Research in Astron. Astrophys. 201X Vol. X No. XX, 000–000

http://www.raa-journal.org http://www.iop.org/journals/raaResearch inAstronomy andAstrophysics

A Q-band two-beam cryogenic receiver for the Tianma radio

telescope ∗

Wei-Ye Zhong1,2,3, Jian Dong1,2, Wei Gou1,2, Lin-Feng Yu1,2, Jin-Qing Wang1,2, Bo Xia1,2,Wu Jiang1, Cong Liu1, Hui Zhang1, Jun Shi3, Xiao-Xing Yin3, Sheng-Cai Shi2,4, Qing-HuiLiu1,2 and Zhi-Qiang Shen1,2

1 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China;

wyzhong@shao.ac.cn2 Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Nanjing 210008, China3 State Key Laboratory of Millimeter Waves, School of Information Science and Engineering,

Southeast University, Nanjing 210096, China4 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China

Received 2017 June 5; accepted 2018 Jan 9

Abstract A Q-band two-beam cryogenic receiver for the Tianma radio telescope (TMRT)

has been developed, and it uses the independently-developed key microwave and

millimeter-wave components operating from 35 to 50 GHz with a fractional bandwidth of

35%. The Q-band receiver consists of three parts: optics, cold unit assembly, and warm

unit assembly, and it can receive simultaneously the left-hand and right-hand circularly

polarized waves. The cold unit assembly of each beam is composed of a feed horn, a noise

injection coupler, a differential phase shifter, an orthomode transducer, and two low-noise

amplifiers, and it works at a 20 K temperature zone to greatly improve the detection sen-

sitivity of the receiving system. The warm unit assembly includes four radio-frequency

amplifiers, four radio-frequency high-pass filters, four waveguide biased mixers, four 4-

12 GHz intermediate-frequency amplifiers and one 31-38 GHz frequency synthesizer. The

measured Q-band four-channel receiver noise temperatures are roughly 30-40 K. In ad-

dition, the single-dish spectral line and international very long baseline interferometry

(VLBI) observations between the TMRT and East Asia VLBI Network at Q-band have

been successfully carried out, demonstrating the advantages of the TMRT equipped with

the state-of-the-art Q-band receiver.

Key words: telescopes — instrumentation: interferometers — methods: observational

1 INTRODUCTION

The Tianma radio telescope (TMRT) is a newly-built 65 m diameter fully-steerable instrument located

in the western suburbs of Shanghai, China. The objective of highest frequency for the telescope is 50

GHz. The phase I of project construction was accomplished in Dec. 2013. As the key parts of the radio

telescope, four cryogenic receivers covering the frequency ranges 1.33-1.73 GHz, 2.2-2.4 GHz, 4.0-8.0

∗ Supported by the Astronomy-Financial Special of Chinese Academy of Sciences, the National NaturalScience Foundation of China (No. 11403080, 11590780, and 11590783), the Knowledge Innovation Program ofthe Chinese Academy of Sciences (No. KJCX1-YW-18), the Scientific Program of Shanghai Municipality (No.08DZ1160100) and the Youth Innovation Promotion Association of Chinese Academy of Sciences (No. 2017315).

2 W.-Y. Zhong et al.

GHz and 8.2-9.0 GHz, respectively, are available (Yan et al. 2015; Li et al. 2016). The telescope has an

active surface control utilizing actuators to compensate for gravity deformation in the main reflector dur-

ing the observations. To fulfill the highest frequency observation window of the TMRT, the microwave

and millimeter-wave key components for the Q-band receiver have been developed during 2013-2016,

and they include feed horns, noise injection couplers, differential phase shifters (DPS), orthomode trans-

ducers (OMT), and 4-12 GHz intermediate frequency (IF) amplifiers. By the second-quarter of 2016,

four high frequency cryogenic receivers covering the frequency ranges 12.0-18.0 GHz (Li et al. 2016),

18.0-26.5 GHz, 30.0-34.0 GHz and 35.0-50.0 GHz have been installed on the telescope.

The Q-band receiver can be used for mapping massive star forming regions in the Milky Way

with dense gas tracers, i.e. CS J=1-0 at the rest frequency of 48.990 GHz and HC3N J=5-4 at the rest

frequency of 45.490 GHz, to study dense gas properties and star formation in these molecular clouds,

as well as using CS 1-0 and HC3N 5-4 as dense gas tracers to study star formation law in galaxies (Gao

& Solomon 2004). SiO J=1-0 (v = 0) at the rest frequency of 43.423 GHz can also be used to study

shocked gas in molecular clouds. It will double mapping speed with two-beam system, while it can also

double the effective on-source time with the nodding mode for observing point sources.

In this paper, the TMRT Q-band two-beam cryogenic receiver is presented. In section 2, Q-band

receiver system configurations worldwide are compared with the TMRT Q-band receiver diagram. The

designs of optics and feed horn, cold unit assembly (CUA), and warm unit assembly (WUA) are intro-

duced in sections 3, 4, and 5 respectively. The laboratory test results and characteristics on the telescope

including preliminary spectral line and international VLBI observations are also shown in section 6.

Finally, a brief summary is given in section 7.

2 Q-BAND RECEIVER TECHNOLOGY AND DIAGRAM

In the world, there are a variety of radio astronomy Q-band cryogenic receivers which have been in-

stalled on the radio telescopes or developed in laboratories (Wollack & Srikanth 1995; Anderson 2007;

Perley et al. 2009; Lee et al. 2011; Guzman 2013; Tsuboi et al. 2000; Nakamura et al. 2015). The de-

tailed information of international Q-band cryogenic receivers is shown in Table 1. Only the Nobeyama

45 m telescope in 2000 (Tsuboi et al. 2000) employed the superconductor-insulator-superconductor

(SIS) technology. All the others including the new receiver Z45 in 2015 (Nakamura et al. 2015) on the

Nobeyama telescope use or are going to utilize the High-Electron-Mobility-Transistor (HEMT) technol-

ogy. The TMRT Q-band two-beam cryogenic receiver configuration follows the traditional design of low

frequency bands. The diagram of the receiver is depicted in Figure 1 and consists of three subsystems:

optics, CUA, and WUA. The receiver configuration was optimized and reviewed several times since the

project was approved in 2013. The radio signals are received by the feed horn, then being separated into

left-hand circular polarization (LCP) and right-hand circular polarization (RCP) signals by the DPS and

OMT. After that, the receiving signals are amplified by the LNAs to further the signal-to-noise ratio

(SNR). The coupler is used to inject the noise source to do the system calibration. A down-converter

module, including a room-temperature waveguide biased mixer and an radio-frequency (RF) high-pass

filter (HPF), is used in each polarization channel. The phase-locked oscillator with high output power

of +17 dBm is divided in four paths to be used as the local oscillators of four mixers. Therefore, a fixed

intermediate-frequency (IF) band from 4 to 12 GHz, which has a constant 8 GHz bandwidth for simul-

taneously astronomical observation. The IF band is outputted from a down-converter module where the

RF band is from 35 to 50 GHz and the phase locked oscillator is from 31 to 38 GHz with 1 Hz in steps.

The four-channel 4-12 GHz IF signals are transmitted to the observation room, roughly 400 m away

from the telescope, utilizing an RF-over-fiber link with low attenuation, compression, and noise temper-

ature contribution. In addition, a WR-22 standard waveguide diode noise source with injection through

two circular waveguide couplers (Yuan et al. 2014) is used to calibrate the system noise temperatures of

four channels including LCP and RCP.

TMRT Q-band receiver 3

Table 1 The technical specifications of Q-band cryogenic receivers onthe radio telescopes around the world

Telescope Frequency Technology Trx Status Reference(GHz) (K)

Nobeyama 40.0-50.0 SIS 40 Developed Tsuboi et al. 2000Nobeyama 42.0-46.0 HEMT 50 Developed Nakamura et al. 2015

GBT 38.2-49.8 HEMT 20-45 Developed Wollack & Srikanth 1995EVLA 40.0-50.0 HEMT 48 Developed Perley et al. 2009ATCA 30.0-50.0 HEMT 40 Developed Moorey et al. 2008KVN 42.0-44.0 HEMT 50 Developed Lee et al. 2011

Effelsberg 41.0-49.7 HEMT 60-70 Developed Furst 2003QUIET 36.0-44.0 HEMT 35 Developed Newburgh 2010Planck 39.6-48.4 HEMT 16.6 Developed Bersanelli et al. 2010WMAP 35.0-46.0 HEMT 59 Developed Jarosik et al. 2003ALMA 35.0-50.0 HEMT 26-33 Developing Hwang et al. 2014

SRT 33.0-50.0 HEMT 40 Developing Prandoni et al. 2017TMRT 35.0-50.0 HEMT 30-40 This Work

Fig. 1 The diagram of the TMRT Q-band two-beam cryogenic receiver.

3 OPTICS AND FEED HORN

The main TMRT requirement for Q-band receiver optics is the antenna aperture efficiency (Rudolf et

al. 2007; Akgiray et al. 2013a) at Cassegrain focus consisting of illumination, spillover, phase, cross-

polarization, and body-of-revolution-1 (BOR1) sub-efficiencies (Kildal 2015), which must be greater

than 40% from 35 to 50 GHz. Figure 2 shows the far-field pattern mapping of Q-band feeds in the focal

plane of the TMRT with the feed spacing of 70 mm.

In view of the existing experiences of international focal-plane-array receivers, such as the

Nobeyama telescope (Tsuboi et al. 2000), the Green Bank telescope (GBT) (Wollack & Srikanth 1995;

Norrod & Srikanth 1999), the Sardinia radio telescope (SRT) (Orfei et al. 2010), and scientific objec-

tives of the TMRT, the physical distance of two feeds in the focal plane was determined to be 70 mm,

roughly 100” interval in the sky. The calculated aperture efficiency of the feed horn is more than 66%

4 W.-Y. Zhong et al.

Fig. 2 Far-field pattern mapping of two feeds (D = 70 mm) with the unshaped 65 m Cassegrain reflector.

over the entire frequency band without inclusion of the RMS errors of reflector panels. These panels

meet the aperture efficiency specification of 40% at Q-band.

The requirement of a feed on the radio telescope which has symmetric beam, low sidelobes, and low

cross polarization characteristics can be satisfied by a horn that creates linear electric fields. Corrugated

horns (Thomas et al. 1986; Olver & Xiang 1988; Mckay et al. 2013) are usually used as feeds in the

satellite communication and radio astronomy. These properties are typically obtained by coupling ef-

ficiently from the fundamental circular waveguide TE11 mode to the corrugated section HE11 hybrid

mode with roughly a combination of 85% TE11 and 15% TM11. The mode converter section is one of

the most difficult parts of the feed to design and optimize for return loss and efficiency. Any impedance

mismatch between the modes in the circular waveguide and the modes in the throat section of the feed

will excite higher-order modes. Profiled corrugated horns have the advantages of being short, compact,

and lightweight. In the TMRT Q-band receiver, a sine-profiled corrugated feed horn is selected to ob-

tain a compact configuration of 130 mm x 50 mm x 50 mm depicted in Figure 3. This corrugated horn

employed platelet fabrication process at a low cost (Torto et al. 2011) to obtain the same outstanding

performance as electroformed equivalents.

After fabrication by copper materials using the platelet technique, excellent return loss of more

than 20 dB at the output port of the feed was obtained, which agrees well with the simulation result

shown in Figure 4. In addition, the insertion loss is roughly 0.1 dB via the total insertion loss of feed

network subtracting the ones of noise injection coupler, DPS, OMT, etc. Far-field radiation patterns of

the corrugated feed horn at 42.5 GHz are also presented in Figure 5. The edge taper at the subtended

half-angle of 13◦ is from -18 dB to -10 dB with an average value of -16.5 dB to achieve the optimal

sensitivity.

Cryogenic radio astronomy receivers always have RF vacuum windows to propagate the signal to

the feed network. An HDPE RF vacuum window with the thickness of 15 mm is adopted in front of feed

horns. In order to decrease the reflection coefficient of the vacuum window which is less than -15 dB,

circular holes or grooves on two sides of the window are added. In addition, infrared filters between the

RF vacuum window and feed network are required to avoid heat loading of the cryogenic components

TMRT Q-band receiver 5

Fig. 3 The mechanical drawing of the Q-band corrugated feed horn through platelet fabrication tech-niques.

35 40 45 50-60

-50

-40

-30

-20

-10

0

Refle

ctio

n M

ag. (

dB)

Frequency (GHz)

Test Simulation

Fig. 4 Simulated and measured reflection of the feed horn.

of the receiver. The filters should be opaque to infrared radiation while remaining highly transparent to

microwaves and millimeter-waves, as well as being capable of operating at cryogenic temperatures, for

example 77 K in the Q-band receiver. Black polyethylene, Zitex, and Fluorogold (Lamb 1993; Miao et

al. 2015; Koller et al. 2006) have been proposed as such materials. In this receiver, Zitex was chosen to

be the candidate operating at 77 K. Four layers of Zitex with spacing of 1 mm between different layers

are finally used based on trade-off between insertion loss of the filter and physical temperature of the

feed at 25 K.

4 COLD UNIT ASSEMBLY

The TMRT Q-band two-beam cryogenic receiver is a HEMT receiver, with a cryogenic low-noise am-

plifier (LNA) (Weinreb 1980; Akgiray et al. 2013b; Schleeh et al. 2013) employing gallium arsenide

(GaAs) or indium phosphide (InP) HEMT technology. With the high gain cryogenic LNA in front of the

6 W.-Y. Zhong et al.

-50 -40 -30 -20 -10 0 10 20 30 40 50-50

-40

-30

-20

-10

0

Nor

mal

ized

Pat

tern

(dB)

( )

E-Plane 42.5 GHz H-Plane 42.5 GHz

Fig. 5 Measured far-field patterns of the corrugated feed horn in = 0◦, and = 90◦ planes at 42.5 GHz.

mixer of the receiver, the noise contribution is mainly from the optics, vacuum window, infrared filter,

feed network, and LNA. Besides, unlike the SIS mixer which needs a 4 K operating temperature, the

HEMT LNA achieves low noise performance at a 15-20 K temperature zone.

The prototype of the TMRT Q-band two-beam CUA is shown in Figure 6. The key components in

the CUA are the corrugated feed horn, noise injection coupler, differential phase shifter, OMT, and cryo-

genic LNAs. The feed networks shown in Figure 7 are supported with several G-10 thermal-insulated

brackets, and they operate at a 20 K temperature zone via the cold copper straps from the 2nd stage of

cold head. The cryogenic LNA of each polarization is directly connected to the output standard WR-22

waveguide port of the OMT. A combined waveguide tube is chosen to connect from the cryogenic LNA

to the cryostat outer wall with a low heat transfer, and it consists of 50 mm length of copper and 150

mm length of stainless steel.

4.1 Differential Phase Shifter

A waveguide DPS from 35 to 50 GHz with an axial ratio less than 1 dB by the CNC machining is

presented. The DPS core design is to provide the proper transformation between circularly polarized

signals and corresponding linearly polarized signals. A wideband rectangular waveguide phase shifter

with transverse corrugations on all four walls was introduced in (Srikanth 1997) which has been suc-

cessfully used in many cryogenic receivers. However, the electroforming process is usually needed for

the four-wall corrugated phase shifter to ensure the electrical performance, and it is high-cost to some

extent. A configuration of the waveguide DPS used in the TMRT Q-band receiver is shown in Figure 8.

The DPS is made of a square waveguide with one set of opposite walls loaded with corrugations and

another set of smooth walls (Chung et al. 2010).

Measured return losses better than 17 dB from 35 to 50 GHz for the two orthogonal polarizations

including the adaptors are shown in Figure 9. The measured insertion losses for both orthogonal po-

larizations are less than 0.1 dB displayed in Figure 10 which has subtracted the insertion losses of the

TMRT Q-band receiver 7

Fig. 6 TMRT Q-band two-beam CUA (Dimensions: 345 mm x 345 mm x 680 mm; Weight: 95 Kg).

four adaptors via the multiple tests and calibrations. The measured phase shift between two orthogonal

modes is 90◦±6◦ corresponding to an axial ratio of 0.9 dB depicted in Figure 11.

4.2 Orthomode Transducer

OMTs are critical passive components in radio astronomy receivers for simultaneously receiving orthog-

onal polarization radio waves (Coutts 2011; Henke & Claude 2014; Virone et al. 2014). A waveguide

OMT generally consists of three physical ports, a common input port which can propagate two orthog-

onal modes and two standard rectangular waveguide output ports, one for each polarization. The OMT

is designed to have a compact configuration and for ease of fabrication shown in Figure 7.

A turnstile-junction OMT has been designed in (Henke & Claude 2014) at Q-band. However, this

kind of configuration can easily generate spikes in receiver noise if the assembly alignment is not good.

Figure 12 shows the overall diagram of the designed Boifot-junction double-ridge OMT (Kamikura et

al. 2010). The input port of the device is a mode converter, which converts the input from a circular

8 W.-Y. Zhong et al.

Fig. 7 TMRT Q-band two-beam feed network prototype: corrugated feed horn, noise injection coupler,DPS and OMT (from left to right).

Fig. 8 Waveguide DPS with two-wall corrugations.

to a square waveguide propagating the two orthogonal polarization modes. These orthogonal modes

are separated by means of the Boifot-junction double-ridge structure. Vertical polarization (VP) goes

forward via an E-Bend structure, while horizontal polarization (HP) is recombined by the Y-Junction

configuration. The two outputs of the OMT are standard WR-22 waveguide ports for each orthogo-

nal polarization. The component is measured using a Vector Network Analyzer model N5245A from

Keysight Technologies. The measured insertion losses consisting of horizontal and vertical polariza-

tions are less than 0.4 dB as shown in Figure 13, and measured return losses at the output ports are more

than 20 dB as shown in Figure 14. Figure 15 exhibits the isolation between the two output ports of the

OMT combining with the feed horn, the noise injection coupler and the DPS. It is shown that the LCP

and RCP port isolation is more than 20 dB over the entire frequency band.

TMRT Q-band receiver 9

Horizontal polarization Vertical polarization

Fig. 9 Measured reflection at the DPS output ports.

4.3 Cryogenic Low-Noise Amplifier

The cryogenic LNA in our Q-band receiver is an ultra-low noise cryogenic amplifier operating in the 28-

52 GHz at 15 K. The LNA is packaged in a standard WR-22 waveguide module with Nano-D DC power

supply connectors and was provided by the Low Noise Factory (LNF) in Sweden. The dimensions of the

gold-plated aluminum module are roughly 28.0 mm x 19.5 mm x 19.2 mm. The amplifier modules use

monolithic microwave integrated circuit (MMIC) technology to ensure high reliability and uniformity

of four receiving channels. The measured noise temperature of the cryogenic LNA at 10 K is roughly

18-20 K with the gain of 28-30 dB. Due to the limited cryogenic test bench at LNF in 2014, only the

cryogenic results up to 40 GHz shown in Figure 16 were supplied.

4.4 Vacuum Waveguide Feedthrough

The output of the cryogenic LNA is then connected to the home-made WR-22 Vacuum waveguide

feedthrough at room temperature. An RF-choke ring (Pozar 2011) is used to suppress the resonant

frequency within the operating band. The detailed design layout is depicted in Figure 17. The mylar with

the thickness of 100 µm is used between the two standard WR-22 waveguide whose leakage rate does

not exceed 1e-10 cc/sec of helium at 1 atm. Figure 18 presents the different insertion loss comparisons

between with an RF choke and without an RF choke.

5 WARM UNIT ASSEMBLY

Most of the TMRT Q-band two-beam receiver components are located in the WUA shown in Figure 19.

The major function blocks in the WUA are four down-converter chains connected to the CUA, and a

phased locked tuning oscillator. The down-converter chain incorporates the warm LNA, HPF, waveguide

biased mixer, etc., where the measured sideband rejection ratio of the HPF at 29.7 GHz is more than

45 dB. The local oscillator is using the Hittite Microwave T2240 with a frequency range of 31-38 GHz

which can be remotely controlled by the LAN port. Each IF channel of the WUA is composed of a

10 W.-Y. Zhong et al.

35 40 45 50-0.20

-0.18

-0.16

-0.14

-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

Tran

smiss

ion

Mag

. (dB

)

Frequency (GHz)

Horizontal polarization Vertical polarization

Fig. 10 Measured transmission of the DPS.

coaxial bandpass filter, a broadband coaxial isolator, and an IF amplifier. An IF amplifier which can

provide a gain of at least 30 dB from 4 to 12 GHz has also been successfully designed and fabricated

(Zhang et al. 2016).

The measured conversion gain of the down-converter gain chain is shown in Figure 20. With excel-

lent gain flatness of the warm RF LNA and IF LNA with smooth conversion loss of the waveguide biased

mixer, the IF output gain flatness is within ±3 dB in any 2 GHz bandwidth as shown in Figures 21-24.

With the help of fixed coaxial attenuators, 1 dB power compression points referring to four-channel

output ports of the receiver system are all above +10 dBm.

6 RECEIVER PERFORMANCE

The receiver noise temperature, power gain and dynamic range can be predicted from noise, gain and

power compression point performances of the key components shown in Table 2. The gain and dynamic

range of the CUA are mainly determined by the performance of cryogenic LNA due to the fact that the

insertion losses of the passive components in front of the cryogenic LNA are generally no more than 1

dB. In our receiver, microwave components consisting of the feed network and cryogenic LNAs inside

the cryostat are fixed, and the gain of the WUA is adjusted by adding fixed coaxial attenuators before

and after the IF amplifier. It has a negligible effect on the receiver noise temperature using this method.

As shown in Figure 25, the receiver average noise temperatures are roughly 30-40 K using the liquid

nitrogen and a warm microwave absorber. In addition, the interval of two beams in the sky is measured

about 90” (3-4 HPBWs). After the Y-factor measurement with a microwave absorber and cold sky

respectively, the four-channel system noise temperatures from 55 to 125 K are shown in Figure 25. It is

expected that the system noise temperature is increased at the high end of the operating frequency band

due to the oxygen absorption line.

The performance of the Q-band beam-2 at 43 GHz was tested assuming the atmospheric opacity in

the zenith direction was τ0=0.1. The overall performance is shown in Figure 26. The extended out-of-

focus (e-OOF) technique is proposed for measurement of the gravitational deformation of the TMRT.

Applying the gravitational model with the main-reflector surface accuracy of 0.27 mm RMS, it improves

TMRT Q-band receiver 11

35 40 45 500.0

0.5

1.0

1.5

Axi

al R

atio

(dB)

Frequency (GHz)

Fig. 11 Measured axial ratio of the DPS.

Fig. 12 Model of the Boifot-junction double-ridge OMT.

the aperture efficiency at both low and high elevations. In the case of active surface model, the aperture

efficiency can reach more than 50%. The system noise temperature in the zenith direction, consisting

of the sky, antenna ohmic loss, etc., is roughly 80 K with the system equivalent flux density (SEFD)

of about 120 Jy and the degrees per flux unit (DPFU) of 0.6 K/Jy. In a word, in the case of 65 m

main-reflector active surface control system turned on, all the Q-band electrical performances meet the

required system specifications.

The Q-band receiver, together with the digital back-end system (DIBAS), was used to do spec-

troscopy observations in the winter of 2016-2017. Three independent IFs can be obtained simultane-

ously within 8 GHz in the tuning range of the Q-band receiver. On-the-Fly (OTF) mode and standard

position switching mode can be used. Figure 27 shows the velocity integrated map of one dense gas

12 W.-Y. Zhong et al.

35 40 45 50-0.5

-0.4

-0.3

-0.2

-0.1

0.0

Tran

smiss

ion

Mag

. (dB

)

Frequency (GHz)

Horizontal Polarization Vertical Polarization

Fig. 13 Measured transmission of the OMT.

tracer: CS 1-0 at the rest frequency of 48.990 GHz toward a massive star forming region G188.94+0.88,

with about 40 minutes telescope time with the OTF mode. Based on the testing results of OTF mapping

for these lines, the TMRT Q-band receiver provides a powerful tool for studying dense gas in the Milky

Way sources. In addition, the TMRT uses the data processing to eliminate the image rotation when

making extended source mapping.

Some international joint VLBI observations between the TMRT and East Asia VLBI network at

Q-band have been successfully carried out in Spring 2017. The high sensitivity of the TMRT at Q-band

can be seen from the high SNR of the VLBI fringe results shown in Figure 28. The TMRT will play a

key role in the East Asian region for the millimeter VLBI observations.

7 CONCLUSION

A Q-band two-beam cryogenic receiver for the TMRT has been built. The measured receiver noise

temperature for the four channels are roughly 30-40 K with the system noise temperature of 55-125 K.

Several single-dish and VLBI observations have been successfully carried out with good results. It is

believed that the TMRT will play an important role in the astronomical observations.

Acknowledgements The authors would like to thank Dr. Sander Weinreb, Director of Microwave

Research Group of California Institute of Technology, Pasadena, CA, USA, for his kindest revision

and suggestion of the paper. This work was supported by the Astronomy-Financial Special of Chinese

Academy of Sciences, the National Natural Science Foundation of China (No. 11403080, 11590780, and

11590783), the Knowledge Innovation Program of the Chinese Academy of Sciences (No. KJCX1-YW-

18), the Scientific Program of Shanghai Municipality (No. 08DZ1160100) and the Youth Innovation

Promotion Association of Chinese Academy of Sciences (No. 2017315).

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Frequency (GHz)

Noi

se T

empe

ratu

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50

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35 40 45 50-5

-4

-3

-2

-1

0

Tran

smiss

ion

Mag

. (dB

)

Frequency (GHz)

With an RF Choke Without an RF Choke

Fig. 18 Transmission of the vacuum waveguide feedthrough with an RF choke and without an RF choke.

Rudolf H., Carter M., & Baryshev A. 2007, IEEE Trans. Antennas Propag., 55, 2966

Schleeh J., Wadefalk N., Nilsson P., et al. 2013, IEEE Trans. Microw. Theory Techn., 61, 871

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Tsuboi M., Kasuga T., Ohno T., et al. 2000, in Proc. of SPIE. Vol. 4015, 278

16 W.-Y. Zhong et al.

Fig. 19 3-D mechanical outline of TMRT Q-band two-beam WUA.

Virone G., Peverini O. A., Lumia M., et al. 2014, IEEE Trans. Microw. Theory Techn., 62, 1487

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Wollack E., & Srikanth S. 1995, GBT MEMO, 141

Fig. 20 Down-converter chain consisting of waveguide isolator, RF LNA, waveguide high-pass filter,waveguide isolator, waveguide biased mixer, directional coupler, coaxial isolator, IF LNA, IF band-passfilter (from left to right).

TMRT Q-band receiver 17

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16-90

-80

-70

-60

-50

-40

-30

-20

-10Beam-1 LHCP

IF S

pect

rum

(dBm

)

Frequency (GHz)

LO=31 GHz; RF=35-43 GHz LO=35 GHz; RF=39-47 GHz LO=38 GHz; RF=42-50 GHz

Fig. 21 IF output spectrum of the beam-1 LHCP channel.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16-90

-80

-70

-60

-50

-40

-30

-20

-10Beam-1 RHCP

IF S

pect

rum

(dBm

)

Frequency (GHz)

LO=31 GHz; RF=35-43 GHz LO=35 GHz; RF=39-47 GHz LO=38 GHz; RF=42-50 GHz

Fig. 22 IF output spectrum of the beam-1 RHCP channel.

18 W.-Y. Zhong et al.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16-90

-80

-70

-60

-50

-40

-30

-20

-10Beam-2 LHCP

IF S

pect

rum

(dBm

)

Frequency (GHz)

LO=31 GHz; RF=35-43 GHz LO=35 GHz; RF=39-47 GHz LO=38 GHz; RF=42-50 GHz

Fig. 23 IF output spectrum of the beam-2 LHCP channel.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16-90

-80

-70

-60

-50

-40

-30

-20

-10Beam-2 RHCP

IF S

pect

rum

(dBm

)

Frequency (GHz)

LO=31 GHz; RF=35-43 GHz LO=35 GHz; RF=39-47 GHz LO=38 GHz; RF=42-50 GHz

Fig. 24 IF output spectrum of the beam-2 RHCP channel.

TMRT Q-band receiver 19

Table 2 Performance prediction for the TMRT Q-band receiver at 43 GHz

Components Pout(1dB)(1) Temperature(2) Gain(3) Te(4) ∆T (5) Trx(6) TotalGain(7)

(dBm) (K) (dB) (K) (K) (K) (dB)

Vacuum Window 300 -0.10 6.99 6.99Infrared Filter 77 -0.10 1.79 1.84

Feed Horn 20 -0.10 0.47 0.49DPS+OMT 20 -0.50 2.44 2.61Cryo LNA -10 20 26.00 18.00 21.64

Copper WG 20 -0.10 0.47 0.00SS WG 150 -1.00 38.84 0.12

WG Feedthru 300 -0.20 14.14 0.06 34 24WG Isolator 300 -1.00 77.68 0.32RF Amplifier 0 300 33.00 150.00 0.77

High-Pass Filter 300 -0.40 28.94 0.00WG Isolator 300 -1.00 77.68 0.00

Mixer 300 -8.00 1592.87 0.01Attenuator 300 -6.00 894.32 0.02

Coupler 300 -0.20 14.14 0.00Coax Isolator 300 -1.00 77.68 0.01

Attenuator 300 -3.00 298.58 0.04IF Amplifier +10 300 33.00 149.00 0.03Attenuator 300 -3.00 298.58 0.00

Band-Pass Filter 300 -2.00 175.47 0.00 35 64Attenuator 300 -6.00 894.32 0.00 58

(1)The output power 1 dB compression point; (2)The physical working temperature ofthe component; (3)The gain of the component; (4)The noise temperature of the com-ponent; (5)The cascaded noise temperature of the component in the system; (6)The re-

ceiver noise temperature (sum of ∆T (5)); (7)The receiver total gain (sum of Gain(3))

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1162

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This paper was prepared with the RAA LATEX macro v1.2.

20 W.-Y. Zhong et al.

35 40 45 500

50

100

150 Beam1-LHCP System Noise Temperature Beam1-RHCP System Noise Temperature Beam2-LHCP System Noise Temperature Beam2_RHCP System Noise Temperature Beam1-LHCP Receiver Noise Temperature Beam1-RHCP Receiver Noise Temperature Beam2-LHCP Receiver Noise Temperature Beam2-RHCP Receiver Noise Temperature

Frequency (GHz)

Trec

eive

r (K

)

0

50

100

150

Tsys

tem

(K)

Fig. 25 Measured four-channel receiver and system noise temperatures.

TMRT Q-band receiver 21

0 10 20 30 40 50 60 70 80 900

20

40

60

80

100 Beam-2 LHCP Beam-2 RHCP

Ape

rture

Effi

cien

cy (%

)

Elevation (¡ã)

0 10 20 30 40 50 60 70 80 90

100

200

300

400

500

SEFD

(Jy)

Elevation (¡ã)

0 10 20 30 40 50 60 70 80 900

50

100

150

200

250

300

350

Tsys

(K)

Elevation (¡ã)

0 10 20 30 40 50 60 70 80 900.0

0.2

0.4

0.6

0.8

1.0

DPF

U (K

/Jy)

Elevation (¡ã)

Fig. 26 TMRT Q-band beam-2 aperture efficiency, SEFD, system noise temperature, DPFU over eleva-tion angles at 43 GHz.

22 W.-Y. Zhong et al.

Fig. 27 Map of CS 1-0 at the rest frequency of 48.990 GHz.

Fig. 28 VLBI fringe between TMRT and KVN-YS baseline at Q-band (source: 3C273).