［ポスター講演］搬送波漏洩を抑圧したKa帯UWBレーダの開発

摘要

Modulated impulse radars have been most commonly used for Ka-band ultra-wideband (UWB)short-range vehicular applications, where a carrier frequency is amplitude-modulated with short-duration impulse trains. Carrier leakage due to finite isolation of microwave mixers (functioning as modulators) limits total transmitting power and effective maximum detection range to comply with spectral mask. Instead of a single mixer serving as a modulator, the authors propose a use of dual-stage mixers to generate modulated Gaussian monopulse trains. The carrier frequency was gated with a mixer by a gating pulse wider than the monopulse; and then the pulsed carrier was modulated with the other mixer by the monopulse. Without gating, the level of the carrier frequency tone was 25-dB higher than maximum level of sideband components, and occupied 60% within the total transmitting power. When the gating pulse duration = 5 ns, the carrier tone was suppressed nearly 15-dB below the maximum level of the sidebands, and occupied less than 0.04% within the total transmitting power. The sideband spectra were virtually unchanged. To comply with the spectral mask, the proposed radar can expand the maximum detection range by a factor of 4.2 (= (10~( 25/10))~(1/4)).%Ka帯UWB短距離レーダの放射電力は，平均EIRP（等価等方放射電力）のスペクトルマスクおよび尖頭電力で規制されている．搬送波を短パルスで振幅変調したモデュレイティドインパルスレーダにおいては，変調器として用いるミキサのアイソレーション次第で搬送波が送信信号に漏洩する．物体の検出や測距に関わらない搬送波電力の割合が大きいと，EIRPマスクの制約に収めると，最大探知距離が短くなる．搬送波漏洩を抑圧するために，搬送波を短パルスで振幅変調させるミキサに加えて，搬送波を短パルスと同期したゲートパルス信号によってON／OFFさせるもう1個のミキサを用いる方式を提案する．通常入手可能なKa帯ミキサを用いて，両測波帯の最大電力以下に搬送波漏洩を抑圧した場合，最大探知距離を4．2倍延長することができることを，計算および試作機による実験により確認した．