Modifying the Keysight (Agilent/HP)
85105A for use with OML Millimeter
Wave VNA Modules
Many of OML's customers have found the cost of a new Keysight 85105A-K10 a stumbling
block to their acquisition of full "S" parameter capable millimeter wave vector analysis above
110 GHz. Many of these customers already owned the Keysight (HP) 85105A Millimeter-Wave
Controller and asked if there was not some manner in which it could be adapted to working with
the OML series of millimeter wave VNA modules (OMLMM). OML investigated several
methods of adapting the 85105A to interfacing with the OMLMM and, as a result, has
developed, is using and recommends the following approach. It will allow the use of any of the
OMLMM between 33 and 325 GHz.
The Keysight 85105A provides DC bias voltage, RF and L.O. interfaces for the Keysight
85106A millimeter Wave Test Sets. Its front panel interfaces are R.F. and L.O. SMA compatible
connectors and a special Sub D connector for DC bias and I.F. interconnections. The 85105A is
set up to provide 11 to 20 GHz leveled amplification (R.F.) with switching between Port 1 and
Port 2 for "S" parameter testing to the 85106A Millimeter Wave Test Set (Momadillo). It also
provides 2 to 8 GHz leveled amplification (L.O.) simultaneously to Port 1 and Port 2.
The bias voltages and L.O. frequency range were found not to be appropriate for use with the
OMLMM. The OMLMM re12 VDC and employs a higher L.O. frequency range (8 to 20
GHz), to reduce the multiple of the harmonic mixers in the OMLMM for lower conversion loss
and higher dynamic range. OML was able to determine that the local oscillator amplifiers used in
the 85105A were standard HP components that were designed to be capable of 2 to 20 GHz
operation. It was further found that the leveling loops of these amplifiers were quite tolerant of
operation up to 20 GHz. In fact, the only component the L.O. subsystem that limited the
frequency range to 8 GHz was the L.O. input power divider that was used to drive the two L.O.
amplifier chains.