A 6-to-31-GHz reflection-mode $N$ -path filter is implemented in 45-nm SOI technology. The filter includes an on-chip hybrid coupler with through and coupled ports terminated with four-phase passive mixers. Each mixer provides a high impedance in-band and a matched, 50- $\Omega $ impedance out-of-band (OOB) that is provided by the ON-resistance of the switches. As such, in-band signals are reflected by the mixers, and OOB signals are absorbed. This enables reflection-mode bandpass filtering of the signal, with the center frequency set by the local-oscillator frequency. To increase selectivity, an active baseband (BB) load with adjustable bandwidth can be enabled to provide a second-order capacitive response, which increases the roll-off to 12 dB/octave. Measurements show that the filter can be tuned across 6–31 GHz with a maximum 3-dB RF bandwidth of 0.47 GHz for the passive BB and either 0.22 or 1.22 GHz for the active BB in narrowband or wideband modes. Filter insertion loss (IL) is < 7 dB in all three modes, whereas the noise figure exceeds IL by 1 dB at 6 GHz and 11 dB at 29 GHz in the active-wide mode. The filter provides a return loss of < 10 dB both in-band and OOB. In all three modes of the filter, the in-band input-referred third-order intercept point (IIP3) is<−2.2 dBm and the OOB IIP3 is > 11 dBm, whereas the maximum in-band input-referred P1 dB is −2 dBm. Clock circuitry consumes 75–320 mW from 6 to 31 GHz, whereas the active BBs consume 70 mW in the wideband mode and 90 mW in the narrowband mode.