What This Adapter Solves
The Hirose HRMJ-U.FLP(40) is a between-series coaxial adapter that converts an SMA jack (female socket) to a U.FL (UMCC) plug (female socket). This is the adapter you reach for when a board-mounted U.FL connector needs to connect to test equipment, a cable assembly, or an antenna that terminates in SMA — without soldering a pigtail or redesigning the RF path. It's a straight, free-hanging (in-line) body, so the signal path stays coaxial through the transition, and the 50 Ohm impedance is maintained across the band from DC to 6 GHz. It's part of the Hirose BWA series and carries an active lifecycle status.
RF Performance and the 6 GHz Ceiling
Rated to 6 GHz maximum frequency, the adapter covers the common wireless bands without breaking the impedance match. The PTFE dielectric keeps the loss low and the phase stable across temperature.
Mating Cycles and Contact Construction
The gold-plated beryllium copper centre contacts resist fretting corrosion and maintain low contact resistance across those cycles. The fastening type is a hybrid: snap-on on the U.FL side (the standard U.FL latch) and threaded on the SMA side (the standard SMA coupling nut). That combination means the SMA end stays secure under vibration while the U.FL end allows quick disconnect without tools.
The closest functional alternative is the Hirose HRMP-U.FLJ(40), which also converts an SMA jack to U.FL but uses a male-to-male centre contact arrangement (SMA jack to U.FL jack, male pin to male pin). The HRMJ-U.FLP(40) is female-to-female (SMA jack to U.FL plug, female socket to female socket). That difference in centre gender decides which cable or connector each adapter mates with: the HRMJ-U.FLP(40) accepts a male-pin U.FL plug on one end and a male-pin SMA plug on the other; the HRMP-U.FLJ(40) accepts a female-socket U.FL jack and a male-pin SMA plug. The body material also differs — the HRMJ-U.FLP(40) uses brass, the HRMP-U.FLJ(40) uses stainless steel — but the RF ratings (50 Ohm, 6 GHz, 500 cycles) are identical. Choose the HRMJ-U.FLP(40) when your U.FL side needs a female socket (plug) to mate with a male-pin U.FL jack on the board.