, "Design of a single chip GaAs MESFET dielectric resonator deriving s-parameters of the dielectric resonator becomes more oscillator at 26 GHz" in Canadian Conference on Electrical accurate and Computer Engineering , Canada, pp. 671-674, 2007. The phase noise measurement gives an overview of the noise [13] G.D. Vendelin, A.M. Pavio and U.L. Rohde, "Microwave performance of the realized DRO despite the drawbacks of the Circuit Design Using Linear and Nonlinear Techniques 2nd measurement method. -43.55 dBc/Hz at10 kHz from the carrier ed. ", John Wiley & Sons, New Jersey, USA, 2005. was observed. However, very low noise DRO designs are [14] V. Rizzoli, A. Costanzo and A. Neri, "Harmonic-balance available in the literature [12]. analysis of microwave oscillators with automatic As a result, the designed oscillator works with an error of suppression of degenerate solution", IEEE Electronic Letters , 1.46 percent in terms of oscillation frequency compared to the vol . 28, no. 3, pp. 256-257. January, 1992. simulation results. The main reason for this is that the bias [15] G. Lan, D. Kalokitis, E. Mykietyn, E. Hoffman and K. conditions were obtained with an error of 1.36 percent in terms Sechi, "Highly stabilized, ultra low-noise FET oscillator of the device current. The difference of harmonic powers with dielectric resonator" in IEEE MTT-S International between the simulation of the oscillator and the practical one is Microwave Symposium , Baltimore, MD, USA ,1986, pp. mainly due to the mismatch at the output which occurs as a 83-86. result of improper soldering of the SMA connector. Beside, the chassis should be at the same size of the printed circuit board in order to concentrate the electromagnetic energy inside the chassis. These improvements can be applied in order to obtain more accurate results.

7. References

[1] R.D. Richtmyer, “Dielectric Resonators” Journal of Applied Physics, vol.10, no.9, pp. 391-398. June 1939. [2] J.K. Plourde, and C. Ren, "Application of dielectric resonators in microwave components." IEEE Transactions

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