Switch, which uses only two p-i-n diodes on microstrip substrate, has been developed for application in spacecraft radio systems. Switch features improved power drain, weight, volume, magnetic cleanliness, and reliability, over currently-used circulator and electromechanical switches

Choi, S. D.

English

NASA Technical Reports Server

March 1974
	 B73-10451 
r NASA TECH BRIEF 
NASA Pasadena Office 
NASA Tech Briefs announce now technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
High-Power Microstrip Switch 
The problem: 
The successful completion of lengthy space missions 
in the future requires improvement of the state of the 
art in the hardware design of the spacecraft radio 
system. The RF switches, used for switching between 
antennas and redundant receivers and transmitters, 
should be extremely reliable and as simple and free 
from interference with other subsystems as possible. 
The solution: 
A microstrip-type RF switch, which uses only two 
PIN (p-intrinsic n) diodes on a microstrip substrate, has 
been developed for application in spacecraft radio 
systems. The single-pole double-throw (SPDT) switch is 
fabricated by a 5-by 5-by 0.127-cm (2-by 2-by 0.050-in.) 
alumina substrate, and it can handle as much as 100 
watts of CW RF power easily. It weighs only 6 oz 
(0.2 kg) whereas its currently used counterpart (circu-
lator switch) weighs 6 lbs (2.7 kg). 
How it's done: 
The switch uses PIN diodes exclusively as switching 
elements, because of their extremely high impedance 
under a reverse-biased condition and low impedance 
under a forward-biased condition. In a PIN diode,
highly-doped p and n regions are separated by a layer 
of intrinsic semiconductor. When the diode is forward 
biased, carriers are injected into the intrinsic region and 
it exhibits a very low impedance during the entire RF 
cycle. When the diode is reverse biased, all the carriers 
in the intrinsic region are swept out and the region 
appears as a 16w4oss dielectric. 
The microstrip circuits used in the switch are 
fabricated on 99.5% pure alumina substrates 1.27 mm 
(0.050 in.) thick, with a 0.05-tm surface finish on the 
circuit side and a 0.25-pm finish on the ground-plane 
side. The thickness of the gold metallization is 7.62 pm, 
which is about six times the skin depth at 2295 MHz. 
The relative permittivity and loss tangent of 99.5% pure 
alumina at 10 GHz are 9.7 and 0.001, respectively. 
The dielectric loss and the conductor loss for a trans-
mission line 1.27 mm (0.050 in.) wide, at 2.3 GHz, are 
calculated to be 5.lx10 dB/cm and 0.02 dB/cm, 
respectively. The adapter used between the microstrip 
line and the coaxial line (called the launcher) has an 
insertion loss of 0.02 dB, at 2.3 GHz. 
The figure shows a new single-pole single-throw 
(SPST) switch configuration used as part of the RF 
switch. As shown, the configuration does not require 
the previously-used dc blocking capacitor or a ground 
Z	 (Transmission Line) 
Input	 Output 
Z	
[.4	 23 
z3 
Bias 
z.
Schematic Diagram of the Shunt Stub SPST Switch
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000451 2020-03-17T07:29:29+00:00Z
post for the diode. The elimination of one capacitor 
and one ground post per stub amounts to considerable 
improvement in reliability and ease of manufacturing 
for multipole switches. The stub lengths 22 and £3 
shown should be approximately one-quarter wavelength 
long at the band-center frequency, to make the input 
impedance Zm maximum for the switch on and mini-
mum for the switch off. 
An SPDT switch is formed by combining two of these 
SPST switches, with the bias so arranged that one port 
is on and the other off. Typical performance of the 
switch is as follows: 
Band center frequency	 2295 MHz 
Input voltage-standing-wave-
ratio	 Lower than 1.07 
Insertion loss	 0.25 dB over 30 MHz 
Isolation (minimum)	 36 dB over 30 MHz 
Input to bias port isolation 	 Greater than 45 dB
Notes: 
1. The developed switch features improved power drain, 
weight, volume, magnetic cleanliness, and reliability, 
over the currently-used circulator and electrome-
chanical switches. 
2. Requests for further information may be directed to: 
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP73-1045 1 
Patent status: 
NASA has decided not to apply for a patent. 
Source: Soon D. Choi of 
çaltech/JPL
under contract to 
NASA Pasadena Office 
(NPO-1 1965) 
B73 . 10451	 Category 02


High-power microstrip switch

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