simplified multiband front-end architecture using a

Simplified multiband front-end architecture using amultifunction circuit

Jae-Hyun Kim1a), Min-Ho Go2, Sun-Gook Hwang1,and Hyo-Dal Park11 Department of Electronic Engineering, InHa University,

253 YongHyun-dong, Nam-gu, Incheon 402–751, Republic of Korea2 EW center, Hanwha Thales,

235 PanGyoYeok-ro, BunDang-gu SeongNam-si Gyeonggi-do 463–400,

Republic of Korea

a) [email protected]

Abstract: A multifunction circuit to simplify a multiband front-end oper-

ating at very different bands is proposed. The multifunction circuit operates

as a sub-harmonic mixer or an attenuator depending on a control voltage.

A multiband front-end using the proposed multifunction circuit can reduce

component, is 23 percent smaller, and is less expensive compared to a

conventional architecture with a switching circuit.

Keywords: receiver, mixer, RF front-end, multifunction

Classification: Microwave and millimeter-wave devices, circuits, and

modules

References

[1] A. G. Huizing: “Wideband vs. multiband trade-offs for a scalable multi-function RF system,” IEEE International Radar Conference (2005) 155 (DOI:10.1109/RADAR.2005.1435811).

[2] M. I. Skolnik: Introduction to Radar Systems (McGrawHill, 2001).[3] C. Kim, et al.: “Design of multi-standard RF front-end using reconfigurable

mixer,” IEEE International Conference on Consumer Electronics (2005) 413(DOI: 10.1109/ICCE.2005.1429893).

[4] R. Malmqvist, et al.: “Multi-band and reconfigurable front-ends for flexible andmulti-functional RF systems,” Proc. of APMC (2007) 1 (DOI: 10.1109/APMC.2007.4554995).

[5] Eiji Taniguchi, et al.: “A 2 to 5GHz-band self frequency dividing quadraturemixer using current re-use configuration,” submitted to IEICE Trans. Commun.

[6] T. Kaho, et al.: “Multi-band concurrent RF frontend for user-centric wirelesssystem,” submitted to IEICE Trans. Electron.

[7] M. Cohn, et al.: “Harmonic mixing with an anti-parallel diode pair,” IEEETrans. Microw. Theory Techn. 23 (1975) 667 (DOI: 10.1109/TMTT.1975.1128646).

[8] M. Shimozawa, et al.: “A novel sub-harmonic pumping direct conversionreceiver with high instantaneous dynamic range,” IEEE International Micro-wave Symposium Digest (1996) 879 (DOI: 10.1109/MWSYM.1996.511063).

[9] Y. H. Liew and J. Joe: “RF and IF ports matching circuit synthesis for asimultaneous conjugate-matched mixer using quasi-linear analysis,” IEEE

© IEICE 2016DOI: 10.1587/elex.13.20160829Received August 23, 2016Accepted September 2, 2016Publicized September 20, 2016Copyedited October 10, 2016

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LETTER IEICE Electronics Express, Vol.13, No.19, 1–6

http://dx.doi.org/10.1109/RADAR.2005.1435811





http://dx.doi.org/10.1109/ICCE.2005.1429893




http://dx.doi.org/10.1109/APMC.2007.4554995




http://dx.doi.org/10.1109/TMTT.1975.1128646




http://dx.doi.org/10.1109/MWSYM.1996.511063




Trans. Microw. Theory Techn. 50 (2002) 2056 (DOI: 10.1109/TMTT.2002.802316).

[10] Y.-S. Hwang: “A 2GHz and 5GHz dual-band direct conversion RF frontendfor multi-standard applications,” Proc. 2005 IEEE International SOC Conf. 50(2005) 189 (DOI: 10.1109/SOCC.2005.1554492).

1 Introduction

Research on multiband transceivers capable of implementing various functions

with a single system is proceeding actively. Multifunction system performing

various functions simultaneously requires a multiband radio frequency (RF) struc-

ture capable of many RF functions. This multiband RF structure should be designed

for good performance and low power consumption [1, 2]. A multiband RF front-

end to meet these conditions can be realized by a multiband circuit such as a

reconfigurable mixer and low noise amplifier (LNA), or by a multifunction circuit

such as an active filter has the features of a LNA and a passive filter simultaneously.

However, implementation for a multiband RF front-end receiving very different

frequency bands has significant technical limitations [3, 4, 5, 6].

In this study, a multifunction circuit which can be useful to embody as a small,

low-power multiband front-end operating at very different bands such as X-band,

Ku-band, K-band and Ka band is proposed and demonstrated. The multifunction

circuit operates as a sub-harmonic mixer or an attenuator depending on a control

voltage applied to an anti-parallel diode. The proposed circuit enables a multiband

front-end to be simpler than a conventional structure using a switching circuit.

2 Operation and applied to multiband front-end

Fig. 1 shows to the operational principle of the proposed multi-function circuit. As

shown in the figure. The proposed circuit behaves as a sub-harmonic mixer because

of the symmetric current-voltage characteristic of anti-parallel diodes D1 and D2

when a control voltage is not applied. A sub-harmonic mixer was used to realize

a stable signal source from microwaves and millimeter-waves band because its

local oscillator (LO) frequency is half that of other fundamental pumped mixers

[7]. The mixer is also used as a method to improve the performance of a direct

conversion receiver by features of extremely low even-order spurious response and

LO noise [8].

In contrast to operation as a sub-harmonic mixer, as shown in Fig. 1b, diode D1

under a forward bias condition behaves as a short circuit and diode D2 under a

reverse bias condition behaves as an open circuit when a control voltage is applied.

At this instant, diode D1 allows an input signal to pass without frequency

conversion unless the pumping LO signal exists. A quarter-wavelength short stub

at the LO port operates as an open circuit for the LO signal and a short circuit for

the RF signal, and provides a direct current (DC) path. Similarly, a quarter-

wavelength open stub at the RF port operates as an open circuit for the RF signal

and a short circuit for the LO signal [9, 10].© IEICE 2016DOI: 10.1587/elex.13.20160829Received August 23, 2016Accepted September 2, 2016Publicized September 20, 2016Copyedited October 10, 2016

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IEICE Electronics Express, Vol.13, No.19, 1–6





http://dx.doi.org/10.1109/SOCC.2005.1554492




A matching circuit for each port was designed using a quasi-linear method, and

the frequency response of RF port was coordinated as a band-pass filter by

combining a low-pass and a band rejection property. A low pass filter with

Chevyshev response was applied at the intermediate frequency (IF) port.

Fig. 2a shows a front-end architecture which uses the conventional method

with a switching circuit. By adjusting a nonlinear characteristic of a device, the

reconfigurable mixer for receiving a multiband signal selectively maximizes the

magnitude of the output signals (j!LO � !Xj, j!LO � !Kuj, j2!LO � !K j and

j2!LO � !Kaj) which are generated by mixing an RF signal (!X, !Ku, !K and !Ka)

with a LO signal (!LO). However, a multiband front-end using a reconfigurable

mixer has a different IF in each band because of the limitation of tuning bandwidth

for voltage controlled oscillator (VCO), as operating at very separate frequency

bands.

Two IFs, vinð!IF X =K ; !IF KaÞ corresponding to X band, K band and Ka band,

are converted by a mixer to output frequency, voutð!IFÞ, and the IF at Ku band,

vinð!IF KuÞ which is equal to output frequency is bypassed by a switching circuit

without frequency conversion. As a result, to allow multi-functional operation, a

conventional multiband front-end is complex, bulky (46 � 46mm2) and requires a

current consumption of 50mA.

Fig. 2b shows the front-end with a multifunction circuit. As described in Fig. 1,

a multiband front-end can be composed with a simpler structure than a method

using a switching circuit because the proposed multifunction circuit has both

frequency conversion and attenuation properties depending on the level of a control

voltage. As shown in Fig. 2, when excluding a reconfigurable mixer and VCO, the

proposed low cost multiband front-end using the multifunction circuit is 23 percent

smaller (35 � 35mm2) and less expensive compared to a conventional structure

with a switching circuit.

(a) (b)

Fig. 1. Operation of the proposed multifunction circuit: (a) Frequencyconversion function without control voltage; (b) Attenuationfunction with a control voltage


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Fig. 3 shows the transfer characteristics of the RF and IF matching circuits. In

Fig. 3(a), the RF matching circuit is designed so that it bypasses the X-, K-, and

Ka-band signals but operates with a band-stop transfer characteristics to the LO

band signal. Meanwhile, the IF matching circuit shown in Fig. 3(b) stops the X-,

K-, and Ka-band signals and the LO-band signal but has a high-pass characteristics

with respect to the Ku band.

3 Fabrication and measurement results

The design and optimization was accomplished using the Advanced Design System

(ADS) from Agilent. An anti-parallel diode (BAT15-04W, Infineon) was used. The

printed circuit board used was a low-loss Teflon, which has a relative dielectric

constant of 2.5, a loss tangent of 0.0017, a dielectric thickness of 0.5mm, and a

copper thickness of 0.018mm. Fig. 4 shows a photograph of the implemented

multi-function circuit.

(a) (b)

Fig. 3. The transfer characteristics of the RF and IF matching circuits;(a) RF matching circuit; (b) IF matching circuit.

(a)

(b)

Fig. 2. Structure of the front-end with multiple IFs: (a) Conventionalmultiband front-end using a switching circuit; (b) Simplifiedmultiband front-end using a multifunction circuit


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The circuit was measured using an 8348C signal generator, 8564EC spectrum

analyzer, and 8510C network analyzer (Agilent).

Fig. 5 shows a conversion gain characteristic which depends on LO power

when the multifunction circuit operates as a sub-harmonic mixer. This circuit has a

conversion gain of −13 dB in both RF bands when the LO level is above 2 dBm.

Two band signals, 4500MHz (!IF X =K) and 6000MHz (!IF Ka), generate a

corresponding IF signal, 750MHz (!IF ), by sub-harmonically mixing with the

LO signal, 2625MHz (!LO). In addition to the conversion gain characteristic, this

circuit has a 1 dB compression point of −10 dBm in each band, LO-RF isolation

above −44 dB, and LO-IF and RF-IF isolation above −65 dB.

As shown in Fig. 6, when the multifunction circuit operated as an attenuator,

the third RF signal at 750MHz (!IF Ku) passed through with a −7 dB insertion loss

without frequency conversion, and rejection performance at the unexpected bands

was above −50 dB. Diode under a forward bias condition consumed 2mA current

only when a control voltage 5.0V is applied.

Fig. 4. Photograph of the implemented multifunction circuit

Fig. 5. Conversion gain depending on the LO level in each band whenoperating as a sub-harmonic mixer


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4 Conclusion

We proposed a multifunction circuit operating as a sub-harmonic mixer or an

attenuator, depending on the control voltage. The proposed multifunction circuit

has better electrical characteristics in both modes, and could be useful to implement

as a less expensive, reduce component and smaller microwave multiband front-end

compared to a conventional method with a switching circuit.

Fig. 6. Insertion loss in each band when operating as an attenuator


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simplified multiband front-end architecture using a

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