High Isolation Lange-Ferrite Circulators with NF Suppression for Simultaneous Transmit and Receive
Siu K. Cheung, William H. Weedon, and Craig P. Caldwell Applied Radar Inc., 210 Airport
Street, RI 02852 (Emails: email@example.com. firstname.lastname@example.org, email@example.com)
Abstract- This paper presents a new type of circulator that
consists of three Lange couplers and two ferrite circulators for broadband, simultaneous principal of high the isolation, and circulator transmit receive is based noise on suppression The quadrature and transmit (STAR). operation phase
as isolation, bandwidth, insertion loss and NF at receive port versus Gain-NF product of transmit power amplifier (PA). The initial work is to develop a broadband STAR circulator with high isolation and NF-suppressed capabilities for radar system applications.
cancellation and combination techniques. Preliminary results show that the isolation between the transmit and receive port is >24 dB in frequency range of5-12 GHz without optimization and
60 dB isolation with 800 MHz bandwidth with optimization. The
NF data at the receive port show significant suppression of transmit noise for Gain-NF product that exceeds 21 dB.
Lange coupler HFSS model ?.(;::::::?
Ferrite circulator (Measured data)
circuits, ferrite circulators, ferrite devices, phase matching.
OST of the circulator development to date has involved the use of ferrite devices, which rely on bulk physical properties of magnetic materials -. While most of the circulators have seldom addressed their functional performance for system operation -, a new architecture of a non-reciprocal circulator, the so-called Lange-ferrite circulator, which combines the properties of phase cancellation/combination of a three Lange configuration ?  and the circulatory property of a typical ferrite circulator [4, 9], is proposed for high isolation, broadband and suppression of NF for simultaneous transmit and receive (STAR) applications. The architecture of the Lange-ferrite circulator consists of three quadrature Lange hybrids and two set of ferrite circulators, as shown in Fig. 1. The set of ferrite circulators can be implemented by one or more ferrite circulators. The proposed architecture is suitable for TxlRx applications by integrating the Lange couplers with typical circulators using either ferromagnetic or gyroelectric semiconductor substrate . The paper presents some preliminary results on the performance of the Lange-ferrite circulator. This study quantifies the operational parameters for STAR systems such
This work was supported by DARPA under Contract W31 P4Q-07-C-0006. Distribution Statement "A" (Approved for Public Release, Distribution Unlimited). The views, opinions, and/or findings contained in this article/presentation are those of the author/presenter and should not be interpreted as representing the official views or policies, either expressed or implied, of the Defense Advanced Research Projects Agency or the Department of Defense.
Fig.I. Circuit schematic and operation mechanism of the Lange-ferrite circulator.
II. OVERVIEW OF THE LANGE-FERRITE CIRCULATOR
The basic building block of the device contains three Lange couplers and two sets of typical circulators such as ferrite circulators. The three Lange couplers are connected in such a way that it will split the transmit signals from the Tx port into quadrature signals of which part of the quadrature signals will be recombined in phase by the Lange coupler at the Ant port while the rest of the transmit quadrature signals will be phase cancelled at the Rx port. Similarly, the received signal from the Ant port are split in quadrature signals of which part of the signals will recombined in phase at the Rx. Under perfect operation, there will be no transit signal at the Rx port due to phase cancellation of the quadrature signals that provide high isolation. The phase combination and cancellation techniques using Lange couplers can be applied to a typical ferrite circuit to enhance isolation between the Tx and Rx ports and NF suppression at the Rx port. In addition, Lange couplers are being used due to their inherent properties of (1) good impedance matching in a balanced configuration or low return loss, (2) size scaling for higher frequency of operation up to
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the W-band in MMIC form, (3) good power handling up to 8 Watt , and (4) readiness for MMIC and SOC integration. For transmit mode operation of the Lange-ferrite circulator, the transmit input signal is split into quadrature signals with equal magnitude by the Lange coupler at the Transmit port. The split quadrature signals are then circulated to the antenna port where they are recombined constructively in phase by the Lange coupler at the Antenna port. Any leakage of the ferrite circulator or reflection from the inner ports of the Ant Lange coupler are recombined destructively in phase by the Lange coupler at Port 3 to provide high isolation between the transmit and receive port. For receive mode operation, the received signal at the antenna port has similar operation as the transmit signal except that the received signals from the antenna are now recombined constructively in phase at the receive port. All the internal transmission lines are phase matched from the inner three-port junctions to their corresponding hybrids for high isolation performance.
phase cancellation at the receive port. The insertion loss of the device is shown to have < 5dB with a return loss>18 dB from 5 to 15 GHz. Once the 3-Lange device using phase combination/cancellation concept shows high isolation operation, the s-parameters of the Lange coupler is then used to simulate the performance of the Lange-ferrite circulator with configuration as shown in Fig. 4. From the substrate compatibility point of view, this configuration is suitable for Tx/Rx applications by integrating the Lange couplers with typical circulators using either ferromagnetic or gyroelectric semiconductor substrate [1, 2].
in.Morlion 105S (562, 536)
Port5 Lange Coupler
?o ?------?--? 10 12 i 14 16
Frequency [GHzl Port 1
Fig. 3. EM Simulated results of the 3-Lange device.
Air Bridge Port 2
Trcnsrrit (Tx) Port 1
Fig. 2. A HFSS model of the 3-Lange device.
In order to study the isolation enhancement and NF suppression at the Rx port of the proposed device, simulations were done based on the measurement data and the HFSS model of the ferrite circulator and the Lange coupler, respectively. A 3-Lange circuit architecture was firstly designed using Agilent ADS and then Ansoft HFSS to optimize device performance by matching the signal delays of the Lange couplers to demonstrate the concept of phase cancellation and combination techniques to achieve high isolation performance. The preliminary design goals for the Lange-ferrite circulator include a 15% BW of operation with >30 dB isolation from Tx to Rx (Tx-Rx); with insertion loss 1.5 dB from Tx to Antenna (Tx-Ant); and NF of 2 dB from Antenna to Receive (Ant-Rx) port with connection of external PA; and, > 5 watt of power handling. Fig. 2 depicts the HFSS model of the 3-Lange structure and the simulation result is shown in Fig. 3. The HFSS simulation results of the 3-Lange device show approximately -32 dB forward transmission from the Tx-to-Rx path with> 35 % bandwidth at X-band based on the
Ferrite o rcu ator
? Receive (Rx) Port 3
Fig. 4. Circuit layout of the Lange-ferrite circulator. Two broadband ferrite circulators from Renaissance Electronics were measured to obtain their 3-port s-parameters to simulate and demonstrate the performance of the Lange? ferrite circulator. Fig. 5 presents the measurement data of the ferrite circulator (PN:3A8BG1). The ferrite circulator shows an 8-12 GHz of operation with performance of isolation slightly below 16 dB across the whole band. The simulation results of the Lange-ferrite circulator using the measured s-parameters of the ferrite circulator and the HFSS data of the Lange couplers is shown in Fig. 6, with all ports 50-ohm terminated. The preliminary results show that
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the isolation from the Tx port to the Rx port is below 24 dB in frequency range of 5-12 GHz without optimization. In fact, the whole band is well below 20 dB from 5 to 15 GHz. The trade-off is an approximately 1 dB degradation of the insertion losses for the Tx-to-Ant and the Ant-to-Rx paths due the additional insertion losses of the Lange couplers.
o ??? ??????????
Optimized Performance of a Lange-Ferrite Circulator
521 (lx-AnI) 532 (AnI-Rx,
-10 -20 W ? ? -30
/ .? red)
Single Ferrite Circulator 0 -5 521 S32 (red)
-50 -60 8 9 10 11 12 13 14 1E
? ? Q; E ?
-10 -15 -20 -25 -30 -35 7 8 9 10 11 12 13 14 15
Fig. 7. High isolation performance of a Lange-ferrite circulator using 3 Lange couplers (HFSS model) and two ferrite circulators (measured data).
Frequency [GHzl For STAR operation, the noise of the PA could be circulated Fig. 5. Measured s-parameters of a broadband ferrite circulator to the Rx port due to mismatch at the Ant port and the magnitude of isolation between the Tx and Rx port. The NF (PN: 3A8BGl). study of the Lange-ferrite circulator for Tx/Rx STAR application was performed using PA behavior models with Gain-NF product below 21 dB (PN# CMM0016, Gain=9.5 Lange-Ferrite Circulator dB, NF=7.5 dB) and above 21 dB (PN# HMC487LP5, Gain=20 dB, NF=8.5 dB) for Tx/Rx applications. The 521 (Tx-Ant) 532 (red, Ant-Rx) simulated performance of the noise figure at the Rx port is co -10 obtained by replacing the transmit source with a 50 ohm noisy ? 531 522 CJl load. For Tx/Rx operation using PA with Gain-NF product < (Tx-Rx) Qj 'v " 21 dB, the NF performances of the proposed Lange-ferrite W -20 E circulator show no significant difference (? 1 to 2 dB) when ? til a. compared to typical ferrite circulator architectures that use en -30 single ferrite circulator or 3-ferrite circulator configurations -, as shown in Fig. 8. The comparison was done among the above Lange-ferrite circulator and the ferrite circulators - 40???????? ???????rM 7 8 9 10 11 12 13 14 15 using the same measurement data of the ferrite circulator (PN# 3A8BGl). However, for TxlRx operation using transmit PA Frequency [GHzl with Gain-NF product> 21 dB, say 28.5 dB, the preliminary Fig. 6. Performance of the Lange-ferrite circulator with all data show a significant suppression of transmit noise at the Rx port matched to 50 ohm. port due to the phase cancellation mechanism of the 3-Lange quadrature architecture, as shown in Fig. 9. The data show It is feasible to optimize the performance of the proposed that the Lange-ferrite circulator has little change (? 1 dB) of architecture for high isolation operation as shown in Fig. 7. NF at the receive port while the single-ferrite and three-ferrite The simulation data show that a performance of 60 dB circulators show> 9.5 dB in NF when the Gain-NF product of isolation with an isolation bandwidth of ?800 MHz. The the transmit PA is ? 28.5 dB. optimization is done based on impedance matching at ports
and phase matching in internal paths between the split signals from the Lange devices.
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PA: CMM0016 (G, N F) (9.5, 7.5) dB 15 ,-------?
Single Ferrite Circulator
z Q) CJ)
Lange-ferrite architecture seems feasible to obtain 60-dB isolation with 800 MHz bandwidth, provided that it needs a well-controlled manufacturing process to ensure the performance symmetry of the ferrite circulator and the Lange coupler. The 3-Lange configuration can be used in conjunction with other type of circulators to provide broadband and suppression of NF operations.
The authors would like to acknowledge Ron Esman for his supports and technical discussions. The authors also wish to thank TriQuint for fabrication of the MMIC devices, and Photonic Systems Inc. for performing the measurements.
Fig. 8. Compares NF performance between single ferrite, 3ferrite and the Lange-ferrite circulators for TxlRx STAR operation using PA with Gain-NF < 21 dB (in this demo, Gain-NF product 17 dB).
PA: HMC487LP5 (G, NF) (20, 8.5) dB 15 .------.
  
Fig. 9. Compares NF performance between single ferrite, 3ferrite and the Lange-ferrite circulators for TxlRx STAR operation using PA with Gain-NF> 21 dB (in this demo, Gain-NF product 28.5 dB).
C. Vittoria, Microwave Properties of Magnetic Films, New Jersey,US,World Scientific,1994,Chap. VI-VIII,pp. 125-184. V. Mok, L. Davis,"Oblique Incident at a Gyroelectric/dielectric Interface at Sub-terahertz and Terahertz Frequencies," IEEE High Frequency Postgraduate Student Colloquium, v. 6, Issue 2001,pp. 158-163. R. Billings and T. Edridge, "Ferrite Circulator Switches and their Applications," Microwave Journal, Vol. 46, No. II, pp. 124-125,Nov. 2003. L. Douglas, Microwave Circulator Design, MA. , US, Artech, c1989,Chap. 5,pp. 83-121. S. Cheung and W. Weedon, "Lange-ferrite Circulator," US Provisional Patent application number 6105783,2008. S. Cheung, T. Halloran, W. Weedon, and C. Caldwell, "Active Quasi-Circulators using Quadrature Hybrids for Simultaneous Transmit and Receive," IEEE MIT-S Int. Microwave Symp., Boston, MA., US, June,2009. S. Cheung, T. Halloran, W. Weedon, "Quasi Active MMIC Circulator," US Patent 7541890 B2, June 2,2009. S. Cheung, T. Halloran, W. Weedon and C. Caldwell, "MMIC? Based Quadrature Hybrid Quasi-Circulators for Simultaneous Transmit and Receive," IEEE Trans. Microwave Theor. Techniques, to appear,201O. L. E. Davis, R. Sloan, "Predicted Performance of Semiconductor Junction Circulators with Losses," IEEE MIT vAl,No. 12,Dec. 1993,pp. 2243-2247.
The work presents a new architecture of a non-reciprocal circulator that uses phase cancellation/combination techniques in addition to the circulatory operation of typical ferrite circulators to achieve broadband and enhanced isolation performance with suppression of transmit noise to the receive port for STAR radar system operation. With a trade-off of 1 dB insertion loss, the transmit noise at the receive port of the Lange-ferrite circulator is suppressed significantly when the transmit Gain-NF product exceeds 21 dB for a Tx/Rx subsystem operation due to additional phase cancellation property of the 3-Lange device. The NF data show that the Lange-ferrite circulator has little change ( 1 dB) of NF at the receive port while the single-ferrite and three-ferrite circulators show> 9.5 dB in NF when the Gain-NF product of the transmit PA is 28.5 dB. A further optimization of the
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