Design of a 5.305 Ghz Dielectric Resonator Oscillator with Simulation and Optimization

342 JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY OF CHINA, VOL. 6, NO. 3, SEPTEMBER 2008

Design of a 5.305 GHz Dielectric Resonator Oscillator with Simulation and Optimization

Jina Wan

Abstract⎯The design of a 5.305 GHz series feedback It is made of ceramic material with high dielectric constant, free running dielectric resonator oscillator (DRO) is high Q factor (typically 9000 at 10 GHz), and low presented. Its simulation and optimization are realized temperature coefficient (typically ±6 ppm/°C). The most by obtaining the unloaded Q factor of the cavity frequently used DR shapes are disc and puck since they can dielectric resonator (DR) and analyzing the linear and be easily manufactured than other shapes. nonlinear models of the DRO. CAD packages of A DR puck with diameter of 7.05 mm, thickness of DR_Rez and Agilent Advance Design System (ADS) are 2.65 mm, and dielectric constant of 88 is used in current used and the best tradeoff among the output power, design. It is housed in a copper cavity. The unloaded Q phase noise, and frequency stability is achieved. With factor with cavity effect is simulated by DR_Rez package, the result of simulation, a physical oscillator prototype is which can provide better uncertainty than traditional CARD constructed. The measured results show the good package. The simulation result shows that the unloaded Q agreement with those of simulation. factor for the cavity resonator Q is 6406. u Index Terms⎯ Agilent advance design system (ADS), The DR puck is closely positioned to a 50Ω-straight- dielectric resonator oscillator (DRO), negative resistance, microstrip line which is terminated with a 50 Ω resistor to unloaded Q factor . avoid spurious oscillation. The coupling between the DR and the microstrip line is modeled as a parallel RLC circuit, 1. Introduction as shown in Fig. 1, where d is the lateral distance between the DR and the microstrip line; R, L and C are the parallel Dielectric resonator oscillators (DROs) are widely used resistance, inductance and capacitance of the equivalent today in applications of communication systems, electronic circuit, respectively. warfare, missile, and radar, etc[1]. Compared with other conventional oscillators such as microstrip oscillators, multiplied crystal oscillators, and cavity oscillators, they have features of small size, low cost, and ease of integration, etc. With the use of high Q dielectric resonators (DRs), Fig. 1. Model for the coupling between the DR and the microstrip excellent phase noise and temperature stability can be line. achieved. In this paper, a 5.305 GHz DRO is presented. It has a The amount of the coupling is defined as the coupling common-source topology with a DR puck serially coefficient β, which can be adjusted by changing the d connected at the base port. The DR puck is activated at its value. The R, L and C values can be deduced from the

TE01δ resonant mode. Compared with the other DRO following formulas with the known unloaded Q factor Qu, [2] design , the cavity effect on the unloaded Q factor of the the coupling coefficient β, and the resonant frequency f0 : DR puck has been considered and simulated by DR_Rez ω00= 2π f package, with the accuracy of the resonant frequency being RZ= 2β =× 2 50ββ = 100 improved by 1% or so. A prototype DRO is constructed and 0 R Q the measurement results are given. L = , C = u . ω0Qu ω0 R 2. DR Construction In order to get minimum phase noise and sufficient output power, β is optimized to 9.00. DR is the frequency-determining element of the DRO. 3. DRO Design Manuscript received December 18, 2007; revised January 29, 2008 J. Wan is with School of Electronic and Information Engineering, South The common-source series feedback topology is chosen China University of Technology, Guangzhou, 510640, China (e-mail: for the DRO. It consists of a resonator network, a feedback [email protected]). element, a bias, and a matching network as shown in Fig. 2. WAN: Design of a 5.305 GHz Dielectric Resonator Oscillator with Simulation and Optimization 343 increased to 2.645 and 2.122, respectively, which are larger Bias network than 1, and the stability factor k has been decreased to Resonator −0.306, which is less than 1, indicating potentially unstable network Matching performance. The electrical length of the open stub line is network ° optimized to 52 , to ensure the magnitudes of S11 and S22 Z L being at least 1.2 to generate adequate negative resistance Z0 and the locus being symmetrically centered on the Feedback oscillating frequency, as depicted in Fig. 3. Fig. 4 shows element that the unstable regions for the source and the load sides of

Fig. 2. Schematic of a series feedback DRO. the active device have been greatly enlarged when feedback element is added. 3.1 Analysis on Start-up Condition for the DRO The bias point is set at Vds = 3 V and Ids = 10 mA with On the basis of negative resistance theory, the DRO is passive self-bias circuit, and the matching network is designed to make the resistance generated by the feedback implemented with single stub line circuit. The design is element negative enough to compensate the loss generated realized by the DC simulator and the impedance matching by the resonator. As a rule of thumb, at least 1.2 times of modules in ADS. the load resistance is required by the negative resistance in With the feedback element and matching network a series circuit in order to satisfy the start-up condition for added, the constant and maximum power transfer between [3] the oscillator . the source and the load is achieved, and the oscillating

3.0 condition can be obtained. 2.5 Nyquist criterion is a method to verify the oscillating 2.0 condition in the simulation environment. If the simulated 1.5 locus encircles the point +1 (i.e. 1∠0), moving in a 1.0

0.5 clockwise direction as frequency increases, the circuit 0.0 oscillates, and vice versa. Fig. 5 shows that the simulated -0.5 locus satisfies the requirements of Nyquist criterion and the -1.0 11023456789 DRO oscillates at 5.305 GHz.

Frequency (GHz)

Fig. 3. Magnitude of S11 (upper), magnitude of S22 (middle) and stability factor k (lower) of FHX35LG HEMT with 52° open stub line.

Source Solid line m1

Unstable Load ---without feedback -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Region Solid line with square ---with feedback

Unstable Region Load freq (1.000GHz to 10.00GHz)

Fig. 5. Nyquist criterion plot.

Source 3.2 Linear and Nonlinear Analysis During the design process, both linear and nonlinear (b) Fig. 4. Source and load stability circles of FHX35LG HEMT at analysis of the DRO has been performed for their 5.305 GHz with and without feedback. respective advantages. Linear analysis is based on small-signal, linear S-parameters. It only guarantees that the The super low noise Fujisu FHX35LG HEMT, which DRO would oscillate and the oscillation frequency is a has been adopted successfully in other DRO design[4], is approximate value. The nonlinear analysis is based on true employed here as the active device for present DRO. It is large signal conditions. It can be used to precisely simulated and optimized by simulator ADS with feedback determine the frequency of oscillation under steady state, as element added[5]. A portion of open stub line with electrical well as several crucial nonlinear parameters, such as output length of 52° is attached to the source port. The simulation power, phase noise, pushing and pulling, etc[6]. results show that the magnitudes of S11 and S22 have been The linear model has the same topology as the 344 JOURNAL OF ELECTRONIC SCIENCE AND TECHNOLOGY OF CHINA, VOL. 6, NO. 3, SEPTEMBER 2008 nonlinear model, except for the following differences: (1) resonating at 5.303 GHz with output power of 8.369 dBm The active device in linear model is sp_fuj_FHX35LG_ and second-order harmonic of −20.101 dBm. The phase 19920501, while in nonlinear model it is replaced by noise at 10 kHz offset is −129.7 dBc/Hz. The simulation ph_fuj_FHX35LG_19921222, and the bias point is set at results on pushing and pulling show that frequency pushing Vds=3 V and Ids=10 mA; (2) Osctest in linear model is is 105 kHz/V, which is approximately 0.00198 percent of alternated with Oscport in nonlinear model; and (3) S the oscillation frequency, and pulling is 380 kHz at the parameter simulator is used in linear model, while in typical value of 1.2 VSWR. nonlinear model, harmonic balance is utilized. The simulation results for linear analysis show that the 10 DRO would oscillate around 5.3 GHz. 0 The nonlinear model for the DRO is illustrated in Fig. 6. -10 In nonlinear analysis, the R, L, C values of the equivalent -20 circuit of the resonator are set to vary upon the known -30 coupling coefficient β, unloaded Q factor Q and the

u (dBm) spectrum Output Output spectrum (dBm) -40 oscillating frequency f0. Therefore, the position of the DR 07123456 puck can be optimized by adjusting the value of β in the Harmonic index (a) nonlinear model when Qu and f0 have been decided. -80 Phase noise is an important parameter in oscillator -100 design. Many researches have been done to reduce it[7]-[10]. -120 [11] According to Leeson’s model , the loaded Q factor QL is -140 one of the main causes resulting in phase noise. In order to -160 achieve low phase noise, QL is optimized in our design. -180 Because Q is affected by the choice of active device, the L Phase noise (dBc/ Hz) -200 operating bias point, the supporting circuit components, the 100. 1.00k 10.0k 100.k 1.00M 10.0M unloaded Q factor of the resonator, and even the pushing Frequency offset from carrier (Hz) figure, all the related parameters in nonlinear model have to (b) be fine adjusted in order to achieve minimum phase noise, Fig. 7. Simulation results: (a) output spectrum (8.369 dBm at sufficient output power, and good frequency stability. harmonic index 1; and −20.101 dBm at harmonic index 2) and Fig. 7 shows the final simulation results for the DRO, (b) phase noise (−129.73 dBc/Hz @10 kHz offset).

Var MRSTUB Eqn VAR VAR2 Stub3 b=9.00 R=100*b Ohm MLIN R MLIN V_DC Qu=6406 TL15 R8 TL8 SRC1 f0=5.305 GHz MLOC MTEE_ADS w0=2*pi*f 0 TL12 MLIN Tee4 L=R/(w0*Qu) H I_Probe PRLC TL10 I_Probe C=Qu/(w0*R) F Id1 PRLC1 MTAPER Id2 R=R Taper4 MTAPER MLIN MTEE_ADSC MLIN L=L OscPort MLSC MLIN MLIN MTAPER Taper1 TL4 Tee1 C8 TL6 R C=C Osc1 TL14 TL1 TL2 Taper3 R7 MTEE_ADS vout Tee2 Term Term2 ph_fuj_FHX35LG_19921222 MLEF Num=2 X1 TL5 MLIN Z=50 Ohm MLSC R MLIN MTEE_ADSMLIN MTAPER TL13 TL9 R9 TL16 Tee5 TL11 Taper2

MRSTUB Stub2

Fig. 6. Nonlinear model for the DRO.

4. Experimental Results is used to rest the DR in order to achieve optimized Q factor. The DR puck is finely tuned horizontally first and With the success in simulation, a prototype board vertically later to obtain the best position adjacent to the housed in a copper-made cavity was constructed as shown microstrip until the compromise between low phase noise in Fig. 8. The cavity, 16 mm × 51 mm × 47 mm, is and good output power is strike. designed for the purpose of preventing radiation losses. The The measured result shows that the DRO resonates at board is built on substrate of RT/Duriod 5870 and a spacer 5.305 GHz with +8.50 dBm output power. Fig. 9 illustrates WAN: Design of a 5.305 GHz Dielectric Resonator Oscillator with Simulation and Optimization 345 that the second-order harmonic at 10.63 GHz is −25.17 noise, output power, and frequency stability is achieved. dBm which agrees with the simulation results. The The measured results show that the DRO resonates at measured oscillation frequencies for the DRO at DC bias 5.305 GHz with output power of +8.50 dBm and voltage of 4 V and 6 V are 5.304306 GHz and 5.305065 second-order harmonic of −25.17 dBm, which are in good GHz, respectively. Namely, the measured frequency agreement with the results of simulation. pushing for the DRO is 379.5 kHz/V, which is approximately 0.00715 percent of the oscillation frequency, and is References a little bigger than the simulation result of 0.00198 percent. [1] D. Kajfez and P. Guillon, Dielectric Resonators; Norwood,

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Journal, vol. 23, pp. 199-201, Dec. 2001. [5] A. S. Maas, Nonlinear Microwave and RF Circuits, 2nd ed. Boston, London: Artech House, 2003. [6] A. Goel and H. Hashemi, “Frequency switching in dual-resonance oscillators,” IEEE Journal of Solid-State Circuits, vol. 42, no. 3, pp. 571-582, 2007. [7] F. Lenk, M. Schott, J. Hilsenbeck, and W. Heinrich, “A new design approach for low phase-noise reflection-type mmic oscillators,” IEEE Trans. on Microwave Theory and Techniques, vol. 52, no. 12, pp. 2725-2731, 2004. [8] L. Zhou, Z. Wu, M. Sallin, and J. Everard, “Broad tuning ultra low phase noise dielectric resonator oscillators using SiGe amplifier and ceramic-based resonators,” IET Microw. Antennas Propag., vol. 1, no. 5, pp. 1064-1070, 2007. Fig. 9. Measured output harmonic levels. [9] R. Navid, T. H. Lee, and R. W. Dutton, “Minimum achievable phase noise of RC oscillators,” IEEE Journal of The DRO is mechanically tunable using a 25 mm-long Solid-State Circuits, vol. 40, no. 3, pp. 630-637, 2005. tuning screw made of copper. A tuning screw is put [10] J.-F. Gravel and J. S. Wight, “On the conception and through the cavity cover and positioned right above the analysis of a 12 GHz push-push phase-locked DRO,” IEEE DR. By perturbing the fringing fields outside the DR, a Trans. on Microwave Theory and Techniques, vol. 54, no. 1, tuning range of about 250 MHz, from 5.243250 GHz to pp. 153-159, 2006. 5.493217 GHz, is achieved. [11] D. B. Leeson, “A simple model of feedback oscillator noise spectrum,” Proc. of IEEE, vol. 54, no. 2, pp. 329-330, 1966. 5. Conclusions

An approach to design a 5.305 GHz free running DRO has been described. The effect of the cavity enclosure on Jina WAN was born in Wuhan, China, in 1975. She received the unloaded Q factor of the DR is considered, and the the B.S. and M.S. degrees from Hunan University, China, and linear and nonlinear model of the DRO has been analyzed. University of Bradford, UK, in 1998 and 2005, respectively. Now The DRO optimization is realized by finely adjusting the she is a staff member with South China University of Technology. DR position adjacent to the microstrip and the related Her research interests are in the area of RF circuit design and parameters in the circuit. The best tradeoff among phase wireless communications.