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acoustic wave) even FBAR (film bulk acoustic resonator) filters are only able to produce at ..... imaginary, it is easy to re-write equation (4) in the following form:.
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Date of publication xxxx 00, 0000, date of current version xxxx 00, 0000. Digital Object Identifier 10.1109/ACCESS.2018.Doi Number

A High-Pass Antenna Interference Cancellation Chip for Mutual Coupling Reduction of Antennas in Contiguous Frequency Bands 1

1

1

Luyu Zhao , Member, IEEE, Feng Liu , Student Member, IEEE, Xiumei Shen , 2,3 1 1 Guodong Jing , Yuanming Cai , Member, IEEE and Yingsong Li , Member, IEEE Key Laboratory of Antennas and Microwave Technologies, Xidian University, Xi’an 710071, China College of Information Engineering, Harbin Engineering University, Harbin 150001, China 3 Key Laboratory of Microwave Remote Sensing, National Space Science Center, CAS, Beijing 100190, China 1 2

Corresponding author: Yingsong Li (e-mail: [email protected]).

This work was supported by the Natural Science Foundation of China under Grant No. 61701366, the China Postdoctoral Science Foundation under Grant 2016M602769, National Key Research and Development Program of China (2016YFE0111100), Key Research and Development Program of Heilongjiang (GX17A016), the Science and Technology Innovative Talents Foundation of Harbin (2016RAXXJ044), and the Fundamental Research Funds for the Central Universities (HEUCFM180806).

ABSTRACT In this paper, an Antenna Interference Cancellation Chip (AICC) with high-pass response is proposed to mitigate the mutual coupling of two antennas resonating in contiguous frequency bands. Using the most up-to-date LTCC technology, the chip only occupies a compact volume of 1.6×0.8×0.6 mm3. Two external tuning capacitors and two shunt inductors together with the LTCC AICC device which are in shunt with two coupled antennas, are able to improve the antenna isolation near band-edge by more than 15 dB without sacrificing antenna performance in its useful resonating bands. The high-pass property of the AICC device prevent the decoupling design near 2.4GHz affecting the successful operation of GPS at 1.575 GHz. The superiority of the proposed method is verified with active measurement of a Mi-Fi (mobile Wi-Fi) device in Wi-Fi hotspot mode using the AICC device. The proposed AICC device and corresponding decoupling method with the device can find plenty of applications in LTE and future 5G wireless platforms. INDEX TERMS Antenna array mutual coupling, decoupling network, interference suppression, in-device coexistence (IDC), high-pass filter.

I. INTRODUCTION

For the past ten years, our society has witnessed an amazing tendency that the mobile terminal has inevitably become a versatile device that are equipped with long-termevolution (LTE), Wi-Fi, Global Navigation Satellite System (GNSS), Near Field Communication (NFC) and many other wireless protocols and systems. The integration of these systems into one physical platform brings great convenience to our life. However, in the meantime, it put us in a predicament that it is becoming increasingly difficult to design and implement antennas for these wireless systems in a more and more limited space. Moreover, the crowded frequency spectrum has also made things even worse. One typical example would be the contiguous frequency bands of the LTE Band-40 and the 2.4 GHz Wi-Fi band, where no guard band is reserved as shown in Fig. 1 [1]. As the advance of 5-th generation (5G) wireless communication systems, the in-device coexistence issue

VOLUME XX, 2017

concerning the incumbent LTE systems and other developing systems will be more and more severe in the “long term”. Antennas of these systems are resonating at adjacent frequencies or even the same frequency band. As a result, the coexistence interferences of these radio transceivers and antennas becomes a very serious problem, especially when metal frame mobile terminals are more and more popular and when MIMO technologies demand even more antennas for one wireless system. The Wi-Fi Hotspot operation mode of a mobile terminal, either for a smart phone, a Mobile Wi-Fi (Mi-Fi) or a USB data card dongle, would be a good illustration of the abovementioned coexistence interference issue. As shown in Fig. 2, in Wi-Fi hotspot mode, the Wi-Fi transmitter emits at around 15 dBm level, while a TD-LTE Band-40 receiver is in its receiving mode whose sensitivity is around -85 dBm level. Conventional antenna design can only provide at most 15 dB isolation between the Wi-Fi antenna 1

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and the LTE Band-40 antenna. Furthermore, today’s offthe-shelf SAW (surface acoustic wave) or BAW (bulk acoustic wave) even FBAR (film bulk acoustic resonator) filters are only able to produce at most out-of-band rejection of 55~60 dB. The out-of-band emission of Wi-Fi signal is still far beyond the LTE receiver sensitivity, which will produce interference for the adjacent LTE receiver that must be taken care of. WiFi Channels (Ch) Unit: MHz

TD-LTE Band 40 (B40) Unit: MHz

Ch13 2461-2483 Ch12 2456-2478 Ch11 2451-2473 Ch10 2446-2468

0

EARFCN: 38750 2310 EARFCN: 38850 2320 EARFCN: 38950 2330 EARFCN: 39050 2340 EARFCN: 39150 2350 EARFCN: 39250 2360 EARFCN: 39350 2370 EARFCN: 39450 2380 EARFCN: 39550 2390

fL

Ch9 2441-2463 Ch8 2436-2458 Ch7 2431-2453 Ch6 2426-2448 Ch5 2421-2443 Ch4 2416-2438 Ch3 2411-2433 Ch2 2406-2428 Ch1 2401-2423

Frequency

fH

f0

Fig. 1. Mutually interfered Channels of the LTE band-40 and the 2.4GHz Wi-Fi band. (EARFCN: E-UTRA Absolute Radio Frequency Channel Number) Power Level Tx Signal Level of Transceiver A

Pt Filter Rejection (Typ. 55 ~ 60 dB)

Wi-Fi

Antenna Isolation (Typ. 15 dB)

Po High-pass AICC

Pi Interference to Tranceiver B

Pr

ANT B Rx Signal of Transceiver B

Pn Noise floor Pa

Coexistence of A and B

Bandpass Filter Response

ANT A

LTE Band 40

Isolation Improved by High-pass AICC (Typ. 15 ~ 25 dB)

SNR

Frequency Transceiver B

Transceiver A

Fig. 2. The application of the proposed high-pass AICC for reducing coexistence interference from transmitter A to receiver B working in contiguous frequency bands.

Recently, both the industry and the academia strive to find a proper solution for the above-mentioned problem. Their endeavors mainly fall into the following three categories: base band solution, active/passive filter solution and antenna decoupling solution. Coordinating between two transceivers with adjacent operation frequency bands and avoiding coexistence interference by time division multiplexing is a good choice to deal with the corresponding interferences [2]. An active interference suppression method, which uses a generated cancellation signal with the help of complex system architecture and algorithm, is proposed in [3]. Interference suppression filters are used in [4] based on CMOS process. FBAR/SAW based filtering solution proposed by Murata and Avago are also available on the market, but they need to sacrifice VOLUME XX, 2018

either the performance of the first few channels of Wi-Fi band [5] or the performance of the last few channels of LTE band-40 [6-7]. Another category of solutions aims to reduce antenna mutual couplings (shorted as antenna decoupling) [8]-[26]. However, most of them are only proved to be effective for mutual interfering antennas resonating at exactly the same band. Furthermore, it is well-known that almost all of the antennas in practical applications operate at multiple frequency bands, for instance, the WBG (Wi-Fi-BluetoothGPS) antenna occupies the 1.575GHz, 2,4GHz bands; the LTE and its diversity antennas must cover 690 MHz~960 MHz bands, 1.7 GHz~2.7 GHz and even 3.3 GHz ~3.7GHz bands for 5G systems. For most of the antenna decoupling solutions, only single band operation is assured, while the performance of the antennas at other operating frequency bands after antenna decoupling are untended, resulting in mismatch and efficiency loss. The proposed method in this paper for interference suppression of contiguous frequency bands possesses the following unique features: 1) The high-pass frequency selectivity makes the proposed AICC effective at around 2.3~2.5 GHz while it generates little interference on the operation bands below 2.1 GHz. 2) It uses the up-to-date Low Temperature Co-fired Ceramic (LTCC) process to ensure a good product yield and very compact size. 3) It has external tuning mechanism to fine tune the extent of mutual coupling reduction as well as the antenna matching. The remaining part of the paper is organized as the following: Section II illustrates the design procedure using AICC with a practical example. Performance evaluation including active measurements of antennas with an AICC in a commercially available Mi-Fi product is presented in Section III. Section IV gives the conclusions. II. DESIGN PROCEDURE ILLUSTRATED BY AN EXAMPLE

Unlike conventional antenna decoupling problems that two antennas are resonating at the same frequency band or even symmetrical in dimension, for antennas working in contiguous frequency bands, the antennas could be distinct from one another in shape and other characteristics. With the design theory well-illustrated in [11] and [17], it is easy to obtain the decoupling and matching conditions for the admittance parameters of the two antennas in contiguous bands: Decoupling Conditions:





Re Y21A ( f0 )  0 ,

(1a)

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and





j  Im Y21A ( f0 )  Y21C ( f0 )  0

(1b)

Matching Conditions (Suppose Antenna 1 resonating in low band and Antenna 2 resonating in high band):





Re Y11A ( f )  Y0 , f  f0 , f H  ,

(2a)



(2b)



j  Im Y11A ( f )  Y11C ( f )  0, f  f0 , f H  ,

(a)

and





Re Y22A ( f )  Y0 , f  f L , f0  ,

(3a)



(3b)



j  Im Y22A ( f )  Y22C ( f )  0, f  f L , f0  .

where superscript “A” refers to the parameters related with antennas, superscript “C” refers to the parameters of the AICC.Y0 is the characteristic admittance of the system. As shown in Fig. 1, f0 is the center frequency of the two contiguous frequency bands [fL, f0] and [f0, fH], respectively. The low band in this design begins from fL and ends at f0; while the high band in this design range from f0 to fH. To illustrate the detail design procedure of the proposed AICC decoupling method, a practical example is given in this section as shown in Fig. 3 (a). Two FPC (Flexible PCB) antennas are placed on antenna holders constructed by ABS (Acrylonitrile Butadiene Styrene) substrate. One antenna resonates at LTE bands including LTE Band-40 from 2.3 GHz to 2.4 GHz, while the other antenna is WBG (Wi-Fi, Bluetooth and GPS) antenna enabling dual-band operation in both 1.575 GHz and 2.4 GHz bands. The antennas with holders are then installed on PCB board including all components, chips and shielding. The antennas are fed by two 50 ohm rigid coaxial cables. It should be noted that during measurement, the PCB with antennas is also put into the Mi-Fi case with screen and battery inside to emulate its real working condition. The measured scattering parameters of the original antennas without any AICCs around 2.4 GHz are shown in Fig. 3 (b) (the curves with hollow markers). It is clear that both Antenna 1 (WBG antenna) and Antenna 2 (LTE antenna) resonate at their pre-specified frequency bands. However, since the two bands are contiguous, and the two antennas are in close proximity, the isolation between them is no more than 15 dB. From the budget calculation in the previous section, the isolation is far below the demand. Effective decoupling measures must be taken to significantly reduce VOLUME XX, 2018

(b)

(c)

(d) Fig. 3. (a) Photo of the Mi-Fi product motherboard with antenna holder, FPC (Flexible PCB) antennas, feeding cables, components and shielding; (b)The (measured) scattering parameters of the antenna without and with AICC; (c) The mutual admittance parameters of the antennas and the designed AICC; and (d) The self-admittance parameters of the antennas and the designed AICC. (A: Parameters for Antennas; C: Parameters for the AICC only; D: Parameters for the AICC with two external capacitors; M: Parameters for the AICC chip with external capacitors and two shunt inductors.)

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Port 2

Port 1 C2 C

Antenna1

t1

50 ohm

C

Antenna2

t2

(a)

LM2 AICC Module

L01

50 ohm

Port 2

CM2

C01

L1 C1

The Antennas

Port 1

C2

L02

External Coupling

External Coupling

C01

Port 2

Port 1 C01 50 ohm

L01

C2

L1

C2

C01 L02

50 ohm

C1

Fig. 4. Schematic diagram of the proposed AICC in shunt with the two coupled antennas with extra matching circuits.

AICC Module

TABLE I DESIGNED VALUES OF THE COMPONENTS IN FIG. 4

Components t1 t2 L01 L02

Value 25 degree 25 degree 8.2 nH 12 nH

Components C01 CM2 LM2 /

Value 2.2 pF 2.2 pF 4.7 nH /

(b) -Y12 L01

Y11+Y12

Y22+Y12

L01

the mutual coupling between the two antennas at band-edge, where filter rejection is not high enough yet. Step1: Extract the mutual admittance of the two antennas and determine the type of AICC that is needed. As shown in Fig 3 (a), before using the vector network analyzer (Keysight E5080A in this example) to measure the scattering parameters of the antennas, port extension must be done using the two rigid cables that are to be soldered near the feeding points of two antennas. This operation is to shift the reference planes to the feeding position to exact the scattering parameters with the correct phase, which is important for successfully transforming the measured Sparameters to Y-parameters. The extracted admittance parameters are shown in Fig. 3 (c). To satisfy decoupling condition (1a), two sections of transmission lines with electric length of t1 and t2 respectively are connected to the two antennas to transform the mutual admittance of the two antennas, Y21A, to purely imaginary [11], as shown in Fig. 4 (a). After admittance transformation, the remaining imaginary part of the mutual admittance of the two antennas, Im(Y21A), is positive. From equation (1b), it is found that an AICC with negative mutual admittance is demanded. Step2: Design the circuit model of the AICC. To create a two-port passive network/circuit with a negative mutual admittance, capacitive components/capacitors should be placed in-between the two ports by intuition. Furthermore, since the admittance parameters for a lossless network are all purely imaginary, the self-admittances of the AICC, Y11C(f) and Y22C(f) must approach to zero within the frequency band of interest VOLUME XX, 2018

-Y12 ’+Y12 Y11

’+Y12 Y22

(c) Fig. 5. Equivalent network model transformation with the shunt inductor L01.

according to matching conditions (2b) and (3b) since the original antennas are already well matched. For any realizable passive networks, the slope of selfadmittance parameters with respect to frequency (Y11C(f) and Y22C(f)) in this case must always be positive [27]. To balance the matching performance within the entire band of interest, it is favorable to place the zero of Y11C(f) and Y22C(f) in the center frequency of each desired operation band. To introduce a reflection zero, an L-C series resonant circuit that is shorted to ground is introduced and shown in Fig. 5 (a), with two capacitors are connected to the two ports of the network. The designed circuit model of the AICC, as indicated in Fig. 5 (a), has the following component values: C2 = 0.47 pF, L1 = 19 nH and C1 = 0.48 pF. Step3: Translate the circuit model of the AICC to physical realization using LTCC technology. The designed circuit can now be realized using LTCC process, which is given in Fig. 6 (a). The substrate used in this example has the relative permittivity of 9.8 and the loss

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Substrate

Smith Chart

C2

Ground

C2

Open Circuit

S11

Port 2

Band of interest: 1.5-2.1 GHz

L1

Port 1

C1 (a) 4 Layers

Frequency:1 GHz to 4 GHz

(a)

Cond7 Cond6

Via5

5 Layers

Cond5 Via4

2 Layers

5 Layers

Cond4

Via3

5 Layers

Via2

5 Layers

Cond3

Cond2 5 Layers

Via1

Cond1 GND

z

x

1 Layer

4 Layers

y

(b)

Ground

Port2 Port1

Marker Ground (c) Fig. 6. (a) Physical model of the proposed high-pass AICC. (b) The layer stack of the proposed high-pass AICC. (c) Photo of the AICC chip soldered on a PCB.

tangent of only 0.003. The thickness of each finalized substrate layer is 21μm, and the conductor thickness is 10 μ m. There are totally 8 layers of silver conductors including the ground in this design. There are five via holes in the LTCC module indicated as Via1~ Via5 in Fig. 6 (b). Thanks to the advanced fabrication process, we can make all via holes padless (no via-pad needed). The diameters of the via holes are all chosen to be 100 μm. All capacitors (C1, C2) in this design are implemented using parallel plates. It is worth mentioning that the upper plates of capacitors C2 are intentionally made larger than their lower plates so that the capacitance can be stable while there are VOLUME XX, 2018

(b) Fig. 7 (a) Smith Chart plot of the AICC and (b) S-parameters of the connected antennas and the AICC from 1.4 GHz to 2.8 GHz.

slight misalignments between the layers. The inductor L1 is realized in a meandering fashion to be fitted in a compact volume. The line width is designed as narrow as possible to enlarge the inductance, which is finally determined to be 80 μm according to our fabrication process tolerance. Two ground electrodes and two input/output electrodes are plated on the outside of the LTCC block, which is depicted in Fig. 6 (a). The two ground electrodes together with the ground layer could also serve as shielding for the internal components. The finalized AICC, which is then soldered on the PCB board, is shown in Fig. 6 (c). Step4: Adjust the external couplings and connect the fabricated AICC module with the antennas in shunt to obtain the desired performance. The admittance parameters of the finalized AICC (Fig. 6a), Y11C and Y21C are already shown in Fig. 3 (c) and (d), respectively. Because the network is still symmetric at this moment, Y22C is the same as Y11C. At 2.4 GHz, the mutual admittance between the two antennas, Y21A is about 0.0064 S, while the mutual admittance parameter of the designed AICC, Y21C at the very same frequency is -0.0085 S. To perfectly eliminate the mutual coupling at this frequency, 9

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Y21C needs to be adjusted. Two external capacitors C01 are connected to the AICC to slightly modify the mutual admittance at 2.4 GHz to be -0.0063 S (Y21D), which cancels out Y21A at 2.4 GHz. The sum of Y21A and Y21D is plotted in Fig. 3 (c) as Y21T, which approach to zero around 2.4 GHz as we desired. The matching conditions in (2) and (3) are more complicated to be satisfied. As is already pointed out in Step2, to leverage the matching performance within the entire band of interest, it is demanded to set Y11C(f) and Y22C(f) to be zero in the center frequency of the desired operation band. In another word, the zero of the Y11 of the AICC should be around 2.45 GHz while the zero of the Y22 of the AICC should be around 2.35 GHz. In this case, the zeros of Y11D, Y22D are all located at around 2.26 GHz, and then, effective measures must be taken to move their zeros to 2.35GHz and 2.45GHz, respectively. Two shunt inductors, L01 and L02, are connected to the two I/O ports of the AICC which is illustrated in Fig. 5 (b). The mechanism to move zeros of Yii (i=1,2) using shunt inductors is described in Fig. 5 (c). Using Pi-equivalent circuit, any two-port microwave network can be expressed by two shunt components: (Y11+Y12), (Y22+Y12), and one series component: (–Y12). The two shunt components will be combined with two extra shunt inductors L01 and L02, and they will be converted to (Y11’+Y12) and (Y22’+Y12), where:

frequency f should have positive slope. It is obvious that the zeros of Y11’(f) and Y22’(f) denoted by f01’ and f02’ shall have the following relation if L01≠L02

f01'  f02' ,

(7)

f01' , f02'  f0 ,

(8)

and

It can also be concluded from (6) that if will have:

f01'  f02'  f0 ,

, we

(9)

In this example, we intentionally place the zero of the symmetric AICC at frequency point of 2.26GHz that is lower than 2.35GHz. Then, L01 is designed to be 8.2 nH and L02 is designed to be 12 nH. By doing this, the admittance parameter of the AICC with two shunt inductors become Y11M and Y22M which are shown in Fig. 3 (d). At this time, we are able to move the zeros of Y11M and Y22M to 2.45 GHz and 2.35 GHz, respectively. Finally, the AICC together with two external capacitors C01 and two shunt inductors L01 & L02 are parallel connected to the coupled antennas as shown in Fig. 4. The 1 Y11' ( f )  Y11 ( f )  j  . (4a) precise values are listed in Table I. The responses of the 2 f  L01 entire connected network in high frequency ranging from and 2.2 GHz to 2.65 GHz are already shown in Fig. 3 (b) (with solid markers). The isolation between the two antennas is 1 Y22' ( f )  Y22 ( f )  j  . (4b) improved from around 15 dB to more than 30 dB near the 2 f  L02 band edge of 2.4 GHz, showing more than 15 dB improvement. The matching performance of Port 1 is better Since all admittance parameters of the AICC than 15 dB within the Wi-Fi 2.4 GHz band, while the are purely imaginary, it is easy to re-write matching performance of Port 2 is better than 10 dB within equation (4) in the following form: the LTE band-40. It should be mentioned that a L-type 1 Im Y11' ( f )   Im Y11 ( f )  . (5a) matching circuit (series CM2 and shunt LM2) is used at Port 2   to further enhance its performance. 2 f  L01

and

Step5: Check the open-circuit condition in low-band after using the AICC. (5b) To ensure that the decoupling of the two antennas near 2.4 GHz does not affect the performance in the GPS band For a symmetrical network, supposing the zeros of the WBG antenna (connected to Port 1), one of the AICC port that is connected to WBG antenna shall be openof Y11(f) and Y22(f) locate at f0, we shall have: circuited at least in the GPS band whose center frequency is 1 Im Y11' ( f0 )    1.575GHz. This is achieved by design the AICC model . (6a)   2 f  L01 with very small I/O capacitors, C2 together with the highpass nature of the circuit model shown in Fig. 5 (a). In the physical model shown in Fig. 6, this small capacitor is and realized by increasing the distance between the upper and 1 ' lower plate of the capacitors. In this LTCC design, we   Im Y22 ( f0 )   . (6b)   increase this distance to two substrate layers to reduce the 2 f  L02 I/O capacitance.

1 Im Y22' ( f )   Im Y22 ( f )  .   2 f  L02

Considering the positive real nature of any realizable networks [27], both Im[Y11’(f)] and Im[Y22’(f)] against VOLUME XX, 2018

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Mi-Fi (DUT)

TABLE II TRP AND TIS MEASUREMENT RESULTS OF THE MI-FI DEVICE

Test 1

Link Antenna

TRP

TIS

Channels

38750

39150

39550

39150

39550

With AICC

21.2

20.5

20.1

90.69

90.29

Without AICC

21.1

21

20.7

91.65

78.95

4G mobile phone

Test 2

Azimuth Positioner

TRP

TIS

Channels

38750

39150

39550

39150

39550

With AICC

20.9

20.2

20.1

91.58

90.35

Without AICC

21.3

20.8

20.5

91.9

76.5

(a)

Probe Array

LTE B40

Wi-Fi Mi-Fi

Mobile Phone

Link Antenna Down Link

Up Link Communication Tester (RS. CMW500)

(b) Fig. 8 (a) The photo; (b) The block diagram of the active measurement configuration in a near field 24-probe anechoic chamber

The smith chart of the designed AICC is plotted in Fig. 7 (a). It is obvious that we are able to control the open circuit frequency of the AICC to work around 1.575 GHz. The overall S-parameters of the coupled antennas only as well as the connected coupled antennas and AICC from 1.4 GHz to 2.8 GHz are also superposed in Fig. 7 (b). At the GPS band, the reflection and isolation curves are almost unchanged after adding the AICC. III. PERFORMANCE EVALUATION BY ACTIVE MEASUREMENT

To verify that our decoupling measures are effective in real-world applications, active measurements are carried out in an anechoic chamber. VOLUME XX, 2018

A. Measurement Setup As shown in Fig. 8. The active measurement of the Mi-Fi device with coupled LTE Band-40 and Wi-Fi antennas is conducted in a SATIMO SG-24 near field anechoic chamber [28]. To eliminate interference from other wireless transmission, other antennas are removed, keeping only LTE Band-40 and Wi-Fi antennas. The DUT (Mi-Fi) is placed on the azimuth positioner and put in the center of the probe array. A mobile phone is also placed in the chamber near the DUT. The TIS (total isotropic sensitivity) measurement of the DUT is conducted using conventional method but with the DUT’s Wi-Fi in hotspot mode. That is to say, as the measurement is ongoing, the DUT’s Wi-Fi module is always communicating with the mobile phone while the LTE Band-40 transceiver of the DUT is only in its receiving mode as shown in Fig. 8 (b). To ensure that our decoupling design do not affect the efficiency of the Band40 antennas, TRP (total radiated power) measurement is also conducted. B. Results and Discussion The measured TRP values of the following three channels of LTE Band-40 are recorded for the DUT with and without the AICC we designed: channel 38750 (2.30262 GHz), channel 39150 (2.35 GHz) and channel 39550 (2.39738 GHz). TIS measurement is only carried out in channel 39150 (2.35 GHz) and channel 39550 (2.39 GHz). The measurement is conducted twice, and their respective results are listed in Table II, showing good 9

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repeatability. We can draw the following conclusions from the tests: 1) The strong mutual coupling between the LTE Band40 and Wi-Fi antennas significantly deteriorates the TIS in the high band of LTE Band-40. The measured TIS of the DUT without AICC in channel 39550 located at 2.39 GHz, is around 76~78 dBm, which is about 12~14 dB lower compared to the TISs in channel 38750 and channel 39150. 2) In channel 38750 and channel 39150, the Wi-Fi filter rejection characteristic successfully helps to eliminate unwanted interference from Wi-Fi. 3) Using the AICC will not affect the TRP of LTE Band- 40, as the TRP values in all three measured channels of the DUT with and without the AICC differ from each other by no more than 1 dB, which is within measurement uncertainty. 4) A good decoupling design using the AICC, not only improves the passive isolation between the two coupled antennas, but also recovers the TIS of the channel 39550 of the LTE Band-40 transceiver to around 90 dBm. ACKNOWLEDGEMENT

The authors would like to thank Mr. Fujimoto at Hirai corporation for the help on LTCC fabrication. We would also express our gratitude to the testing engineers: Chao Jing, Xudong Zhang at Innowave Wireless Ltd. for the active measurement. We are also grateful to Dr. Kewei Qian and Mr. Li Liu from Filter Group for preparation of the samples and helpful discussions. REFERENCES 3GPP TR 36.816: “Study on signalling and procedure for interference avoidance for in-device coexistence,” V11.2.0, 2011. [2] Z. Hu, R. Susitaival, Z. Chen, I.-K. Fu, P. Dayal, and S. K. Baghel, “Interference avoidance for in-device coexistence in 3GPP LTEadvanced: Challenges and solutions,” IEEE Commun. Mag., vol. 50, no. 11, pp.60-67, Nov. 2012. [3] A. Raghavan, E. Gebara, E. Tentzeris, and J. Laskar, “Analysis and design of an interference canceller for collocated radios,” IEEE Trans. Microwave Theory Tech., vol. 53, no. 11, pp. 3498–3508, Nov. 2005. [4] H. Khatri, P. S. Gudem, and L. E. Larson, “Integrated RF interference suppression filter design using bond-wire inductors,” IEEE Trans. Microw. Theory Techn., vol. 56, no. 5, pp. 1024–1034, May. 2008. [5] Murata Manufacturing Co., Ltd, “SAW Single Filter for Band40”, SAFEB2G35FB0F0A datasheet, Feb., 2014. [6] Murata Manufacturing Co., Ltd, “SAW Single Filter for WLAN 2.4GHz”, SAFEA2G45MA1F0A datasheet, June, 2014. [7] Avago Technologies, “ISM Bandpass Filter”, ACFF-1024 datasheet, Oct., 2014. [8] F. Yang and Y. R. Samii, “Microstrip antennas integrated with electromagnetic band-gap EBG structures: A low mutual coupling design for array applications,” IEEE Trans. Antennas Propag. vol. 51, no. 10, pp. 2936-2946, Oct. 2003. [9] L. K. Yeung and Y. E. Wang, “Mode-based beamforming arrays for miniaturized platforms,” IEEE Trans. Microw. Theory Tech., vol. 57, no. 1, pp. 45-52, Jan. 2009. [10] C. Y. Chiu, C. H. Cheng, R. D. Murch, and C. R. Rowell, “Reduction of mutual coupling between closely-packed antenna element,” IEEE Trans. Antennas Propag. vol. 55, no. 6, pp. 1732-1738, Jun. 2007. [1]

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2169-3536 (c) 2018 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.