Implementation of the EDGES AntennaSimulator

Raul MonsalveSESE, Arizona State University

July 26, 2012

Abstract

The antenna simulator circuit proposed by A. Rogers was implemented. Its purposeis to bias an incandescent lamp for it to act as a resistor at temperatures ∼ 1800 K. Itis connected to the rest of the EDGES system in place of the four-point antenna.

1 Implementation

The circuit schematic is described in Memo 82 [2] and shown in figure 1. It was built usingthe balun described in Memo 43 [1] available in the lab and depicted in figure 2. The othercomponents of the circuit are:

• 4 capacitors of 0.02 µF, 50 V.

• 3 inductors of 1 µH, SRF of 200 MHz.

• 1 inductor of 0.1 µH, SRF of 250 MHz.

• 1 resistor of 280 Ω, ± 0.1%.

• 1 tungsten-filament incandescent lamp, JKL 1829, 28 V, Mouser part# 560-1829.

Figure 3 shows the assembled circuit during tests. The connector on the right correspondsto the 28 VDC input. The connector on the left is the unbalanced output monitored by theVNA.

The resistance of the lamp when OFF is 35 Ω. When the circuit is powered on, the DCcurrent drawn is 0.048 A and the voltage drop across the lamp is 14.26 VDC, which meansthat the lamp resistance is 297 Ω under these conditions. When the lamp is connecteddirectly to 28 VDC it draws a current of 0.072 A, implying a resistance of 389 Ω.

The full circuit was simulated as detailed in section 2 and the comparison with the VNAmeasurements is presented in section 3.

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Figure 1: Schematic of the antenna simulator circuit proposed in Memo 82 [2].

Figure 2: Choke balun with balance compensation described in Memo 43 [1] and used forthe antenna simulator testing.

2

Figure 3: Implementstion of the antenna simulator. DC input is on the right and VNAoutput on the left.

3

1 2

3

SUBCKTID=S1NET="balun_s3p"

PORTP=1Z=50 Ohm

PORTP=2Z=50 Ohm

PORTP=3Z=50 Ohm

50 100 150 200Frequency (MHz)

Balun

-15

-10

-5

0

dB

S11 S22 S33 S21 S23 S13

Figure 4: Left : Balun block created in Microwave Office using the S-parameters of the balun.Ports 1 and 3 correspond to the balanced inputs and port 2 is the unbalanced output. Right :S-parameters of the balun when terminated in 50 Ω loads.

2 Software Simulations

The circuit was simulated using Microwave Office. Since the software does not have a modelfor the balun, a block was created for this device using its S-parameters measured with theVNA in a 3-port configuration. Figure 4 shows the balun block and its S-parameters whenterminated with 50 Ω loads.

Figure 5 shows S22 (voltage reflection coefficient for the unbalanced output) when a50 Ω load is connected across the balanced inputs, and compared to the case with two 50Ω terminations. Clearly, a 50 Ω load across the balanced inputs produces a much betteradaptation.

Figure 6 shows the full simulated circuit, whose results are presented in the next section.

4

RESID=R1R=50 Ohm

1 2

3

SUBCKTID=S1NET="balun_s3p"

PORTP=2Z=50 Ohm

50 100 150 200Frequency (MHz)

Balun

-20

-15

-10

-5

0

dB

S22 (2 x 50 ohm loads at inputs) S22 (balanced 50 ohm load at inputs)

Figure 5: Left : 50 Ω resistor connected to the balanced inputs of the balun. Right : Improve-ment in S22 when a 50 Ω resistor is connected to the balanced inputs (magenta), comparedto terminating each input with 50 Ω loads as in figure 4 (blue).

DC_VID=V1Sweep=NoneV=28 V

CAPID=C1C=0.02 uF

INDID=L1L=100 nH

CAPID=C2C=0.02 uF

RESID=R1R=280 Ohm

CAPID=C3C=0.02 uF

INDID=L2L=1000 nH

CAPID=C4C=0.02 uF

RESID=R2R=297 Ohm

INDID=L3L=1000 nH

1 2

3

SUBCKTID=S1NET="balun_s3p"

PORTP=2Z=50 Ohm

Figure 6: Schematic of the antenna simulator circuit during the simulations with MicrowaveOffice. The lamp is modeled as a resistor of 297 Ω.

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50 100 150 200Frequency (MHz)

Measurament v/s Simulation

-10

-8

-6

-4

-2

0dB

-80

-60

-40

-20

0

20

Pha

se (d

egre

es)

Mag(S22) simulated (L)

Ang(S22) simulated (R, Deg)

Mag(S22) measured (L)

Ang(S22) measured (R, Deg)

Figure 7: Simulations and measurements of the unbalanced output of the antenna simulator,labeled as port 2 in figure 6. There is very good agreement between them in magnitude andphase.

3 Results

Figure 7 shows the comparison between the simulation and measurements of the unbalancedoutput of the antenna simulator. There is a very good agreement between them, and thedifferences are most likely due to the frequency dependence of the lamp biasing circuit,inductors in particular. This also confirms that assigning a resistance of 297 Ω to the lampis adequate.

References

[1] A. Rogers. Edges memo 043. http://www.haystack.mit.edu/ast/arrays/Edges/EDGES_memos/043.pdf.

[2] A. Rogers. Edges memo 082. http://www.haystack.mit.edu/ast/arrays/Edges/EDGES_memos/082.pdf.

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