Converters and harmonic mixers that are any of the following: (a) Designed to extend the frequency range of ‘signal analysers’ beyond 90 GHz; (b) Designed to extend the operating range of signal generators as follows: 1. Beyond 90 GHz; 2. To an output power greater than 100 mW (20 dBm) anywhere within the frequency range exceeding 43,5 GHz but not exceeding 90 GHz; (c) Designed to extend the operating range of network analysers as follows: 1. Beyond 110 GHz; 2. To an output power greater than 31,62 mW (15 dBm) anywhere within the frequency range exceeding 43,5 GHz but not exceeding 90 GHz; 3. To an output power greater than 1 mW (0 dBm) anywhere within the frequency range exceeding 90 GHz but not exceeding 110 GHz; or (d) Designed to extend the frequency range of microwave test receivers beyond 110 GHz;